Collective dynamics of active dumbbells near a circular obstacle

TL;DR

This study investigates the collective behavior of active dumbbells around a circular obstacle, revealing aggregation, rotational motion, polar order, and complex tracer dynamics influenced by activity and density.

Contribution

It provides new insights into how active dumbbells organize and move near obstacles, highlighting the effects of activity, curvature, and many-body interactions.

Findings

Active dumbbells aggregate on the obstacle surface beyond a critical radius.

The aggregate exhibits persistent rotational motion with angular speed increasing with activity.

Tracer particle speed shows a crossover behavior with size and activity.

Abstract

In this article, we present the collective dynamics of active dumbbells in the presence of a static circular obstacle using Brownian dynamics simulation. The active dumbbells aggregate on the surface of a circular obstacle beyond a critical radius. The aggregation is non-uniform along the circumference, and the aggregate size increases with the activity and the curvature radius. The dense aggregate of active dumbbells displays persistent rotational motion with a certain angular speed, which linearly increases with the activity. Further, we show the strong polar ordering of the active dumbbells within the aggregate. The polar ordering exhibits a long-range correlation, with the correlation length corresponding to the aggregate size. Additionally, we show that the residence time of an active dumbbell on the obstacle surface grows rapidly with area fraction due to many-body interactions that lead to a slowdown of the rotational diffusion. The article further considers the dynamical behavior of a tracer particle in the solution of active dumbbells. Interestingly, the speed of the passive tracer particle displays a crossover from monotonically decreasing to increasing with the tracer particle's size upon increasing the dumbbells' speed. Furthermore, the effective diffusion of the tracer particle displays the non-monotonic behavior with area fraction; the initial increase of the diffusivity is followed by a decrease for larger area fraction.