Are short-pitch bistable ferroelectric liquid crystal cells surface stabilized?

Abstract

Recent papers have described the short-pitch bistable ferroelectric liquid crystal effect (SBF) attributing its bistability to its stripe layer texture [1]. We have studied the bistability of this SBF effect for the short-pitch ferroelectric liquid crystal (FLC) mixture ZhKS-76 using thin planar aligned cells. Both the SBF texture (the stripe texture) and a uniform texture (uniform tilt layer structure with the extinction direction along the layer normal) were observed in different regions of a given cell when the cell was cooled down slowly from the isotropic phase to the chiral smectic C phase. Upon applying external fields, both regions are characterized by the formation of helix unwinding lines. The stripe area showed zig-zag unwinding lines and the uniform area exhibited straight unwinding lines, both running parallel to the layers. The bistability study shows a similar hysteresis curve and threshold behaviour on switching for both the SBF texture area and the uniform area, although the uniform area gcve better contrast. These facts strongly indicate that as in the long pitch FLCs, the surfaces rather than the layer stripe texture hinder the formation of the helix in the cell, and this produces dynamic bistable switching.