掲載種別：研究論文（学術雑誌）   出版者・発行元：Polymer Chemistry  

The aggregation states of polymer chains at solid interfaces are strongly related to their adhesion properties. In this study, we focused on sum-frequency generation (SFG) vibrational spectroscopy, which offers the best depth resolution at the sub-nanometer level among available techniques, and explored its potential as an imaging method. A poly(methyl methacrylate) (PMMA) thin film with a line-and-space pattern was prepared on a quartz substrate. Imaging of the interfacial line-and-space structure in the film was successfully achieved based on SFG signals arising from ester methyl groups as well as carbonyl groups. Once SFG imaging was established, it was applied to blend films of polystyrene (PS) and PMMA with different compositions on the quartz substrate, enabling the direct and non-destructive observation of wetting layers and phase-separated structures buried at the substrate interface for the first time. The interfacial adhesion strength between the blend films and the quartz substrate, evaluated using the surface and interfacial cutting analysis system, showed a clear correlation with the interfacial structure of the blend. This study, which enables the analysis of the relationship between the local orientation of polymer chains at the interface and adhesion strength, is expected to contribute greatly to the design of next-generation adhesives and adhesion technologies.

DOI： 10.1039/d4py00951g

Web of Science

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記述言語：英語  

DOI： https://doi.org/10.1021/acs.macromol.4c01925

掲載種別：研究論文（学術雑誌）   出版者・発行元：Macromolecules  

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

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   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

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry A  

BODIPY (boron-dipyrromethene) compounds are extensively utilized in various applications. Typically, their activity is modified by altering the functional groups at the α-, β-, and meso-positions of the substituents. However, no systematic information has been provided regarding the effects of substituted F- positions and hydrophobicity on the activity of BODIPY sensitizers in photosensitizing chemistry. Dyes (7a-7c) with different alkyl chain lengths were synthesized and compared with the unsubstituted compound 3 to discuss the effects of -F position substituents and the hydrophobicity of BODIPY dyes on photocatalytic activity. Density functional theory (DFT) calculations showed that -F-substitution induced an intramolecular charge transfer (ICT) effect, enhancing visible-light absorption. Longer alkyl chains provided a favourable second coordination sphere reaction environment for hydrogen production. Experimentally, dye 7c demonstrated the highest activity, with a hydrogen production rate of 496.5 μmol gcat−1 h−1, which is 3 times higher than that of 3, and a 9.6 times higher turnover frequency (TOF) than that of 3. The apparent quantum yield (AQY) at 650 nm was 1.4%. This study highlights the importance of -F position substitution and optimizing hydrophobicity to enhance the photocatalytic activity of metal-free organic dyes through the creation of a new second coordination sphere.

DOI： 10.1039/d3ta03682k

Web of Science

Scopus

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