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Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.264, 1-10, 1995
Interfacial Molecular-Interactions Between Ferroelectric Liquid-Crystal and Polyvinylalcohol Films as Probed by Infrared Reflection-Absorption Spectroscopy
Infrared reflection absorption spectroscopy (IRAS) was used to study the molecular alignment of the ferroelectric liquid crystal material, (S)-4-(alpha-methylheptyloxy)-4’-(4 "-n-octylphenyl-oxycarbonyl)biphenyl (MHOPOB), on a highly-purity polyvinylalcohol (PVA) film. The molecular alignment was characterized as a function of the temperature and the thickness of the liquid crystal. For the film of 200 nm in thickness, the molecules in the chiral smectic C phase (SmC*) were aligned with their long axes perpendicular rather than parallel with respect to the PVA substrate surface. This alignment was found to disappear at the isotropic phase temperature. A similar molecular alignment was observed for a 20 nm-thick MHOPOB film in the SmC* phase, but the detailed alignment was different from that in the 200 nm-thick fiim. This alignment in the SmC* phase was sustained even at the isotropic temperature in contrast to the 200 nm-thick film, suggesting a short-range interaction between the PVA film surface and MHOPOB molecules. An experimental support for this short-range interaction is furnished by our polarization modulation IRAS measurements. The effect of PVA rubbing on the alignment is also discussed.