Photoinduced orientation in photoreactive hydrogen-bonding liquid crystalline polymers and liquid crystal alignment on the resultant films

摘要

The photoinduced orientation in polymethacrylate, which has a hexamethylene spacer group terminated with a 4-oxycinnamic acid in its side chain (P6CAM), is explored using linearly polarized ultraviolet (LPUV) light irradiation. Because of the hydrogen- (H-) bonding among the cinnamic acid groups, P6CAM exhibits a liquid crystalline phase, and the axis-selective photoreaction of the cinnamic acid moiety generates the optical anisotropy of the film. When the exposed film is annealed or a virgin film is exposed to LPUV light at elevated temperatures, molecular reorientation both perpendicular and parallel to the polarization (E) of LPUV light is achieved, and the generated birefringence is 0.15. The orientation behavior of the film is determined by polarization UV and FTIR spectroscopies. Furthermore, the molecular orientation is erased by annealing at elevated temperature, while reexposing to LPUV light reorganizes the orientation. Finally, homogeneous alignment control of low-molecular liquid crystals on P6CAM films is demonstrated both perpendicular and parallel to E by adjusting the exposure energy.