Depletion forces on circular and elliptical obstacles induced by active matter

TL;DR

This study uses numerical simulations to analyze how active particles exert shape- and orientation-dependent depletion forces on passive obstacles, revealing conditions for attraction and repulsion.

Contribution

It demonstrates how active matter induces shape-sensitive depletion forces on passive objects, including the emergence of attractive forces at high area fractions.

Findings

Repulsive forces increase with obstacle distance up to one particle diameter.

Attractive forces can occur for vertical ellipses at high area fractions.

Force magnitude decreases with increasing distance beyond one particle diameter.

Abstract

Depletion forces exerted by self-propelled particles on circular and elliptical passive objects are studied using numerical simulations. We show that a bath of active particles can induce repulsive and attractive forces which are sensitive to the shape and orientation of the passive objects (either horizontal or vertical ellipses). The resultant force on the passive objects due to the active particles is studied as a function of the shape and orientation of the passive objects, magnitude of the angular noise, distance between the passive objects. By increasing the distance between obstacles the magnitude of the repulsive depletion force increases, as long as such a distance is less than one active particle diameter. For longer distances, the magnitude of the force always decrease with increasing distance. We also found that attractive forces may arise for vertical ellipses at high enough area fraction.