Molecular-statistical theory of ferroelectricity in smectic C liquid crystals

Abstract

The general molecular-statistical theory of ferroelectric liquid crystals is developed in the molecular field approximation. The ferroelectric ordering in the smectic C* phase is determined by chiral and polar intermolecular interactions. The model for a chiral molecule, proposed by Van Der Meer and Vertogen, is specified and used in the description of ferroelectric liquid crystals composed of molecules with large dipoles in the chiral part. It is shown, that in this case the dipolar ordering is caused by the induction interaction between the dipole and the polarizability of the neighbor molecule, modulated by the asymmetric molecular shape. The chiral part of the dipole–quadrupole induction interaction contributes also to the spontaneous polarization. We discuss the ferroelectric ordering both in one-component ferroelectric liquid crystal and in mixtures of liquid crystal and express the macroscopic polarization via the electric and steric molecular parameters. The results of the present theory agree with the available experimental data.