Enhanced Liquid Crystal Alignment Using Photo-Irradiation of Photo-Dissociative Polyimide

Exposure of photo-labile polyimide film to linearly polarized 254 nm UV incurred anisotropic dielectric orientation of film surface. The anisotropic surface resulted from the liquid crystal (LC) alignment is perpendicular to polarization direction of the UV irradiation. The polyimide (1,2,3,4-cycolbutanetetrcatboxylic dianhydride di(4 aminophenyl)methane-dianhydride)(CBDA-DAPM-DA) contains cyclobutane rings for photoinduced ring opening reaction. The LC alignments were obtained through polarized and unpolarized UV by exposing them to rubbed polyimide film. Dichroic ratio of LC cells increased with irradiation time until 20 min and was followed by disordering of further UV irradiation. Unpolarized UV irradiation on the rubbed polyimide film showed increased dichroic ratio compared to the films irradiated with a polarized UV light.