Importance of transverse dipoles in the stability of biaxial nematic phase: A Monte Carlo study

TL;DR

This Monte Carlo study investigates how transverse dipoles influence the stability and phase behavior of biaxial nematic liquid crystals, revealing the splitting of the Landau point into a Landau line and enhanced phase stability.

Contribution

It demonstrates that transverse dipoles significantly modify the phase diagram, stabilizing the biaxial nematic phase and inducing long-range anti-ferroelectric order, which is a novel insight.

Findings

Splitting of Landau point into a Landau line.

Enhanced stability of biaxial nematic phase at higher temperatures.

Induction of long-range anti-ferroelectric order by transverse dipoles.

Abstract

Monte Carlo simulation performed on a lattice system of biaxial molecules possessing $D_{2h}$ symmetry and interacting with a second rank anisotropic dispersion potential yields three distinct macroscopic phases depending on the biaxiality of the constituent molecules. The phase diagram of such a system as a function of molecular biaxiality is greatly modified when a transverse dipole is considered to be associated with each molecule so that the symmetry is reduced to $C_{2v}$. Our results indicate the splitting of the Landau point i.e. the point in the phase diagram where a direct transition from the isotropic phase to the biaxial nematic phase occurs, into a Landau line for a system of biaxial molecules with strong transverse dipoles. The width of the Landau line becomes maximum for an optimal value of the relative dipolar strength. The presence of transverse dipoles leads to the stabilization of the thermotropic biaxial nematic phase at higher temperature and for a range of values of molecular biaxiality. The structural properties in the uniaxial and biaxial phases are investigated by evaluating the first rank and second rank orientational correlation functions. The dipole induced long range order of the anti-ferroelectric structure in the biaxial nematic phase, is revealed.