Role of interfacial friction for flow instabilities in a thin polar ordered active fluid layer

TL;DR

This paper develops a unified coarse-grained model for thin polar-ordered active fluid layers coupled to passive media, revealing how interfacial friction influences flow instabilities across various active matter systems.

Contribution

It introduces a generic framework that captures the effects of interfacial friction on flow instabilities in thin polar active layers, applicable to both wet and dry active matter.

Findings

Identification of moving and static instabilities influenced by friction coefficient

Unified description applicable to diverse active matter systems

Estimation of friction bounds relevant for experiments

Abstract

We construct a generic coarse-grained dynamics of a thin inflexible planar layer of polar-ordered suspension of active particles, that is frictionally coupled to an embedding isotropic passive fluid medium with a friction coefficient $\Gamma$. Being controlled by $\Gamma$, our model provides a unified framework to describe the long wavelength behaviour of a variety of thin polar-ordered systems, ranging from {\em wet} to {\em dry} active matters and free standing active films. Investigations of the linear instabilities around a chosen orientationally ordered uniform reference state reveal generic moving and static instabilities in the system, that can depend sensitively on $\Gamma$. Based on our results, we discuss estimation of bounds on $\Gamma$ in experimentally accessible systems.