Density Functional Theory of Model Systems with the Biaxial Nematic Phase

TL;DR

This theoretical study uses Local Density Functional Theory to analyze the stability and phase diagrams of biaxial nematic liquid crystals in various model systems, highlighting molecular parameters affecting phase stability.

Contribution

It presents phase diagrams and stability criteria for biaxial nematic phases in three model systems, extending understanding of molecular influences on liquid crystal phases.

Findings

Landau points from the square root rule are qualitatively accurate for Gay-Berne ellipsoids.

Dipole interactions and arm biaxiality affect biaxial nematic stability.

Temperature influences elastic constants near the Landau point.

Abstract

Present work is a theoretical study on the stability of the thermotropic biaxial nematic liquid crystal phase in model systems. Its main aim is to present the phase diagrams of spatially uniform liquid mesophases and to identify the molecular parameters that influence the stability of the biaxial nematic. The diagrams are obtained by means of the Local Density Functional Theory in low density approximation, and the relation between the molecular parameters of the models and macroscopic properties of the system close to the transition point are obtained by means of bifurcation analysis. We consider three model systems; the so-called L=2 model (the lowest coupling model of the orientational part of pair potential), the biaxial Gay-Berne interaction, and the bent-core system. For the second one, we also briefly investigate the temperature dependence of elastic constants in rod-like regime and in the vicinity of the Landau point and comment on the smectic phases. In every case we take into account rigid molecules. We find that the Landau points acquired from the square root rule for hard biaxial ellipsoids retain its significance, and provide qualitatively correct estimations of Landau points positions for Gay-Berne biaxial ellipsoids. In case of the bent-core model molecules build from uniaxial and biaxial Gay-Berne ellipsoids we find that the dipole-dipole interaction and degree of arms biaxiality change the stability of the biaxial nematic phase.