Chirality transfer in lyotropic twist-bend nematics

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.