Defect annihilation and proliferation in active nematics

TL;DR

This paper explores how topological defects in active nematic liquid crystals behave differently from passive ones, showing that activity type influences defect annihilation or proliferation, supported by models and experiments.

Contribution

It introduces a simple analytical model capturing defect dynamics in active nematics, explaining the contrasting behaviors of contractile and extensile systems.

Findings

Contractile systems enhance defect annihilation.

Extensile systems cause defect proliferation and swarming.

Model aligns with experimental observations.

Abstract

Liquid crystals inevitably possess topological defect excitations generated through boundary conditions, applied fields or in quenches to the ordered phase. In equilibrium pairs of defects coarsen and annihilate as the uniform ground state is approached. Here we show that defects in active liquid crystals exhibit profoundly different behavior, depending on the degree of activity and its contractile or extensile character. While contractile systems enhance the annihilation dynamics of passive systems, extensile systems act to drive defects apart so that they swarm around in the manner of topologically well-characterized self-propelled particles. We develop a simple analytical model for the defect dynamics which reproduces the key features of both the numerical solutions and recent experiments on microtuble-kinesin assemblies.