「お互いに溶け合うことがない液体と高分子の組み合わせでも、界面をナノレベルで見るとセグメントレベルでは溶解し、膨潤する」こと、「異種固体と接触した高分子は熱的に緩和できない」ことを見いだすなど、独自の方法論に基づいて表面や界面、あるいは超薄膜のような界面と接する部分が大きいナノサイズの高分子の振る舞いを学術的に体系化した。

材料・デバイス創出におけるイノベーションを目的として高分子を使用する際、界面における構造・物性制御は必須の基盤技術である。なかでも、近年の社会の複雑・多様化に対応できる高度水分離膜や高発電効率を実現する燃料電池用高分子電解質膜や、テーラーメード医療に使用されるバイオチップなどのバイオ応用においては、液体、とくに非溶媒である水界面における高分子鎖の凝集状態、ひいてはダイナミクスを制御し、機能発現を設計する戦略が必要となる。そこで本研究では、独自の方法論に基づき非溶媒界面における高分子の構造と物性、また、機能化への影響について検討している。

Publisher：Polymer Journal  

The presence of structural heterogeneities in glassy epoxy networks can strongly affect the adhesiveness and mechanical properties of epoxy-based materials. Recent studies have demonstrated that the size and architecture of structural heterogeneities can be monitored during the curing process, thus providing an effective way to control multiple physical properties of epoxy resins. However, because the size of heterogeneities is believed to be at the nanoscale, obtaining insights into the direct correlation between the local behavior of heterogeneities and the preparation conditions remains challenging. Here, we combine two recently developed atomic force microscopy (AFM)-based methods, bimodal amplitude and frequency modulation and nanoscale dynamic mechanical analysis (nDMA), to directly visualize and quantify the nanoscale mechanical properties of epoxy resins obtained via different curing conditions. Our AFM maps clearly show a correlation between the curing conditions and the heterogeneous behavior of the resulting epoxy networks, which is in excellent agreement with those predicted from macroscopic measurements. Notably, our nDMA results revealed a relationship between network heterogeneity and the glass transition behavior of the epoxy resins.

DOI： 10.1038/s41428-024-01006-4

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Publisher：Polymer Journal  

In this study, the crosslink inhomogeneities in two types of epoxy resins cured with a phenolic hardener under organophosphine catalysts were successfully clarified by small-angle X-ray scattering (SAXS) using a solvent-swelling technique. Herein, triphenylphosphine (TPP) and tetraphenylphosphonium tetra-p-tolylborate (TPPTTB) were investigated as the curing catalysts. The SAXS profiles in a fully tetrahydrofuran (THF)-swollen state clearly revealed a difference between the two types of resins. The profiles at the early, middle, and late stages of gelation were effectively explained by a sum of structural functions representing the crosslinking inhomogeneity and concentration fluctuations of the polymer chains. Furthermore, the change in the profiles indicated that the characteristic size of inhomogeneity was associated with the size of the minor, low-crosslink density region. The correlation lengths of the mesh size decreased to 1 nm for both resins. These results confirmed the formation of a well-developed crosslinked network structure. Moreover, the correlation lengths of the crosslink inhomogeneity at the late stage of gelation were 1 and 5 nm for the TPP- and TPPTTB-cured resins, respectively. Thus, the phenolic-cured epoxy resins using an organophosphine catalyst system exhibited a THF-swellable, low crosslink density region due to inhomogeneity at the late stage of gelation.

DOI： 10.1038/s41428-024-00993-8

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Publisher：Composites Part A: Applied Science and Manufacturing  

In the adhesion of carbon fiber reinforced plastics (CFRP), the boundary regions were composed of only epoxy resins of CFRP matrix and adhesives, and their similar epoxy structures pose significant difficulty in studying the adhesion mechanism. Herein, we focused on structure and properties of laminates of epoxy resin substrates and adhesives with different curing conditions of substrates. We prepared laminates using deuterated epoxy adhesives or fluorinated epoxy adhesives, and their boundary regions were identified through confocal Raman scattering measurements. The regions were distributed into “penetration” and “interphase”. In particular, the penetration phase is a key of the adhesion properties. The penetration behaviors strongly depended on the crosslinking densities of the adherends, suggesting that the penetration regions would be directly impacted by the curing conditions of the substrates and molecular size of epoxy adhesive precursors. Our findings provide insights into novel designs of the reliable adhesion-based manufacturing systems of CFRP.

DOI： 10.1016/j.compositesa.2024.108511

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Publisher：Polymer Journal  

Amines generally tend to segregate at the interface of the epoxy resins cured with amines. To gain better insight into the aggregation states and physical properties at the adhesive interface, we examined the cross-linking structure and physical properties of the cured epoxy resins with an off-stoichiometric ratio of epoxy and amine. As the excess amine increased, the amine not only remained as unreacted monomers or low-molecular-weight isolated chains within the cross-linking structure but also formed dangling chain ends, increasing heterogeneity in the cured epoxy resin. As a result, the cross-linking density and mass density decreased, along with a reduction in the glass transition temperature. On the other hand, Young’s modulus increased with the excess amount of amine. Wide-angle X-ray scattering experiments, in conjunction with molecular dynamics simulations, revealed that the excess amine suppressed the widening of the distance between phenyl groups during the curing reaction, suggesting that this could act as steric resistance during deformation.

DOI： 10.1038/s41428-024-00983-w

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Publisher：Macromolecules  

Improving the heat resistance of epoxy resins remains an important and challenging issue across a wide variety of applications. One strategy to address this challenge is the design of cured resins based on multifunctional epoxy. Compared to conventional difunctional epoxy resins, multifunctional epoxy resins are expected to easily form a highly cross-linking structure, which is anticipated to contribute to enhanced heat resistance. However, there is a lack of information about the detailed mechanisms of the formation of such cross-linking structures and their effects on the physical properties. We herein tracked the kinetics of curing reactions of difunctional and trifunctional epoxies with an amine hardener. Despite the identical reactivity of epoxy groups in both base monomers, the trifunctional epoxy system cured faster. In addition, in the difunctional epoxy system, gelation was followed by vitrification, while in the trifunctional epoxy system, gelation and vitrification occurred simultaneously. The accelerated curing reaction observed in the trifunctional epoxy system could be explained in terms of the localized temperature increase from the reaction heat, which subsequently accelerated the following reactions. The resulting post-cured trifunctional epoxy resin did not exhibit a clear glass transition. This, so-called Tg-less behavior was due to the glass transition temperature of the trifunctional epoxy unit being higher than its decomposition temperature. This mechanism for the Tg-less behavior, combined with the accelerated curing reactions, provides valuable insights for the design of thermosetting resins with enhanced thermal stability.

DOI： 10.1021/acs.macromol.4c02178

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

The aggregation states of polymer chains at solid interfaces are strongly related to their adhesion properties.

DOI： 10.1039/d4py00951g

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

The surface wettability of polymers can be controlled by van der Waals interactions, which include induction, orientation, and dispersion forces. For most fluoropolymers, the effect of orientation interactions is markedly smaller than the others, particularly in structures with antiparallel packing, where permanent dipoles may cancel each other out. However, poly(vinylidene fluoride) (PVDF), a semicrystalline polymer, exhibits unique piezoelectric properties when its polar β-form crystals are oriented via poling treatment. This study investigates how such orientation influences surface wettability. We demonstrate that the wettability of uniaxially oriented PVDF films changes with poling treatment. Using sum frequency generation spectroscopy and grazing incidence X-ray diffraction measurements, we found that the b-axis of the β-form crystals near the surface aligns perpendicular to the surface under sufficient electric field strength. This alignment facilitates a transition in wettability, which is discussed in terms of dipole interactions near the surface. Our findings contribute to a deeper understanding of the interplay between molecular orientation and surface properties in semicrystalline polymers.

DOI： 10.1021/acs.macromol.4c01925

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Publisher：Polymer Journal  

External fields are often present when polymers contact solids, potentially affecting chain adsorption onto a substrate. The adsorbed chains, which are difficult to relax thermally, could semipermanently influence the dynamics of the surrounding chains and bulk chains. In this study, we examined the effect of a force field induced by spin coating on the adsorption of a model polymer chain, DNA. Observations using atomic force microscopy indicated that the morphologies of adsorbed chains were affected not only by the force field but also by the incubation time (tinc) after deposition and before spinning. A longer tinc caused a greater amount of chains to transition from being present in two-dimensional random coil states to stretched states. Conversely, shorter tinc values resulted in many chains being adsorbed in a stretched state. The orientations of the stretched chains reflected the presence of competition between the effects of the centrifugal force and those of the flow rate gradient. At tinc = 0, the adsorbed chains were stretched, and they exhibited many kinks. It was anticipated that this macromolecular information could aid in controlling buried morphologies near solid surfaces and in fabricating promising materials, such as polymer composites and layered organic devices.

DOI： 10.1038/s41428-024-00937-2

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DOI： https://doi.org/10.1063/5.0220611

Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

A better understanding of the dynamic behavior of polymer chains on solid surfaces is indispensable for the design and construction of high-performance polymer composites. We herein visualized the in-plane movement of isolated poly(methyl methacrylate) (PMMA) and poly(tert-butyl methacrylate) (PtBMA) single chains on hydrophilic silicon wafers under ambient conditions by atomic force microscopy. Isolated PMMA chains adsorbed to the substrate, whereas PtBMA chains diffused, the degree of which was dependent on the humidity. Neutron reflectivity revealed the formation of a layer of condensed water on the substrate. All-atomistic molecular dynamics simulations implied that the diffusivity difference of the two polymers was based on the submerged depth in which a part of a chain existed. That is, the interaction of a polymer with the surface of the hydrophilic substrate primarily governs its lateral movement, or adsorption behavior, facilitated by the presence of water.

DOI： 10.1021/acs.macromol.4c00724

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Langmuir  

The adhesion of epoxy adhesives to aluminum materials is an important issue in assembling parts for lightweight mobility. Aluminum surfaces typically possess an oxide layer, which readily adsorbs water. In this study, the aggregation states of water and its effect on the curing reaction were examined by placing a water layer between an amorphous alumina surface and a mixture of epoxy and amine components. This study used molecular dynamics simulations and density functional theory calculations. Before the reaction, water molecules strongly adsorbed onto the alumina surface, aggregating excess water. Some water diffused into the epoxy/amine mixture, accelerating the diffusion of unreacted substances. This led to faster reaction kinetics, particularly in proximity to the alumina surface. The adsorption of water molecules onto the alumina surface and the aggregation of excess water were similarly observed even after the curing process. Subsequently, the interaction between the alumina surface and various functional groups of the epoxy/amine mixture was evaluated before and after the reaction. Epoxy monomers had little interaction with the alumina surface before the reaction, whereas hydroxy groups formed by the ring-opening reaction of epoxy groups exhibited notable interaction. Conversely, sulfonyl and amino groups in amine compounds formed hydrogen bonds with OH groups on the alumina surface before the reaction. However, after the reaction, amino groups weakened their interaction with the alumina OH groups as they transformed from primary to tertiary during the curing reaction. Both epoxy and amine monomers/fragments similarly interacted with water molecules, both before and after the reaction. The insights gained from this study are expected to contribute to a better understanding of the impact of moisture absorption on the application of epoxy resins.

DOI： 10.1021/acs.langmuir.4c01081

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Language：English   Publisher：Journal of Physical Chemistry B  

Epoxy resins are essential for various applications, and their properties depend on the curing reactions during which epoxy and amine compounds form the network structure. We here focus on how the presence or absence of two methyl groups in common epoxy bases, diglycidyl ether of bisphenol A and F (4,4′-DGEBA and 4,4′-DGEBF), affects the curing kinetics. The chemical reactions of both 4,4′-DGEBA and 4,4′-DGEBF, when cured with the same amine, were monitored by Fourier-transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Despite no difference in the reactivity of epoxy groups between 4,4′-DGEBA and 4,4′-DGEBF, the initial curing reaction was slower for the latter. This delay for the 4,4′-DGEBF system was attributed to intermolecular stacking, which hindered the approach of unreacted epoxy groups to amino groups and vice versa. This conclusion was drawn from the results obtained through ultraviolet (UV) spectroscopy, wide-angle X-ray scattering (WAXS), density functional theory (DFT) calculation, and all-atom molecular dynamics (MD) simulation.

DOI： 10.1021/acs.jpcb.4c01152

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

A better understanding of the aggregation states of adhesive molecules in the interfacial region with an adherend is crucial for controlling the adhesion strength and is of great inherent academic interest. The adhesion mechanism has been described through four theories: adsorption, mechanical, diffusion, and electronic. While interfacial characterization techniques have been developed to validate the aforementioned theories, that related to the electronic theory has not yet been thoroughly studied. We here directly detected the electronic interaction between a commonly used thermosetting adhesive, cured epoxy of diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenylmethane (DDM), and copper (Cu). This study used a combination of density functional theory (DFT) calculations and femtosecond transient absorption spectroscopic (TAS) measurements as this epoxy adhesive-Cu pairing is extensively used in electronic device packaging. The DFT calculations predicted that π electrons in a DDM molecule adsorbed onto the Cu surface flowed out onto the Cu surface, resulting in a positive charge on the DDM. TAS measurements for the Cu/epoxy multilayer film, a model sample containing many metal/adhesive interfaces, revealed that the electronic states of excited DDM moieties at the Cu interface were different from those in the bulk region. These results were in good accordance with the prediction by DFT calculations. Thus, it can be concluded that TAS is applicable to characterize the electronic interaction of adhesives with metal adherends in a nondestructive manner.

DOI： 10.1021/acs.langmuir.4c00711

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Language：English   Publisher：The Society of Rheology, Japan  

<p>In silica-filled epoxy resins, amorphous silica particles are generally covered with silanol groups on their surfaces, rendering them susceptible to moisture adsorption. Thus, the importance lies in better understanding the aggregation states of epoxy resins on the surface of amorphous silica and the influence of adsorbed water on the silica surface on the curing reaction. Here, we propose a method to generate amorphous silica by inserting oxygen atoms into the Si-Si bonds of amorphous silicon, serving as a model construction for molecular dynamics (MD) simulations. The surface structure of the silica was then extracted, and a mixture of an epoxy base (diglycidyl ether of bisphenol-A, DGEBA) and an amine hardener (4,4’-diaminodiphenyl sulfone, DDS) was placed on top of it. SO₂ groups of DDS strongly adsorbed on the silica surface through hydrogen bonding and remained after curing, although this interaction was weakened due to the reduced degree of freedom caused by cross-linking. On the other hand, DGEBA did not exhibit such a strong interaction with the silica surface. After curing, OH groups generated by the ring-opening of epoxy groups formed slight hydrogen bonds with the silica surface. When a small amount of water was adsorbed onto the silica surface, it diffused slightly into the epoxy resin, enhancing the mobility of the reactants in the system, and consequently accelerating the curing reaction.</p>

DOI： 10.1678/rheology.52.91

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Language：Japanese   Publisher：Japanese Society for Engineering Education  

DOI： 10.20549/jseeja.2024.0_408

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Polymer chains at a buried interface with an inorganic solid play a critical role in the performance of polymer nanocomposites and adhesives. Sum frequency generation (SFG) vibrational spectroscopy with a sub-nanometer depth resolution provides valuable information regarding the orientation angle of functional groups at interfaces. However, in the case of conventional SFG, since the signal intensity is proportional to the square of the second-order nonlinear optical susceptibility and thereby loses phase information, it cannot be unambiguously determined whether the functional groups face upward or downward. This problem can be solved by phase-sensitive SFG (ps-SFG). We here applied ps-SFG to poly(methyl methacrylate) (PMMA) chains in direct contact with a quartz surface, shedding light on the local conformation of chains adsorbed onto the solid surface. The measurements made it possible to determine the absolute orientation of the ester methyl groups of PMMA, which were oriented toward the quartz interface. Combining ps-SFG with all-atomistic molecular dynamics simulation, the distribution of the local conformation and the driving force are also discussed.

DOI： 10.1063/5.0184315

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Repository Public URL： https://hdl.handle.net/2324/7165107

DOI： https://doi.org/10.1038/s41428-023-00864-8

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

Synchrotron radiation X-ray computed tomography (CT) provides information about the three-dimensional electron density inside a sample with a high spatial resolution. Recently, the need to examine the internal structure of materials composed of light elements, such as water and carbon fibers in resins, has increased. Small density differences in these systems give low X-ray contrast; segmentation methods suited for this type of problem are necessary. Machine learning is typically used to analyze CT data, and a large amount of training data is required to train a machine learning model. Conversely, transfer learning, which uses existing learning models, can develop a learning model using only a small amount of training data. In this study, the synchrotron radiation X-ray CT images of an epoxy resin containing water have been analyzed using transfer learning as the validation of a method for analyzing low-contrast CT data with high accuracy. Circular domain structures in the resin have been observed using the X-ray CT method, and statistical information about these structures has been successfully obtained by transfer learning-based analysis. Here, transfer learning is performed using twelve slices within an X-ray CT 3D image, demonstrating that low-contrast synchrotron CT data can be segmented with a small amount of training data.

DOI： 10.1080/27660400.2023.2270529

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

We present a strategic approach for enhancing the ionic conductivity of block copolymer electrolytes. This was achieved by introducing mixed ionic liquids (ILs) with varying molar ratios, wherein the imidazolium cation was paired with either tetrafluoroborate (BF4) anion or bis(trifluoromethylsulfonyl)imide (TFSI) anion. Two polymer matrices, poly(4-styrenesulfonate)-b-polymethylbutylene (SSMB) and poly(4-styrenesulfonyl (trifluoromethanesulfonyl)imide)-b-polymethylbutylene (STMB), were synthesized for this purpose. All the SSMB and STMB containing mixed ILs showed hexagonal cylindrical structures, but the type of tethered acid group significantly influenced the interfacial properties. STMB electrolytes demonstrated enhanced segregation strength, which was attributed to strengthened Coulomb and hydrogen bonding interactions in the ionic domains, where the ILs were uniformly distributed. In contrast, the SSMB electrolytes exhibited increased concentration fluctuations because the BF4 anions were selectively sequestered at the block interfaces. This resulted in the effective confinement of imidazolium TFSI along the ionic domains, thereby preventing ion trapping in dead zones and facilitating rapid ion diffusion. Consequently, the SSMB electrolytes with mixed ILs demonstrated significantly improved ionic conductivities, surpassing the expected values based on the arithmetic average of the conductivities of each IL, whereas the ionic conductivity of the STMB was aligned with the expected average. The methodology explored in this study holds great promise for the development of solid-state polymer electrolytes.

DOI： 10.1063/5.0173322

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Publisher：Polymer Journal  

In response to the problem of microplastics, polyesters are attracting great attention due to their degradability in underwater environments. We recently demonstrated that the hydrolysis of linear polyglycolide (PGA) in a fiber state strongly depends on segmental dynamics in aqueous phases. This finding implies that the degradation of PGA can be controlled by tuning the segmental dynamics in water. Our choice of fiber geometry was based on its relatively large surface area-to-volume ratio. Herein, we examined the effects of the addition of a hyperbranched polymer (HBP) with a polyester skeleton and with many terminal hydroxy groups on the degradability characteristics of fiber mats. Dynamic mechanical analysis revealed that HBP acted as a plasticizer, especially in underwater environments. The weight loss of the PGA fiber mats was accelerated with increasing HBP content. In addition, structural analyses confirmed that crystal degradation had occurred and that hydrolysis-cleaved chains had crystallized. Considering that the structural changes in the PGA crystals depended on the feed amount of HBP, we claimed that HBP promoted PGA degradation in both the amorphous and crystalline phases. We believe that our simple strategy for accelerating the degradation of polyesters can provide suggestions for solving issues with microplastics.

DOI： 10.1038/s41428-023-00828-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Recently, environmentally degradable polymers have received great attention from the perspective of sustaining the aquatic environment. To control the degradation behavior of solid polymer materials in an aqueous phase, it is crucial to better understand the thermal molecular motion of polymer chains in water. We herein focus on polyglycolide (PGA), which is one of the representative aliphatic polyesters that are hydrolytically degradable. Three kinds of fiber mats of PGA with different fiber diameters and comparable crystallinities were prepared using an electrospinning method. Our choice of fiber mats was because the ratio of the surface area, where the hydrolytic degradation starts to occur, to the volume was larger than that for the films. Dynamic mechanical analysis (DMA) enabled us to gain direct access to the dynamic glass transition temperature (Tg & alpha;) of PGA in the fiber mats both in dry gaseous nitrogen and liquid water. The Tg & alpha; value varied not only with the presence of water molecules, but also with the fiber diameter, or the specific surface area. The degradation behavior of PGA fiber mats was examined by immersing the samples in phosphate-buffered saline at various temperatures. When the segmental motion of PGA in the fiber mats was released, the apparent crystallinity of the mats increased, meaning that PGA amorphous chains were cleaved and thus partially eluted into the aqueous phase. It was also shown that partially cleaved chains crystallized.The release of segmental motion of polyglycolide in fiber mats caused cleavage and partial elution of chains into aqueous phases.

DOI： 10.1039/d3sm00613a

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Optimizing hydrogen production in ascorbic acid solutions: enhancing BODIPY dye-sensitized processes through alkyl-chain-enhanced second coordination sphere effects.

DOI： 10.1039/d3ta03682k

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Language：English   Publisher：ACS Applied Materials and Interfaces  

Interfacial polymer layers with nanoscale size play critical roles in dissipating the strain energy around cracks and defects in structural nanocomposites, thereby enhancing the material’s fracture toughness. However, understanding how the intrinsic mechanical dynamics of the interfacial layer determine the toughening and reinforcement mechanisms in various polymer nanocomposites remains a major challenge. Here, by means of a recently developed nanorheology atomic force microscopy method, also known as nanoscale dynamic mechanical analysis (nDMA), we report direct mapping of dynamic mechanical responses at the interface of a model epoxy nanocomposite under the transition from a glassy to a rubbery state. We demonstrate a significant deviation in the dynamic moduli of the interface from matrix behavior. Interestingly, the sign of the deviation is observed to be reversed when the polymer changes from a glassy to a rubbery state, which provides an excellent explanation for the difference in the modulus reinforcement between glassy and rubbery epoxy nanocomposites. More importantly, nDMA loss tangent images unambiguously show an enhanced viscoelastic response at the interface compared to the bulk matrix in the glassy state. This observation can therefore provide important insights into the nanoscale toughening mechanism that occurs in epoxy nanocomposites due to viscoelastic energy dissipation at the interface.

DOI： 10.1021/acsami.3c06123

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Water absorbed by epoxy resins from a humid atmosphere considerably influences their structure and properties. Examining the effects of absorbed water on epoxy resins at their interfaces with solid substrates is crucial because of their adhesive applications in various fields. The spatial distribution of absorbed water in epoxy resin thin films under high humidity was investigated in this study by neutron reflectometry. Water molecules were found to accumulate at the SiO2/epoxy resin interface after exposure at a relative humidity of 85% for 8 h. The formation of an ∼1-nm-thick condensed water layer was observed, and the thickness of this layer varied with curing conditions of epoxy systems. Furthermore, water accumulation at the interface was noted to be affected by high-temperature and high-humidity environments. The formation of the condensed water layer is presumed to be related to the features of the polymer layer near the interface. The construction of the interface layer of epoxy resin would be affected by the interface constraint effect on the cross-linked polymer chain during the curing reaction. This study provides essential information for understanding the factors influencing the accumulation of water at the interface in epoxy resins. In practical applications, the process of improving the construction of epoxy resins near the interface would be a reasonable solution to resist water accumulation in the interface.

DOI： 10.1021/acs.langmuir.3c01091

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Epoxy resins, which possess a three-dimensional network obtained by a curing reaction between epoxy and amine compounds, are in a glassy state at room temperature. They are therefore generally brittle and exhibit rather poor resistance to crack propagation, which is one of the greatest drawbacks for their practical application. To solve this problem, a better understanding of their fracture behavior, which is related to long-term durability, is strongly desired. We herein report on how the extent of network heterogeneity affects the fracture behavior of epoxy resins. Three types of epoxy resins were obtained under different curing conditions, which generated different extents of heterogeneity. The fracture behavior of the three epoxy resins was examined by in situ scanning electron microscopy in conjunction with microbeam X-ray scattering experiments. When the epoxy resin in which a notch was pre-introduced was stretched under a small strain, the internal network structure was deformed, and the extent was more significant with increasing heterogeneity. As further stretching was applied, a crack propagated from the notch. This occurred more easily with increasing heterogeneity. That is, the toughness of the epoxy resins decreased with increasing network heterogeneity. The knowledge obtained here will be useful for understanding and controlling the toughness of epoxy resins.

DOI： 10.1021/acs.macromol.3c00341

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Macromolecules  

In general, the network structure formed in epoxy resins is heterogeneous, and its extent is dependent on the curing temperature. Based on Fourier-transform infrared spectroscopy in conjunction with coarse-grained molecular dynamics simulations, we herein discuss the origin of mesoscopic heterogeneity in an epoxy resin composed of a typical epoxy base and diamine hardener, which react with each other in two steps. The rate balance of the first and second step reactions, which led to chain extension and branching, respectively, depended on the curing temperature; at a higher temperature, the second-step reaction became faster. Since the reaction proceeded more slowly at lower temperatures, a homogeneous domain was formed as unreacted substances were incorporated into the network. At higher temperatures, on the other hand, the reaction proceeded rapidly before unreacted substances were incorporated into the network, leaving isolated small fragments and nanoscale voids or free spaces in the domain. We also found that an actively reacting domain with a length scale of several tens of nanometers was formed even at a conversion lower than the gel point, regardless of the curing temperature. The connection of domains was also key to better understanding the temperature dependence of the hierarchical heterogeneity. The final network was found to be denser and more homogeneous at a lower temperature, while heterogeneous with many free spaces at a higher temperature. Our molecular picture of the network formation drawn by combining experimental and simulation techniques advances our current understanding of the heterogeneity formed in epoxy resins.

DOI： 10.1021/acs.macromol.3c00411

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Language：English   Publisher：Langmuir  

Nanofiber mats composed of polymers, having a large surface-to-volume ratio and high porosity, have been widely applied in the environmental and biomedical fields but fundamental knowledge on the polymer chains in the mats seems to be limited. We here report the aggregation states and segmental dynamics of poly(methyl methacrylate)s (PMMAs) with different stereoregularities in electrospun nanofiber mats. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy revealed that, in the case of atactic PMMA (at-PMMA), the population of the trans-trans conformation of the main chain part, which allows carbonyl groups of the side group to interact affirmatively with each other, increased in the electrospun nanofiber mat. On the other hand, in the case of isotactic PMMA (it-PMMA), the skeletal conformation was unchanged even in the nanofiber mat. As a result of the aggregation states of PMMA chains, the glass-transition temperature (Tg) of the electrospun nanofiber mats increased and remained unchanged from the corresponding bulk value for at- and it-PMMA, respectively. These findings should be useful for designing materials and devices composed of electrospun nanofibers.

DOI： 10.1021/acs.langmuir.3c00698

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

The relaxation of the local conformation of ethylene-propylene-diene terpolymer (EPDM) rubber at the quartz interface was examined by sum frequency generation (SFG) spectroscopy in conjunction with all-atom molecular dynamics (MD) simulations. At room temperature, SFG peaks due to the CH symmetric stretching vibration of methyl (CH3s) and methylene (CH2s) groups were observed, and the intensity was stronger for CH3s than for CH2s. The CH3s to CH2s intensity ratio was reversed during the heating process, meaning that the local conformation of EPDM at the interface changed. MD simulations revealed that the fraction of ethylene units in the trans conformation on the substrate surface decreased once the temperature was greater the interfacial glass transition temperature (Tg), which was determined based on the temperature dependence of the mass density. Moreover, the temperature-induced change in the fraction of propylene units in the trans conformation was less remarkable than that of ethylene units. Both SFG spectroscopy and MD simulation confirmed that the Tg was higher in the interfacial region than in the bulk.

DOI： 10.1038/s41428-023-00764-x

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Other Link： https://www.nature.com/articles/s41428-023-00764-x

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Polymer adhesion with inorganic materials is a key technology for realizing the diversification of materials. When a polymer contacts with inorganic materials, a layer containing strongly- and loosely-adsorbed chains is formed at the surface. The former and latter are chains that adopt mainly train and loop/tail conformations, respectively. To improve the interfacial adhesion, it is of pivotal importance to control the interaction between loosely-adsorbed chains, which are in part directly attached to the solid surface, and bulk free chains. We here succeeded in increasing the interfacial strength by chemically cross-linking them. Polymer chains were attached to the surface of a silicon wafer and then a film of isotactic polypropylene or polyamide 6 was mounted on it to produce our model system. As loosely-adsorbed chains have photo-cross-linkable moieties, the polyolefin or engineering plastic film could be strongly adhered to the silicon wafer via the adsorbed layer. On the other hand, the film could be easily detached from the wafer having loosely-adsorbed chains without photo-cross-linkable groups. Our facile idea that loosely-adsorbed interfacial chains chemically bond to the polymer bulk shows promise for the design and construction of not only interfacial adhesion but also composite materials.

DOI： 10.1016/j.polymer.2022.125581

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Effects of Acid Value and Volume Fraction of Maleic Anhydride-modified Polypropylene on Mechanical Properties for Polypropylene-based Composites

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Squaraine dyes are organic dyes having strong and narrow absorption properties in the near-infrared region that are widely used in photovoltaic and biomedical applications. In this work, squaraine dye (SA1) was synthesized as a dye sensitizer for a dye-sensitized photocatalytic system, which was composed of SA1 and Pt-loaded TiO2 powder photocatalyst (SA1/Pt-TiO2). The SA1/Pt-TiO2 system exhibited a good hydrogen production performance within 150 h and an apparent quantum yield of 1.4% under 800 nm monochromatic light irradiation. However, during the photocatalytic reaction, the photocatalytic activity of SA1/Pt-TiO2 decreased due to photodecomposition. Ultraviolet–visible absorption spectroscopy, 1H nuclear magnetic resonance spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry measurements were performed to investigate the mechanism of the decomposition of the squaraine moiety of SA1, the decomposition process, and the structure of the decomposed material. The results show that even without the Pt-loaded TiO2 powder photocatalyst, SA1 undergoes photodissociation, which cleaves the bond between the indoline moiety and the square acid. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s00339-022-06281-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Association for the Advancement of Science (AAAS)  

Natural systems, composite materials, and thin-film devices adsorb macromolecules in different phases onto their surfaces. In general, polymer chains form interfacial layers where their aggregation states and thermal molecular motions differ from the bulk. Here, we visualize well-defined double-stranded DNAs (dsDNAs) using atomic force microscopy and molecular dynamics simulations to clarify the adsorption mechanism of polymer chains onto solid surfaces. Initially, short and long dsDNAs are individually and cooperatively adsorbed, respectively. Cooperative adsorption involves intertwining of multiple chains. The dependence of adsorption on the chain affects the formation of the interfacial layer, realizing different mechanical properties of DNA/filler bulk composites. These findings will contribute to the development of light and durable polymer composites and films for various industrial, biomedical, and environmental applications.

DOI： 10.1126/sciadv.abn6349

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

A better understanding of the carrier formation process for semiconducting polymers, especially in thin films, is essential for designing and constructing highly functionalized polymeric optoelectronic devices. Here, the effects of aggregation states and thermal molecular motion on photocarrier formation in melt-crystallized thin films of monodispersed poly(3-hexylthiophene) (P3HT) are discussed. Grazing incidence X-ray diffraction measurements revealed that the crystalline ordering in the films was greatly influenced by the molecular weight (MW) of P3HT. In contrast, dynamic mechanical analysis (DMA) revealed that the MW had no significant effects on the α1 relaxation process, which corresponded to the twisting motion of thiophene rings in the crystalline phase unless the MW was quite small. Femtosecond transient absorption (TAS) spectroscopy showed that better crystalline ordering led to the direct formation of polarons (P) from hot excitons at room temperature. Once the temperature went beyond Tα1, at approximately 310 K, the P formation process from polaron pairs (PP) was activated. Thus, it can be claimed that the P formation for P3HT could be regulated by the thermal molecular motion in addition to the crystalline structure. The knowledge obtained here should be useful for a better molecular design of semiconducting polymers that can be applied to optoelectronic devices.

DOI： 10.1038/s41428-022-00713-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Macromolecules  

Aqueous solutions of atactic poly(N-isopropylacrylamide) (PNIPAM) exhibit complex phase transitions at 20–33 °C, that is, the phase behaviors of lower critical solution temperature (LCST) and physical gelation. The LCST phase behavior has been successfully described by the “pearl-necklace” chain model (Macromolecules 2005, 38, 4465); however, the formation of the physical gel is still elusive. In this study, atactic PNIPAM (a-PNIPAM) was used and the gel point (GP) of semidilute solutions was validated by observing the frequency-independent loss tangent (Winter–Chambon criterion) from the oscillatory shear measurements to derive the gel temperature Tgel. It was found that the relaxation exponent n at GP is independent of solution concentration to be 0.76 with the fact that entanglement couplings play no effect on n. Tgel decreases with a-PNIPAM concentration from 29.5 °C for the 5 wt % unentangled solution to 25 °C for the 12 wt % entangled solution. The binodal point (Tb) was obtained from the extrapolated cloud-point temperature at zero heating rate, at which an initial drop of the light transmittance was observed. Based on these derived data, a phase diagram was constructed to show three typical phase domains composed of an one-phase solution at T < Tgel, a clear gel at Tgel < T < Tb, and an opaque gel at T > Tb. At 30 °C, the clear gels of 5 and 12 wt % samples possess extremely low equilibrium moduli of 0.2 and 41 Pa, respectively, suggesting that many a-PNIPAM single chains are associated and connected in between two gel junctions. Synchrotron small-angle/wide-angle X-ray scattering was performed to disclose the radius of gyration of gel junctions (with functionality f ≥ 3) to be 30–55 Å above Tgel. Within the gel junctions, the collapsed subchains (pearls), which belong to different chains, become more compact with the interchain distance decreasing from 15 Å at 20 °C to 11 Å at 30 °C for the 12 wt % solution. We proposed that the origin of physical gelation is relevant to the inter-amide hydrogen bonding between collapsed subchains in the gel junctions to develop a strong physical bonding for interchain connectivity. At an elevated temperature approaching the GP but still below the spinodal temperature, the physical crosslinking of the developing pregel clusters is further facilitated by the enhanced concentration fluctuations with a small-q Fourier-mode driven by the interchain associations, eventually giving rise to the critical gel at Tgel prior to solution phase separation.

DOI： 10.1021/acs.macromol.1c02476

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The mechanical properties of glassy polymer thin films change as film thickness decreases below the average polymer molecule size. These changes have been associated with a reduction in interchain entanglements due to confinement and an increase in molecular mobility from the mobile surface layer. Here, using experiments and simulations, we determine how entanglements and surface mobility each individually impact the failure behavior of a glassy polymer film as the film becomes confined. We utilize a custom-built uniaxial tensile tester for ultrathin films and dark-field optical microscopy to characterize the complete stress–strain response and the associated strain localizations for ultrathin polystyrene films of varying thicknesses (h = 10 to 150 nm) for a range of molecular weights Mn of 61 to 2135 kDa. To directly correlate the changes in the molecular network to changes in the failure properties of ultrathin films, we perform nonequilibrium molecular dynamics simulations on N = 250, N = 60, with h = 10 to 30 films. From our results, accounting for both the changes in entanglements and mobility, we propose a semiempirical model that captures the failure response in both simulated and experimental glassy polymer thin films.

DOI： 10.1021/acs.macromol.2c01435

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We have succeeded in visualizing the spatial heterogeneity of the reaction ratio in epoxy resins by combining medium-angle X-ray scattering (MAXS) and computed tomography (CT). The reaction ratio is proportional to the degree of cross-linking between epoxy and amine in epoxy resins. The reaction ratio and its spatial inhomogeneity affect the toughness of epoxy resins. However, there has been no non-destructive method to measure the spatial inhomogeneity of the reaction ratio, although we can measure only the spatially averaged reaction ratio by Fourier-transform infrared spectroscopy (FT-IR). We found that the scattering peak reflected the cross-linking structures in the q region of MAXS and that the peak intensity is proportional to the reaction ratio. By reconstructing CT images from this peak intensity, we visualized the spatial heterogeneity of the reaction ratio. The application of this method may not be limited to epoxy resins but may extend to studying the heterogeneity of cross-linked structures in other materials.

DOI： 10.1021/acs.langmuir.2c01741

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The addition of a small fraction of solid nanoparticles to thermosetting polymers can substantially improve their fracture toughness, while maintaining various intrinsic thermomechanical properties. The underlying mechanism is largely related to the debonding process and subsequent formation of nanovoids at a nanoscale nanoparticle/epoxy interface, which is thought to be associated with a change in the structural and mechanical properties of the formed epoxy network at the interface compared with the matrix region. However, a direct characterization of the local physical properties at this nanoscale interface remains significantly challenging. Here, we employ a recently developed bimodal atomic force microscopy technique for the direct mapping of nanoscale elastic and adhesive responses of an amine-cured epoxy resin filled with ∼50 nm diameter silica nanoparticles. The obtained elastic modulus and dissipated energy maps with high spatial resolution evidence the existence of a ∼20-nm-thick interfacial epoxy layer surrounding the nanoparticles, which exhibits a reduced modulus and weaker adhesive response in comparison with the matrix properties. While the presence of such a soft and weak-adhesive interfacial layer is found not to affect the architecture of structural heterogeneities in the epoxy matrix, it conceivably supports the toughening mechanism related to the debonding and plastic nanovoid growth at the silica/epoxy interface. The incorporation of this soft interfacial layer into the Halpin–Tsai model also provides a good explanation for the effect of the silica fraction on the tensile modulus of cured epoxy nanocomposites.

DOI： 10.1021/acsami.2c12335

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

A chemical reaction between epoxy and amine compounds at an outermost solid interface was studied by sum-frequency generation spectroscopy, X-ray and neutron reflectivity and a full atomistic molecular dynamics simulation.

DOI： 10.1039/d2cp03394a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The adhesive strength of epoxy resins is generally dependent on the surface chemistry of an adherend. Although the free space, or the nanoscopic void space, formed at the adhered interface due to the curing shrinkage is expected to have a significant impact on the adhesive strength, the molecular picture is not yet well understood. In this study, all-atom molecular dynamics simulations were used to investigate how the curing reaction and thereby adhesive strength of an epoxy resin differed on hydrophilic and hydrophobic silicon substrates. Before the reaction, a hardener of amine with a smaller molecular size was segregated at the silicon surface, and the extent became more remarkable on the hydrophilic surface with hydroxy groups that formed hydrogen bonds with amine. The epoxy resin shrank as the curing reaction proceeded, forming the overall 5-10% free space. The resin remained attached to the hydrophilic substrate, but was partly separated from the hydrophobic surface, resulting in the 15% free space in the 0.2 nm adhered interfacial region and thus a lesser contact area. Reflecting this, under tensile deformation, cohesive failure and interfacial delamination occurred for the hydrophilic and hydrophobic surfaces, respectively, under a yield stress of 200 MPa and a strain of 0.1. Our findings make it clear that the surface chemistry of an adherend was crucial for the adhesive strength of the epoxy resins via the microstructure formation at the interface.

DOI： 10.1021/acsapm.2c00855

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Biomacromolecules  

Microplastics have recently been identified as one of the major contributors to environmental pollution. To design and control the biodegradability of polymer materials, it is crucial to obtain a better understanding of the aggregation states and thermal molecular motion of polymer chains in aqueous environments. Here, we focus on melt-spun microfibers of a promising biodegradable plastic, polyamide 4 (PA4), with a relatively greater number density of hydrolyzable amide groups, which is regarded as an alternative to polyamide 6. Aggregation states and thermal molecular motion of PA4 microfibers without/with a post-heating drawing treatment under dry and wet conditions were examined by attenuated total reflectance-Fourier transform infrared spectroscopy and wide-angle X-ray diffraction analysis in conjunction with dynamic mechanical analysis. Sorbed water molecules in the microfibers induced the crystal transition from a meta-stable γ-form to a thermodynamically stable α-form via activation of the molecular motion of PA4 chains. Also, the post-drawing treatment caused a partial structural change of PA4 chains, from an amorphous phase to a crystalline phase. These findings should be useful for designing PA4-based structural materials applicable for use in marine environments.

DOI： 10.1021/acs.biomac.2c00618

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Langmuir  

To ensure the quality and reliability of products bonded by epoxy resin adhesives, elucidation of the microscopic adhesion mechanism is essential. The adhesive interaction and bonding strength between epoxy resins and hydroxylated γ-alumina (001) surfaces were investigated by using a combined molecular dynamics (MD) and density functional theory (DFT) study. The curing reaction of an epoxy resin consisting of diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenyl sulfone (DDS) was simulated. The resin structure was divided into fragmentary structures to study the interaction of each functional group with the alumina surface using DFT calculations. From the characteristics of the adhesive structures and the calculated adhesion energies, it was found that the fragments forming hydrogen bonds with hydroxy groups on the alumina surface resulted in large adhesion energies. On the other hand, the fragments adsorbed on the alumina surface via dispersion interactions resulted in small adhesion energies. The adhesion forces evaluated from the Hellmann–Feynman force calculations indicated the significant contribution of the hydroxy groups and benzene ether moieties derived from DGEBA to the adhesive stress of the DGEBA/DDS epoxy resin. The direction of hydrogen bonding between the epoxy resin and the surface and the difference in geometry at the interface between the donor and acceptor of hydrogen bonding played a central role in maintaining the adhesive strength during the failure process of the adhesive interface.

DOI： 10.1021/acs.langmuir.2c00529

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Adhesion is a molecular event where polymer chains contact with a material surface to form an interfacial layer. To obtain a better understanding of the adhesion on a molecular scale,...

DOI： 10.1039/d1sm01833g

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The interfacial strength of polystyrene (PS) with and without PS oligomers in contact with a glass substrate was examined to determine the relationship between the interfacial aggregation state and adhesion. The shear bond strength and adsorbed layer thickness of neat PS exhibited a similar dependence on the thermal annealing time: they increased to constant values within almost the same time. This implies that the adhesion of the polymer is closely related to the formation of an adsorbed layer at the adhesion interface. Nevertheless, in the case of PS with a small amount of oligomer, the shear bond strength decreased, while the adsorbed layer thickness was almost the same as that of neat PS. Based on the results of interfacial analyses, we propose that the interfacial segregation of the oligomer reduced the entanglement between the interfacial free chains in the adsorbed layer and the bulk chains.

DOI： 10.1021/acsmacrolett.2c00062

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The molecular weight of the adsorbed layer on a substrate affects the suppressed dynamics of supported thin polystyrene films.

DOI： 10.1039/D2SM00067A

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Sum-frequency generation (SFG) spectroscopy is a powerful tool to study the molecular orientation in confined systems such as interfaces on the basis of the second-order nonlinear optical effect. We herein demonstrated SFG imaging for films of uniaxially oriented poly(vinylidene fluoride) and spin-coated isotactic polypropylene and successfully identified the orientational difference of lamellar fibrils in the two films. SFG chemical mapping was finally performed by taking advantage of the different absorption wavelengths for methylene groups in the two samples. To the best of our knowledge, this is the first report dealing with SFG mapping for synthetic polymers.

DOI： 10.1038/s41428-021-00613-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Due to the importance of the interface in the segmental dynamics of supported macromolecule ultrathin films, the glass transition temperature (Tg) of polystyrene (PS) ultrathin films upon solid substrates modified with a cross-linked PS (CLPS) layer has been investigated. The results showed that the Tg of the thin PS films on a silica surface with a ∼5 nm cross-linked layer increased with reducing film thickness. Meanwhile, the increase in Tg of the thin PS films became more pronounced with increasing the cross-linking density of the layer. For example, a 20 nm thick PS film supported on CLPS with 1.8 kDa of cross-linking degree exhibited a ∼35 and ∼50 K increase in Tg compared to its bulk and that on neat SiO2 substrate, respectively. Such a large Tg elevation for the ultrathin PS films was attributed to the interfacial aggregation states in which chains diffused through nanolevel voids formed in the cross-linked layer to the SiO2–Si surface. In such a situation, the chains were topologically constrained in the cross-linked layer with less mobility. These results offer us the opportunity to tailor interfacial effects by changing the degree of cross-linking, which has great potential application in many polymer nanocomposites.

DOI： 10.1021/acsmacrolett. 1c00611

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ポリプロピレン(PP)/フィラー複合材料に無水マレイン酸変性ポリプロピレン(PP-g-MA)を添加した際の引張降伏応力(σy)について検討した。フィラーとして,同程度の平均粒子径を有する球状シリカ(SiO2)または球状アルミナ(Al2O3)を用いた。Al2O3系複合材料はSiO2系よりも大きなσyを示した。また,PP-g-MAとフィラーを混合した後,PP-g-MAを溶かし出した試料の熱重量測定を行った。Al2O3上に吸着したPP-g-MA鎖の熱分解に由来する重量減少は,SiO2上のそれよりも顕著であった。この結果は,PP-g-MAは,SiO2よりAl2O3上により吸着すること,すなわち,PP-g-MAはAl2O3とより強く相互作用することを示している。以上の結果は,高分子系複合材料にマトリックスとフィラー両方に強く相互作用する第三成分を添加することは,フィラー界面,ひいては,複合材料の力学特性を改善する有効な戦略であると結論できる。

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Herein, we report the in situ transmission electron microscopy observation of the deformation and fracture processes of an epoxy resin thin film containing silica nanoparticles under tensile strain. Under tensile strain, the dispersed silica nanoparticles in the composite arrest the progress of the crack tip and prevent crack propagation. Concomitantly, the generation and growth of nanovoids at the epoxy matrix/nanoparticle interfaces were clearly observed, particularly in the region near the crack tip. These nanovoids contribute to the dissipation of fracture energy, thereby enhancing the fracture toughness. We also analyzed the local distributions of the true strain and strain rate in the nanocomposite film during tensile testing using the digital image correlation method. In the region around the crack tip, the strain rate increased by 3 to 10 times compared to the average of the entire test specimen. However, the presence of large filler particles in the growing crack suppressed the generation of strain, potentially contributing to hindering crack growth.

DOI： 10.1039/D1SM01452H

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Surface modification without changing the physical properties in the bulk is of pivotal importance for the development of polymers as devices. We recently proposed a simple surface functionalization method for polymer films by partial swelling using a nonsolvent and demonstrated the incorporation of poly(2-methoxyethyl acrylate) (PMEA), which has an excellent antibiofouling ability, only into the outermost region of a poly(methyl methacrylate) (PMMA) film. We here extend this technology to another versatile polymer, polystyrene (PS). In this case, PS and PMEA have different solubility parameters making it difficult to select a suitable solvent, which is a nonsolvent for PS and a good solvent for PMEA, unlike the combination of PMMA with PMEA. Thus, such a solvent was first sought by examining the swelling behavior of PS films in contact with various alcohols. Once a mixed solvent of methanol/1-butanol (50/50 (v/v)) was chosen, PMEA chains could be successfully incorporated at the outermost region of the PS film. Atomic force microscopy in conjunction with neutron reflectivity revealed that chains of PMEA incorporated in the PS surface region were well swollen in water. This leads to an excellent ability to suppress the adhesion of platelets on the PS film.

DOI： 10.1021/acs.langmuir.1c02852

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The mechanical properties in the outermost region of a polymer film strongly affect various material functions. We here propose a novel and promising strategy for the two-dimensional regulation of the mechanical properties of a polymer film at the water interface based on an inkjet drawing of silica nanoparticles (SNPs) underneath it. A film of poly(2-hydroxyethyl methacrylate) (PHEMA), which exhibits excellent bioinertness properties at the water interface, was well fabricated on a substrate with a pattern of SNPs. X-ray photoelectron spectroscopy and atomic force microscopy confirmed that the surface of the PHEMA film was flat and chemically homogeneous. However, the film surface was in-plane heterogeneous in stiffness due to the presence of the underlying SNP lines. It was also noted that NIH/3T3 fibroblast cells selectively adhered and formed aggregates on the areas under which an SNP line was drawn.

DOI： 10.1021/acs.langmuir.1c02776

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The physical performance of an epoxy-based material is largely influenced by the formation of heterogeneous nanostructures (HNSs) in the glassy three-dimensional epoxy network. Thus, understanding the connectivity and local mechanical properties of HNSs formed in cured epoxy networks is of critical importance in the development of advanced epoxy-based materials for innovative adhesion technology. Here, we use bimodal atomic force microscopy (AFM) to map the local mechanical responses of HNSs evolved in an epoxy–amine system during curing. Both modulus and dissipated energy quantities describing the elastic and adhesive responses, respectively, were simultaneously obtained at different harmonic vibrations in each bimodal AFM measurement. HNSs exhibiting different elastic and adhesive responses were clearly visualized for all epoxy networks at different levels of curing. The architecture and local mechanical responses of HNSs were visibly altered with increasing degree of conversion. Soft domains representing network regions with relatively lower elastic moduli and weaker adhesive interactions were dominant and continuously connected at initial stages of curing up to conversion degrees of ∼91%. However, hard domains became increasingly connected upon approaching the fully cured stage. In combination with previously reported results obtained using the particle tracking technique to study the network heterogeneity at lower conversion degrees of the same epoxy system, we were able to provide a full picture describing the generation and development of mechanical heterogeneities in the network during curing in which the length scale of the heterogeneities decreased from several hundred nanometers at the pregelation stage to ∼10 nm at the fully cured stage.

DOI： 10.1021/acsanm.1c02692

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DOI： 10.1039/D1CP03959H

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DOI： 10.1021/acs.macromol.1c01293

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A new method is proposed to measure the longitudinal thermal conductivity of fibers and films. The thermal conductivity of novel one- and two-dimensional materials has previously been measured using a T-type probe. Although this method is applicable to polymer fibers and films, the measurements are influenced by the thermal contact resistance between the probe and the sample. We therefore propose a so-called ITX method, which determines the inherent thermal conductivity of a sample from measurements made in three geometric configurations (“I”, “T”, and “X” shape) of the sample, heat sinks, and measurement probe. Application of the method to DNA solid films demonstrated that the thermal conductivity can be accurately determined irrespective of the relative contribution of the thermal contact resistance to the overall thermal resistance.

DOI： 10.1016/j.ijheatmasstransfer.2021.121501

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ナノクリープ実験に基づき、高分子ガラス表面では分子鎖の長さに依存しない絡み合いセグメントが存在することを観測しました。従来は、高分子鎖の絡み合いはその長さのみで規定されると考えられていましたが、本研究では、高分子表面に存在する分子鎖が内部領域まで繋がるため、表面近傍でセグメントが緩和しても疑似ループコンフォメーションが形成され、短い分子鎖でも一時的に絡み合ったような粘弾性挙動を示すことを明らかにしました。

DOI： 10.1038/s41586-021-03733-7

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DOI： 10.1038/s41428-021-00528-5

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Epoxy resins with a network structure, which are obtained by curing reactions of epoxy and amine compounds, are an important class of thermosetting resins. We here report the segmental dynamics of epoxy resins in which the three-dimensional network was well-defined and systematically varied. What we found by experiments in conjunction with atomistic molecular dynamics simulation was that when the cross-linking density in the epoxy resins increased, the glass transition temperature increased with an associated reduction in the spatial scale of the cooperative rearranging region and the increase in the dynamic heterogeneity. The knowledge here obtained should be useful for a better understanding of the physical properties of thermosetting polymers.

DOI： 10.1021/acs.macromol.1c00513

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DOI： 10.1039/D1SM00529D

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DOI： 10.1063/5.0041881

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A better understanding of the aggregation states of polymers in contact with water is a pivotal issue for the development of highly functional polymer devices that work under water. As a direct experimental method to achieve the above, we used near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) on a poly(methyl methacrylate) (PMMA) film mixed with a small amount of a bottlebrush-type methacrylate polymer with oligo(2-ethyl-2-oxazoline) in its side chain portions, referred to as P[O(Ox)(n)MA], in a hydrated state. The results showed that P[O(Ox)(n)MA] was segregated at the surface of the PMMA film and suppressed the adhesion and activation of platelets on the film.

DOI： 10.1038/s41428-021-00485-z

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The thickness effect on the relaxation behavior and chain entanglements was investigated for thin polystyrene films. By following the time evolution of the wetting ridge at the surface induced by a droplet of ionic liquid, the characteristic time (tau*) at which the ridge height started to change was obtained. Here, we demonstrated experimentally that the characteristic time was associated with the disentanglement time tau(d), tau* similar to tau(d) similar to M-w(3.4)/M-e(1.4), where M-e denotes the entanglement molecular weight. The critical thickness (h(c)) at which tau* started to decrease was approximately 3.3R(g). That is, the M-e increased, or the interchain entanglement density decreased, as the film became thinner than the h(c). This might be explained in terms of the conformational change from "spherical" to "ellipsoidal", leading to a reduction in the pervaded volume (V-p) of chains in the ultrathin films.

DOI： 10.1021/acs.macromol.1c00224

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DOI： 10.1678/rheology.49.55.

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DOI： 10.1039/D0SM01600D

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DOI： 10.1038/s41428-020-00459-7

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A better understanding of the structure of polymers at solid interfaces is crucial for designing various polymer nano-composite materials from structural materials to nanomaterials for use in industry. To this end, the first step is to obtain information on how synthetic polymer chains adsorb onto a solid surface. We closely followed the trajectory of a single polymer chain on the surface as a function of temperature using atomic force microscopy. Combining the results with a full-atomistic molecular dynamics simulation revealed that the chain became more rigid on the way to reaching a pseudo-equilibrium state, accompanied by a change in its local conformation from mainly loops to trains. This information will be useful for regulating the physical properties of polymers at the interface.

DOI： 10.1038/s41598-020-77761-0

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The local conformation of polystyrene (PS) at the phase-separated lamellar interface with poly(methyl methacrylate) (PMMA) in their diblock copolymer (BCP) was examined by sum-frequency generation spectroscopy in conjunction with a full-atomistic molecular dynamics simulation. While PS phenyl groups of BCP were oriented in the interfacial region, they were random in the bulk. Such an interfacial orientation of phenyl groups was not clear for the corresponding blend of PS and PMMA. The PS backbone of BCP was in-plane oriented and folded near to the chemical junction point located in the interfacial region and the orientation became random at several nanometers distant. No evidence for the chain folding at the interface was found for the blend system.

DOI： 10.1021/acsmacrolett.0c00638

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DOI： 10.1021/acs.macromol.0c02292

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We designed an amphiphilic block copolymer, poly(methyl methacrylate)-block-poly[oligo(2-ethyl-2-oxazoline) methacrylate] (PMMA-b-P[O(Ox)MA]), suitable for bioinert coating. Angular-dependent X-ray photoelectron spectroscopy and neutron reflectivity measurements revealed that the outermost surface of a dried film of PMMA-b-P[O(Ox)MA] was covered with the PMMA block-rich layer. Once the film came into contact with water, the P[O(Ox)MA] bottlebrush block was segregated toward the water interface. This structural rearrangement in the outermost region of the film resulted in the formation of the swollen oligo(oxazoline) layer with excellent bioinertness in terms of the suppression of serum protein adsorption and NIH3T3 fibroblast adhesion.

DOI： 10.1021/acsabm.0c01118

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DOI： 10.1039/d0sm00625d

Language：English   Publishing type：Research paper (scientific journal)  

A simple way to control only the surface properties of polymer materials, without changing the bulk properties, has long been desired. The segregation behavior when a component with a tiny amount fed into the matrix is thermodynamically enriched at the surface is one of the candidate methods. This capability was examined herein by focusing on a star-shaped polyhedral oligomeric silsesquioxane (s-POSS), where the central POSS unit is tethered to eight isobutyl-substituted POSS cages as a surface modifier. X-ray photoelectron spectroscopy revealed that the surface of a film of poly(methyl methacrylate) (PMMA) was almost completely covered with POSS units by adding just 5 wt % s-POSS to it. The segregated POSS dramatically altered the physical properties such as molecular motion and the mechanical and dielectric responses at the surface of the PMMA film. These findings make it clear that s-POSS is an excellent surface modifier for glassy polymers.

DOI： 10.1021/acs.langmuir.0c01785

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.eurpolymj.2020.109812

Language：English   Publishing type：Research paper (scientific journal)  

Dynamics of polymer chains near an interface with an inorganic material are believed to strongly affect the physical properties of polymers in nanocomposites and thin films. An effect of molecular architecture on the conformational relaxation behavior of polystyrene (PS) chains at the quartz interface using sum-frequency generation spectroscopy is reported here. The relaxation dynamics of chains in direct contact with the quartz interface is slower with a star-shaped architecture than that with its linear counterpart. The extent of the delay becomes more pronounced with increasing number of arms. This can be explained in terms of the superior interfacial activity to the quartz surface for the star-shaped PS.

DOI： 10.1002/marc.202000096

Language：English  

DOI： 10.1039/d0tb00219d

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.macromol.9b02064

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.langmuir.9b03964

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsabm.0c00028

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.biomac.9b01207

Language：English   Publishing type：Research paper (scientific journal)  

Epoxy is a class of thermosetting resins and has been widely used as a representative example of structural adhesives. Nevertheless, it remains unclear how the epoxy resin and curing agent are present on the adherend surface and how they move around dynamically and react with each other to form a three-dimensional network. We here adopt a fully atomistic molecular dynamics (MD) simulation to study molecular events of an epoxy resin composed of hydrogenated bisphenol A diglycidyl ether and 1,4-cyclohexanebis(methylamine) at the interface using a narrow gap, which was sandwiched between copper surfaces. The depth profiles of the density, molecular orientation, and concentration in addition to molecular diffusivity at the interface are addressed. These are finally combined with the kinetics for the curing reactions at the interface. Although some of the information here obtained is accessible by experimentation, most is not. We believe that the findings of this study will lead to a better understanding of the adhesion phenomenon.

DOI： 10.1021/acsapm.9b01154

Language：English   Publishing type：Research paper (scientific journal)  

Frictional properties play a key role in the performance of hydrogels in applications such as soft contact lenses, cell sheets, artificial articular cartilage, etc. Here we characterize the swollen state and frictional properties of thin hydrogel films composed of poly(2-methoxyethyl vinyl ether) on a nanometer scale using neutron reflectivity (NR) in conjunction with lateral force microscopy, leading to the discussion about the extent to which surface chains impact the frictional properties of gels. NR measurement revealed that the density profile for the hydrogel films in the interfacial region with water along the direction normal to the interface was well described by a parabolic function, which was generally used for swollen polymer brushes in a liquid. Lateral, or frictional, force (F_L) first increased with increasing normal force (F_N) and then reached a region where the dependence of F_L on F_N was extremely subtle. That is, there exist two regimes, I and II, for the relationship between F_N and F_L. The thickness of the interfacial layer composed of dangling chains, which should behave like brush chains, as determined by NR measurement, was in good accordance with the depth at which the regime transited from region I to II. The frictional properties of the thin hydrogel films could be better understood by considering the two contributions from the interfacial layer and the internal bulk region.

DOI： 10.1021/acs.macromol.9b01786

Language：English   Publishing type：Research paper (scientific journal)  

A high-density poly(methyl methacrylate) (PMMA) brush (σ = 0.77 chain/nm²) with a lower molecular weight distribution was prepared onto a silicon wafer by surface-initiated atom transfer radical polymerization. The surface of the PMMA brush chains was characterized upon the process of the environmental change, from air to water, using contact angle measurements in conjunction with sum-frequency generation spectroscopy. The surface structure and properties altered less with the changing environment from air to water for the PMMA brush than for a spin-coated film; that is, the extent of surface reorganization could be suppressed by grafting densely-packed chains onto a substrate. Also, the water penetration into the brush surface was inhibited because of the densely packed chain structure.

DOI： 10.1021/acs.langmuir.9b02581

Language：English   Publishing type：Research paper (scientific journal)  

Nanocellulose (NC), which consists of a bundled structure of cellulose chains, is a class of shape-anisotropic materials with a diameter of several tens of nanometers and a length of over several hundreds of nanometers. Because the production of NC is based on the extraction process from natural resources in water, NC is generally obtained in an aqueous dispersion state. Thus, an aqueous dispersion of NC can be regarded as a precursor for NC-reinforced polymer composites. The objective of this study is to gain a better understanding of (1) local rheological properties of the NC aqueous dispersion at various length scales using a particle tracking measurement and (2) how they affect the mechanical properties of the resultant NC-reinforced polymer composite. The observation of individual particles at different positions revealed that the NC aqueous dispersion was spatially heterogeneous at the characteristic length of a few tens of micrometers. When the NC aqueous dispersion was sonicated and subsequently left undisturbed at room temperature, the length scale of the heterogeneity decreased. From the NC aqueous dispersion with and without the sonication treatment, having smaller and larger length scale of heterogeneity, respectively, poly(vinyl alcohol) (PVA) films containing NC were fabricated. The dispersion state of NC in the PVA matrix was improved by the prior sonication treatment. The addition of NC remarkably enhanced the ductility of the PVA film. However, this was the case only after the sonication treatment. The knowledge here obtained should provide a novel concept for polymer composites with tunable mechanical properties, based on the precursor-based design.

DOI： 10.1021/acs.macromol.9b01866

Language：Others   Publishing type：Research paper (scientific journal)  

© 2019 Here, we combine two strategies i.e., Förster resonance energy transfer and plasmonic effect, to enhance the photovoltaic performance in organic solar cells by introducing gold nanoparticles and squaraine in a binary mixture of poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester. In this configuration, the Förster resonance energy transfer between poly(3-hexylthiophene) and squaraine reduces the electrical loss arising from the exciton recombination in poly(3-hexylthiophene), while gold nanoparticles enable an efficient charge carrier generation in poly(3-hexylthiophene):squaraine mixture as optically confirmed by photoluminescence measurement and transient absorption spectroscopy. The multicomponent organic solar cells demonstrate an enhancement of ~36% in power conversion efficiency over the reference device.

DOI： 10.1016/j.jpowsour.2019.227031

Language：English   Publishing type：Research paper (scientific journal)  

Instability, glass transition temperature (T-g), and thermal expansion of polystyrene (PS) films are evaluated with respect to the thickness of a silicon oxide (SiOx) interlayer that mediates favorable long-range interaction from the non-oxide Si substrate. Taking into account that a SiOx interlayer is less favorable with an overlying PS film, we designed a systematic set of H-passivated (H-Si), native SiOx (N-Si), and non-native SiOx interlayer (P-Si) substrates. Here, P-Si denotes a substrate prepared by a plasma surface activation with oxygen to create an effective minimum SiOx thickness (similar to 9 nm) that is sufficient for the instability of PS films. The wetting-dewetting behavior differs in 100 and 43 kg/mol PS films supported on the three different substrates. Reflected in T-g and thermal expansion coefficient at the rubbery state for the overlying PS films, P-Si is found to be enough to promote the nontrivial instability of the films, leading to a marked decrease in T-g and increase in alpha(r) with decreasing film thickness (more than those on N-Si). Our results demonstrate the ability to use P-Si to effectively modulate favorable long-range interaction from the Si substrate better than a typical N-Si does.

DOI： 10.1021/acs.macromol.9b01284

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41428-019-0254-8

Language：English   Publishing type：Research paper (scientific journal)  

We report that the nanometer-scale architecture of polymer chains plays a crucial role in its protein resistant property over surface chemistry. Protein-repellent (noncharged), few nanometer thick polymer layers were designed with homopolymer chains physisorbed on solids. We evaluated the antifouling property of the hydrophilic or hydrophobic adsorbed homopolymer chains against bovine serum albumin in water. Molecular dynamics simulations along with sum frequency generation spectroscopy data revealed the self-organized nanoarchitecture of the adsorbed chains composed of inner nematic-like ordered segments and outer brush-like segments across homopolymer systems with different interactions among a polymer, substrate, and interfacial water. We propose that this structure acts as a dual barrier against protein adsorption.

DOI： 10.1021/acsmacrolett.9b00518

Language：English   Publishing type：Research paper (scientific journal)  

石英界面におけるポリイソプレン鎖およびニトリルゴム鎖の緩和ダイナミクスをエバネッセント波励起蛍光偏光解消法、誘電緩和測定および和周波発生分光測定に基づき、界面からの距離の関数として評価した。その結果、界面層には分子鎖ダイナミクスの勾配が存在することを明らかにし、それが弱く吸着した鎖と強く吸着した鎖によるものと説明した。強く吸着した鎖の緩和はバルクのそれと比較して10桁以上遅くなることを示している。

DOI： 10.1021/acsmacrolett.9b00351

Language：English   Publishing type：Research paper (scientific journal)  

We here report that adsorbed chains composed of one of the constituent blocks can be used as a new surface modification approach to induce perpendicularly oriented lamellar microdomains in block copolymer thin films. A nearly symmetric polystyrene-block-poly(methyl methacrylate) (PS-block-PMMA) diblock copolymer was used as a model. Densely packed PS- or PMMA-adsorbed chains of about 2-3 nm in thickness ("polymer nanocoatings") were deposited on silicon (Si) substrates using a solvent-rinsing approach. Spin-cast films of 40 or 60 nm-thick PS-block-PMMA (equivalent to two or three interdomain spacings) were subsequently deposited onto the PS or PMMA nanocoatings. Grazing incidence small-angle X-ray scattering experiments revealed the formation of perpendicularly oriented lamellar microdomains within the entire films at 200 °C, where balanced interfacial interactions at the polymer-air interface were achieved. Additionally, X-ray photon correlation spectroscopy studies demonstrated the dynamics of the fully standing lamellar microdomains in the melt, which are coupled to cooperative interdomain movement. We demonstrate that the "neutrality" of the nanocoating is attributed to its noninteractive property against both blocks. This "structurally neutral" property prevents adsorption of the PS-block-PMMA chains on the bare Si substrate that causes the undesirable substrate field effect.

DOI： 10.1021/acs.macromol.9b00597

Language：English   Publishing type：Research paper (scientific journal)  

We investigated the swelling behaviors of poly(vinyl alcohol) (PVA) films deposited on Si wafers with water vapor, which is a good solvent for PVA for elucidating structural and dynamical heterogeneities in the film thickness direction. Using deuterated water vapor, structural and dynamical differences in the thickness direction can be detected easily as different degrees of swelling in the thickness direction by neutron reflectivity. Consequently, the PVA film with a degree of saponification exceeding 98 mol % exhibits a three-layered structure in the thickness direction. It is considered that an adsorption layer consisting of molecular chains that are strongly adsorbed onto the solid substrate is formed at the interface with the substrate, which is not swollen with water vapor compared with the bulk-like layer above it. The adsorption layer is considered to exhibit significantly slower dynamics than the bulk. Furthermore, a surface layer that swells excessively compared with the underneath bulk-like layer is found. This excess swelling of the surface layer may be related to a higher mobility of the molecular chains or lower crystallinity at the surface region compared to the underneath bulk-like layer. Meanwhile, for the PVA film with a much lower degree of saponification, a thin layer with a slightly lower degree of swelling than the bulk-like layer above it can be detected at the interface between the film and substrate only under a high humidity condition. This layer is considered to be the adsorption layer composed of molecular chains loosely adsorbed onto the Si substrate.

DOI： 10.1021/acs.langmuir.9b01665

Language：English   Publishing type：Research paper (scientific journal)  

The ability to freely control the surface of bioscaffolds in a water environment is desirable to regulate cellular behaviors in vitro. Herein, we study the surface aggregation states of scaffold films composed of a multifunctional hyperbranched polymer (HBP) with perfluorohexylethyl, carboxy, and cyano groups that was prepared using a spin-coating method. Static contact angle measurements in conjunction with X-ray photoelectron spectroscopy revealed that perfluorohexylethyl groups were segregated at the surface of the HBP film in air, and these findings were more remarkable for the film treated with thermal annealing. Once the HBP film contacted water, HBP chains reorganized at the surface to minimize the free energy, resulting in the formation of a relatively hydrophilic surface. This surface reorganization was discernably faster and more remarkable for the non-annealed HBP film than for the annealed film. As fundamental characteristics of a cellular scaffold, protein adsorption, in addition to the initial adhesion and proliferation of fibroblasts, was examined using microscopy. The amount of fibronectin adsorbed depended on the presence of thermal annealing during the scaffold preparation process. A relatively larger amount of fibronectin adsorbed to the non-annealed HBP film promoted the initial adhesion and subsequent proliferation of fibroblasts.

DOI： 10.1038/s41428-019-0212-5

Language：Japanese   Publishing type：Research paper (scientific journal)  

Aggregation state and thermal molecular motion of a bio-inert polymer at the water interface

DOI： 10.1295/koron.2019-0013

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Others   Publishing type：Research paper (scientific journal)  

© 2019 American Chemical Society. Harvesting low-energy photons by strategically exploiting the photocatalytic properties of plasmonic and upconversion nanocomponents is a promising route to improve solar energy utilization. Herein, a rationally designed 3D composite photoanode integrating NIR-responsive upconversion nanocrystals (UCNs) and visible-responsive plasmonic Au nanoparticles (NPs) into 3D TiO2 inverse opal nanostructures (Au/UCN/TiO2) has been shown to extend the solar energy utilization in the UV-vis-NIR range. The NIR-responsive properties of NaYF4:Yb3+-based UCNs doped with Er3+ or Tm3+ ions, and the effect of an alternating sequential introduction of UCN and Au, have been assessed. With an extended overlap between the emission of Er-UCN and the characteristic SPR band of Au, our ternary Au/Er-UCN/TiO2 hybrid nanostructure unveiled a notable 10-fold improvement in photocurrent density under UV-vis-NIR illumination compared with a pristine TiO2 reference. The Au incorporation was confirmed to play a key role in enhancing the efficiency of light harvesting and to synergistically facilitate the energy transfer from UCNs to TiO2. This work further dissected plausible mechanistic pathways combining collected photoelectrocatalytic results, with electrochemical impedance measurements and transient absorption spectroscopic measurements. The synthesis and catalytic performance of our Au/UCN/TiO2 and the underlying mechanism here proposed are expected to reflect extended applicability in analogous applications for efficient solar-to-energy sustainable platforms.

DOI： 10.1021/acsaem.9b00469

Language：English   Publishing type：Research paper (scientific journal)  

Adhesion of a model rubbery material, cross-linked poly(dimethylsiloxane) (PDMS), onto a solid surface was studied by sum-frequency generation spectroscopy and X-ray photoelectron spectroscopy. To do so, here, we have focused on the adhesive deposit and insoluble layer. The former and latter were defined as the residual amount on the substrate after the peeling and residual layer after washing with a good solvent, respectively. The peel strength of a PDMS sheet adhered onto a glass plate increased with the contact time. Both adhesive deposit and insoluble layer also exhibited comparable contact time dependence. Once a hyperbranched polymer (HBP), which was segregated to the adhesive interface, was incorporated into PDMS, the peel strength and adhesive deposit decreased, although the thickness of the insoluble layer remained almost unchanged. These results suggest that the formation of loosely adsorbed chains on the solid surface, which possess not only trains but also many loop portions and tail parts, plays an important role in the macroscopic adhesion behavior of the PDMS sheet and the interfacial segregation of HBP can prevent it.

DOI： 10.1021/acsmacrolett.8b00971

Language：English   Publishing type：Research paper (scientific journal)  

© 2018, The Society of Polymer Science, Japan. Epoxy resins, which are obtained by the curing reaction of epoxy- and amine-compounds mixture, have been often utilized in contact with metals. We herein report on the chemical composition of the epoxy resin in close proximity to the copper interface on the basis of a non-destructive method. The concentration of the amine component in the interfacial region was 2-fold higher than that in the bulk, and the interfacial enrichment extended over at least 10 nm. [Figure not available: see fulltext.].

DOI： 10.1038/s41428-018-0129-4

Language：English   Publishing type：Research paper (scientific journal)  

Epoxy resins are composed of a three-dimensional network formed by chemical reactions between epoxy and amino compounds, which plays an important role in the mechanical properties. Thus, to use epoxy resins in various applications, it is necessary to gain a better understanding of their network structure. Here, we study the structural heterogeneity evolved in an epoxy-amine mixture during the curing process on the basis of a particle tracking technique, in which the thermal motion of probe particles in the mixture was tracked, small-angle X-ray scattering measurements in conjunction with coarse-grained molecular dynamics simulation. The heterogeneous environment was generated even at the initial stage of the curing process. Notably, the characteristic length scale was on the order of several hundreds of nanometers down to several tens of nanometers, depending on the extent of curing. Once a reaction occurs between a pair of epoxy and amino groups, the temperature at the site is locally elevated due to the heat of formation, accelerating a subsequent reaction nearby. Repeating such a situation, actively and scarcely reacted domains are formed. This is the main origin of the structural heterogeneity in epoxy resins.

DOI： 10.1021/acs.macromol.8b02416

Language：English   Publishing type：Research paper (scientific journal)  

A star-like hyperbranched polymer having hydrophilic poly(ethyleneoxide acrylate) arms (HB-PEO9A) was prepared by a core-first method based on atom transfer radical polymerization. The PEO9A layer coated on a solid substrate was dissolved by water, and effectively inhibited protein adsorption and cell adhesion.

DOI： 10.1039/c8tb03104e

Language：English   Publishing type：Research paper (scientific journal)  

A thin film of poly(4-methylpentene-1) (P4MP1) was prepared on a quartz substrate, which was a model system of an interface in filler-reinforced semicrystalline polymer composites. Grazing-incidence wide-angle X-ray diffraction measurements revealed that P4MP1 in the thin film after isothermal crystallization formed a Form I crystal polymorph composed of a tetragonal unit cell with a 7₂ helix, in which the chain axis was oriented along the direction parallel to the quartz interface. Combining sum-frequency generation vibrational spectroscopy with molecular dynamics simulation enabled us to gain access to the local conformation of P4MP1 chains at the quartz interface and the changes that occurred with isothermal crystallization. Finally, the way in which the initial chain orientation at the substrate interface impacted the crystalline structure in the thin film was discussed.

DOI： 10.1038/s41428-018-0134-7

Language：English   Publishing type：Research paper (scientific journal)  

Proton conductivity of polyelectrolytes in the interfacial region with a solid is key to the performance of polyelectrolyte-based fuel cells. The proton conductivity of Nafion thin films was examined as a function of the thickness along both directions, normal and parallel to the interface. Neutron reflectivity measurements revealed that a water-containing multilamellar structure was formed at the substrate interface. The presence of the interfacial layer, or the two-dimensional proton-conductive pathway, suppressed and enhanced the out-of-plane and in-plane proton conductivities, respectively. The method of proton conductivity in the interfacial region differed from that in the bulk, namely, the Grotthuss mechanism. Using laminated films, we conclude by showing that the proton conductivity in the Nafion thin film changes on the basis of the interface-to-volume ratio. This knowledge will be helpful for the design of devices containing polyelectrolytes with solid materials.

DOI： 10.1021/acs.langmuir.8b03396

Language：English   Publishing type：Research paper (scientific journal)  

Sum-frequency generation spectroscopy was employed to follow the conformation evolution of polystyrene chains at the surface of a spin-coated film in a temperature-ramping mode as well as under isothermal annealing. The conformation of surface chains in an as-cast film was observed to be in a nonequilibrium state, in accordance with reported results for polymer chains in thin spin-coated films. While the relaxation of surface nonequilibrium chains was induced by the enhanced surface mobility, the whole chain motion such as reptation might be a key factor in determining the time scale for equilibrating the surface chain conformation.

DOI： 10.1021/acsmacrolett.8b00411

Language：English   Publishing type：Research paper (scientific journal)  

Dynamic secondary-ion mass spectroscopy (DSIMS) was used to investigate the change in the failure mechanism at a heterogeneous polymer-polymer interface (polystyrene (PS)/polyamide (nylon 6, Ny6)) reinforced with in situ graft copolymers produced by the reaction between Ny6 molecules and poly(styrene-co-maleic anhydride) at the interface. The variation in fracture toughness with bonding time and temperature has been explained by two different failure mechanisms: adhesive failure at the interface for short bonding times and when the bonding temperature is low and cohesive failure between chains at the interface and bulk PS for longer bonding times and when the bonding temperature is high. DSIMS results provide the direct experimental evidence that the nonreactive molecules (PS) diffuse away from the high-potential interface, which induces the cohesive failure in the bulk of the nonreactive molecules (PS) after long annealing times. The change in the adhesion strength with temperature could also cause a change in the failure mechanism. Common features of the fracture mechanisms at heterogeneous interfaces reinforced by the in situ graft copolymers are outlined, which are independent of the polymer crystallinity.

DOI： 10.1021/acs.langmuir.8b01860

Language：English   Publishing type：Research paper (scientific journal)  

The local conformation of polystyrene (PS) and deuterated PS at the interface with quartz substrates, which were covered with phenyl groups using phenyltrimethoxysilane (PTS) under various conditions, was examined by sum frequency generation spectroscopy. As evidenced by the red-shift of the wavenumber of the v
₂
vibration mode for phenyl groups, it was claimed that PTS phenyl groups standing vertically from the quartz surface induced the perpendicular orientation of PS phenyl rings by energetically favorable parallel-displaced π-π interactions at the interface. The local conformation of PS chains strongly anchored onto the substrate by the π-π interactions remained almost unchanged for 48 h even at a temperature 60 K higher than the bulk glass transition temperature. That is, the interfacial π-π interactions facilitated the adsorption of PS chains on the substrate to attain a large enthalpic gain, resulting in significantly slower dynamics of PS chains at the interface. Our results illustrate the importance of the interfacial noncovalent interactions in controlling the structure and dynamics of macromolecular chains at the interface as well as in the thin film geometry.

DOI： 10.1021/acs.macromol.8b01012

Language：English   Publishing type：Research paper (scientific journal)  

There has been a considerable interest in developing new types of gels based on a network of fibrous aggregate composed of low molecular weight gelators, also known as supramolecular gels (SMGs). Unlike conventional polymer gels with chemical cross-linking, the network formation in SMGs does not involve any covalent bonds. Thus, the network in SMGs has been often regarded as homogenous or less heterogeneous in comparison with that in chemically cross-linked polymer gels. In this study, we have experimentally verified the existence of the network heterogeneity even in SMGs. The thermal motion of probe particles in SMGs, which were prepared from aqueous dispersions of gelators having a different number of peptide residues, PalGH, PalG₂H, and PalG₃H, was tracked. The gels were spatially heterogeneous in terms of the network pore size, as evidenced by the variation in the particle motion depending on the location, at which a particle existed. With varying particle size, it was found that the characteristic length scale of the heterogeneity was in the order of (sub)micrometers and was smaller in the order of the PalG₂H, PalG₃H, and PalGH gels.

DOI： 10.1021/acs.langmuir.8b00641

Language：English   Publishing type：Research paper (scientific journal)  

We propose a novel concept for cellular scaffolds with 2D-patterned mechanical properties. Thin films of glassy polystyrene (PS) with thicknesses ranging from 100 nm to 1 μm were prepared on epoxy resin-based line and space (L&S) patterned substrates. Although the outermost surface of PS on the L- and S-regions was sufficiently flat at the same level, the mechanical responses differed depending on the presence of the underlying resin foundation. The initial cell adhesion and spreading and the proliferation on the scaffolds were affected by the 2D-patterned mechanical properties, that is, cellular behavior was suppressed on mechanically unstable S-regions.

DOI： 10.1038/s41428-018-0043-9

Language：English   Publishing type：Research paper (scientific journal)  

The local conformation of poly(styrene-co-butadiene) rubber (SBR) chains in direct contact with a quartz substrate was examined by interface-sensitive sum-frequency generation (SFG) spectroscopy. SFG signals, which could be obtained from functional groups only oriented at the interface, were clearly observed for SBR in a film at room temperature which was much higher than the bulk glass transition temperature (T_g). When the film was thermally annealed, SBR chains at the quartz interface changed their conformation to one with a lower energy state, accompanied by the randomization of both the main and side chain parts. The characteristic temperature, at which interfacial chains started to lose their orientations, was much higher than the bulk T_g. Also, the extent found to be more remarkable for the spin-coated film than for the solvent-cast one. This implies that the stress accumulated at the interface, which resulted from the centrifugal force during the spin-coating process, accelerates the mobility of chains there. Finally, the kinetics experiment well supports the slower orientation relaxation at the interface.

DOI： 10.1021/acs.macromol.7b02756

Language：English   Publishing type：Research paper (scientific journal)  

Atomic processes giving rise to the photoinduced fluidity have been studied for amorphous selenium. Ab initio molecular orbital calculations of Se clusters suggest that distorted atomic structures such as curled and intersecting chains have smaller optical gaps. Those atomic sites are likely to be excited by subgap (Urbach-edge) light, which undergo structural relaxation including bond breakages and interchanges. Such photo-electro-structural transformations could originate the macroscopic fluidity. Possibility of electronic glass-transition is also discussed.

DOI： 10.1016/j.jnoncrysol.2017.12.005

Language：English   Publishing type：Research paper (scientific journal)  

Fibroblastic adhesion behaviour on films of a poly[(2-methoxyethyl vinyl ether) (PMOVE)-block-(l-lactic acid) (PLLA)], in which the surface was covered with PMOVE, was studied. Fibroblasts were sufficiently sensitive to identify crystalline/non-crystalline regions existing beneath the surface PMOVE layer.

DOI： 10.1039/c7tb03250a

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： .org/10.2115/fiber.74.P-6

Language：English   Publishing type：Research paper (scientific journal)  

Self-Assembled monolayer (SAM) with amphiphilic linear molecules has been studied as a surface modifier. In general, the surface properties of a SAM are dependent on the chain end chemistry of the molecules. Thus, a SAM composed of alkane loops from cyclic alkanedisulfide on a gold substrate, in which both sulfurs arc bound to gold, may possess unique surface properties due to the chain folding as well as a lack of chain ends. We here focus on the frictional properties of the linear and cyclic SAMs. For the cyclic SAM, the load dependence of the frictional force became more striking beyond a threshold. Such a frictional transition was not observed for the corresponding linear SAM. The load-induced transition in the frictional response from the alkane loops could be related to the conformational change of the alkane loops, which collapsed along the direction normal to the SAM surface.

Language：English   Publishing type：Research paper (scientific journal)  

The performance of a polymer composite material, in which inorganic fillers are dispersed, is closely related to the aggregation states and dynamics of polymer chains at the interface with the filler. In this study, the local conformation of polyisoprene (PI) at a quartz substrate interface was studied as a model system for the rubber/filler composite material. PI films were prepared from a toluene solution onto quartz substrates by a spin-coating method. Sum-frequency generation spectroscopy revealed that the local conformation of PI chains at the quartz interface depended on the spinning rate. The tilt angle of methyl groups increased with the rotational speed, probably due to the centrifugal force applied to chains and probably also the evaporation rate of the solvent during the solidification process. This result indicates that the interfacial orientation of PI chains can remain even at room temperature, which is 87 K higher than the bulk glass transition temperature (T_g ^b). The interfacial orientation disappeared at a temperature approximately 120 K higher than T_g ^b.

DOI： 10.1021/acsmacrolett.7b00927

Language：English   Publishing type：Research paper (scientific journal)  

Self-assembly of block copolymers (BCPs) into arrays of well-defined nanoscopic structures has attracted extensive academic and industrial interests over the past several decades. In contrast to the bulk where phase behavior is controlled by the segmental interaction parameter, the total number of segments in BCPs and volume fraction, the morphologies and orientations of BCP thin films can also be strongly influenced by the substrate surface energy/chemistry effect (considered as a "substrate field"). Here, we report the formation of locally favored structures where all constituent blocks coexist side-by-side on nonneutral solid surfaces irrespective of their chain architectures, microdomain structures, and interfacial energetics. The experimental results using a suite of surface-sensitive techniques intriguingly demonstrate that individual preferred blocks and nonpreferred blocks lie flat on the substrate surface and form a two-dimensional percolating network structure as a whole. The large numbers of solid-segment contacts, which overcome a loss in the conformational entropy of the polymer chains, prevent the structure relaxing to its equilibrium state (i.e., forming microdomain structures) even in a (good) solvent atmosphere. Our results provide direct experimental evidence of the long-lived, nonequilibrium structures of BCPs and may point to a new perspective on the self-assembly of BCP melts in contact with impenetrable solids.

DOI： 10.1021/acs.macromol.7b02506

Language：English   Publishing type：Research paper (scientific journal)  

Poly(vinyl ether), with short oxyethylene side chains which possess a simple and relatively polar structure, should be a unique candidate for a bioinert material thanks to its solubility in water. On the basis of living cationic copolymerization and subsequent ultraviolet light irradiation, thin films of poly(2-methoxyethyl vinyl ether) with different cross-linking densities were prepared on solid substrates. The films were thickened in water, and the extent was dependent on the cross-linking density. Although the surface chemistry and aggregation states were almost identical to one another, the stiffness, or the softness, of the outermost region in the film was strongly dependent on the cross-linking density. That is, the interface between polymer and water became thicker, or more diffused, with decreasing cross-linking density. The blood compatibility based on the platelet adhesion on to the hydrogel films was better for a more diffused interface.

DOI： 10.1021/acs.langmuir.7b03427

Language：English   Publishing type：Research paper (scientific journal)  

It is known that when nanoparticles are added to polymer thin films, they often migrate to the film-substrate interface and form an "immobile interfacial layer", which is believed to be the mechanism behind dewetting suppression. We here report a new mechanism of dewetting suppression from the structural aspect of polymer chains accommodated at the film-substrate interface. Dodecanethiol-functionalized gold (Au) nanoparticles embedded in relatively low molecular weight PS thin films prepared on silicon (Si) substrates were used as a model. We mimicked the previously reported conditions, where the nanoparticles preferentially migrate to the substrate, and successfully stabilized the PS thin films via thermal annealing. A suite of surface-sensitive techniques including atomic force microscopy, grazing incidence small-angle X-ray scattering, X-ray/neutron reflectivity, and sum frequency generation spectroscopy in conjunction with the established solvent leaching process enabled us to unveil the polymer chain conformation and the dispersion structure of the nanoparticles at the film-substrate interface. The results evidenced that thermal annealing promotes irreversible polymer adsorption onto the substrate surface along with the migration of the nanoparticles. In addition, we found that the migration of the nanoparticles causes the changes in the conformations and interfacial orientations of the adsorbed polymer chains compared to those of the adsorbed polymer chains formed in the nanoparticle-free PS thin film. The resultant interfacial polymer structure allows for the interpenetration between free chains and the adsorbed chains, thereby stabilizing the thin film.

DOI： 10.1021/acs.macromol.7b01187

Language：English   Publishing type：Research paper (scientific journal)  

When a peptide amphiphile is dispersed in water, it self-assembles into a fibrous network, leading to a supramolecular hydrogel. When the gel is physically disrupted by shaking, it transforms into a sol state. After aging at room temperature for a while, it spontaneously returns to the gel state, called sol-gel transition. However, repeating the sol-gel transition often causes a change in the rheological properties of the gel. To gain a better understanding of the sol-gel transition and its reversibility, we herein examined the thermal motion of probe particles at different locations in a supramolecular hydrogel. The sol obtained by shaking the gel was heterogeneous in terms of the rheological properties and the extent decreased with increasing aging time. This time course of heterogeneity, or homogeneity, which corresponded to the sol-to-gel transition, was observed for the 1st cycle. However, this was not the case for the 2nd and 3rd cycles; the heterogeneity was preserved even after aging. Fourier-transform infrared spectroscopy, small-angle X-ray scattering, and atomic force and confocal laser scanning microscopies revealed that, although the molecular aggregation states of amphiphiles both in the gel and sol remained unchanged with the cycles, the fibril density diversified to high and low density regions even after aging. The tracking of particles with different sizes indicated that the partial mesh size in the high density region and the characteristic length scale of the density fluctuation were smaller than 50 nm and 6 mm, respectively.

DOI： 10.1039/c7sm01612c

Language：English   Publishing type：Research paper (scientific journal)  

In this letter, it is proposed that the impact ionization in amorphous Se films, which triggers avalanche carrier multiplications, occurs through transformations of electron and hole motions from polaronic to supersonic states, the situation resembling those envisaged for semiconducting one-dimensional organic polymers. However, reflecting unique origins of the conduction and the valence band in Se, the electron-lattice interaction appears stronger than the hole-lattice interaction, which seems to be responsible for characteristic properties such as less efficient electron multiplication. The idea is consistent with the fact that a-Si:H having three-dimensional structures exhibits no corresponding phenomena.

DOI： 10.1002/pssr.201700254

Language：English   Publishing type：Research paper (scientific journal)  

The rotational relaxation time (τ_rot) of a fluorescent molecule, coumarin 153 (C153), dispersed in different rubbery polymers is characterized by time-resolved fluorescence anisotropy measurement, and an attempt is made to quantitatively combine it with the segmental relaxation time (τ_seg) of the corresponding matrix polymer obtained by dielectric relaxation spectroscopy. This study here demonstrates that τ_seg extrapolated to higher temperatures using the Vogel–Fulcher–Tammann law can be superimposed on τ_rot, resulting in a single curve. This behavior is common for polymers with different glass transition temperatures such as polyisoprene and acrylonitrile/butadiene copolymer, implying that the rotational dynamics of C153 is a useful tool for the characterization of polymer dynamics.

DOI： 10.1002/macp.201700329

Language：English   Publishing type：Research paper (scientific journal)  

水界面における高分子鎖のダイナミクスは、生体関連機能の発現において重要な役割を果たすと考えられている。したがって、分子鎖ダイナミクスの制御のための一つの戦略は、ポリマー鎖を環状化合物で包接し、複合体を形成することであるが、そのような検討はこれまでバルク試料に限られていた。本研究では、典型的なガラス状高分子であるポリメタクリル酸メチルの膜を調製し、クリック反応とLangmuir-Blodgett法を組み合わせることで、膜最表面にポリ（エチレンオキシド）（PEO）と-シクロデキストリン（CD）からなるポリロタキサン構造を導入することに成功している。また、水界面でのPEOの熱運動が、CD分子の導入によって抑制され、その結果、タンパク質吸着や血小板接着のような生物学的応答が変化することを始めて示している。

DOI： 10.1021/acs.langmuir.7b03130

Language：English   Publishing type：Research paper (scientific journal)  

As a polymer interfacial modifier, poly(methyl methacrylate) (PMMA) terminated with elemental blocks of polyhedral oligomeric silsesquioxane (POSS) has been exploited through the phenomenon of preferential segregation in PMMA films. The modifier synthesized by living anionic polymerization using a bifunctional initiator is segregated at the surface in the mixture of PMMA due to a “buoy” effect of the POSS blocks. This further results in the surface wettability of PMMA being regulated on the basis of the amount of the modifier fed into the matrix. Finally, it is shown that the amount of the modifier in the PMMA films affects the cell proliferation behavior via the wettability. (Figure presented.).

DOI： 10.1002/macp.201600473

Language：English   Publishing type：Research paper (scientific journal)  

By means of sum-frequency generation spectroscopy, we report a depth-resolved measurement of the local conformation and chain relaxation of polystyrene (hPS) located at different distances from the quartz interface. To control the distance from the quartz interface, deuterated polystyrene (dPS) layers with thicknesses of 3.4, 7.5, and 20 nm were coated on the quartz substrates. The hPS chains in direct contact with the substrate surface predominantly orient their phenyl rings in a direction normal to the substrate. This conformation was found to be barely relaxed when the film was annealed for 24 h at 423 K, higher than the bulk glass transition temperature. In contrast, for the hPS chains supported on the dPS layer, the orientation of phenyl rings of hPS became weaker with the annealing and this trend was more significant with increasing distance from the quartz substrate. In particular, the orientation of phenyl rings of hPS after annealing vanished at a distance of 20 nm. These results might provide an important evidence of the difference in the relaxation dynamics of the PS chains located at different distances from the quartz interface.

DOI： 10.1063/1.4976523

Language：English   Publishing type：Research paper (scientific journal)  

Ultrafast and single exponential responsive materials were achieved by encapsulating donor-acceptor linked molecules into cucurbitunitl[8], CB[8], as nanocavity hosts. Various aromatic groups were linked with various types of 4,4'-bipyridinium groups through propyloxy linker. They showed characteristic charge-transfer (CT) absorption with specific colors in aqueous solutions. Upon addition of CB[8], they showed remarkably different colors due to intramolecular CT complex formation in CB[8]. Upon femtosecond laser excitation of CT band extremely fast electron transfer occurred from a donor to an acceptor unit accompanying new absorption in the visible to near-infrared region due mainly to photoreduced bipyridinium derivatives. Thermal back electron transfer reactions in CB[8] were found to follow a single exponential decay with rate constants ranging more than two orders depending on the combination of a donor and an acceptor unit. Their rate constants vs. free energy changes for oxidized donors and reduced acceptors in linked molecules were expressed by the Marcus theory. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2017.02.051

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

A better understanding of controlling factors in the control of bio-events on polymer surfaces is the first benchmark toward realization of life innovation. Although it has been accepted that a family of poly(vinyl ether) (PVE) with various side chain structures is a good candidate for a blood compatible material, the reasons are not fully understood. In this study, poly(vinyl ether) with a simple side chain structure, poly(ethyl vinyl ether) (PEVE), was studied. Since the glass transition temperature of PEVE is lower than room temperature, its thin films can be difficult to prepare. Thus, PEVE was mixed with a glassy polymer of poly(p-vinylphenol) (PVPh). The aggregation states of polymer chains and water molecules at the interface were characterized by the interfacial sensitive spectroscopy. The relationship between the structural information and the platelet adhesion behavior is discussed. This leads to a hypothesis that the states of water molecules affect platelet adhesion and activation behaviors on PVE. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2017.01.036

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c6tb02617f

Language：English   Publishing type：Research paper (scientific journal)  

Oxidative degradation of polypropylene (PP) is accelerated by not only sunlight but also temperature. Here we propose how the degradation behavior of PP under ultraviolet light irradiation conditions at elevated temperatures, which are more severe than the standards set by the Japanese Industrial Standards (JIS), can be examined. Fourier-transform infrared spectroscopy in conjunction with gel permeation chromatography revealed that the combination of light and heat definitely accelerated the chain scission, or oxidative degradation, of PP, resulting in deterioration of mechanical properties for PP.

DOI： 10.2472/jsms.66.238

Language：English   Publishing type：Research paper (scientific journal)  

自己組織化単分子膜（SAM）は、材料表面に望みの物性・機能性を与えるための分子ツールとして注目され、実デバイスなどにも広く用いられてきた。しかしながら、これまで、SAM形成は線状分子に限定されており、表面物性・機能性への分子末端の影響が避けられないなどの問題があった。しかしながら、本研究では、環状アルカンジスルフィドを用いることで炭化水素環状鎖からなるSAMを形成することに成功し、表面物性・機能性への分子末端の影響を明確にしている。この結果は、材料表面の物性・機能性設計へ新たな指針を提案するものとして高く評価されている。

DOI： 10.1021/acs.langmuir.6b04042

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.macromo1.6b02740

Language：English   Publishing type：Research paper (scientific journal)  

The chain dynamics of well-defined poly(2-methoxyethyl acrylate) (PMEA), which has been used in practice as a bioinert coating for heart-lung machines, was examined as a function of water content by dielectric relaxation spectroscopy (DRS). Two relaxation processes observed in both dried and hydrated films were assigned to the segmental motion (alpha-process) and the relatively smaller scale motion such as the hindered rotation of side chains (beta-process). Water molecules adsorbed on PMEA made the alpha-process faster, meaning that water molecules in PMEA played the role of a plasticizer. Combining the above knowledge with the depth dependence of water content in the PMEA film previously obtained by neutron reflectivity, the segmental dynamics of PMEA at the water interface, which should be crucial to bio-inertness, is discussed. We found that the segmental motion was markedly faster than that in the bulk and almost comparable to the side chain motion.

DOI： 10.1039/c6cp07322k

Language：English   Publishing type：Research paper (scientific journal)  

A poly[2-(2-ethoxy) ethoxyethyl vinyl ether] macromonomer with a terminal vinyl group synthesized by living cationic polymerization was successively copolymerized with methyl methacrylate by atom transfer radical polymerization. The branched polymer mixed into poly(methyl methacrylate) was preferentially segregated at the film surface, leading to an anti-biofouling polymer surface.

DOI： 10.1039/c6py01984f

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c6cc07648c

Language：English   Publishing type：Research paper (scientific journal)  

The density profile in a thin cross-linked polyisoprene (PI) film spin-coated on a quartz substrate in n-hexane was examined by specular neutron reflectivity. We found two layers with different PI densities at the substrate interface. The characteristics of the layers are discussed in terms of bound rubber typically associated with the field of rubber materials and adsorbed layers typically associated with the field of glassy materials. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2016.07.047

Language：Japanese   Publishing type：Research paper (scientific journal)  

Photo-degradation of polymers for outdoor use are accelerated by degradation factors such as heat and moisture. Polypropylene(PP) is excellent in water resistance, but is inferior to weatherability. Therefore, in this study, PP was exposed under the water spray condition by using Xenon arc lamp. We evaluated the synergistic effect of light and moisture using the quantification technique of degradation. Results from the Fourier-transform infrared spectroscopic and X-ray Photoelectron Spectroscopy revealed that moisture accelerated the oxidative degradation of PP. In addition, with the progress of the oxidative degradation, melting point and thermal decomposition temperature of PP was lowered. The resulting collapse of crystal structure and chain scission therefore deteriorated the mechanical properties (Charpy impact strength, elongation) of PP.

DOI： 10.2472/jsms.65.812

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cnma.201600222

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/pj.2016.58

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.160373

Language：English   Publishing type：Research paper (other academic)  

The objective of this study is to carry out nanoscale characterization of the epoxy resin interface on silica by determining the glass-transition temperature (T_g) and molecular conformation at the interface by means of a novel non-destructive method. The T_g was determined by fluorescence lifetime measurements using evanescent wave excitation. It was revealed that the T_g of epoxy resin at a distance of 30 nm from the interface was 10 K higher than that at a distance of 80 nm. The chemical composition and molecular conformation were analysed by X-ray photoelectron spectroscopy and sum-frequency generation (SFG) spectroscopy, respectively. The SFG data revealed that unreacted epoxy group remained at the interface. The T_g of epoxy resin increased in the regions near the interface, and the epoxy group remained unreacted at a distance of ca. 10 nm or less from the interface.

DOI： 10.1109/ICD.2016.7547549

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c6cp03614g

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/admi.201600034

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/admi.201670058

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsmacrolett.6b00169

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/pj.2015.118

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.160061

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c5pp00453e

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpclett.5b02255

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.polymer.2015.10.001

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c5ta04991a

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c5cp04800a

Language：English   Publishing type：Research paper (scientific journal)  

Melting behavior in thin films of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) was studied by local thermal analysis (mu TA). Even in the films thinner than 100nm, the melting temperature (T-m) was successfully observed by mu TA. For LLDPE, T-m decreased as the thickness became thinner than 150nm. For HDPE, T-m increased with decreasing thickness. Polarized infrared spectroscopy revealed that an edge-on lamellar structure formed in both cases, meaning that the crystallite orientation may not be a reason why the thickness dependence of T-m was not the same for both resins. A possible explanation is that for LLDPE the segmental mobility in the amorphous region predominates with decreasing thickness, and for HDPE the chain orientation in the region predominates with decreasing thickness.

DOI： 10.1177/8756087915594418

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.macromol.5b01780

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsmacrolett.5b00592

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.polymer.2015.07.054

Language：English  

Aggregation states and dynamics of polymers at the surface are generally different from those in the corresponding bulk state. To what extent they differ from that of the bulk strongly depends on the polymer primary structure. Therefore, finetuning the surface properties of polymers can be achieved by exhibiting control over their structure using precision polymer synthesis. We here show how the polymer design effectively impacts the structure and dynamics at the surfaces.

DOI： 10.1007/978-4-431-54186-8_19

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c5cp01972a

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/pj.2015.30

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/pj.2015.6

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.150013

Language：English   Publishing type：Research paper (scientific journal)  

本論文は、ポリ（３-ヘキシルチオフェン）（P3HT）膜の光電荷生成と分子運動について検討したものである。
P3HT 膜に光照射すると、正電荷と負電荷との対が形成された後、自発的に正および負電荷に分離されることを見出した。また、この電荷生成の速度定数は、低温では一定であるが、主鎖のねじれ運動に対応する緩和温度から
温度とともに増加した。
このことから、P3HT膜において分子運動は光電荷生成を支配する因子のひとつであると結論した。

DOI： 10.1038/srep08436

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.langmuir.5b00258

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcis.2014.10.071

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.140924

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jnoncrysol.2014.09.010

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c4cp04395b

Language：English   Publishing type：Research paper (scientific journal)  

We propose a novel method to treat polymeric scaffold surfaces for cell culture with water containing nanobubbles, called ultrafine bubbles (UFBs), with typical diameters less than 1 mu m. A thin film of polystyrene (PS) prepared on a solid substrate was exposed to UFB water for 2 days at room temperature. The PS surface was characterized by X-ray photoelectron spectroscopy (XPS), static contact angle measurements in water, and atomic force microscopy (AFM). The surface chemical composition and wettability of PS films remained unchanged after treatment, so that aggregation states of PS at film surfaces remained unaltered by UFB water. On the other hand, after treatment, many UFBs were adsorbed on hydrophobic PS surfaces. To study the effect of UFBs on scaffold properties, the adsorption behavior of fibronectin, which is a typical extracellular matrix protein involved in cell adhesion and proliferation, was examined. While the effect on the adsorption was unclear, the structural denaturation of fibronectin was enhanced after UFB treatment, so that the proliferation of fibroblast cells on PS surfaces was promoted.

DOI： 10.1021/la5035883

Language：English   Publishing type：Research paper (scientific journal)  

Well-defined poly(methacrylate)s with liquid crystal side chains, designated as PPHM, were synthesized by a living anionic polymerization method. Introducing a short-length alkyl chain at the end of the side chain, the solubility of the polymer was improved, resulting in higher molecular weight polymers. While the highest weight-average molecular weight (M-w) of PPHM was 68k, it exceeded 100k for a slight-polydisperse PPHM. Wide-angle X-ray diffraction (WAXD) revealed that PPHM formed a smectic A phase with 2.7 nm layer spacing and that the layer structure is present even in the glassy state at room temperature. Molecular aggregation states of PPHM in surface regions of films were characterized by sum-frequency generation, grazing-incidence WAXD, and contact angle measurements. The results show that the PPHM with a larger M-w formed a layer structure parallel to the film plane. Although low M-w PPHM also maintained a layer structure, the structure became more random within internal regions. The surface reorganization of PPHM with larger M-w was suppressed in comparison with smaller ones.

DOI： 10.1021/ma5010265

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c4ta02720e

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/la500829p

Language：English   Publishing type：Research paper (scientific journal)  

Protein adsorptions onto non-annealed (NA) and thermally annealed (TA) polyetherimide films were examined by surface plasmon resonance measurements. Proteins adsorbed onto the NA films with smaller adsorption constants in comparison with the TA films. Neutron reflectivity measurements of the two films suggested that the outermost region of the NA films swelled with larger amounts of water molecules than the TA films. It is plausible that the aforementioned difference in the protein adsorption properties is derived from the difference in the interfacial aggregation structures of the two films.

DOI： 10.1166/jnn.2014.8580

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/am.2014.4

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/la404802j

Language：English   Publishing type：Research paper (scientific journal)  

We investigated the conformation of PMMA in thin films at the air-water interface by sum frequency generation (SFG) spectroscopy and discuss the effect of stereoregularity on the interfacial structure of PMMA. At the air interface, isotactic PMMA takes a helical conformation where the hydrophilic carbonyl groups are oriented towards the interfacial region of the film. Thus, even though the polymer chains come in contact with water, the chain conformation at the interface changes very little. The structure of syndiotactic PMMA at the air and water interfaces is significantly different. Poly(methyl 2-propenyl ether) (PMPE), synthesized via living cationic polymerization, is structurally similar to PMMA, but it lacks the carbonyl group. We discuss the effect of the carbonyl group on the water structure at the interface by comparing the results of our measurements to the previously reported PMMA-water system. This knowledge is crucial for the design and construction of highly-functionalized polymer interfaces for biological applications.

DOI： 10.1295/koron.71.343

Language：English   Publishing type：Research paper (scientific journal)  

Molecules are often assembled by themselves with a large aspect ratio, leading to the formation of network structure based on their entanglements. Such systems, so-called "supramolecular network systems" possess hierarchical structure with various length scales ranging from nanometer to micrometer. Thus, to give a better understanding of dynamics for the supramolecular network systems, it is necessary to examine the structure and physical properties at various length scales, and clarify the correlation. By using optical tweezers and particle tracking techniques, we here show the local rheological properties in a worm-like micelle solution and a supramolecular hydrogel, which are formed by the networks based on the self-assembly of the amphiphilic molecules in water. In these techniques, viscoelastic information can be accessed on the basis of the movement of probe particles dispersed in a sample to be measured. For the worm-like micelle solution, we found that the viscoelastic functions (G′ and G″ ) varied depending on the location measured and the location-dependent variation of G′ and G″ was observed only at the measurement timescale being shorter than the relaxation time. This can be understood by taking into account that there exists a concentration fluctuation in the solution. Such fluctuation can be regard as a spatial heterogeneity when one takes a snapshot of the solution at a time shorter than the relaxation time. Also, the heterogeneity in the rheological properties was observed in a sol obtained by physically disrupting the supramolecular hydrogel. The extent of the heterogeneity decreased as a solto-gel transition proceeded. Such homogenization was associated with the change in the network structure rather than that in the molecular assembled state, which remains comparable in the sol and gel.

DOI： 10.1678/rheology.42.89

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/mz400322q

Language：Japanese  

Structures and Physical Properties at Surfaces and Interfaces of Polymers

DOI： 10.18914/tribologist.58.10_742

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/la4027706

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ja404701s

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c3ra23066j

Language：English   Publishing type：Research paper (other academic)  

Aggregation states of polymers at the surface generally tend to alter to their most stable ones in response to their surrounding environment. We here apply a time-resolved contact angle measurement to examine the rate of the surface reorganization of poly(methyl methacrylate) (PMMA) in water. By doing these measurements at various temperatures, it is possible to extract the apparent activation energy of the surface dynamics based on the relation of the surface relaxation time and temperature. Also, sum-frequency generation spectroscopy revealed that the surface reorganization involves the conformational changes in the main chain portion as well as the side chains. Hence, the dynamics observed here might reflect the segmental motion at the outermost region of the PMMA film, in which water plays as a plasticizer.

DOI： 10.1063/1.4794616

Language：English   Publishing type：Research paper (scientific journal)  

The ability of hyperbranched polymers (HBPs) to preferentially segregate to the surface of its matrix owing to its unique structure makes it a good candidate as a surface modifier. One particular challenge in its application as an efficient surface modifier, however, is its possible elimination from the surface due to the lack of attachments between a HBP (modifier) and its host material (polymer matrix). Here, we present a novel approach to efficiently prevent the removal of HBPs from the surface of its host material by directly reacting a HBP containing fluoroalkyl segments (F-HBP) to a multi-functional acrylate monomer prior to curing. We also have characterized surface structure and wettability of the acrylic hard coating material by X-ray photoelectron spectroscopic and contact angle measurements, respectively. The results show that since F-HBP was segregated at the surface, the surface became hydrophobic and more stable. Thus, we claim that our approach results in the formation of a water-repellent acrylic hard coating material. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2012.11.160

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.apsusc.2012.10.070

Language：English   Publishing type：Research paper (scientific journal)  

We introduce a setup of optical tweezers, capable of carrying out temperature-dependent rheological measurements of soft materials. In our setup, the particle displacement is detected by imaging a bright spot due to fluorescence emitted from a dye-labeled particle against a dark background onto a quadrant photodiode. This setup has a relatively wide space around the sample that allows us to further accessorize the optical tweezers by a temperature control unit. The applicability of the setup was examined on the basis of the rheological measurements using a typical viscoelastic system, namely a worm-like micelle solution. The temperature and frequency dependences of the local viscoelastic functions of the worm-like micelle solution obtained by this setup were in good accordance with those obtained by a conventional oscillatory rheometer, confirming the capability of the optical tweezers as a tool for the local rheological measurements of soft materials. Since the optical tweezers measurements only require a tiny amount of sample (∼40 μL), the rheological measurements using our setup should be useful for soft materials of which the available amount is limited. © 2013 American Institute of Physics.

DOI： 10.1063/1.4789429

Language：English   Publishing type：Research paper (scientific journal)  

An important step in understanding molecular assembled systems is to examine the structure and physical properties at various length scales and clarify the correlation between them. However, while the structures of these systems have been extensively studied from nanoscopic to macroscopic scales, their viscoelastic properties have been often limited to bulk rheological measurements. By using optical tweezers and particle tracking, we here show the local viscoelastic properties and their spatial distributions for the following systems: worm-like micelle solution, supramolecular hydrogel and lyotropic liquid crystal, which are formed by self-assembly of amphiphilic molecules in water. We found that all systems studied possessed a spatial heterogeneity in their viscoelastic properties and this was originated from the heterogeneous structures. It is interesting to note that there is the heterogeneity with the characteristic length scale of sub-micrometer or micrometer scale, thereby structures, although the systems are formed by molecules with nanometer size. The findings of these studies should lead to a better understanding of the dynamics of such systems.

DOI： 10.1007/s10118-013-1193-z

Language：English  

In this review, we show the distribution of glass transition temperature (T _g) in monodisperse polystyrene (PS) films coated on silicon oxide layers along the direction normal to the surface. Scanning force microscopy with a lateral force mode revealed that surface T _g () was lower than the corresponding bulk T _g (). Interestingly, the glass transition dynamics at the surface was better expressed by an Arrhenius equation than by a Vogel-Fulcher-Tamman equation. Interdiffusion experiments for PS bilayers at various temperatures, above and below, enabled us to gain direct access to the mobility gradient in the surface region. T _g at the solid substrate was examined by fluorescence lifetime measurements using evanescent wave excitation. The interfacial T _g was higher than the corresponding. The extent of the elevation was a function of the distance from the substrate and the interfacial energy. The T _g both at the surface and interface was also studied by the coarse-grained molecular dynamics simulation. The results were in good accordance with the experimental results. Finally, dynamic mechanical analysis for PS in thin and ultrathin films was made. The relaxation time for the segmental motion became broader towards the faster and slower sides, due probably to the surface and interfacial mobility. Graphical Abstract:

DOI： 10.1007/12_2012_175

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

The glass transition temperature (T-g) of thin polystyrene (PS) films supported on silicon wafers with oxide layers of varying thickness was characterized by the temperature dependence of the film thickness using ellipsometry. This allowed us to uncover how a long-range interaction affects the T-g of polymer films. As previously reported using a variety of methods, the T-g decreased with decreasing film thickness. However, the extent was not the same among the reports. In this study, we found that the T-g attenuation of a PS film of a given thickness was dependent on the oxide layer thickness of the silicon wafer via the long-range interaction.

DOI： 10.1021/mz300391g

Language：English   Publishing type：Research paper (scientific journal)  

Thermal molecular motion of poly(methyl methacrylate) (PMMA) at various interfaces, gases and liquids, was discussed. The α _a- and β-relaxation processes were clearly observed even at the air interface. Both relaxation temperatures at the air interface were lower than the corresponding ones in the bulk. In addition, the extent to which the peak temperature for the surface relaxation processes fell below that of the bulk strongly depended on the stereoregularity of the films. Then, thermal molecular motion of PMMA was analyzed at gaseous carbon dioxide (CO ₂) interface. It was more enhanced than that at gaseous nitrogen interface because CO ₂ molecules were sorbed in the interfacial region, which played as plasticizing agents. Finally, mechanical properties of PMMA were also studied at interfaces with liquids such as water, hexane and methanol. The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film. Therefore, it can be claimed that interfacial molecular motion of polymers can be regulated on the basis of the aggregation states.

DOI： 10.1678/rheology.40.143

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c2jm31923c

Language：English   Publishing type：Research paper (scientific journal)  

Initiator-fragment incorporation radical polymerization (IFIRP) of commercially available fluorinated monomers was performed in the presence of cross-linking agents, resulting in a hyperbranched polymer with perfluoroalkyl groups (F-HBP). In our one-step method, a F-HBP was successfully prepared without gelation within 1 h. The F-HBP exhibited interesting properties based on both the hyperbranched architecture and the perfluoroalkyl groups, such as good solubility in common organic solvents, high thermal stability, and low surface free energy.

Language：English   Publishing type：Research paper (scientific journal)  

At the outermost surface, aggregation states of polymers generally tend to alter to their most stable ones in response to their surrounding environment. We here apply a time-resolved contact angle measurement to study the rate of the surface reorganization of poly(methyl methacrylate) (PMMA) in water. By doing these measurements at various temperatures, it is possible to determine the apparent activation energy of the surface dynamics based on the relation of the surface relaxation time and temperature. Also, the sum-frequency generation spectroscopy revealed that the surface reorganization involves the conformational changes in the main chain part as well as the side chains. Hence, the dynamics observed here may reflect the segmental motion at the outermost region of the PMMA film, in which water plays as a plasticizer.

DOI： 10.1021/ma3002559

Language：English   Publishing type：Research paper (scientific journal)  

The local conformation of polymer chains in a film at a substrate interface was examined by sum-frequency generation spectroscopy. When a polystyrene (PS) film was prepared on a quartz substrate by a spin-coating method, the chains were aligned in the interfacial plane of the substrate. A dissipative particle dynamics simulation revealed that a spinning torque induced the chain orientation during the film preparation process and the extent of the orientation was a function of the distance from the interface. This interfacial orientation of chains was not observed for a PS film prepared by a solvent-casting method. Interestingly, the local conformation of chains at the substrate interface was unchanged even at a temperature that was 80 K higher than the bulk glass transition temperature (T-g). This observation means that polymer chains at the substrate interface can be only partially relaxed under conditions where the bulk chains are fully relaxed. On the other hand, interfacial chains could be easily relaxed by solvent annealing.

DOI： 10.1021/ma3007202

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c2sm25549a

Language：English   Publishing type：Research paper (scientific journal)  

Non-ionic surfactant hexaethylene glycol, C ₁₂E ₆, in water self-assembles into various kinds of mesophases by varying the surfactant concentration. A spatial heterogeneity was discussed on the basis of the diffusion of probe particles dispersed in the C ₁₂E ₆-water solution. Interestingly, at 50 wt% C ₁₂E ₆ where the hexagonal structure was formed, two kinds of motion of probe particles were observed: some particles normally diffused while others were restricted, indicating the existence of a heterogeneity in the physical properties. Such heterogeneity can be explained in terms of heterogeneous structures composed of hexagonal domains with isotropic-like regions.

DOI： 10.1039/c2cp40284j

Language：English   Publishing type：Research paper (scientific journal)  

A novel method to modify the surface of rubbery polymer films on the basis of the preferential segregation of inorganic materials fed into the system in tiny amounts is proposed. The surface so prepared had several prominent properties such as surface hardness, anti-oxidant properties, transparency, and so forth.

DOI： 10.1039/c1py00488c

Language：Japanese  

Molecular Aggregation Structure of Polymer Materials at the Water Interface and Its Biocompatibility
Poly(2-methoxyethyl acrylate) (PMEA)-enriched surface was prepared by blending it with poly(methyl methacrylate) (PMMA) under appropriate annealing conditions. Atomic force microscopy revealed that the surface of the PMEA/PMMA blends was sufficiently flat and stable even in water. Contact angle of an air bubble on the blends in water decreased with increasing immersion time. These results indicate that aggregation states of polymer chains at the outermost region of the films were changed at the water interface. The blend surfaces showed excellent blood-compatibility by reducing platelet adhesion.

Language：English   Publishing type：Research paper (scientific journal)  

本論文はエポキシ/アミンのモデル反応に基づき、固体界面近傍における反応動力学評価を行ったものである。活性化エネルギー、衝突頻度因子の算出から、反応の活性化エネルギーはバルク、界面で不変である一方、バルクの衝突頻度因子は界面近傍におけるそれと比較して6倍程度であった。このことから、固体界面の存在はエポキシ硬化反応の化学的な因子には影響を与えず、物理的因子に大きな影響を与えることを明らかにした。

Language：English   Publishing type：Research paper (scientific journal)  

We have studied the fluorescence behavior of a dye, 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoic acid (NBD), in thin films of polymers with various polarities, such as poly(methyl rnethacrylyate) (PMMA), Arton, poly(styrene) (PS), hydrogenated polystyrene (H-PS), and Zeonex. In the case of well-dispersed systems,.the fluorescence behavior of NBD could - be explained in terms of the mobility of the polymer matrix. This was the case for PMMA, Arton, and PS. On the other hand, when H-PS or Zeonex was.used, NBD aggregated in the films, leading to unusual fluorescence behavior: the fluorescence lifetime and maximum wavelength increased with a decrease in the film thickness. Time- and space-resolved fluorescence spectroscopy using an evanescent wave excitation revealed that the aggregation states of NBD near the interface varied with the film thickness, While NBD molecules near the interface aggregated in a thick film, such was not the case in a thin film. Angular dependent X-ray photoelectron spectroscopy (ADXPS) structurally confirmed the above observations; that is, the film thickness greatly influenced the depth profile of the NBD composition in the polymer films.

DOI： 10.1021/ma201901x

Language：English   Publishing type：Research paper (scientific journal)  

To study the thickness dependence of methanol diffusion into poly(methyl methacrylate) (PMMA) films, an experimental method based on optical reflectivity was proposed. The method can cover a thickness range from the micrometre down to the nanometre scale using a single set-up. Methanol molecules diffuse into PMMA following a Case II mechanism in which they induce segmental motion of the matrix polymer. We observed two diffusion modes, fast and slow, assignable respectively to the outermost layer and the remaining internal region including the substrate interface. When the film becomes thinner, the ratio of the interfacial area to the total volume increases. This results in slowing down of the methanol diffusion due to the contribution of the depressed segmental mobility at the substrate interface. Interestingly, the thickness of the mobility-enhanced layer at the outermost region of the film similarly decreased with decreasing total thickness owing to the effect of the substrate interface.

DOI： 10.1039/c1sm06098h

Language：Japanese  

Development of a Method to Identify Recycled Polycarbonate
To encourage the recycling of materials, the government provides subsidizes for manufacturers which use recycled materials to process final products. Unfortunately, this causes a camouflage of recycled-content products. Hence, a method to judge whether the material is truly made of previously used source needs to be established. In this study, we focus on recycled plastics, especially, polycarbonate (PC). Plastics are thermally and mechanically damaged during its molding process and practical use. This leads to faster degradation of recycled plastics than the corresponding pristine ones. We here propose how we can identify recycled PC taking into account the degradation kinetics.

DOI： 10.1295/koron.68.731

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.2011.1138

Language：English   Publishing type：Research paper (scientific journal)  

Recently, polymeric materials nave oeen widely used in applications sucn as medical materiais, in tnese applications, the surrace comes into contact with a different phase. Thus, their interfaces should be studied, both their structures as well as their dynamics. The density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film in water, hexane, methanol, ethanol, 1-propanol, and 1-butanol were examined along the direction normal to the interface by neutron reflectivity (NR). Although these liquids are typical non-solvents for dPMMA, the liquid/polymer interfaces were diffuse in comparison with the air/polymer interface probably due to the partial dissolution of polymer segments at the outermost region of the film. Interestingly, in water, an anomalous swollen layer was formed beneath the diffused interface. On the other hand, such a swollen layer was not observed for the dPMMA films in alcohols. This is simply because alcohol molecules deeply penetrated into the films. The amounts of the alcohols penetrated are related to the interaction parameter. The fractional amount of nonsolvents at the substrate interface was higher than that in the internal region of the film.

DOI： 10.1295/koron.68.608

Language：English   Publishing type：Research paper (scientific journal)  

A dispersion of a peptide amphiphile into water forms hierarchical fibril structures, leading to a supramolecular hydrogel. We here report that there exists dynamic heterogeneity in the gel, which might be induced by the heterogeneous fibril network. The network, and therefore, the heterogeneity, can be easily regulated by changing the temperatures used to dissolve the gelator in water. © 2011 The Royal Society of Chemistry.

DOI： 10.1039/c1cc12733k

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.polymdegradstab.2011.05.001

Language：English   Publishing type：Research paper (scientific journal)  

Surface segregation of well-defined N-substituted hyperbranched polyamides (HBPA) with various side chain lengths in linear polystyrene matrix was studied. To what extent HBPA was segregated at the surface was dependent on the side chain length, which regulated intermolecular interactions among HBPA molecules via steric hindrance.

DOI： 10.1246/cl.2011.366

Language：English   Publishing type：Research paper (scientific journal)  

Interfaces of polymers with "non-solvents" play an important role in their functional properties such as wettability, friction with lubricants, cell adhesion, and biocompatibility. To design and construct highly functionalized polymers for applications that exploit these characteristics, aggregation states of the polymers at the liquid interfaces must be understood as the first benchmark. However, this is experimentally difficult because such interfaces are buried. In this review, we introduce recent development of the issue with the advent of modem experimental techniques.

Language：Japanese  

Polymer Structure and Physical Properties at Non-Solvent Interfaces
Interfaces of polymers with "non-solvents" play an important role in their functional properties such as wettability, friction with lubricants, cell adhesion, and biocompatibility. To design and construct highly functionalized polymers for applications that exploit these characteristics, aggregation states of the polymers at the liquid interfaces must be understood as the first benchmark. However, this is experimentally difficult because such interfaces are buried. In this review, we introduce recent development of the issue with the advent of modem experimental techniques. © 2011 The Society of Polymer Science, Japan.

Language：English   Publishing type：Research paper (scientific journal)  

Poly(2-methoxyethyl acrylate) (PMEA) exhibits excellent blood compatibility. To understand why such a surface functionality exists, the surface of PMEA should be characterized in detail, structurally and dynamically, under not only ambient conditions, but also in water. However, a thin film of PMEA supported on a solid substrate can be easily broken, namely it is dewetted. Our strategy to overcome this difficulty is to mix PMEA with poly(methyl methacrylate) (PMMA). Differential scanning calorimetry and cloud point measurements revealed that the PMEA/PMMA blend has a phase diagram with a lower critical solution temperature. The blend surface was also characterized by X-ray photoelectron spectroscopy in conjunction with microscopic observations. Although PMEA is preferentially segregated over PMMA at the blend surface due to its lower surface free energy, the extent of segregation in the as-prepared films was not sufficient to cover the surface. Annealing the blend film at an appropriate temperature, higher than the glass transition temperature and lower than the phase-separation temperature of the blend, enabled us to prepare a stable and flat surface that was perfectly covered with PMEA.

DOI： 10.1039/c0cp02101f

Language：English   Publishing type：Research paper (scientific journal)  

Solid films of deoxyribonucleic acid (DNA) from salmon testes were prepared by a solvent-casting method. The thermal molecular motion of the DNA film was examined by dynamic mechanical analysis (DMA). Four absorption peaks and one shoulder of the loss modulus were observed in the temperature domain from approximately 150 to 490 K. To assign these, thermal analysis employing thermogravimetry (TG) and differential thermal analysis (DTA) was used in cc junction with ultraviolet (UV)-visible and Fourier-transform infrared (FT-IR) spectroscopy. It seems most likely that, in order of increasing temperature, they are a B-I -> B-II, conformational transition, a relatively large-scale movement associated with water molecules, water evaporation, thermal denaturation of DNA, and a glass transition.

DOI： 10.1021/bm1010933

Language：English   Publishing type：Research paper (scientific journal)  

In this study, stereocontrolled poly(N-isopropylacrylamide) (PIPAAm) brushes were grafted from surfaces by atom transfer radical polymerization (ATRP) in the presence of a Lewis acid, and the effect of PIPAAm brash tacticity on the thermoresponsive wettabiliy was investigated. PIPAAm grafted by ATRP in the presence of Y(OTf)(3) showed high isotacticity, while the control brush polymerized in the absence of Y(OTf)(3) was clearly atactic. The isotacticity and molecular weight of PIPAAm brushes were controlled by polymerization conditions. The wettability of isotactic PIPAAm-grafted surfaces decreased slightly below 10 degrees C, although the phase transition temperature of atactic surface was 30 degrees C, and the bulk isotactic polymer was water-insoluble between 5 and 45 degrees C.

DOI： 10.1021/la1024229

Language：Japanese  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Neutron reflectivity revealed that the surface aggregation states of poly(methyl methacrylate) film can be altered by water, which is a typical nonsolvent, in a relatively large scale.

DOI： 10.1246/cl.2010.810

Language：English   Publishing type：Research paper (scientific journal)  

The local conformation of poly(methyl methacrylate) (PM MA) chains at the nitrogen (N-2) and water interfaces was studied by infrared-visible sum-frequency generation (SFG) spectroscopy. Although SFG spectra in the C-H region for PMMA at the N-2 interface have been hitherto reported, the peak assignments are not in accord with one another. Thus, we first made accurate assignments of SFG peaks using films, which had been well annealed at a temperature above the glass transition temperature for a long time, of three different deuterated PMMAs as well as normal protonated PMMA. At the N-2 interface, hydrophobic functional groups such as a methyl, ester methyl and methylene groups were present. While the a methyl group was oriented along the direction parallel to the interface, ester methyl and methylene groups were oriented normal to the interface. Quantitative discussion concerning the orientation of the functional groups of PMMA at the N-2 interface was aided by a model calculation. Once the PMMA film contacted water, the carbonyl groups of the PMMA side chains were oriented to the water phase to form hydrogen bonds with water molecules, resulting in the migration of ester methyl into the internal region of the film. Concurrently, the methylene groups became randomly oriented at the water interface and/or in part migrated into the internal region. Interestingly, the a methyl groups still existed at the water interface oriented along the parallel direction. The outermost region of PMMA in water can consist of hydrophilic and hydrophobic domains with sub-nanometre scale. Water molecules H-bond to themselves near the hydrophobic domains, leading to the formation of an ice-like structure of water molecules. However, water molecules adjacent to the hydrophilic domains H-bond with carbonyl groups.

DOI： 10.1039/b9py00227h

Language：English   Publishing type：Research paper (scientific journal)  

The relaxation behavior of poly(methyl methacrylate) (PMMA), spin-coated oil a silicon wafer, at the water interface was examined by lateral force microscopy as a function of temperature and scanning rate. Even in water, the lateral force peak which was assigned to the segmental motion of PMMA plasticized by water Molecules was clearly observed in the temperature domain. The apparent activation energy For the plasticized alpha(a)-relaxation process was Much smaller than those for the original alpha(a)-relaxation processes at the intact surface and in the bulk. The depth profile of the glass transition temperature (T-g) of the PMMA film in water was obtained, showing that T-g decreases with proximity to the water phase, The T-g. depression observed here was best explained in terms of the water Content of the film, rather than a confinement effect.

DOI： 10.1021/jp909373g

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In previous study, proton conductivity increased with increasing pressure under water electrolysis, so the effects of pressure on the stability of Nafion 117 have been studied. It was found that conductivity of Nafion 117 drastically decreased at initial few h and then gradually decreased in the following period under electrolysis condition. Decrease in conductivity can be explained by decomposition of Nafion 117. Decomposition of Nafion 117 is accelerated by increasing pressure. Solid state NMR, IR, and Raman spectroscopy suggested that the electrochemical oxidation of sulfo group was occurred at initial period followed by decomposition of CFn main or side chain. Therefore, initial increase in resistance can be explained by desorption of sulfo group in Nafion 117. Desorption of sulfo, group also forms pin hole in Nafion membrane which may cause gas leakage under water electrolysis. Mechanical strength of Nafion membrane is also drastically decreased at initial electrolysis period. Consequently, chemical stability of Nafion 117 may cause serious problem for water electrolysis application and this study reveals that increasing pressure strongly accelerates the decomposition of Nafion 117.

DOI： 10.5796/electrochemistry.78.42

Language：English   Publishing type：Research paper (scientific journal)  

Qualitatively different thickness dependences have been observed in the glass transition temperature, T-g of polystyrene (PS) films supported by hydrogen-passivated silicon (H-Si). It has been suggested that upon annealing at high temperatures in air, the polymer/substrate interface of these films (i.e., PS/Si), though buried underneath the PS layer, might be oxidized, rendering the films a different polymer/ substrate interface (i.e., PS/SiOx-Si), which may account for the different thickness dependences of the T-g observed. In this experiment, we examine if the buried Substrate interface of PS/H-Si films can indeed be oxidized by annealing the films at 150 degrees C in air. Our result shows that a residual film does form on top of the H-Si surface, but it is a bound layer of PS. X-ray photoelectron spectroscopic (XPS) analyses and independence of the residual film oil the initial PS thickness evidence that the H-Si substrate buried underneath a PS film is not oxidized by annealing. We discuss a possible explanation to how the different thickness dependences may be observed in the T-g of these films.

DOI： 10.1021/ma901851w

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A spin-coating method with the aid of selective solvents has been used to construct m,u. Itilayer struct ures for organic devices under the assumption that the solvents do not invade, a preformed structure. To confirm the assumption, we examined the interfacial width (lambda(i)) of model polymer bilayers, composed of polystyrene and perdeuterated poly(methyl methacrylate), prepared by spin-coating and notation methods. Neutron reflectivity measurements revealed that the lambda(i) value was,larger for the spin-coating method than for the flotation method. These results cast doubt on the validity of the assumption. This knowledge should be kept in mind when this method is applied to construct multilayer structures.

DOI： 10.1021/am9004336

Language：English   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Language：Japanese  

Physical Properties of Polymer Thin Films for Device Application
Nano-adhesion of polystyrene (PS) was studied by atomic force microscopy using a cantilever tip coated with PS. Nano-adhesion strength (G_N) was evaluated as functions of time (t_<ad>) and temperature. Although G_N remained a constant up to t_<ad>=10^3s, it increased proportional to t_<ad>^<1/4> and then again reached a constant. This implies that G_N is composed of two factors such as adhesion force between PS surfaces and interdiffusion of segments. The temperature dependence of G_N could be expressed by a WLF-type equation, indicating that the G_N value is closely related to frictional properties among neighboring chains. Thus, it can be concluded that nano-adhesion is dominated by rheological factors rather than thermodynamic ones.

Language：English   Publishing type：Research paper (scientific journal)  

The segmental mobility of a typical amorphous polymer, polystyrene, at the interfaces with solid substrates was noninvasively examined by fluorescence lifetime measurements using evanescent wave excitation in conjunction with coarse-grained molecular dynamics simulation. The glass transition temperature (T(g)) was discernibly higher at the interface than in the internal bulk region. Measurements at different incident angles of excitation pulses revealed that T(g) became higher closer to the interface. The gradient became more marked with an increasing difference in the free energy at the interface between the polymer and solid substrate. The T(g) value at the interface decreased with decreasing molecular weight. However, the decrement for the interfacial T(g) was not as much as that for the bulk T(g), due to the restriction of chain end portions by the substrate. Finally, it was observed that when a film became thinner than 50 nm, the depressed mobility at the interface coupled with the enhanced mobility induced by the presence of the surface. The experimental and simulation results were in good accord with each other.

DOI： 10.1021/jp810370f

Language：English  

Applications of Synchrotron Radiation and Neutron Beam to Soft Matter Science (Symposium X of IUMRS-ICA2008) Toshiji Kanaya, Kohji Tashiro, Kazuo Sakura Keiji Tanaka, Sono Sasaki, Naoya Torikai, Moonhor Ree, Kookheon Char, Charles C Han, Atsushi Takahara This volume contains peer-reviewed invited and contributed papers that were presented in Symposium X Applications of Synchrotron Radiation and Neutron Beam to Soft Matter Science at the IUMRS International Conference in Asia 2008 (IUMRS-ICA 2008), which was held on 9-13 December 2008, at Nagoya Congress Center, Nagoya, Japan. Structure analyses of soft materials based on synchrotron radiation (SR) and neutron beam have been developed steadily. Small-angle scattering and wide-angle diffraction techniques clarified the higher-order structure as well as time dependence of structure development such as crystallization and microphase-separation. On the other hand, reflectivity, grazing-incidence scattering and diffraction techniques revealed the surface and interface structural features of soft materials. From the viewpoint of strong interests on the development of SR and neutron beam techniques for soft materials, the objective of this symposium is to provide an interdisciplinary forum for the discussion of recent advances in research, development, and applications of SR and neutron beams to soft matter science. In this symposium, 21 oral papers containing 16 invited papers and 14 poster papers from China, India, Korea, Taiwan, and Japan were presented during the three-day symposium. As a result of the review of poster and oral presentations of young scientists by symposium chairs, Dr Kummetha Raghunatha Reddy (Toyota Technological Institute) received the IUMRS-ICA 2008 Young Researcher Award. We are grateful to all invited speakers and many participants for valuable contributions and active discussions. Organizing committee of Symposium (IUMRS-ICA 2008) Professor Toshiji Kanaya (Kyoto University) Professor Kohji Tashiro (Toyota Technological Institute) Professor Kazuo Sakurai(Kitakyushu University) Professor Keiji Tanaka (Kyushu University) Dr Sono Sasaki (JASRI/Spring-8) Professor Naoya Torikai (KENS) Professor Moonhor Ree (POSTECH) Professor Kookheon Char (Seoul National University) Professor Charles C Han (CAS) Professor Atsushi Takahara(Kyushu University) Frontier of Polymeric Nano-Soft-Materials, Precision Polymer Synthesis, Self-assembling and Their Functionalization (Symposium Y of IUMRS-ICA2008) Seiichi Kawahara, Rong-Ming Ho, Hiroshi Jinnai, Masami Kamigaito, Takashi Miyata, Hiroshi Morita, Hideyuki Otsuka, Daewon Sohn, Keiji Tanaka It is our great pleasure and honor to publish peer-reviewed papers, presented in Symposium Y Frontier of Polymeric Nano-Soft-Materials Precision Polymer Synthesis, Self-assembling and Their Functionalization at the International Union of Materials Research Societies International Conference in Asia 2008 (IUMRS-ICA2008), which was held on 9-13 December 2008, at Nagoya Congress Center, Nagoya, Japan. Polymeric nano-soft-materials are novel outcomes based on a recent innovative evolution in polymer science, i.e. precision polymer synthesis, self-assembling and functionalization of multi-component systems. The materials are expected to exhibit specific functions and unique properties due to their hierarchic morphologies brought either by naturally-generated ordering or by artificial manipulation of the systems, e.g., crystallization and phase-separation. The emerging precision synthesis has brought out new types of polymers with well-controlled primary structures. Furthermore, the surface and interface of the material are recognized to play an important role in the outstanding mechanical, electrical and optical properties, which are required for medical and engineering applications. In order to understand structure-property relationships in the nano-soft-materials, it is indispensable to develop novel characterization techniques. Symposium Y aimed to provide recent advances in polymer synthesis, self-assembling processes and morphologies, and functionalization of nano-soft-materials in order to initiate mutual and collaborative research interest that is essential to develop revolutionarily new nano-soft-materials in the decades ahead. Four Keynote lectures, 15 invited talks and 30 posters presented important new discoveries in polymeric nano-soft-materials, precision polymer synthesis, self-assembling and their functionalization. As for the precision polymer synthesis, the latest results were provided for studies on synthesis of polyrotaxane with movable graft chains, organic-inorganic hybridization of polymers, supra-molecular coordination assembly of conjugated polymers, precision polymerization of adamantane-containing monomers, production of high density polymer brush and synthesis of rod coil type polymer. The state-of-the-art results were introduced for the formation of nano-helical-structure of block copolymer containing asymmetric carbon atoms, self-assembling of block copolymers under the electric field, self-assembling of liquid crystalline elastomers, preparation of nano cylinder template films and mesoscopic simulation of phase transition of polymers and so forth. Moreover, recent advantages of three-dimensional electron microtomography and scanning force microscopy were proposed for analyses of nano-structures and properties of polymeric multi-component systems. Syntheses, properties and functions of slide-ring-gel, organic-inorganic hybrid hydrogels, hydrogel nano-particles, liquid-crystalline gels, the self-oscillating gels, and double network gels attracted participants' attention. Modifications of naturally occurring polymeric materials with supercritical carbon dioxide were introduced as a novel technology. Some of the attractive topics are presented in this issue. We are grateful to all the speakers and participants for valuable contributions and active discussions. Organizing committee of Symposium Y (IUMRS-ICA 2008) Chair Seiichi Kawahara (Nagaoka University of Technology, Japan) Vice Chairs Rong-Ming Ho (National Tsing Hua University, Taiwan) Hiroshi Jinnai (Kyoto Institute of Technology, Japan) Masami Kamigaito (Nagoya University, Japan) Takashi Miyata (Kansai University, Japan) Hiroshi Morita (National Institute of Advanced Industrial Science and Technology, Japan) Hideyuki Otsuka (Kyushu University, Japan) Daewon Sohn (Hanyang University, Korea) Keiji Tanaka (Kyushu University, Japan)

DOI： 10.1088/1742-6596/184/1/011001

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Scanning viscoelasticity microscopy (SVM) with a mechanical model analysis was applied to polystyrene (PS) surfaces. When the surface was in a glassy state, that is, in an elastic regime, the SVM vibrational system can be simply expressed by a series model composed of two springs such as a cantilever and the sample surface. Once the surface reaches in a viscoelastic regime, a damping factor must be incorporated into the model surface. The spring constants for the PS surfaces being in glassy and transition states were successfully extracted by the analysis. The surface value even for the glassy state was lower than the corresponding bulk value by a few decades.

DOI： 10.1678/rheology.36.87

Language：English   Publishing type：Research paper (scientific journal)  

Interdiffusion of cyclic polystyrene (c-hPS) / cyclic deuterated polystyrene (c-dPS) laminated film whose molecular weights are ca.50 k was examined by neutron reflectivity and dynamic secondary ion mass spectroscopy. It has been found that time evolution of the interfacial thicknesses of (c-hPS/c-dPS) multi-layer films are similar to those of the corresponding linear hPS/linear dPS (l-hPS/l-dPS) bilayer films at short time region. However, at the annealing time longer than 5×10³ s, the interfacial thicknesses of (c-hPS/c-dPS) multi-layer films are evidently larger than those of the (l-hPS/l-dPS) films at each observing time. These results can be explained in terms of the less entanglement nature of cyclic polymers than that of the linear ones.

DOI： 10.1678/rheology.36.113

Language：English   Publishing type：Research paper (scientific journal)  

X-ray photoelectron spectroscopy (XPS) using fullerene (C(60)) cluster ion bombardment was applied to films of a fluorinated block copolymer. Spectra so obtained were essentially different from those using Ar ion beam. Structure in the surface region with the depth down to 60 nm drawn on the basis of XPS with C(60) beam was essentially the same as the one drawn by the result using dynamic secondary ion mass spectrometry, which is a well-established method for the depth analysis of polymers. This implies that XPS using C(60) beam enables one to gain access to the depth analysis of structure in polymer. films with the depth range over the analytical depth of conventional XPS, that is, three times inelastic mean-free path of photoelectrons. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.02.089

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Nano-Adhesion Mechanism between Polymers

Language：Japanese  

Model Analysis of Scanning Viscoelasticity Microscopy and Its Applications to Polymer Surfaces
Scanning viscoelasticity microscopy (SVM) with a mechanical model analysis was applied to polystyrene (PS) surfaces. When the surface was in a glassy state, that is, in an elastic regime, the SVM vibrational system can be simply expressed by a series model composed of two springs such as a cantilever and the sample surface. Once the surface reaches in a viscoelastic regime, a damping factor must be incorporated into the model surface. The spring constants for the PS surfaces being in glassy and transition states were successfully extracted by the analysis. The surface value even for the glassy state was lower than the corresponding bulk value by a few decades.

DOI： 10.1678/rheology.36.87

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A Special Issue for Rheology in Surfaces, Interfaces and Thin Films

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Language：English   Publishing type：Research paper (scientific journal)  

A novel experimental technique for three-dimensional (3D) visualization of phase-separated structure of polymer blend thin film was proposed. Polystyrene/poly(methyl methacrylate) (PS/PMMA) blend thin films with the thickness of approximately 100 nm were cut at extremely low angle by utilizing surface and interface cutting analysis system (SAICAS), and the cross-section was exposed as gradient surface with the width of approximately 2.5 mu m. SFM investigation for the grazing cross-section imaged the detailed internal and surface phase separated structure of the (PS/PMMA) blend thin films on one image. (c) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.apsusc.2007.10.080

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Morphology for films of poly(methyl methacrylate) with various molecular weights was observed before and after methanol immersion by using atomic force microscopy so that the effect of chain entanglement on film retention of a polymer in a liquid can be discussed.

DOI： 10.1246/cl.2008.326

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Density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate in water, hexane, and methanol, which are "nonsolvents" for dPMMA, were examined along the direction normal to the interface by specular neutron reflectivity (NR). The interfaces of dPMMA with the liquids were diffuse in comparison with the pristine interface with air; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of a swollen layer and the interior region, which also contained water, in addition to the diffused layer. The interface of dPMMA with hexane was sharper than that with water. Although there were slight indications of a swollen layer for the dPMMA in hexane, the solvent molecules did not penetrate significantly into the film. On the other hand, in methanol, the whole region of the dPMMA film was strikingly swollen. To conserve mass, the swelling of the film by the nonsolvents is accompanied by an increase in the film thickness. The change in the film thickness estimated by NR was in excellent accord with the results of direct observations using atomic force microscopy (AFM). The modulus of dPMMA in the vicinity of the interfaces with liquids was also examined on the basis of force-distance curves measured by AFM. The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film.

DOI： 10.1021/la702132t

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Language：English   Publishing type：Research paper (scientific journal)  

Surface relaxation in syndiotactic (st-) and isotactic (it-) poly(methyl methacrylate) (PMMA) films was studied by lateral force microscopy. The α_a- and β-relaxation processes were clearly observed even at the surface, permitting us to deduce the form of the dispersion map for the surface relaxation processes. Both relaxation temperatures at the surface were lower than the corresponding ones in the bulk. In addition, the extent to which the peak temperature for the surface relaxation processes fell below that of the bulk strongly depended on the stereoregularity of the films. The differences in the chain conformations between the surface and the bulk, which were more remarkable in the st-PMMA, produced this variation in surface mobility.

DOI： 10.1295/polymj.PJ2006270

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Language：English   Publishing type：Research paper (scientific journal)  

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DOI： 10.1295/kobunshi.56.38a

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DOI： 10.1295/kobunshi.56.38

Language：Japanese  

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E to Z (trans → cis) photoisomerization of azobenzene (Az) chromophores tagged to polystyrene (PS) in thin films was studied as functions of thickness, PS molecular weight, and temperature, using the change in absorption at 336 nm arising from the Az E isomer remaining upon ultraviolet light irradiation at 350 ± 5 nm. The photoisomerization in solid films exhibited fast and slow modes. The fractional amount of the fast mode (I ₁) started to increase with decreasing film thickness once the films were thinner than a threshold value. This was explained in terms of a surface layer in which the photoisomerization reaction proceeds quickly, the effect of which becomes more noticeable with decreasing thickness due to a larger surface to volume ratio. The thickness dependence of the I₁ fraction was insensitive to the molecular weight of the PS used. The thickness of the surface layer, estimated through a layer model analysis, increased with rising temperature up to 298 K. Interestingly, the surface layer markedly thickened at temperatures at which the molecular motion of PS is on a relatively small scale, namely, at the γ and β relaxation temperatures.

DOI： 10.1021/jp0705065

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Hierarchical thermal molecular motion was studied in thin films of polystyrene (PS). The segmental motion in the thin films was examined by dynamic mechanical analysis. Molecular motions with a relatively small scale in the thin films were discussed on the basis of the kinetics of photoinduced trans to cis isomerization for azobenzene probes tagged to PS. Apparent glass transition temperatures generally decreased with decreasing film thickness. Although relaxation temperatures of β and γ processes in the thin films would be comparable to those in the bulk, the photoisomerization reaction of azobenzene probes became faster with decreasing thickness. Finally, a model for hierarchical thermal molecular motions in thin films was proposed on the basis of the above-mentioned results.

DOI： 10.1295/koron.64.429

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A novel approach to surface modification of polymer films is proposed on the basis of graft polymerization initiated from photosensitizers attached to hyperbranched polymers which are localized at the film surface.

DOI： 10.1246/cl.2007.808

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The effect of chain-end chemistry on surface and interfacial segregation in symmetric blends of polystyrene (hPS)/deuterated polystyrene (dPS) has been investigated by X-ray photoelectron and secondary ion mass spectroscopy in conjunction with neutron reflectivity measurements. alpha,omega-Fluoroalkyl- and alpha,omega-carboxy-terminated polystyrenes (alpha,omega-hPS(R(f))(2) and alpha,omega-hPS(COOH)(2)) were used as end-functionalized polymers; the former possesses chain ends with lower surface energies, and the latter possesses higher surface energies compared with that of the main chain. In the case of an alpha,omega-hPS(R(f))(2)/dPS blend film, alpha,omega-hPS(R(f))(2) was enriched at the surface owing to the surface localization of the R(f) groups, although the surface energy of the hPS segments was slightly higher than that of the dPS ones. On the contrary, in the case of an alpha,omega-hPS(COOH)(2)/dPS blend film, dPS was preferentially segregated at the surface. This may be due to a surface depletion of COOH ends and an apparent molecular weight increase of alpha,omega-hPS(COOH)(2) produced by a hydrogen-bonded intermolecular association of COOH ends in addition to the surface energy difference between hPS and dPS segments. Interestingly, both R(f) and COOH chain ends were partitioned to the substrate interface for the alpha,omega-hPS(R(f))(2)/dPS and alpha,omega-hPS(COOH)(2)/dPS blend films, resulting in the segregation of the hPS component at the substrate interface for both blends. The results presented imply that surface and interfacial segregation in polymer blends could be regulated by incorporating functional groups into the end portions of one component.

DOI： 10.1021/la700418j

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Segmental motion in polystyrene (PS) thin and ultrathin films supported on substrates was studied by dynamic viscoelastic measurement. A polymer film, which has the thickness comparable to or less than twice of radius of gyration of an unperturbed chain (2R _g), is defined as an ultrathin film. In the case of PS, α _a-relaxation process corresponding to the segmental motion was generally observed at approximately 380 K. Even for both the PS thin and ultrathin films, the α _a-absorption peak was clearly observed. A rheological analysis reveals that the α _a-relaxation behavior for the thin films with the thickness of about 200 nm is the same as that of the bulk sample. On the contrary, in the case of the PS ultrathin films, the α _a-absorption peak on temperature-loss modulus (E) curve is broadened toward both lower and higher temperature sides. This can be interpreted by taking into account that the segmental motion in the vicinity of surface and interface is detectable for such ultrathin films, which should be faster and slower than that in the bulk, respectively. And, it is found that the apparent activation energy (ΔH) for the α _a-relaxation in the ultrathin films becomes smaller than the bulk value probably due to the surface effect. Finally, an interfacial effect on the ΔH was studied by using different substrates. When the interaction between PS and substrate becomes stronger, the ΔH value for the α _a-relaxation in the ultrathin films increases. The results imply that the segmental motion in the polymer ultrathin films is strongly influenced by surface and interfacial effects.

DOI： 10.1007/s11771-007-0279-6

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A Fundamental Study of Adhesive Reliability-A Study of PBT-Epoxy Adhesive Interface-

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DOI： 10.1016/j.cardfail.2006.08.171

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The glass transition temperature at the surface of polymer film is studied by the coarse-grained molecular dynamics simulation. By the analysis of the segmental motion, the glass transition temperatures at the surface region and that in the bulk region are determined separately. The glass transition at the surface region is found to be lower than that in the bulk region. The molecular weight dependence of the glass transition temperature obtained by the simulation agrees well with that obtained by the scanning force microscopic measurements.

DOI： 10.1021/ma052632h

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In order to investigate structure of diblock copolymer thin film, gradient shaved surface was prepared by using Surface And Interfacial Cutting Analysis System (SAICAS). The scanning viscoelasticity microscopic observation of sliced film revealed the alternate lamellar structures with different mechanical properties in the depth direction.

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An effect of surface treatment on adhesion behavior of poly (butylene terephthalate) (PBT) with epoxy adhesive was studied. In general, PBT is annealed at a temperature above the glass transition temperature to obtain dimensional stability for the practical use. However, such an annealing procedure makes the adhesion properties poorer. In this study, we demonstrate that tensile adhesive strength for annealed PBT could be improved through plasma treatment. Tensile adhesive strength increased with increasing surface density of C-O and COO groups, which were quantitatively detected by XPS. Finally, it was concluded that chemical interaction between carboxyl and/or ester groups of PBT and hydroxyl groups of epoxy adhesive was a responsible factor in improving adhesive strength between PBT and epoxy adhesive.

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

The interdiffusion behavior between cyclic and linear polystyrenes with high molecular weight based on dynamic secondary ion mass spectroscopy (DSIMS) in conjunction with neutron reflectivity (NR) measurements was investigated. Polymers used in this study are monodisperse cyclic and linear PSs (c-hPS, 1-hPS) and those deuterated counterparts (c-dPS, 1-dPS). Time evolution of interfacial thickness with annealing was evaluated by NR and DSIMS. The broadening of the (c-hPS/c-dPS) interface takes place much more rapidly than that of corresponding linear ones. The diffusion of cyclic polystyrene is much faster than that of linear polystyrene. Both thickness of (c-hPS/c-dPS) and (1-hPS/1-dPS) interfaces increase with increasing temperature at 120°C, and that of (c-hPS/c-dPS) bilayer films is much higher than that of (1-hPS/1-dPS) ones at any given temperature.

DOI： 10.1021/ma060652t

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Language：English   Publishing type：Research paper (scientific journal)  

Two topics, the both being related with localized states in non-crystalline solids, are studied. One is a comparison of photo-induced phenomena in oxide, chalcogenide, and organic materials. Despite of different inorganic and organic structures, there exist many similarities in photo-induced phenomena, which can be ascribed to excitation of localized electronic states. The other topic concerns photo-induced phenomena induced by linear and non-linear excitation. A result on As2S3 demonstrates that band-gap excitation by one- and two-photon processes provides different changes. It is suggested that the two-photon process occurs resonantly at around localized states in amorphous materials, and the process plays important roles in the structural change. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnoncrysol.2006.02.070

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Time evolution of interfacial thicknesses between a cyclic polystyrene (c-hPS) / its deuterated counterpart (c-dPS) and a linear polystyrene (1-hPS) / its deuterated counterpart (1-dPS) bilayer films was investigated by dynamic secondary ion mass spectrometry (DSIMS) and neutron reflectivity (NR). The interfacial thickness of (c-hPS/c-dPS) film was significantly larger than that of (1-hPS/1-dPS) film at any given annealing time, indicating that the diffusion constant of c-PS is constantly larger than that of 1-PS. It might be explained that weaker topological constraint comes from the entanglement for the c-PS than for the 1-PS.

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A cross-section film of a symmetric diblock copolymer, in which lamellar structure was formed, was successfully prepared by a mechanical cutting method using a sharp diamond knife. In this method, the knife was obliquely pushed into the sample from the surface side. The oblique angle was precisely controlled to be 0.57 deg. Thus, periodic lamellar structure was shown up at the surface of the cross-section film Then, scanning viscoelasticity microscopy (SVM), which can image viscoelastic information at the surface, was applied to the cross-section film. Finally, it was demonstrated that a combination of SVM and mechanical cutting method enabled one to gain direct insight into the depth information for structure and physical properties of the diblock copolymer film along the direction normal to the surface.

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Influence of annealing treatment on adhesion behavior of poly(butylene terephthalate) (PBT) with epoxy adhesive was studied. The tensile adhesion strength decreased after the annealing treatment of PBT. In the case of the untreated PBT, the failure depth after the failure was not clearly defined. Once the PBT was annealed, the average failure depth turned to be 4 nm. The above results imply that the failure mechanism for the system transformed from interfacial failure to cohesive fracture upon annealing treatment. This can be easily understood by taking into account that a mechanically weak layer is formed in the surface region of PBT after the annealing. Such a weak boundary layer was observed by scanning viscoelasticity microscopy. Improvement of adhesive property was confirmed by surface treatment.

Language：Japanese   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (other academic)  

Surface mechanical properties of polystyrene (PS) film prepared from single droplet of PS solution by ink-jet (IJ) method, and [PS / Polybutadiene (BDA)] (60/40, w/w) blend film were investigated by scanning force microscope. The scanning viscoelesticity microscopic measurements at various temperatures clarified that the relative difference of contrast of the PS and the PBD phase surface becomes small with an increase of temperature. This is due to the relative difference of elasticity of PS and PBD phases. Based on the temperature dependent lateral force measurements, the surface of the PS film prepared by IJ method was in a glass-rubber transition state even at 343 K, in spite of that the bulk Tg was far above 343 K [Tg _(bulk)=378 K]. Similar temperature dependence of lateral force was also observed on the PS film prepared by spin-coating method.

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DOI： 10.1021/la050901r

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An effect of surface treatment on adhesion behavior of poly (butylene terephthalate) (PBT) with epoxy adhesive was studied. In general, PBT is supposed to be annealed at a temperature above the glass transition temperature to obtain dimensional stability for the practical use. However, such an annealing procedure makes the adhesion properties poorer. In this study, we demonstrate that tensile adhesive strength for annealed PBT could be improved through UV irradiation or chemical etching treatment. Tensile adhesive strength increased with increasing surface density of C-O and C=O groups, which were quantitatively detected by XPS. Finally, it was concluded that chemical interaction between carboxyl and/or ester groups of PBT and hydroxyl groups of epoxy adhesive was a responsible factor in improving adhesive strength between PBT and epoxy adhesive.

Language：English  

Establishment of How to Analyze Molecular Motion for Polymer Chains at Surface and Interfaces

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A block copolymer of deuterated polystyrene (dPS) and 2-[2-(2- methoxyethoxy)ethoxy]ethyl methacrylate (PME3MA) spontaneously exposes the PME3MA block, which is soluble in water, to the surface in a vacuum. dPS-PME3MA mixed with polystyrene (PS) segregates to the PS surface spontaneously and changes the hydrophobic PS surface into hydrophilic surface. The detail of the segregation will be discussed.

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The purpose of this study is to develop transparent super-water-repellent surfaces with a simple way and to apply this coating to polymer substrates. Super-water-repellent surfaces are generally made by controlling chemistry and roughness at the surface. In this study, surface roughness was controlled by the content of colloidal silica particles in a sol-gel thin film covered with fluoroalkyl silane coupling agent. When the fractional amount of colloidal silica was in the range of 10-30 wt%, root mean square roughness at the surface by AFM was around 30-70 nm. X-ray photoelectron spectroscopy revealed that these surfaces were covered with fluoroalkyl groups. Consequently, these surfaces exhibit excellent water repellencies such as contact angles of 150 deg. to water. This coating procedure can be applied to transparent polymer substrates such as poly(ethyleneterephtarate) (PET) films. In that case, transparency and durability of the sol-gel layer on the PET film are sufficient enough to be applied for practical use.

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Influence of annealing treatment on adhesion behavior of poly(butylene terephthalate) (PBT) with epoxy adhesive was studied. The tensile adhesion strength decreased after the annealing treatment of PBT. In the case of the untreated PBT, the failure depth after the failure was not clearly defined. Once the PBT was annealed, the average failure depth turned to be 4 nm. The above results imply that the failure mechanism for the system transformed from interfacial failure to cohesive fracture upon annealing treatment. This can be easily understood by taking into account that a mechanically weak layer is formed in the surface region of PBT after the annealing. Such a weak boundary layer was observed by grazing incidence X-ray diffraction measurement.

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Mechanical relaxation behavior of polystyrene (PS) and poly (2-vinylprydine) (P2VP) thin and ultrathin films on substrates was examined. Even in the case of the ultrathin films, the α₂-relaxation process corresponding to the segmental motion was successfully observed. However, the α_a-absorption peak was broadened toward lower and higher temperature sides because of surface and interfacial effects. Interestingly, when a PS ultrathin film was sandwiched between SiO_x layers, an additional peak come up with the interfacial segmental motion appeared at the higher temperature side. In the case of the P2VP ultrathin films on the SiO_x substrates, the interfacial effect became remarkable due to the strong attractive interaction between chains and the substrate. Finally, it was concluded that chain mobility in the interfacial region was depressed in comparison with that in the internal bulk phase.

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In the field of nanotechnology and nanoscience, dendrimers are key compounds having well-defined chemical structure. We nave already reported synthesis of globular carbohydrate macro molecule "sugar ball" which is applicable to gene and drug carriers [1-4]. Amphiphilic surface-sugar- substituted surface-block dendrimers have been also designed, synthesized and characterized [4]. Supramolecular architeucture based on amphiphilic dendrimers is important to create shape controlled smart nanoobjects[5]. The present report deals with synthesis and assembly of amphiphilic sugar-substituted poly(ethylene glycol) dendrimers. The dendrimers were synthesized by the reaction of N-acetyl-D-glucosamine, galactose, and lactose derivatives with poly(ethylene glycol) dendrimer having a hydroxy group and alkyl groups at the core and the surface, respectively, wnich were prepared by convergent method. The sugar moieties and the poly(ethylene glycol) dendrimer branches are regarded as hydrophilic parts, whereas the alkyl groups act as hydrophobic groups. Although hydrophobicity of the amphiphilic dendrimers is high, nanoparticles based on the amphiphilic dendrimers can be prepared by irradiation of ultrasonic wave. Fortunately the particle size, which is measured using DLS, could be controlled around ca. 200 nm. Monolayer of the amphiphilic dendrimers was successfully formed at the air/water interface. Intermolecular distance, i.e., intersugar distance, of the monolayer was found to be controlled around 2 nm by changing generation and hydrophobic groups of the dendrimers.

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DOI： 10.1016/j.polymer.2004.11.021

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Flat cross-sections of (polypropylene/elastomer) blends were prepared by ultamicrotoming at 150 K. Then, scanning force microscopy (SFM) was applied to each cross-section to evaluate the interfacial thickness between the two phases in the blend. For this purpose, a viscoelastic mode was superior to a conventional topographic mode. The results obtained well reflected the solubility between the two components. Finally, transmission electron microscopy was applied to the sample. The TEM observations supported what was suggested on the basis of SFM results.

DOI： 10.1295/koron.62.432

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ma051143e

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ma050473w

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s00289-004-0329-2

Language：English   Publishing type：Research paper (scientific journal)  

The preparation of poly(amido amine) (PAMAM) dendrimer monolayers at the air/water interface was analyzed. Investigations show the transfer of PAMAM dedrimer monolayers from the air side onto hydrophobic silicon wafers, which were treated by the horizontal lifting method. X-ray reflectivity, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were used to study the aggregation states in the PAMAM monolayers. The results show that the PAMAM molecules sit on the substrate with an oblate shape in which the hydrophilic core and hydrophobic alkyl end groups were towards the substrate and air sides.

DOI： 10.1016/j.cis.2004.09.007

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Surfaces in polymeric materials play an important role in many technological applications. Hence, systematical understanding of aggregation states and physical properties at the surfaces is of pivotal importance as the first benchmark so that highly functionalized polymeric materials based on surface peculiarity can be promisingly designed and constructed. Nevertheless, surface properties, especially rheological properties, had not been studied until early 90s because of technical difficulties. In 1993, we started to embark on this intriguing and challenging issue by mainly scanning force microscopy using monodisperse polystyrene (PS) solid films. Consequently, conclusions obtained thus far are consistently arrived that molecular motion at the PS surfaces is thermally activated in comparison with the corresponding internal bulk region. However, it is far from clear for the moment what the whole picture of such peculiar surface mobility is, although we believe that some parts of it have been successfully clarified to date. Here, experimental methods to examine surface rheological properties, which we have proposed, are mentioned at first, and then, essential points of what we have established are discussed.

DOI： 10.1678/rheology.32.17

Language：English  

Language：English  

Characterizations and Surface Wettability of Fluorinated Block Copolymers Synthesized by Atom Transfer Radical Polymerization

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Surface Segregation of Fluoroalkyl Side Group of Fluorinated Block Copolymers

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Segmental Motion in Polystyrene Thin and Ultrathin Films Based on Dynamic Viscoelastic Measurement

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Influence of annealing treatment on the Adhesion of Poly(butylene terephthalate) and its Interfacial structure

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pola.10873

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DOI： 10.1021/ma048579z

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DOI： 10.1163/1568554041738166

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1163/1568554041738157

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/la049556g

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1295/polymj.36.498

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ma035191f

Language：English   Publishing type：Research paper (scientific journal)  

Surface aggregation states in miscible blends of monodisperse polystyrene (PS) and poly(vinyl methyl ether) (PVME) were studied by X-ray photoelectron spectroscopy (XPS) in conjunction with neutron reflectivity (NR). In the case of symmetric blends in terms of degree of polymerization, N, PVME and PS were preferentially segregated at the film surface and the interface with a silicon wafer, respectively, to minimize free energy of the system. The concentration profile near the surface obtained by experiments was consistent with a mean-field prediction. Also, the surface composition in symmetric blends composed of PS terminated by fluoroalkyl groups at both ends (a,omega-PS(R-f)(2)) and PVME was examined. In this case, the surface enrichment of PVME was suppressed by virtue of the surface localization of fluoroalkyl end groups, and the composition was strongly dependent on N. The surface in asymmetric alpha,omega-PS(R-f)(2)/PVME blend, in which N of alpha,omega-PS(R-f)(2) was much smaller than that of PVME, was mostly covered with the PS segments. The results presented imply a possibility that the surface composition in miscible polymer mixtures could be perfectly regulated combining the chain end effect with the molecular weight disparity between the components.

DOI： 10.1021/ma034117u

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Surface dynamics in monodisperse polystyrene films was examined by lateral force microscopy in conjunction with dynamic secondary ion mass spectroscopy. Glass transition temperature, T_g, at the surface was markedly lower than the corresponding bulk T_g. Also, it was shown that polymer chains present at the surface could diffuse even at a temperature below the bulk T_g. The surface depth, in which molecular motion was activated, was of the order of 5 nm.

DOI： 10.1002/masy.200351111

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A monodisperse polystyrene (PS) film was spin-coated on a silicon wafer with native oxide layer and was in part scratched by a blade. Then, the surface modulus on a given area, in which PS and bared silicon were present, was two-dimensionally mapped as a function of temperature by scanning viscoelasticity microscopy. We visually present evidence that the PS surface started to soften up at a temperature much lower than the bulk glass transition temperature.

DOI： 10.1021/la034542g

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Monodisperse polystyrene (PS) films with various thicknesses were spun-coated on silicon wafers with native oxide layer. Surface relaxation behavior in the PS films was studied as a function of thickness by lateral force microscopy (LFM). In the case of a thick PS film, a clear lateral force peak corresponding to surface alpha(a)-relaxation process of segmental motion was observed at a temperature much lower than the bulk glass transition temperature, T-g. As the film became thinner than 3-4 times the radius of gyration of an unperturbed consistent chain, the peak on lateral force vs temperature curve started to broaden out with decreasing thickness and eventually split into two peaks. The appearance temperature of the surface a alpha(a)-relaxation peak was invariant with respect to the film thickness even in such an ultrathin state, meaning that surface T-g was insensitive to the thickness. On the other hand, the ultrathinning-induced relaxation process, called surface beta-relaxation, was strongly dependent on the thickness in terms of relaxation temperature and apparent activation energy. Finally, possible origins of the surface beta-relaxation process were proposed.

DOI： 10.1021/ma034001y

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alpha,omega-Fluoroalkyl-terminated polystyrenes (alpha,omega-PS(R-f)(2)) with various molecular weights were synthesized by an anionic polymerization. Then, chain end distribution in the surface region of the alpha,omega-PS(R-f)(2) films was studied by angular-dependent X-ray photoelectron spectroscopy in conjunction with neutron reflectivity. The alpha,omega-PS(R-f)(2) films annealed under vacuum exhibited surface localization of chain ends. Since the fluoroalkyl chain ends possess a lower surface free energy compared with the main chain part, they energetically prefer to partition to the surface. The extent to which the chain ends were segregated at the surface was examined as a function of molecular weight. Also, it was presented how surface orientation of the fluoroalkyl end groups was dependent on molecular weight. On the other hand, no segregation of the chain ends was observed at the surface of the alpha,omega-PS(R-f)(2) film annealed in boiled water. This is because the chain ends with a lower surface free energy tend to stay away from the higher energy medium of the boiled water. This result reveals that the surface concentration of chain ends can be regulated by selecting an appropriate annealing condition based on surface thermodynamics. (C) 2003 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0032-3861(03)00391-4

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Surface rheological analyses of polymeric solids were presented on the basis of scanning viscoelasticity microscopy (SVM) and lateral force microscopy (LFM). SVM observation for phase-separated polymer blend films revealed two-dimensional distribution of elasticity. In order to study surface thermal molecular motion of monodisperse polystyrene (PS), SVM and LFM measurements were made at various temperatures. Glass transition temperature, T_g, at the surface was discerned to be markedly lower than the corresponding bulk T_g, and the discrepancy of T_g between surface and bulk became larger with decreasing molecular weight. Such an intensive activation of thermal molecular motion at the PS surface can be explained in terms of an excess free volume induced by the segregated chain ends and a reduced cooperativity at the surface. Bulk T_g of miscible binary blends can be well expressed by the Gordon-Taylor equation. Extending this notion to surface, the surface composition in blends would be obtained by measuring surface T_g of each constituent as well as their blend. The surface composition in blend films of two PSs with different molecular weights was experimentally and systematically elucidated. The surface enrichment of a smaller molecular weight component became more remarkable with increasing molecular weight disparity between the two components due probably to an entropic effect.

DOI： 10.1678/rheology.31.33

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The optical wave behaviour around a subwavelength aperture in a thick metallic screen is examined through three-dimensional computer simulation. Treating the metallic screen as a dielectric slab with complex-valued permittivity, it is possible to design an aperture that simultaneously provides high intensity and small spot size through the excitation of surface plasmon polaritons on the side walls of the aperture.

DOI： 10.1046/j.1365-2818.2003.01155.x

Language：English   Publishing type：Research paper (scientific journal)  

Surface glass transition temperature, T-g(s), of three classes of monodisperse polystyrene, proton-terminated (PS-H), alpha,omega-diamino-tertninated (alpha,omega-PS(NH2)(2)) and ap-dicarboxy-terminated (alpha,omega-PS(COOH)(2)), were studied by scanning force microscopy. T-g(s) of all samples was discernibly lower than the corresponding bulk glass transition temperature, T-g(b). Also, T-g(s) value was strongly dependent on what the chemical structure of chain end groups was. Based on the time-temperature superposition principle, apparent activation energy of the alpha(a)-relaxation process corresponding to surface segmental motion was evaluated to be approximately 230 kJ.mol(-1). This value was much smaller than the reported bulk ones, and was independent of the chemical structure of chain ends. This result implies that the cooperativity for the alpha(a)-relaxation process at the PS surface is reduced in comparison with the bulk due probably to an existence of the free space presented to polymer segments at the surface. Hence, it was concluded that the surface alpha(a)-relaxation process was activated by not only the chain end effect but also the reduced cooperativity at the surface.

DOI： 10.1002/masy.200390036

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/la0261592

Language：English   Publishing type：Research paper (scientific journal)  

Surface mobility in polystyrene (PS) films was studied using (PS/deuterated PS) bilayer films, which were prepared by attaching original two surfaces together. Time evolution of the bilayer interface at various temperatures was examined by dynamic secondary ion mass spectroscopy in conjunction with neutron reflectivity. When the bilayer was annealed at a temperature above bulk glass transition temperature, T-g(b), the interfacial thickening was well expressed by the context of Fickian diffusion. On the other hand, in the case of an annealing temperature above surface glass transition temperature, T-g(s), and below T-g(b), the interface monotonically thickened with the time at first and then turned to be independent. This means that chains went across the "mobile" interface and then reached the "dead" bulk region in which the diffusivity should be frozen. Hence, it was claimed that chains could diffuse discernibly in the surface region even at a temperature lower than the T-g(b). On the basis of temperature and molecular weight dependences of quasi-equilibrium interfacial thickness after a sufficiently long time, a possible model of mobility gradient in the surface region was proposed.

DOI： 10.1021/ma025667f

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1295/polymj.35.44

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0169-4332(02)00748-1

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Surface molecular motion in atactic polypropylene (aPP) films was studied by scanning force microscopy. Glass transition temperature at the surface, T-g(delta), was determined to be 251 +/- 1 K on the basis of temperature dependence of lateral force, whereas its bulk glass transition temperature, T-g(b), by dynamic viscoelastic and differential scanning calorimetric measurements was 262 K. In general, polyolefin is easily oxidized, and thus, many kinds of additives are mixed in it for practical use. Hence, effects of oxidation and additives on surface properties of the aPP surface were examined as well. To achieve oxidation, the aPP films were annealed at 428 K for 100 min under the ambient atmosphere. After this treatment, T-g(delta) decreased by approximately 15 K in comparison with the intact film due to degradation of surface chains. On the contrary, in the case of the aPP containing 10 wt% antioxidant, T-g(delta) was almost the same as that of the intact film before and even after the oxidation treatment. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0032-3861(02)00340-3

Language：English   Publishing type：Research paper (scientific journal)  

The bulk glass transition temperature, T-g(b), of miscible binary blends can be well expressed by the Gordon-Taylor equation. Extending this notion to surface, the surface composition in the blend would be obtained by measuring the surface glass transition temperature, T-g(g), of each constituent as well as their blend. The most intriguing advantage of this technique is that labeling of a component is not necessary, unlike conventional spectroscopy. To confirm the validity of our technique, the surface composition in a mixture of polystyrene (PS) and deuterated PS (dPS) was evaluated and compared with the results by well-established surface characterization techniques, static secondary ion mass spectroscopy, and neutron reflectivity. They were in good accordance with one another within the experimental accuracy. Hence, it was claimed that the proposed method was powerful to study the surface concentration in miscible binary blends. Finally, the surface composition in blend films of two PSs with different molecular weights was experimentally and systematically elucidated. The surface enrichment of a smaller molecular weight component became more remarkable with increasing molecular weight disparity between the two components due to an entropic effect.

DOI： 10.1021/ma011960o

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/la011401a

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/la026161t

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0032-3861(02)00340-3

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ma011689a

Language：English   Publishing type：Research paper (scientific journal)  

Surface glass transition behaviors of monodisperse alpha,omega -diamino-terminated and alpha,omega -dicarboxy-terminated polystyrenes (alpha,omega -PS(NH2)(2) and alpha,omega -PS(COOH)(2)) were studied by scanning force microscopy and were compared with the results of proton-terminated polystyrene (PS-H). All surface glass transition temperatures, T-g(s), of PS-H, alpha,omega -PS(NH2)(2), and alpha,omega -PS(COOH)(2) were discernibly lower than each corresponding bulk glass transition temperature, T-g(b). However, the magnitude of T-g(s) was strongly dependent on the chemical structure of chain end groups, because the surface concentration of chain ends varied with the surface free energy difference between the main chain part and the chain end portion, via the surface segregation or surface depletion of chain ends. This result makes it clear that chain end chemistry is one of determining factors on the magnitude of T-g(s). On the basis of the time-temperature superposition principle applied to the scanning rate dependence of lateral force as a function of temperature, the apparent activation energy, DeltaH(double dagger), of the alpha (a)-relaxation process corresponding to micro-Brownian motion at the surface was evaluated to be approximately 230 kJ mol(-1). This value is much smaller than the reported bulk ones and is independent of the chemical structure of chain ends. This result implies that the cooperativity for the alpha (a)-relaxation process at the PS surface is reduced in comparison with the bulk, probably due to the existence of the free space presented to polymer segments at the surface. Hence, it was concluded that the surface alpha (a)-relaxation process was activated by not only the chain end effect but also the reduced cooperativity at the surface. Finally, possible other factors determining on the magnitude of T-g(s) were discussed.

DOI： 10.1021/ma010126w

Language：English   Publishing type：Research paper (scientific journal)  

Proton- and perfluoroalkyl-terminated poly(2-vinylpyridine) (P2VP-H and P2VP-C2C8F) were anionically synthesized. Surface molecular motions of P2VP-H and P2VP-C2C8F films prepared on hydrophilic silicon wafers were examined by lateral force microscopy (LFM). Surface glass transition temperature, T-g(s), of P2VP-C2C8F was lower than that of P2VP-H probably due to the difference of the surface concentration of chain ends. Also, both T-g(s) values were lower than each corresponding bulk glass transition temperature, T-g(s). Surface molecular motion in an ultrathin film was less activated than that of the thick film, although Tin the ultrathin film remained lower than T-g(b). In the case of ultrathin films, the surface/interface area to volume ratio becomes larger, and thus the thermal molecular motion at the surface is affected by that at the polymer/substrate interface. Since molecular mobility on the substrate might be restricted owing to the polar attractive interaction between polymer segments and the hydrophilic substrate, the activation of surface molecular motion apparently turns weak for such an ultrathin film. (C) 2001 Elsevier Science Ltd. All rights reserved.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ma010012k

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/bcsj.74.765

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0375-9601(01)00150-5

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ma001831s

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.2001.536

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/bcsj.74.1397

Language：English   Publishing type：Research paper (scientific journal)  

Polymer electrolytes that have been developed for battery applications fall into two general classes, neat or "pure" polymer and plasticized or gel in which the polymer is combined with a conducting organic electrolyte. The polyethylene oxide (PEO) and its modifications are typical of the "pure" polymer electrolytes. They have poor conductivity at room temperatures, but at elevated temperatures, their conductivity is of the order of 10
^-3
to 10
^-4
S/cm. The PEO electrolytes have found application in the high temperature (>60°C) lithium metal anode battery systems. The high temperature necessary for good operation makes them unsuitable for use in small consumer appliances. The polymer electrolyte battery development activities have resulted in several high performance battery systems now just entering the market. Not all of the developments have resulted in commercial cell production. The commercialization activities of high performance lithium-ion (Li-Ion) batteries have been based on two general plastic polymer systems: poly-vinylidene difluoride-hexafluoropropylene copolymer (PVdF-HFP) and polyacrylates. The polymer cells are expected to have advantages in manufacturing, flexibility, thin cell formats and lightweight packaging. Important parameters in PVdF gel electrolyte performance include the electrolyte type (combination of organic carbonates), temperature, and HFP copolymer content. Li-Ion coin cells fabricated with a polyolefin separator with either liquid electrolyte or with the PVdF gel polymer electrolyte have equivalent performance.

DOI： 10.1002/1521-3900(200010)159:1<229::AID-MASY229>3.0.CO;2-O

Language：English   Publishing type：Research paper (scientific journal)  

Recent studies of thermal molecular motions at polymer surfaces are reviewed. Although many arguments have been still going on, many results support a consistent notion that surface molecular motion is much more vigorous than that in its interior bulk region. Finally, surface dynamics at temperature below its bulk glass transition is also reviewed.

Language：English   Publishing type：Research paper (scientific journal)  

Surface glass transition temperature, Tg s, of monodisperse polystyrene (PS) films was determined from the temperature dependence of lateral force at a given scanning rate. The end groups of the PS were composed of sec-butyl group and a repeating unit terminated by proton. Tg s of the PS films was discerned to be markedly lower than its bulk Tg, Tg b, in the entire number-average molecular weight, Mn, range, 4.9 K to 1460 K. The Mn dependence of Tg s was analyzed on the basis of a simple power law. The exponent of Mn related to Tg s was -0.60±0.03 in contrast to the power of -0.5 from the Mayes scaling argument that is based on both chain ends being perfectly localized at the surface. This result implies that the surface localization of end groups of the PS used here is not complete. The Tg s extrapolated to the infinite Mn was found to be lower than the corresponding Tg b by approximately 20 K. The apparent activation energy of the surface αa-relaxation process for the PS obtained from Arrhenius plot was 230±10 kJ·mol-1, significantly smaller than that for the bulk PS. Also, it was shown on the basis of Ngai's coupling model that the cooperative motion at the surface can be achieved much easier than its internal bulk phase. Thus, the difference between the Tg s and the Tg b for the infinite Mn PS was explained in terms of the size and/or energy barrier reduction of the cooperative movement for the surface αa-relaxation process, which might be arisen from the existence of the free space presented to polymer segments at the surface.

DOI： 10.1021/ma000406w

Language：English  

Surface Aggregation Structure and Surface Mechanical Properties of Binary Polymer Blend Thin Films.

DOI： 10.1002/1521-3900(200010)159:1<89::AID-MASY89>3.0.CO;2-U

Language：English  

Effect of End Group Chemistry on Surface Molecular Motion of Monodisperse Polystyrene Films.

DOI： 10.1002/1521-3900(200010)159:1<35::AID-MASY35>3.0.CO;2-R

Language：English  

A study was carried out to examine the monolayer dynamics and the hydrolysis kinetics of umbelliferone stearate (UMB-C₁₈) on binary monolayers composed of dilauroylphosphatidylcholine (DLPC) and another viscosifier, PtBMA. Results of this study were compared to previous results using a different viscosifier, cholesterol, of the lipid monolayer.

Language：English   Publishing type：Research paper (scientific journal)  

Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of scanning viscoelasticity microscopic (SVM) and lateral force microscopic (LFM) measurements. SVM and LFM measurements were carried out fur films of conventional monodisperse polystyrene (PS) with sec-butyl] and proton-terminated end groups at room temperature, In the case of the number-average molecular weight, M-n, less than ca. 4.0 x 10(4), the surface was in a glass-rubber transition state even though the bulk glass transition temperature, T-g was far above room temperature, meaning that the surface molecular motion was fairly active compared with that in the bulk. LFM measurements of the monodisperse PS films at various scanning rates and temperatures revealed that the time-temperature superposition was applicable to the surface mechanical relaxation behavior and also that the surface glass transition temperature, T-g(sigma) was depressed in comparison with the bulk one even though the magnitude of M-n was fairly high at 1.40 x 10(5). The surface molecular motion of monodisperse PS with various chain end groups was investigated on the basis of temperature-dependent scanning viscoelasticity microscopy (TDSVM). The T(g)(sigma)s for the PS films with M-n of 4.9 x 10(3) to 1.45 x 10(6) measured by TDSVM were smaller than those for the bulk one, with corresponding M(n)s, and the T(g)(sigma)s for M(n)s smaller than ca. 4.0 x 104 were lower than room temperature (293 K), The active thermal molecular motion at the polymeric solid surface can be interpreted in terms of an excess free volume near the surface region induced by the surface localization of chain end groups. In the case of M-n = ca. 5.0 x 10(4), the T(g)(sigma)s for the alpha,omega-diamino-terminated PS (alpha,omega-PS(NH2)(2)) and alpha,omega-dicarboxy-terminated PS (alpha,omega-PS(COOH)(2)) films were higher than that of the PS film. The change of T(g)(sigma)s for the PS film with various chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region depending on the relative hydrophobicity.

Language：English  

Homogeneous exoplasmic leaflets of biomembrane are mimicked by lipid monolayers at the air/water interface. The reaction rates of lipase (Pseudomonas cepacia) catalyzed hydrolysis of a substrate (umbelliferone stearate) on L-α-dilauroylphosphatidylcholine/cholesterol mixed monolayers at the air/water interface are examined as a function of cholesterol composition, which is to vary the dynamics of the system. Lateral mobility as a measure of dynamics of phospholipids and adsorbed lipase molecules are probed with the technique of fluorescence recovery after photobleaching. Upon correlating the lateral diffusion coefficients of a probe lipid and lipase with the interfacial hydrolysis kinetics, we show for the first time that the catalytic reactions on the monolayers are diffusion-controlled. Moreover, our results are in a quantitative agreement with the two-dimensional reaction dynamics theory of Torney and McConnell.

DOI： 10.1021/la990925w

Language：English   Publishing type：Research paper (scientific journal)  

Surface molecular motion of monodisperse polystyrene (PS) films was examined by scanning viscoelasticity microscopy (SVM) in conjunction with lateral force microscopy (LFM). The dynamic storage modulus, E1, and loss tangent, tan δ, at a PS film surface with a smaller number-average molecular weight, Mn, than 40k were found to be smaller and larger than those for the bulk sample even at room temperature, meaning that the PS surface is in a glass-rubber transition state or a fully rubbery one at this temperature if the Mn, is small. In order to elucidate quantitatively how vigorous the molecular motion at the PS surface is, SVM and LFM measurements were made at various temperatures. The glass transition temperature, Tg, at the surface was discerned to be markedly lower than its bulk Tg, and the discrepancy of Tg between surface and bulk becomes larger with the decreasing Mn. Such an intensive activation of thermal molecular motion at the PS surfaces can be explained in terms of an excess free volume in the vicinity of the film surface induced by the preferential segregation of chain end groups. © 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S1468-6996(99)00005-4

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0954-0083/12/4/314

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1116/1.591191

Language：English   Publishing type：Research paper (scientific journal)  

The proton-terminated and fluoroalkyl-terminated poly(styrene-b-4-vinylpyridine) [P(St-b-4VP)] symmetric diblock copolymers were synthesized by a sequential anionic polymerization. The surface chemical composition, surface morphology and surface mechanical properties of the diblock copolymer thin films were investigated on the basis of the angular-dependent X-ray photoelectron spectroscopic (ADXPS) measurement and transmission electron microscopic (TEM) observations. The XPS results revealed that in the case of the proton-terminated P(St-b-4VP) film, the surface weight fraction of poly(4-vinyl pyridine)(P4VP) decreased dramatically after annealing above the glass transition temperature, Tg of P(St-b-4VP), resulting in the formation of polystyrene (PS) surface layer in order to minimize the interfacial free energy at air-polymer interface. Whereas, in the cases of the fluoroalkyl-terminated P(St-b-4VP) films [P(St-b-4VP)-C
₂
C
^F
_X
where -C
₂
C
^F
_X
shows fluoroalkyl end group], the surface weight fraction of P4VP decreased slightly and still was more than 30% even after the annealing treatment. TEM observation revealed that the lamellar structure was formed in all P(St-b-4VP). The surface order and orientation of lamellar structure were strongly influenced by the chain end group species. That is, in the case of the proton-terminated P(St-b-4VP) film, the lamellar structure was oriented parallel to the film surface and the outermost layer was composed of PS. On the other hand, in the case of P(St-b-4VP)-C
₂
C
^F
_X
, the well-developed lamellae was tilted ca. 45 deg to the film surface and the alternating PS and P4VP layers were exposed to the air interface. These results indicate that the surface order and orientation of microphase-separated lamellar structure strongly depend on the chemical structure of the chain end group.

Language：English   Publishing type：Research paper (scientific journal)  

Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of lateral force microscopic (LFM) and scanning viscoelasticity microscopic (SVM) measurements. SVM measurement revealed that the molecular motion at the surface of the monodisperse polystyrene (PS) film with Mn less than ca.30 k was fairly activated compared with that in a bulk region, mainly due to the surface segregation of chain end groups. Tempereature dependent LFM and SVM measurement revealed that the surface glass transition temperature, Tg of the monodisperse PS film was lower than the bulk one, even though Mn was fairly large as 140 k and also, that the time-temperature superposition was applicable to the surface relaxation process. The chain end group segregation at the air/PS interface was verified from the dynamic secondary ion mass spectroscopic (DSIMS) depth profiling of the proton and deuterium ion for the end-labeled deutrated-PS (dPS) film. These results suggest that the surface Tg is depressed due to an increase in free volume near surface region, being induced by the preferential surface localization of chain end groups.

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Scanning viscoelasticity microscopy (SVM) is used in studies of the surface mechanical properties of polymeric solids. It was revealed that the surface molecular motion is fairly different from bulk one due to the surface segregation of chain end groups. The two-dimensional mapping of the surface mechanical properties for the polymer blend ultrathin films was carried out on nanometer scale.

Language：English   Publishing type：Research paper (scientific journal)  

The surface molecular motion of amorphous polymeric solids has been directly measured by lateral force microscopic (LFM), scanning viscoelasticity microscopic (SVM) and differential X-ray photoelectron spectroscopic (D-XPS) measurements. SVM and LFM measurements revealed that the molecular motion on the surface of the monodisperse PS film with Mn less than ca. 30 k was fairly active compared with that in the bulk, mainly due to the surface segregation of chain end groups. The chain end group segregation at the air/PS interface was verified by dynamic secondary ion mass spectroscopic depth profiling of the proton and deuterium ion for end-labelled PS film. These results suggest that surface T-g is depressed because of an increase in free volume near the surface region, induced by the preferential surface localization of chain end groups. D-XPS was utilized for the characterization of surface molecular motion of symmetric poly(styrene-block-methyl methacrylate) diblock copolymer [P(St-b-MMA)] films. It was confirmed by D-XPS that the surface molecular motion of the PS component in [P(St-b-MMA)] diblock copolymer films was gradually activated with decreasing depth from the air/polymer interface. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0032-3861(98)00049-4

Language：English   Publishing type：Research paper (scientific journal)  

Surface molecular aggregation structure and surface molecular motions of high-molecular-weight polystyrene/low-molecular-weight poly(methyl methacrylate) (HMW-PS/LMW-PMMA) blend films were investigated on the basis of X-ray photoelectron spectroscopic measurements and scanning force microscopic observations. Monodisperse PS with M-n = 1450k, where M-n denotes the number-average molecular-weight, and monodisperse PMMAs with M-n 1.2k, 4.2k, 40.5k, 144k, and 387k were used as HMW-PS and LMW-PMMAs, respectively. Static contact angle measurements revealed that the magnitudes of surface free energy, gamma, of PMMAs for all M(n)s studied here were higher than that of PS with M-n = 1450K. In the case of the (HMW-PS/LMW-PMMA) blend films, in which the M-n for each PMMA was less than 144K, PMMA was preferentially segregated at the air-polymer interface, even though PMMA had a main chain with a higher gamma compared with that of PS. It was found from scanning viscoelasticity microscopic measurements that the surface molecular motion of the (PS with M-n = 1450k/PMMA with M-n = 4.2k) blend film was fairly activated in comparison with that of the bulk one due to the surface segregation of LMW-PMMA. The surface enrichment of LMW-PMMA can be explained by enthalpic and entropic terms as follows. (1) Since the magnitudes of gamma of both chair! end groups of a polymer chain synthesized by an ordinary living anionic polymerization are smaller than that of the main chain part, the chain end groups are preferentially segregated at the surface. Therefore, the chain end effect at the air-polymer interface becomes more remarkable with a decrease of M,, due to an increases in the number density of chain end groups. (2) Since polymeric chains existing in a surface region are compressed along the direction perpendicular to the film surface, the surface chains take smaller conformational entropy in a confined state compared with that of bulk chains. The difference in conformational entropy between the surface chain and the bulk one, that is, the conformational entropic penalty of the polymeric chain at the surface, decreases nith a decrease in M-n. Then, when the enthalpic and entropic effects mentioned above overcome the gamma difference of main chain parts between PS and PMMA, PMMA with higher gamma is stably enriched at the blend film surface.

DOI： 10.1021/ma9709866