Photoinduced Volume Transition in Liquid Crystalline Polymer Gels Swollen by a Nematic Solvent

Nematic liquid crystalline (LC) cross-linked polymer gel sheets containing 3 mol % azobenzene (Az) unit were prepared and swollen by a nematic solvent of 4'-pentyl-4-cyanobiphenyl (5CB). This 5CB-swollen gel sheet exhibited a discontinuous volume change around the nematic-isotoropic phase transition temperature of the LC gel (T_NI^G). UV irradiation at a temperature slightly lower than T_NI^G provoked a large volume transition (expansion) due to a loss of nematic order within the gel sheet caused by the trans-to-cis photoisomerization of Az. The volume was reverted by irradiation with 436 nm light. By templating the colloidal crystal film of monodispersed silica particles, a LC gel sheet possessing a microporous structure was also prepared. Due to the facilitated diffusion of 5CB, the microporous LC gel exhibited significant enhancements in the extent and rate of the photoinduced volume transition.