Symmetry-breaking motility of an active hinge in a crowded channel

TL;DR

This paper investigates how an active hinge moves through a crowded channel, revealing nonmonotonic lifetime behavior and abrupt configuration transitions, which could inform the design of switchable superstructures with passive granular media and active elements.

Contribution

It introduces a novel model of an active hinge in a crowded environment, analyzing its dynamics and phase transitions through extensive numerical simulations.

Findings

Hinge lifetime varies nonmonotonically with packing fraction and propulsion strength.

Abrupt transition in passive particle configuration as hinge angle increases.

Potential for designing switchable superstructures with passive and active components.

Abstract

A recent experiment [Son et al., Soft Matter, 2024, 20,2777-2788] showed that self-propelled particles confined within a circular boundary filled with granular medium spontaneously form a motile cluster that stays on the boundary. This cluster exhibits persistent (counter)clockwise motion driven by symmetry breaking, which arises from a positive feedback between the asymmetry of the cluster and those of the surrounding granular medium. To investigate this symmetry-breaking mechanism in broader contexts, we propose and analyze the dynamics of an active hinge moving through a crowded two-dimensional channel. Through extensive numerical simulations, we find that the lifetime of the hinge's motile state varies nonmonotonically with both the packing fraction of the granular medium and the strength of self-propulsion. Furthermore, we observe an abrupt transition in the configuration of passive particles that sustain hinge motility as the hinge's maximum angle relative to the channel wall increases. These findings point to the possibility of designing superstructures composed of passive granular media doped with a small number of active elements, whose dynamics modes can be switched by tuning the properties of their components.