Order parameter theory of the pre-transitional behaviour in antiferroelectric liquid crystals

We propose an order parameter theory as a possible description of the pre-switching behaviour of antiferroelectric liquid crystals (AFLCs). Assuming that the antiferroelectric state is preserved so that the directors in adjacent layers ape on opposite sides of the smectic cone, we consider changes in the molecular order about these directors. Our theory incorporates interlayer and intralayer dipole-dipole interactions, the dipole-electric field interaction and the thermodynamic potential. The effective optic axis as a function of applied voltage can then be calculated and is found to be in qualitative agreement with experimental observations which show a superlinear dependence.