Shear Induced Orientational Ordering in Active Glass

TL;DR

This study reveals a novel shear-induced orientational ordering in active glasses through simulations and theory, distinguishing three steady states and providing predictive models relevant for dense active matter experiments.

Contribution

The paper introduces the discovery of shear-induced orientational ordering in active glasses and develops an analytical Fokker-Planck model to explain this phenomenon without explicit aligning interactions.

Findings

Identification of three distinct steady states in sheared active glasses

Development of an analytical Fokker-Planck theory predicting ordering behavior

Good agreement between theoretical predictions and simulation data

Abstract

Dense assemblies of self propelled particles, also known as active or living glasses are abundantaround us, covering different length and time scales: from the cytoplasm to tissues, from bacterialbio-films to vehicular traffic jams, from Janus colloids to animal herds. Being structurally disorderedas well as strongly out of equilibrium, these systems show fascinating dynamical and mechanicalproperties. Using extensive molecular dynamics simulation and a number of different dynamicaland mechanical order parameters we differentiate three dynamical steady states in a sheared modelactive glassy system: (a) a disordered phase, (b) a propulsion-induced ordered phase, and (c) ashear-induced ordered phase. We supplement these observations with an analytical theory based onan effective single particle Fokker-Planck description to rationalise the existence of the novel shear-induced orientational ordering behaviour in our model active glassy system that has no explicitaligning interactions,e.g.of Vicsek-type. This ordering phenomenon occurs in the large persistencetime limit and is made possible only by the applied steady shear. Using a Fokker-Planck descriptionwe make testable predictions without any fit parameters for the joint distribution of single particleposition and orientation. These predictions match well with the joint distribution measured fromdirect numerical simulation. Our results are of relevance for experiments exploring the rheologicalresponse of dense active colloids and jammed active granular matter systems.