Elasticity Induced Force Reversal Between Active Spinning Particles in Dense Passive Media

TL;DR

This paper reveals that embedding active spinning particles in a dense passive medium can reverse their interactions from repulsive to attractive, due to coupling between active stresses and medium elasticity, enabling tunable active agent interactions.

Contribution

It introduces a novel mechanism where passive medium elasticity causes force reversal between active particles, expanding understanding of active matter in structured environments.

Findings

Force reversal from repulsive to attractive in active particles

Passive medium elasticity influences active particle interactions

Potential to tune interactions via medium's mechanical properties

Abstract

The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here, we study the interactions between active agents in a dense non-active medium. Our system consists of actuated spinning (active) particles embedded in a dense monolayer of passive (non-active) particles. We demonstrate that the presence of the passive monolayer alters dramatically the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a new mechanism for the interaction between active agents in complex and structured media, opening up new opportunities to tune the interaction range and directionality via the mechanical properties of the medium.