Surface characteristics of photoaligned polyimide film interfacial reacted with bromine or ethanethiol.

The surface characteristics of polyimide films containing cinnamate groups which promote the uniform alignment in adjacent liquid crystal (LC) upon photodimerization by linearly polarized ultraviolet (LPUV) lights were studied [M. Schadt, K. Schmitt, V. Koznikov, V. Chignirov, Jpn. J. Appl. Phys. 31 (1992) 2155.]. But photoalignment methods have an image sticking problem by un-reacted photosensitive functional groups, which can be a severe defect to achieve high reliability of liquid crystal display (LCD) panels. So the un-reacted photosensitive functional groups were deactivated using bromine or ethanethiol. Bromine and ethanethiol lead to the formation of carbon-bromine or carbon-sulfur bonds from carbon-carbon double bonds. The interfacial reaction of bromine or ethanethiol on the polyimide surface has been studied using in situ X-ray photoelectron spectroscopy (XPS). The change of surface tension was observed by using a contact angle analyzer. The photoelastic modulator (PEM) was used to analyze the optical anisotropy on the polyimide surface. Also, the atomic force microscopy (AFM) was used to observe the morphology of polyimide surface [K. Rajesh, M.K. Ram, S.C. Jain, S.B. Samanta, A.V. Narliker, Thin Solid Films 325 (1998) 251.].