Surface analysis of UV-aligned polyimide for liquid crystal alignment

Abstract

The conventional technique for homogenous alignment of liquid crystal (LC) molecules is the mechanical rubbing of aligning surfaces coated with thin polymer films. Liquid crystal molecules align parallel to the rubbing direction believed to be due to the microgrooves created by rubbing process. This technique however, has disadvantages like the static build-up of charges, and generation of dust particles, both of which adversely affect the desired performance of LCDs. Recently, a new alignment technique using polarized UV light was reported. This technique is simple and eliminates mechanical rubbing effects. Alignment of molecules, however, is perpendicular to the polarization direction. Since then, thin films of polymers exhibiting photo-induced anisotropy were used and extensively studied for aligning layers of LC molecules.
The alignment mechanism of liquid crystal molecules on polyimide films is still not completely understood notwithstanding the studies that were done. In this report, surface topography of UV-aligned polyimide thin films are investigated using Atomic Force Microscopy (AFM) and X-ray Reflectivity (XRR).