Twist-induced crossover from 2D to 3D turbulence in active nematics

TL;DR

This paper investigates how active nematics transition from 2D to 3D turbulence as the confinement height increases, highlighting the role of disclination line morphology and twist perturbations in this crossover.

Contribution

It introduces a continuum simulation and analytical framework to understand the 2D-3D crossover in active nematics based on disclination line morphology and twist effects.

Findings

Crossover from 2D to 3D turbulence controlled by disclination line morphology.

Small channels exhibit effectively 2D active turbulence with straight disclinations.

Increasing channel height induces 3D chaos due to disclination contortion caused by twist perturbations.

Abstract

While studies of active nematics in two dimensions have shed light on various aspects of the flow regimes and topology of active matter, three-dimensional properties of topological defects and chaotic flows remain unexplored. By confining a film of active nematics between two parallel plates, we use continuum simulations and analytical arguments to demonstrate that the crossover from quasi-2D to 3D chaotic flows is controlled by the morphology of the disclination lines. For small plate separations, the active nematic behaves as a quasi-2D material, with straight topological disclination lines spanning the height of the channel and exhibiting effectively 2D active turbulence. Upon increasing channel height, we find a crossover to 3D chaotic flows due to the contortion of disclinations above a critical activity. We further show that these contortions are engendered by twist perturbations producing a sharp change in the curvature of disclinations.