Chirality transfer in lyotropic twist-bend nematics

TL;DR

This study uses molecular simulations and density functional theory to explore how chirality in bent rod-like mesogens influences liquid crystal phase behavior, revealing mechanisms of chirality transfer and phase preference.

Contribution

It introduces a detailed analysis of chirality transfer in lyotropic twist-bend nematics, highlighting how particle twist affects phase symmetry and handedness.

Findings

Chirality favors same-handed twist-bend phases as particle twist increases.

Opposite handedness observed between cholesteric and twist-bend phases.

Doping with chiral particles biases the system towards the same chirality as the dopants.

Abstract

Using molecular simulations and classical density functional theory, we study the liquid-crystalline phase behaviour of a series of bent rod-like mesogens with a controlled degree of chirality introduced through a twist at the centre of the particle. In the achiral limit, isotropic, uniaxial nematic, twist-bend nematic and smectic phases form as the packing fraction increases. On introducing chirality, the symmetry between the right- and left-handed twist-bend phases is broken. The phase with the same-handedness as the particles quickly becomes overwhelmingly favoured as the magnitude of the particle twist is increased, because the particles are then able to better follow the helical director field lines in the twist-bend phase and pack more efficiently. By contrast, the cholesteric phase is predicted to have the opposite handedness to that of the particle due to the relatively weakly-twisted nature of the particles. That the cholesteric and twist-bend phases have opposite handedness illustrates the differences in the mechanisms of chirality transfer in the two phases. We also found that doping a system of achiral mesogens with a small fraction of chiral particles led to selection of the twist-bend phase with the same chirality as the particle.