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 usin g polyimide (PI) films containing fluorine atoms by exposure to ultraviolet light (UV). Using a single obliquely polarized UV exposure, we obtained un idirectional LC alignment with any desired pretilt angles from 0 degrees up to 90 degrees. 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 po larized UV exposure breaks the surface order degeneracy of the LC molecules , generating uniform pretilt angles along the optic axis of the PI film.