Structures and Analog Electro-Optics of Chiral De Vries and Polar Bent-Core Smectic A Liquid Crystals

In chiral smectic A (SmA*) liquid crystals (LCs), an applied electric field induces a tilt of the optic axis from the layer normal. When these materials are of the de Vries-type, the electroclinic tilt susceptibility is unusually large, with the field-induced director reorientation accompanied by a substantial increase in optical birefringence, essentially no change in the smectic layer spacing, and a polarization current response that has double peaks. In order to account for this behavior, we assume that the molecular orientation distribution in the smectic A has two degrees of freedom, azimuthal orientation and tilt of the molecular long axis from the layer normal, with the tilt confined to a narrow range of angles. We present a generalized Langevin-Debye model of the response of this distribution to applied field. The resultant evolution of this distribution with increasing applied field yields field-induced tilt, birefringence, and polarization dependence that agree well with experimental measurements.;Fluid ferroelectrics with large macroscopic polarization exhibit block polarization reorientation in applied fields. In the ferroelectric orthorhombic fluid smectic liquid crystal phase (SmAPF), we have shown that this behavior enables a simple mode of analog control of birefringence. When the applied voltage is time-dependent, an E field appears in the LC to generate reorientation of polarization. We have investigated theoretically the dynamic behavior of block polarization in the SmAPF phase. Experimental studies of W623 confirm this behavior, revealing the low resistance of the block reorienting LC.