Active particles with polar alignment in ring-shaped confinement

TL;DR

This paper investigates how active particles with polar alignment behave in a ring-shaped confinement, revealing a surface-population reversal effect influenced by particle alignment and surface curvature, with implications for active matter dynamics.

Contribution

It introduces the discovery of a surface-population reversal in active particles confined in a ring, highlighting the roles of alignment and curvature in particle distribution.

Findings

Active particles can migrate from outer to inner boundaries in a ring.

Population reversal depends on particle alignment and surface curvature.

Chirality and system parameters influence particle distribution and currents.

Abstract

We study steady-state properties of a suspension of active, nonchiral and chiral, Brownian particles with polar alignment and steric interactions confined within a ring-shaped (annulus) confinement in two dimensions. Exploring possible interplays between polar interparticle alignment, geometric confinement and the surface curvature, being incorporated here on minimal levels, we report a surface-population reversal effect, whereby active particles migrate from the outer concave boundary of the annulus to accumulate on its inner convex boundary. This contrasts the conventional picture, implying stronger accumulation of active particles on concave boundaries relative to the convex ones. The population reversal is caused by both particle alignment and surface curvature, disappearing when either of these factors is absent. We explore the ensuing consequences for the chirality-induced current and swim pressure of active particles and analyze possible roles of system parameters, such as the mean number density of particles and particle self-propulsion, chirality and alignment strengths.