Ferro- and Antiferroelectric Liquid Crystals

Abstract

In this section a historical overview will be presented of the development of phenomenological theoretical models of ferroelectric and antiferroelectric liquid crystals. In Sect. 5.1.2 the two order parameters of ferroelectric smectic C* (Sm C*) liquid crystals will be introduced, which are the tilt of long axes of molecules from the normal to the smectic layers and the in-plane electric polarization, that corresponds to the ordering of molecules transverse to their long axes. The phenomenological models of ferroelectric liquid crystals (FLC) will be presented, that correspond to the Landau expansion of the free-energy density in the tilt and the polarization order parameters. An extension of the phenomenological model of FLC will also be demonstrated, that includes as the additional order parameter the transverse quadrupolar ordering and that describes some anomalies of FLC’s, that cannot be accounted by the model with only two order parameters. In these models the layered structure of smectic liquid crystals is not explicitly taken into account and the same is true for the phenomenological models of antiferroelectric liquid crystals (AFLC), that are presented and described in Sect. 5.1.3. Such models cannot describe all existing phases in AFLC and therefore discrete models of AFLC’s were introduced, which take explicitly smectic layers into account and assume some inter-layer interactions, which must have longer range then only between nearest neighboring layers. Discrete models are described in Sect. 5.1.4, while in Sect. 5.1.5 the nature and the structure of the inter-layer interactions is presented together with possible phases predicted by such models.