Driven active and passive nematics

TL;DR

This paper compares the micro-structural dynamics of driven passive and active nematics, revealing similarities in defect formation and flow patterns, and explores how external shear influences active turbulence.

Contribution

It demonstrates that external driving can induce structures similar to active nematics in passive systems and examines how shear suppresses or localizes turbulence in active nematics.

Findings

Driven passive nematics form walls and defects similar to active nematics.

External shear suppresses hydrodynamic instabilities in active nematics.

Shear fields can align walls and localize turbulence.

Abstract

We investigate similarities in the micro-structural dynamics between externally driven and actively driven nematics. Walls, lines of strong deformations in the director field, and topological defects are characteristic features of an active nematic. Similar structures form in driven passive nematics when there are inhomogeneities in imposed velocity gradients due to non-linear flow fields or geometrical constraints. Specifically, pressure driven flow of a tumbling passive nematic in an expanding-contracting channel produces walls and defects similar to those seen in active nematics. We also study the response of active nematics to external driving, confirming that imposed shear suppresses the hydrodynamic instabilities. We show that shear fields can lead to wall alignments and the localisation of active turbulence.