Liquid Crystal Polymer Systems For Rewritable Optical Recording

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Two types of photosensitive liquid crystalline systems were studied to apply to reversible opticak memory.1.Photoinduced phase change of liquid crystal polymers(1) Photoinduced phase change of nematic liquid crystalline polymers into isotropic phase under UV-irradiation for the photoisomerization of doped azobenzenes was considerably enhanced by attaching non-mesogenic residues in the side chains as a result of the reduction of an order parameter of the mesophase. The recovery of the nematic phase was caused by illumination with blue light although an aging period was required.2.Liquid crystal alignment photoregulation mediated by polymer surfaces(1) An azimuthal alignment of nematic liquid crystal layrs was controlled by irradiation of a cell fabricated with substrate plates covered with photochromic molecular layrs with linearly polarized light. Rewriting of an optical memory based on this working principle was realized simply by changing an electric vector of actinic light.(2) Three … More types of photoaligning polymer thin films were developed. The first involves the surface-selective introduction of azo-chromophores on a poly (vinyl alcohol) thin film. The second method is based on spin-coating of a thin film of polymers substituted with azobenzenes in their side chains. The third one consists of the deposition of Langmuir-Blodgett films of a polyimide bearing azobenzene units on a substrate plate.(3) Factors affecting optical quality of photoimages and exposure energy required for liquid crystal reorientation were investigated. Photoimages resolving few mum lines and spaces were quite stable at a temperature below a nematic/isotropic transition temperature (T_<N1>) and erased by heating above T_<N1> or simply by overwriting with polarized actinic light with a different polarization plane.(4) The surface-mediated optical recording is highly of practical significances because they can be operated by irradiation with a single light source emitting visible light which results in no observable photodegradation of azobenzenes. Less