Reversible alignment change of liquid crystals induced by photochromic molecular films, 15. Convenient methods to prepare “command surfaces” by surface‐selective modification of thin films of poly(vinyl alcohol) with azobenzene units

Abstract

Abstract A thin film of poly(vinyl alcohol) (PVA of different saponification degree) coated on a glass plate was subjected to a surface‐selective introduction of azobenzene moieties by treatment with a solution of 4‐(4‐hexylphenylazo) phenoxyacetyl chloride/pyridine or 4‐(4‐hexylphenylazo) phenoxybutanal / p toluenesulfonic acid. Cells were fabricated by sandwiching a nematic liquid‐crystalline material between two surface‐modified glass plates. Alternating exposure to UV and visible light causes a reversible alignment of the liquid crystal molecules. Rubbing of the surface‐modified PVA resulted in an improved optical quality of the cell and enabled us to construct a photoresponsive twisted nematic cell. The advantages of the present method for preparing “command surfaces” are discussed from a practical point of view.