Inhomogeneous Freedericksz effect in a quarter turn twisted achiral smectic C liquid crystal

Abstract

Experimental findings on the electric Freedericksz instability are presented for an achiral, dielectrically slightly negative, 90°-twisted smectic C liquid crystal. In the base state, the smectic layers are perpendicular to the confining electrodes, with the c director sweeping through 180° across the sample thickness. Thresholdless reorientation is inferred from a continuous variation of cell capacitance with voltage. Above a few volts, in the first instance of its kind, the periodic nature of the equilibrium Freedericksz state reveals itself in the stripe morphology. The pattern period increases with applied voltage, and decreases with increasing field frequency. These changes are brought about through creation and movement of edge dislocations. Homogeneous reorientational state is not recovered at increased fields even up to dielectric break down. A model involving an undulatory band, which has the twist localized within it and is flanked by two uniformly and transversely aligned regions, accounts for the optical features of the periodic state.