Study on liquid crystal alignment by polymer alloy film of polyimide and photo-reactive polymer

Abstract

The present work is concerned with the improvement of the thermal stability of the photo-induced liquid crystal alignment based on cinnamate-containing polymer thin film. In chapter III, the structural changes of poly(vinyl cinnamate), a representative material for the use in the photo-induced liquid crystal alignment, at enhanced temperature were investigated by using various spectroscopic techniques. It was found that the cinnamat group is chemically stable upto 200℃, however, the cleavage of the ester group in the linkage of the alkyl main chain and the cinnamate group occurs above 200℃. Thermally induced dimerization, which effectively occurs by UV irradiation, was not observed. In Chapter IV, the photo-induced liquid crystal alignment on the polyimide and poly(vinyl cinnamate) blend layers was investigated. The introduction of thermally stable polyimide into poly(vinyl cinnamate) is aimed to enhance the thermal stability of the liquid crystal alignment provided by the photo-product of the poly(vinyl cinnamate). The transparent blend films were successfully prepared by the solution blending of polyamic acid, the precursor of polyimide, and poly(vinyl cinnamate) followed by thermal imidization of the poly(amic acid) in the blend. The poly(vinyl cinnamate) was found to enhance degree of imidization of the poly(amic acid) by a plasticizing effect. The photo-reaction of poly(vinyl cinnamate) was not hindered by the existence of polyimide. The blend alignment layers showed uniform LC alignment owing to the anisotropic photo-reaction of the PVCi. Thermal stability of liquid crystal alignment was significantly improved by the addition of the polyimide into poly(vinyl cinnamate). The increase of the thermal imidization temperature results in the increase of the thermal stability of the liquid crystal alignment. It indicates that the mobility of the film is mainly governed by the polyimide in the blend. In Chapter V, the azimuthal anchoring energy and the pretilt an...