Manipulation of liquid crystal alignment through interfacial modification of photoresponsive polyimides remotely actuated by dual wavelength linearly polarized light

Abstract

High-quality alignment of liquid crystals (LCs) for large area display has been highly demanding for display market. To achieve a uniform and stable LC alignment, a photoresponsive azo-polyimide with two different substitution ratio of azo-dye moiety in the side chain of the polyimide has been successfully synthesized and characterized. Depending on the ratio of azo-dye substitutions, the solubility and coating nature of polyimides vary greatly and initially show random planar or homeotropic alignment of LCs. In situ photoalignment process has been performed to achieve a homogeneous planar alignment of LCs from the initial random planar state and a uniform pretilt state from the initial homeotropic cells using linearly polarized visible light (LPVL) irradiation in the isotropic phase of LCs. Furthermore, obtained alignment states have been stabilized using unpolarized UV light for RM polymerization in the nematic phase of LCs. Hence, the dual wavelength photoalignment approach has been successfully implemented to obtain the different stable alignments of LCs. Also, the results conclude that the tilt angle varies by dose of LPVL irradiation and gets significantly altered due to change in reactive mesogen (RM) concentrations. The surface investigations reveal a contrasting nature for the planar and vertically aligned substrates before and after RM stabilization.