All-optically controllable polymer liquid crystal composite films containing the azobenzene liquid crystal

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 trans-cis 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.