記述言語：英語   出版者・発行元：一般社団法人 日本レオロジー学会  

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.

DOI： 10.1678/rheology.52.91

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CiNii Research

出版者・発行元：Polymer Journal  

Using X-ray absorption spectroscopy (XAS) with linearly polarized soft X-rays, we investigated the local conformation of poly(methyl methacrylate) (PMMA) adsorbed to a SiOx/Si(111) surface. The preedge intensity of the O K-edge XAS for PMMA, originating from the O 1s → π* transition at a C=O group in the side chain, was stronger for vertically polarized incident X-rays than for horizontally polarized ones. Conversely, the XAS intensity originating from the O 1s → σ* transition showed the opposite trend. These findings suggest that the C=O group in the side chain of PMMA exhibited preferential orientation rather than an amorphous arrangement. To gain further insights, we conducted a depth profile analysis of the local conformation of PMMA using XAS combined with an argon gas cluster ion beam (GCIB). GCIB-XAS analysis revealed that the orientation of the C=O group in the side chain of PMMA differs between the region from the SiOx interface to a distance on the order of 1 nanometer and the bulk PMMA region.

DOI： 10.1038/s41428-023-00864-8

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DOI： 10.1080/27660400.2023.2270529

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記述言語：英語   出版者・発行元：Journal of Chemical Physics  

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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PubMed

記述言語：英語  

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.

CiNii Research

記述言語：英語   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.macromol.3c00341

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Polymer Journal  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Chemistry Chemical Physics  

A better understanding of the chemical reaction between epoxy and amine compounds at a solid interface is crucial for the design and fabrication of materials with appropriate adhesive strength. Here, we examined the curing reaction kinetics of epoxy phenol novolac and 4,4′-diaminodiphenyl sulfone at the outermost interface using sum-frequency generation spectroscopy, and X-ray and neutron reflectivity in conjunction with a full atomistic molecular dynamics simulation. The reaction rate constant was much larger at the quartz interface than in the bulk. While the apparent activation energy at the quartz interface obtained from an Arrhenius plot was almost identical to the bulk value, the frequency factor at the quartz interface was greater than that in the bulk. These results could be explained in terms of the densification and orientation of reactants at the interface, facilitating the encounter of the reactants present.

DOI： 10.1039/d2cp03394a

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Materials and Interfaces  

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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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Langmuir  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Polymer Materials  

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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記述言語：英語   出版者・発行元：JACS Au  

Epoxy resins are used in various fields in a wide range of applications such as coatings, adhesives, modeling compounds, impregnation materials, high-performance composites, insulating materials, and encapsulating and packaging materials for electronic devices. To achieve the desired properties, it is necessary to obtain a better understanding of how the network formation and physical state change involved in the curing reaction affect the resultant network architecture and physical properties. However, this is not necessarily easy because of their infusibility at higher temperatures and insolubility in organic solvents. In this paper, we summarize the knowledge related to these issues which has been gathered using various experimental techniques in conjunction with molecular dynamics simulations. This should provide useful ideas for researchers who aim to design and construct various thermosetting polymer systems including currently popular materials such as vitrimers over epoxy resins.

DOI： 10.1021/jacsau.2c00120

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記述言語：英語   出版者・発行元：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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記述言語：英語   出版者・発行元：Soft Matter  

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, we herein examined the conformational change of polystyrene (PS) chains at the film surface after contacting with hydrophobic or hydrophilic surfaces using sum-frequency generation (SFG) spectroscopy. Chains altered their local conformations with a quartz surface more quickly than a hydrophobic alkyl-functionalized one. A full-atomistic molecular dynamics simulation showed that these results, which were coupled with the contact process of PS chains with the solid surface, could be explained in terms of the Coulomb interaction between them.

DOI： 10.1039/d1sm01833g

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Macro Letters  

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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記述言語：英語   出版者・発行元：Soft Matter  

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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記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.macromol.1c01293

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/D1CP03959H

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.macromol.1c00513

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/D1SM00529D

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41428-021-00528-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/D0SM01600D

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1678/rheology.49.55

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-020-77761-0

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsmacrolett.0c00638

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/D0SM00625D

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsapm.9b01154

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcb.9b00680

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.macromol.8b02416

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41428-018-0134-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcb.7b07062

記述言語：英語  

DOI： 10.1007/978-981-10-0815-3_25

記述言語：英語  

DOI： 10.1007/978-981-10-0815-3_26

記述言語：英語  

DOI： 10.1007/978-981-10-0815-3_28

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/jp307058s

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1252/kakoronbunshu.38.221

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.1914767

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1063/1.1563613

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1063/1.1456031

担当区分：筆頭著者   記述言語：英語  

DOI： https://doi.org/10.1063/1.474681

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1002/pen.10638

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1002/pen.760351210

記述言語：英語  

DOI： https://doi.org/10.1063/1.468746

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1063/1.466423

担当区分：筆頭著者   記述言語：英語  

DOI： https://doi.org/10.1063/1.464607