Alignment of ferroelectric liquid crystal on polyimide Langmuir-Blodgett film

Abstract

A electric switching behaviors of ferroelectric liquid crystal device and its alignment layer with PMDA-3,3``-ODA film prepared by Langmuir-Blodgett technique was investigated. LB films were built up on ITO glass at various surface pressure. The defects in LB film tested by cyclic voltammogram were significantly reduced. 5 layers of PMDA-3,3``-ODA PAAS and 7 layers of polyimide indicated the sufficient coverage of films over the surface of ITO glass. The orientation of PAAS and polyimide on ITO glass determined by polarized FT-IR spectroscopy were found to be oriented parallel to the dipping direction. Textures of FLC on Alignment layers prepared at different deposition pressure, 5, 15, 25 and 35 mN/m were observed with polarizing microscope. The apparent spontaneous polarizations of FLC determined by the triangular method depends on cell thickness, cooling rate from smectic A to chiral smectic C, transfer condition. Closely packed LB film at 35 mN/m showed the better alignment of FLC on it and the larger spontaneous polarization than those at low surface pressure did. Concerning the effect of cooling process, and cell thickness, slowly cooled and thin cell had the larger spontaneous polarization. Characteristic behavior such as response time, decay time and light transmission in optic device were also used to evaluate the alignment layer. Alignment layer prepared at 35mN/m showed faster response and decay, which is consistent to the larger spontaneous polarization of FLC on it. The effect of ion in FLC on switching behavior was observed to reduce the magnitude of effective electric field but disapper as frequency of field increase. Comparing rubbed polyimide alignment layer, LB alignment film showed sufficient optic behavior in comparison with the alignment layer by rubbing method.The monolayer behavior at the air/water interface.