Permeative flows in cholesteric liquid crystals

TL;DR

This study uses lattice Boltzmann simulations to analyze permeative flow in cholesteric liquid crystals, revealing significant viscosity changes depending on boundary conditions and identifying complex flow-induced structures.

Contribution

It extends analytic models by numerically exploring flow effects on cholesteric textures, highlighting boundary-dependent viscosity and flow-induced double twist structures.

Findings

Enormous viscosity increase when helix is pinned at boundaries.

Flattened velocity profile with free helix, unchanged viscosity.

Flow-induced double twist structure resembling blue phases.

Abstract

We use lattice Boltzmann simulations to solve the Beris-Edwards equations of motion for a cholesteric liquid crystal subjected to Poiseuille flow along the direction of the helical axis (permeative flow). The results allow us to clarify and extend the approximate analytic treatments currently available. We find that if the cholesteric helix is pinned at the boundaries there is an enormous viscosity increase. If, instead, the helix is free the velocity profile is flattened but the viscosity is essentially unchanged. We highlight the importance of secondary flows and, for higher flow velocities, we identify a flow-induced double twist structure in the director field -- reminiscent of the texture characteristic of blue phases.