Active nematic defects in compressible and incompressible flows

TL;DR

This paper investigates how active nematic films behave under different flow constraints, revealing stable arch formations in compressible flows and distinct defect organizations, advancing understanding of active matter dynamics.

Contribution

It introduces a combined simulation and theoretical framework to analyze active nematic defect dynamics under compressible and incompressible flows, highlighting new defect organization patterns.

Findings

Stable arch patterns in compressible flows at high activity

Formation of smectic-like patterns with global polar order

Local nematic order with anti-aligned defect pairs in incompressible flows

Abstract

We study the dynamics of active nematic films on a substrate driven by active flows with or without the incompressible constraint.Through simulations and theoretical analysis, we show that arch patterns are stable in the compressible case, whilst they become unstable under the incompressibility constraint. For compressible flows at high enough activity, stable arches organize themselves into a smectic-like pattern, which induce an associated global polar ordering of $+1/2$ nematic defects. By contrast, divergence-free flows give rise to a local nematic order of the $+1/2$ defects, consisting of anti-aligned pairs of neighboring defects, as established in previous studies.