Alignment of liquid crystals on polyimide films exposed to ultraviolet light

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 forces 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.