Multiple Types of Aging in Active Glass

TL;DR

This paper investigates how active, non-equilibrium glasses differ from passive glasses by studying aging behaviors in a model active glass system, revealing complex aging dynamics influenced by activity persistence.

Contribution

It introduces a detailed simulation study of aging in active glasses, highlighting the effects of propulsion force persistence on aging regimes and developing a method to access long-time dynamics.

Findings

Short persistence times lead to effective thermal aging.

Long persistence times cause a two-step aging process.

Active athermal aging dominates at late times.

Abstract

Recent experiments and simulations have revealed glassy features in the cytoplasm, living tissues as well as dense assemblies of self propelled colloids. This leads to a fundamental question: how do these non-equilibrium (active) amorphous materials differ from conventional passive glasses, created either by lowering temperature or by increasing density? To address this we investigate the aging behaviour after a quench to an almost arrested state of a model active glass former, a Kob-Andersen glass in two dimensions. Each constituent particle is driven by a constant propulsion force whose direction diffuses over time. Using extensive molecular dynamics simulations we reveal rich aging behaviour of this dense active matter system: short persistence times of the active forcing lead to effective thermal aging; in the opposite limit we find a two-step aging process with active athermal aging at short times followed by activity-driven aging at late times. We develop a dedicated simulation method that gives access to this long-time scaling regime for highly persistent active forces.