Twist-bend nematic phases of bent-shaped biaxial molecules

TL;DR

This study extends a mean-field model to explore how molecular biaxiality and bend angle influence the stability of twist-bend nematic phases in bent-shaped molecules, revealing conditions for multiple phase stability.

Contribution

It introduces an extended model that predicts the stability of various nematic phases based on molecular biaxiality and bend angle, highlighting the conditions favoring twist-bend nematic phases.

Findings

Biaxiality can stabilize up to four different ordered phases.

Twist-bend nematic phase is more readily stabilized than biaxial nematic phase.

Biaxial nematic phase appears only at bend angles >140° and high biaxiality.

Abstract

How change in molecular structure can affect relative stability and structural properties of the twist-bend nematic phase (N$_\text{TB}$)? Here we extend the mean-field model [C. Greco et al., Soft Matter, 2014, 10, 9318] for bent-shaped achiral molecules, to study the influence of arm molecular biaxiality and the value of molecule's bend angle on relative stability of N$_\text{TB}$. In particular we show that by controlling biaxiality of molecule's arms up to four ordered phases can become stable. They involve locally uniaxial and biaxial variants of N$_\text{TB}$, together with the uniaxial and the biaxial nematic phases. However, the V-shaped molecule show stronger ability to form stable N$_\text{TB}$ than a biaxial nematic phase, where the latter phase appears in the phase diagram only for bend angles greater than $140^\circ$ and for large biaxiality of the two arms.