Polarization reversal in antiferroelectric liquid crystals

Abstract

We studied the change in polarization direction during field reversal in binary mixtures possessing antiferroelectric phase. Due to the coupling ofthe electric field with the spontaneous polarization of each smectic layer, the transition from antiferroelectric to the ferroelectric phase was induced. This transition was accompanied by changes in optical properties. Both three-state and V-shaped switching was observed. After removing the field, the sample transformed back to the antiferroelectric state. We have found that in some cases, the kinetics of this transition was very slow -its time constant ranged from minutes to days, depending on temperature. In the same mixtures, we observed a large thermal hysteresis of the phase transition between the ferroelectric and antiferroelectric phases. We argue that all three phenomena: V-shaped switching, slow kinetics and thermal hysteresis have the same origin. They occur, when the ferroelectric and antiferroelectric interactions acting between smectic layers are of comparable strength. We compare our results with the existing models ofV-shaped switching and propose a modification ofthe models.