Séminaire Paul van der Schoot (Eindhoven University)

Chirality Amplification and Deracemisation in Nematic Liquid Crystals

Liquid crystal mesophases of achiral molecules are normally achiral, yet in some materials they spontaneously deracemise and form right- and left-handed chiral domains. One mechanism that drives deracemization is molecular shape fluctuations between axial chiral conformations, where molecular interactions favour matching chirality and promote helical twist. Cooperative chiral ordering may also play a role in chirality amplification, as when a tiny fraction of chiral dopant drives a nematic phase to become cholesteric. We present a model of cooperative chiral ordering in nematic liquid crystals using a switchable chiral Lebwohl-Lasher model, where each rotor is also assigned a spin that switches between two states representing right- and left-handed chiral states [1]. Mean-field theory and Monte Carlo simulations predict a phase diagram with a deracemised cholesteric phase as well as racemic nematic and isotropic phases. Our model also predicts chirality amplification in the nematic phase and softening of the nematic twist constant, which may be observed even in materials where the deracemization transition is preempted by a transition to another phase. Our simulations also reveal unusual coarsening dynamics in the deracemised phase. We conclude that cooperative chiral ordering via molecular shape transitions must be a common mechanism in liquid crystals [1].

[1] M. Deutsch et al., arXiv:2506.05053; doi: 10.48550/arXiv.2506.05053