Ultraviolet-light Induced Liquid-Crystal Alignment on Polyimide Films

Bond-breaking and oxidation occur during broadband ultraviolet light (UV light) illumination of the polyimide film in the air according to spectroscopic analysis. Surface tension and polarity are increased based on the measurements of contact angles. The liquid-crystal (LC) pretilt angles of the rubbed polyimide films are reduced by both unpolarized and polarized UV light illumination. Both the LC alignment and pretilt angle are generated on unrubbed polyimide films through the photoalignment process. The mechanism of photoalignment of LC is discussed.