Ferroelectric ordering in chiral smectic C^* liquid crystals determined by nonchiral intermolecular interactions

TL;DR

This paper presents a microscopic theory explaining ferroelectric ordering in chiral smectic C* liquid crystals, emphasizing the role of nonchiral intermolecular interactions and molecular symmetry in polarization.

Contribution

It introduces a general statistical framework for ferroelectric ordering, incorporating models based on electrostatic quadrupole interactions and off-center dipoles, expanding understanding beyond classical models.

Findings

Spontaneous polarization linked to biaxial order parameters.

Polarization depends on molecular symmetry and chirality.

Explicit analytical and numerical expressions for polarization.

Abstract

General microscopic mechanism of ferroelectric ordering in chiral smectic C* liquid crystals is considered. It is shown that if the mesogenic molecules have a sufficiently low symmetry, the spontaneous polarization is proportional to one of the biaxial vector order parameters of the smectic C phase. This order parameter may be determined by intermolecular interactions which are not sensitive to molecular chirality. At the same time, the polarization is also proportional to a pseudoscalar parameter which vanishes if the molecules are nonchiral. The general statistical theory of ferroelectric ordering is illustrated by two particular models. The first model is based on electrostatic quadrupole-quadrupole interactions, and it enables one to obtain explicit analytical expressions for the spontaneous polarization. In the second model, the molecular chirality and polarity are determined by a pair of off-center nonparallel dipoles. For this case, the spontaneous polarization is calculated numerically as a function of temperature. The theory provides a more general interpretation of the previous approaches including the classical Boulder model.