Molecular–Statistical Theory for the Description of Re-Entrant Ferroelectric Phase

Alexander V Emelyanenko

doi:10.3390/cryst9110583

Abstract

The re-entrant ferroelectric phase (Sm- C re * ) is investigated in the framework of a molecular–statistical approach. It was found that anticlinic synpolar along the smectic layer normal phase can arise below the antiferroelectric phase (Sm- C A * ) in the temperature scale, and we suggest this phase to be Sm- C re * . We have shown that in the vicinity of Sm- C A * –Sm- C re * phase transition temperature, a very small electric field can cause a transition into the bidomain synclinic phase, where the helical pitch is unwound and the tilt planes have contributions either along or against the electric field. The helical rotation, elasticity and deformation of the Sm- C * , Sm- C A * and Sm- C re * structures without electric field or in the presence of electric field, as well as the dielectric response, are investigated. It is shown that Sm- C re * can arise solely due to the dipole–dipole interaction, and thus, in contrast to the conventional (improper) ferroelectric Sm- C * , appears to be the proper ferroelectric phase.

Highlights

Ferroelectricity in smectic liquid crystals was discovered by Meyer [1]
We have confirmed the experimental data [5,7,8,9,10] showing that sufficiently long molecular tails with several transverse electric dipoles near their own chiral centers promote the re-entrant ferroelectric phase observed in lactic acid derivatives [3,4]
∗ can arise solely due to the dipole–dipole the re-entrant ferroelectric phase

Summary

Introduction

Ferroelectricity in smectic liquid crystals was discovered by Meyer [1]. Antiferroelectric smectic phases were discovered later in [2]. If we suppose that the molecular flexible tails are very long and contain several transverse dipole moments attached to their own chiral centers, in particular, far from the molecular core, we can imagine that some of them can be oriented along the smectic layer normal. That in the long molecular tails, which are flexible in prime direction, some dipoles can point perpendicular to the smectic layer, and contribute to the “head-and-tail” dipole–dipole interaction in the neighboring smectic layers Their azimuthal orientation will automatically be transmitted into the molecular core, and the dipole–dipole interaction of dipoles located in the molecular tails will result in the appearance of proper polarization due to the induced in this way particular orientation of transverse dipoles located in the molecular cores

Molecular Model

Polarization in the Presence of Electric Field

Dielectric Response

Conclusions