ALIGNMENT OF LIQUID-CRYSTALS ON POLYIMIDE FILMS EXPOSED TO ULTRAVIOLET-LIGHT

The influence of unpolarized and linearly polarized UV exposure on pre viously rubbed as well untreated thin polyimide (PI) alignment layers was studied. Optical retardation and surface morphology measurements w ere carried out to understand the nature of surface modification as a function of the polarization and the exposure time of the UV light und er different surface conditions. The exposure of the UV light on the P I layer was found to change drastically the morphological anisotropy d ue to photochemical dissociation. The control of anisotropic surface f ords by the linearly polarized UV (LPUV) exposure combined with the ru bbing process is important to study the alignment mechanism of liquid crystals on various substrates. A simple model incorporating the effec t of the LPUV exposure is presented together with the essential featur es of the experimental results.