Hydrodynamics of chiral nematics in a channel and sudden contraction geometry

TL;DR

This paper explores how chirality, confinement, and flow influence defect structures and dynamics in cholesteric liquid crystals through numerical simulations, revealing complex defect formations and flow regimes relevant for advanced material applications.

Contribution

It provides new insights into defect formation and flow behavior in cholesteric liquid crystals under various geometries and chiral strengths, including the emergence of skyrmion-like structures.

Findings

Formation of $ au^-$ defects around vortices

Chaotic flow regimes at low Ericksen numbers

Flow disturbances linked to aspect ratio and elastic interactions

Abstract

This study investigates the influence of chirality, viscous effects, and confinement geometry on the flow dynamics and defect structures of cholesteric liquid crystals (CLCs) using numerical simulations. As chiral strength increases, $\pi$-twist defects form at low chirality and progressively organize into hexagonal domains resembling blue phase--like (BP-like) structures at higher chirality. At sufficiently high chirality and aspect ratios, skyrmion-like configurations emerge, indicating the formation of dynamic analogs of equilibrium phases under flow. Sudden contraction geometries reveal how aspect ratio and elastic interactions promote flow disturbances and defect development. Analyses of velocity and scalar order parameter ($S$) distributions demonstrate strong coupling between molecular alignment and hydrodynamic fields, with localized vortices forming around $\tau^-$ defects in regions of low $S$ and velocity. Temporal evaluations of velocity fluctuations uncover chaotic flow regimes at low Ericksen numbers, characterized by irregular defect motion and skewed probability density functions. These findings offer new insights into CLC structure formation and flow behavior, with potential applications in defect engineering, microfluidics, soft robotics, and photonic materials.