Collective dynamics of active dumbbells near a circular obstacle

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.