The Role of Elastic Anisotropy in Active Nematics

TL;DR

This paper investigates how elastic anisotropy influences the hydrodynamics of active nematics, revealing new active torques, modifications in dipole propulsion, and minor effects on defect dynamics, thereby advancing understanding of anisotropic active materials.

Contribution

It introduces a framework for understanding the effects of elastic anisotropy on active nematic hydrodynamics, including new active torques and modified defect behaviors.

Findings

New active torque proportional to anisotropy for monopole distortions

Dipole propulsion speed can change by up to 50% due to anisotropy

Elastic anisotropy has minimal impact on defect self-propulsion speeds (<5%)

Abstract

We analyse the effect of anisotropy in elastic constants on the hydrodynamics of active nematics. Building on the multipole framework for a single elastic constant, we determine the leading effect of elastic anisotropy on the active response of generic distortions. The key findings are a new active torque, proportional to the anisotropy, in response to monopole distortions, and modifications to the propulsion of dipoles in both the direction of motion and changes in speed of up to 50\%. For point defects in two dimensions we find that, despite the large morphological changes in the director field, elastic anisotropy has only a minor impact on their hydrodynamics, with the self-propulsion speed of $+1/2$ defects lowered by less than 5\%. Finally, we determine the elastic torques exerted on defect pairs due to elastic anisotropy.