Switching behaviors of ferroelectric liquid crystal cells on polyimide alignment layer

Abstract

The surface charateristics of alignment layers for ferroelectric liquid crystals and the electrooptical effects of ferroelectric liquid crystal cells were investigated. The surface characteristics of PI LB films prepared on substrates were measured by AFM, cyclic voltammetry, and contact angle meter. It could be known that the surface roughness of the LB films on Si-wafer decreased as the transferred number of layer increased, and in rubbing on the surface produced the scratches in rubbing direction. Using cyclic voltammogram, the defects of LB layers found to be decreased transferred layer increased. In the measurement of contact angle, as the transferred layer number, surface pressure, and curing temperature increased, contact angle increased and surface became hydrophobic. The crossly polarized microscopy of ferroelectric liquid crystal cells, prepared with the LB alignment layers, showed poorer alignment than that of cells prepared by rubbing method. The characteristics of spontaneous polarizations, response times, decay times and light transmittances of ferroelectric liquid crystal cells were also observed. When the field was applied, the spontaneous polarization of ferroelectric liquid crystal by rubbing method was higher than that by LB technique, and also the spontaneous polarization increased with rubbing strength. In the cases of response and decay times, the FLC cell treated by rubbing method at once faster than that by LB method. Especially, response time of ferroelectric liquid crystal cell having alignment layer treated by LB 1 layer after rubbing was similar to that by rubbing, but decay time falls in between the cells of rubbed surface and LB film.