Hydrodynamic Switching Fronts Polarize Deformable Particle Trains

TL;DR

This paper demonstrates how propagating switching fronts in deformable particle trains induce collective polarization through local bistability and directional coupling, with potential applications in passive many-body systems.

Contribution

It introduces a minimal model capturing front propagation and arrest, revealing mechanisms for polarization in passive particle suspensions.

Findings

Switching fronts mediate directional state transmission.

Fronts coarsen into polarized states in periodic trains.

Persistent polarized domains form in long open trains.

Abstract

We show that propagating switching fronts mediate directional state transmission and polarity selection in a passive many-body suspension. In confined trains of slipper-shaped deformable particles in Poiseuille flow, this behavior originates from directionally biased switching between neighboring particles: owing to the fore-aft asymmetry of the slipper, an upstream particle drives switching of its downstream neighbor more effectively than in the reverse direction. A local transition from an opposite-sign pair to a same-sign pair therefore launches a streamwise front that relays the inclination sign from particle to particle. A minimal coarse-grained model with local bistability and directional coupling captures front propagation and arrest. In periodic trains, the fronts coarsen into a uniformly polarized state, whereas in long open trains they arrest and leave persistent polarized domains. Our results point to local bistability and directional coupling as a route to collective polarization in passive many-body systems.