The influence of unpolarized and linearly polarized UV exposure on previously rubbed as well untreated thin polyimide (PI) alignment layers was studied. Optical retardation and surface morphology measurements were carried out to understand the nature of surface modification as a function of the polarization and the exposure time of the UV light under different surface conditions. The exposure of the UV light on the PI layer was found to change drastically the morphological anisotropy due to photochemical dissociation. The control of anisotropic surface fords by the linearly polarized UV (LPUV) exposure combined with the rubbing process is important to study the alignment mechanism of liquid crystals on various substrates. A simple model incorporating the effect of the LPUV exposure is presented together with the essential features of the experimental results.
Control of Nematic Director Orientation By Exposing Rubbed Polyimide Films To Linearly Polarized Ultraviolet Light11/24/1997
The delicate interplay between the effects of mechanical rubbing and subsequent photo-induced chemical reactions on polyimide films has been studied for aligning liquid crystals. Exposure to linearly polarized ultraviolet (LPUV) light was found to profoundly alter the direction and the degree of molecular orientations obtained by rubbing. A simple model is presented to describe the observed changes in the director orientation. The results show that LPUV exposure can be very effectively used to control and fine-tune liquid crystal alignment.