Shaking-induced motility in suspensions of soft active particles

TL;DR

This paper presents a theoretical study of how soft active particles in a viscous fluid can exhibit collective movement and spatial order due to hydrodynamic interactions, even without inherent motility.

Contribution

It introduces a minimal model for non-motile active particles, deriving effective equations of motion and analyzing their collective behaviors under random stresses and external shaking.

Findings

Small groups of non-motile particles can move collectively due to hydrodynamic correlations.

External shaking induces spatial ordering in the suspension.

Hydrodynamic interactions enable non-trivial locomotion modes.

Abstract

We investigate theoretically the collective dynamics of soft active particles living in a viscous fluid. We focus on a minimal model for active but non-motile particles consisting of $N>1$ elastic dimers deformed by active stresses and interacting hydrodynamically. We first derive a set of effective equations of motion for the positions of the particles. We then exploit these equations in two experimentally-relevant cases: uncorrelated random internal stresses, and uniform monochromatic external shaking. In both cases, we show that small groups of intrinsically non-motile particles can display non-trivial modes of locomotion resulting from the hydrodynamic correlations between the particle-conformation fluctuations. In addition, we demonstrate that a coherent shaking yields spatial ordering in suspension of soft particles interacting solely through the fluid.