Rheology of cholesteric blue phases

TL;DR

This study uses numerical simulations to explore how cholesteric blue phase liquid crystals respond to shear flow, revealing complex defect dynamics, shear thinning behavior, and oscillatory stress responses.

Contribution

It provides new insights into the hydrodynamic behavior and defect dynamics of blue phases under flow conditions through detailed numerical analysis.

Findings

Shear forces bend, twist, and unzip disclination lines.

The network opposes flow, increasing viscosity at low shear.

Strong shear thinning occurs as the defect network disrupts.

Abstract

Blue phases of cholesteric liquid crystals offer a spectacular example of naturally occurring disclination line networks. Here we numerically solve the hydrodynamic equations of motion to investigate the response of three types of blue phases to an imposed Poiseuille flow. We show that shear forces bend and twist and can unzip the disclination lines. Under gentle forcing the network opposes the flow and the apparent viscosity is significantly higher than that of an isotropic liquid. With increased forcing we find strong shear thinning corresponding to the disruption of the defect network. As the viscosity starts to drop, the imposed flow sets the network into motion. Disclinations break-up and re-form with their neighbours in the flow direction. This gives rise to oscillations in the time-dependent measurement of the average stress.