Photoresponsive liquid-crystalline polymers containing a block mesogenic side chain: Systematic studies on structural parameters for nanophase-separated structures

A family of liquid-crystalline polymers (LCPs) containing a block mesogenic side group was synthesized by varying the hydrophilic moiety (oligooxyethylene) ratio. As the oligooxyethylene content increased, the range of the LC phase narrowed or vanished. The polymers were subjected to annealing and exposed on the surface of films, and their morphologies were observed using an atomic force microscope. While the annealed films prepared from the LCPs showed nanophase separation on the surface, the film of the amorphous polymer exhibited no phase separation. Under the optimized conditions, two types of irradiation procedures were adopted: (i) UV (365 nm) light illumination for a phase transition induced by trans-cis photoisomerization and (ii) linearly polarized visible (>436 nm) illumination for a photoinduced alignment change. These results revealed that the photoresponsive behavior of the nanostructure is strongly coupled to the molecular alignments induced by annealing.