SURFACE-SELECTIVE MODIFICATION OF POLY(VINYL ALCOHOL) FILMS WITH AZOBENZENES FOR INPLANE ALIGNMENT PHOTOCONTROL OF NEMATIC LIQUID-CRYSTALS

A surface of poly(vinyl alcohol) (PVA) was treated with an azobenzene acid chloride in hexane in the presence of pyridine to achieve surface-selective introduction of the photoisomerizable azo units. The surface reaction is affected by the solvent, saponification degree of PVA, structure of the acid chloride, and reaction period. Surface morphology of the modified PVA thin films was examined by means of atomic force microscopy. Under optimized reaction conditions, a PVA surface was covered with an average of about 3 azobenzene units per 1 nm(2) to afford a film with excellent flatness. The ate-modified PVA films were employed to regulate in-plane alignment of a nematic Liquid crystal by irradiation with linearly polarized light of a hybrid cell which was fabricated by putting a liquid crystal between a glass plate covered with the modified PVA film and a glass plate which was treated with lecithin for a homeotropic alignment. The efficiency of the photoregularity for azimuthal reorientation of liquid crystal was markedly dependent on the molecular structure of azobenzenes. Various properties of the photoresponsive liquid cells are presented.