Influence of active breathing on rheology and jamming of amorphous solids: insights from microscopic and mesoscale analysis

TL;DR

This study investigates how internal active breathing in particles affects the flow, jamming, and rheology of amorphous solids, revealing a transition from jammed to fluidized states driven by activity levels.

Contribution

It introduces a combined molecular dynamics and mesoscale modeling approach to understand activity-induced unjamming and rheological changes in amorphous materials.

Findings

Low amplitude breathing causes reversible, localized rearrangements.

High amplitude breathing induces fluidization and flow transition.

Mesoscale model successfully captures the activity-driven rheological trends.

Abstract

We study the flow behavior and unjamming transition in dense assemblies of actively deforming particles that periodically change size, a process that we refer to as breathing. Using extensive molecular dynamics simulations and a complementary mesoscale elasto-plastic model, we explore how this internal activity influences plasticity and rheology. At low amplitudes of breathing, the system remains jammed and displays localized, reversible rearrangements. As the amplitude of the breathing increases beyond a critical threshold, the system undergoes an activity-induced fluidization marked by a surge in plastic events and a drop in yield stress. The flow curve analysis reveals a transition from yield-stress behavior to Newtonian flow at high activity. The mesoscale model captures these trends and provides insight into the role of stress redistribution due to local active deformations. Our findings highlight the potential of internal active driving to tune the mechanical state of amorphous materials without external forcing.