Bulk optical properties in binary mixtures of antiferroelectric liquid crystal compounds showing V-shaped switching

In order to clarify the origin of the V-shaped switching observed in thin c ells of antiferroelectric/ferrielectric liquid crystals, bulk properties ha ve been studied by means of helical pitch and conoscope measurements using thick free-standing films of binary mixtures with various mixing ratios. In the temperature range showing V-shaped switching in thin cells, helical st ructure clearly exists, indicating the existence of ordered phases. Some in distinct phase changes with temperature, coexistence of phases and quasi-co ntinuous phase changes with an applied electric field were observed, sugges ting a system with weak inter-layer correlation. By comparing the phase dia grams made using thin homogeneous cells and thick free-standing films, it w as found that V-shaped switching occurs in the region where various subphas es exist in the bulk. The appearance of many indistinct phases is consisten t with the weak interlayer correlation. In this way, it was concluded that the V-shaped switching occurs in tilted smectic layers, in which the tilt d irection is weakly correlated along the layer normal.