Bistable Electro-optical Switching for (Liquid Crystalline Polymer)/(Low Molecular Weight Liquid Crystal) Composite System

A series of thin films composed of liquid crystalline polymer (LCP) and low molecular weight liquid crystal (LMWLC) was prepared by a solvent-casting method. LMWLC is miscible over a whole range of LCP concentrations in isotropic and mesomorphic states. The composite system formed a smectic phase in a LCP weight fraction range above 50%. Reversible and bistable electro-optical effects based on light scattering were recognized for a smectic phase of the binary composite composed of LCP and LMWLC. A light scattering state appeared in the case of application of an a.c. electric field below a threshold frequency (f(c)). Furthermore, application of an a.c. field above f(c) made the transmission light intensity increase. Such phenomena were induced in conjunction with the two types of effect: one is an electricfield effect based on the dielectric anisotropy of the mesogenic side chain; and the other is an electric current effect based on the electrohydrodynamic motion of the main chain. In the case of a smectic mesophase, the turbid and transparent states remained unchanged, even though the electric field is removed (memory effect).