Homeotropic alignment of nematic liquid crystals by a photocross-linkable organic monomer containing dual photofunctional groups

Abstract

In this paper, we report a novel organic monomer containing dual photocross-linkable groups and success in realizing photoinduced homeotropic alignment of nematic liquid crystals (LCs) with it. It was first revealed that direct irradiation of the photoalignment thin film with nonpolarized ultraviolet (UV) light at 365.0 nm brought out homeotropic orientation of the photopolymer as a result of the photocross-linking of the dual photoreactive groups. When the thin film was obliquely irradiated with nonpolarized UV light, the pretilt angles of nematic LC were generated. Interestingly, we find that the hydrophobicity of the photopolymer increases with increasing irradiation time. In discussing the mechanism of the homeotropic alignment, it was found that the incorporation of the dual photofunctional group of the photoalignment molecules as well as the extreme hydrophobicity of the photopolymer play the essential roles. This monomer cross-linked film is expected as a promising homeotropic alignment film with rubbing-free processing for the fabrication of advanced vertical alignment LC displays.