Spontaneous Chiral Symmetry Breaking in Polydisperse Achiral Near-Rigid Nematogens

TL;DR

This study demonstrates how polydispersity and shape fluctuations in achiral nematogens can spontaneously induce chiral symmetry breaking, leading to chiral nematic phases without inherent molecular chirality.

Contribution

It reveals that size dispersity and configurational fluctuations alone can cause spontaneous chiral symmetry breaking in achiral liquid crystals.

Findings

Chiral symmetry breaking occurs in achiral rods with length dispersity.

Long-lived chiral conformations lead to chiral synchronization.

Shape fluctuations and polydispersity can generate macroscopic chirality.

Abstract

Understanding chirality transfer from the molecular to the macroscopic scale poses a significant challenge in soft and biological condensed matter physics. Many nanorods of biological origin not only have chiral molecular features but also exhibit a spread in contour length leading to considerable size dispersity. On top of this, random backbone fluctuations are ubiquitous for non-rigid particles but their role in chirality transfer remains difficult to disentangle from that of their native chirality imparted by their effective shape or surface architecture. We report spontaneous entropy-driven chiral symmetry breaking from molecular simulations of cholesteric liquid-crystals formed from achiral bead-spring rods with a continuous spread in contour length and marginal chain bending. The symmetry-breaking is caused by long-lived chiral conformations of long rods undergoing chiral synchronization leading to a homochiral twisted nematic. A simple theory demonstrates that even without chiral synchronization, the presence of shape-persistent configurational fluctuations along with length-dispersity can be harnessed to generate non-zero chirality at moderate polydispersity.