Rubbingless Control of Alignment of Nematic Liquid Crystal by Photosensitive Polyimide Alignment Layer

Abstract

The alignnaent behavior of liquid crystal (LC) on the surface of four types of polyimide (PI) films exposed to linearly polarized ultraviolet (LPUV) light was investigated with polarizing microscopy.We found that the homogeneous alignment of the LC was induced. The alignment ability of the PIs was strongly depen dent on the chemical structure of PIs and increased with increasing of the absorbed energy of the PIs. The change in the PI structure after UV exposure was evaluated by UV-VIS spectroscopy. The spectra showed that the absorbance change of the aromatic PIs is much smaller than that of the PI with an alicyclic dian hydride when uniform homogeneous alignment of the LC was caused. In particular, the change in the absorbance of the aromatic PI with ether group was only 0.05%. The results mean that the aromatic PIs are more favorable as a photosensitive alignment layer than the PI with an alicyclic moiety and the homogeneous alignment of the LCs can be induced without significant destruction of the chemical structure of PIs.