Polymer/liquid crystal (LC) composite films possessing an azobenzene LC as a photoresponsive molecule (AzoCFs) were prepared by the thermal polymerization-induced phase separation method. The composite films (AzoCFs) showed a strong light-scattering state after polymerization, and their optical properties were strongly affected by the compositional ratio of the liquid crystals in the composite film. Change in the transmittance between a light-scattering and a transparent state could be induced isothermally by photoirradiation. Upon irradiation at 366 nm, AzoCFs changed from the light-scattering state to the transparent state. This is ascribed to nematic (N)-isotropic (I) phase transition due to transcis isomerization of the azobenzene molecules in the LC domains within the polymer matrix. Furthermore, restoration of the initial state could be achieved by visible-light irradiation (>420 nm), resulting from the I-N phase transition induced by cis-trans back-isomerization of the azobenzene guest molecules.

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Induced nematic phase in a polymer/liquid crystal mixtureWe have demonstrated reversible change in transmittance of composite films, which are composed of an isotropic ͑I͒ polymer matrix and a host nematic ͑N͒ liquid crystal ͑LC͒ containing donoracceptor type azobenzene LCs ͑AzoLCs͒ as photoresponsive molecules, by means of reversible phase transition in the LC domain. The composite films were prepared by in situ thermal polymerization-induced phase separation ͑PIPS͒ method from their homogeneous mixtures. Photoisomerization of AzoLCs was induced within the polymer network, and the resultant effect brought about isothermal change in transmittance. The photoinduced reversible and repeatable changes between opaque light scattering and clear transparent states were achieved effectively by irradiation with a monochromatic light at 366 nm. These changes are attributed to photochemical N -I phase transition and rapid thermal I -N phase transition in the host LC domain based on reversible change in molecular sharp of the guest AzoLCs. The optical effects were influenced by such factors as temperature of the composite films in the initial state and photoisomerization ability of the guest AzoLCs. The composite films acted as an optical switching material without polarizers.

Fast optical switching (response time 90 μs) was achieved of ferroelectric liquid crystals doped with a photoresponsive chiral dopant having an azobenzene moiety.