Photoalignment Control of Liquid Crystals on Photo-Cross-Linkable Polymer Liquid Crystal Film

Abstract

Photoinduced reorientation of a liquid crystalline copolymer film, which comprises a methacrylate with a 4-(4-methoxycinnamoyloxy)biphenyl (MCB) side group and N-phenylmaleimide (PM), and its application to alignment layer for low-molecular-weight liquid crystals (LC) are described. Adjusting the exposure energy of linearly polarized ultraviolet (LPUV) light and subsequent annealing controlled the reorientation direction of the copolymer film both perpendicular and parallel to the polarization (E) of LPUV light, and LC aligned along the reorientation direction of the mesogenic groups. When using a copolymer film without annealing, LC aligned perpendicular to E of LPUV light regardless of the exposure doses. The LC alignment behavior changed similar to that using the annealed film when LC was injected in the isotropic temperature range of the LC, where a reorientation of the mesogenic groups of the photoalignment layer in contact with LC materials was observed. It was clarified that the molecular reorientation direction of the copolymer film surface played an important role in the LC alignment direction.