Origin of Persistent Boundary Motion in Confined Active Matter

TL;DR

This study reveals how the coupling of orientational fluctuations and boundary effects in confined active matter leads to persistent boundary motion and complex positional distributions, advancing understanding of active particle dynamics.

Contribution

The paper introduces a combined simulation and analytical framework linking orientational bistability and stochastic switching to boundary accumulation in confined active matter.

Findings

Positional distribution is coupled to orientational fluctuations.

Confinement induces two preferred tangential orientational states.

Waiting time between flips follows a power-law dependence on confinement.

Abstract

Active matter systems under confinement display persistent surface motion and a strong boundary affinity. However, despite extensive studies of their positional dynamics, much less attention has been given to the corresponding orientational behavior. Here, using molecular simulations of an active Brownian particle confined within a hard circular boundary and the Fokker-Planck equation, we show that the positional distribution of the particle is directly coupled to orientational fluctuations, as characterized by the conditional orientational distribution. Confinement generates two preferred tangential orientational states connected by stochastic flipping pathways: rapid boundary-localized switching and slower bulk-mediated excursions. Further, the positional distribution exhibits a nontrivial power-law decay with distance from the boundary that is closely linked to curvature-induced bistable orientational states and the variance of the associated conditional distribution. The mean waiting time between flips exhibits power-law dependence on the confinement strength. Our results establish that the interplay between orientational fluctuations, bistability, positional accumulation, and stochastic switching governs the observed dynamics of active particles under confinement, providing a framework for understanding transport, exploration, and escape processes in confined active systems.