Active nematic gels as active relaxing solids

TL;DR

This paper develops a continuum theory for active nematic gels, integrating active dynamics with viscoelastic response, predicting spontaneous flow or self-organization in active nematic systems.

Contribution

It introduces a novel active nematic gel model where activity acts as an external remodeling force, differing from traditional stress-based activity models.

Findings

Active nematic gels can spontaneously flow or self-organize due to activity.

The theory predicts non-uniform nematic order leads to complex flow patterns.

Activity influences the relaxation dynamics, causing non-equilibrium behaviors.

Abstract

I put forward a continuum theory for active nematic gels, defined as fluids or suspensions of orientable rodlike objects endowed with active dynamics, that is based on symmetry arguments and compatibility with thermodynamics. The starting point is our recent theory that models (passive) nematic liquid crystals as relaxing nematic elastomers. The interplay between viscoelastic response and active dynamics of the microscopic constituents is naturally taken into account. By contrast with standard theories, activity is not introduced as an additional term of the stress tensor, but it is added as an external remodeling force that competes with the passive relaxation dynamics and drags the system out of equilibrium. In a simple one-dimensional channel geometry, we show that the interaction between non-uniform nematic order and activity results in either a spontaneous flow of particles or a self-organization into sub-channels flowing in opposite directions.