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Mechanism of Generation of Pretilt Angles on Polyimides with a Single Exposure to Polarized Ultraviolet Light

Behaviors of pretilt angles of liquid crystal (LC) cells were examined using polyimide (PI) films containing fluorine atoms by exposure to ultraviolet light (UV). Using a single obliquely polarized UV exposure, we obtained unidirectional LC alignment with any desired pretilt angles from 0° up to 90°. The pretilt angles depend on the concentration of fluorine atoms in the PI and the UV exposure time and angle. The results of dichroic ratio and capacitance measurements of the LC cells suggest that oblique polarized UV exposure breaks the surface order degeneracy of the LC molecules, generating uniform pretilt angles along the optic axis of the PI film.