Passive objects in confined active fluids: a localization transition

TL;DR

This paper investigates how confining walls influence passive asymmetric objects in active fluids, revealing wall-induced forces that cause localization of asymmetric objects at the cavity center.

Contribution

It introduces a generalized image theorem to compute wall-mediated forces and demonstrates localization phenomena for asymmetric objects in confined active fluids.

Findings

Walls exert non-conservative long-range forces on passive objects.

Asymmetric objects are repelled by walls regardless of their properties.

Circular cavities can localize asymmetric objects at the center.

Abstract

We study how walls confining active fluids interact with asymmetric passive objects placed in their bulk. We show that the objects experience non-conservative long-ranged forces mediated by the active bath. To leading order, these forces can be computed using a generalized image theorem. The walls repel asymmetric objects, irrespective of their microscopic properties or their orientations. For circular cavities, we demonstrate how this may lead to the localization of asymmetric objects in the center of the cavity, something impossible for symmetric ones.