Characterization of layer-tilted state in ferroelectric liquid-crystal cells by electro-optical switchings

Abstract

Using an electro-optical method, we have determined the director tilt angle, the layer-tilt angle, and the quiescent-state azimuthal angles of a surface-stabilized ferroelectric liquid-crystal (SSFLC) cell as a function of temperature in the smectic C phase. The method is based on a collective switching of the director's conical motion due to the interaction of the external field with the spontaneous polarization and the dielectric anisotropy of the liquid-crystal medium, together with a one-elastic constant free-energy model. Using the equation of total free energy, we have proved that only splayed states could be stabilized in layer-tilted geometry, but bistable cells could still be obtained. When the surface interactions at both substrate surfaces are nonidentical, the SSFLC cell will exhibit two distinct quiescent states: one stable and the other quasistable. The twist angles of the director from top to bottom substrates at quiescent states and the ratio of the surface polar to nonpolar interaction are deduced. The experimental observation and calculation on an overshoot in the rising part of the optical response upon bipolar switching are also presented.