Defect dynamics for self-propelled rods in a doublet of circular confinement

Abstract

Rod-shaped active micro/nano-particles, such as bacterial and bipolar metallic micro/ nano-motors, exhibit emergent collective phenomena far from equilibrium state compared to passive particles. We apply a simulation approach —dissipative particle dynamics (DPD)— to explore the collectively ordered states of self-propelled rods (SPRs) which rely on the defect dynamics in the rod cluster. The SPRs are confined in a doublet of circular confinement and repel each other when two rods touch each other. When the rod flow in the connecting passage of the circles is suppressed, namely the small passage width, the steady vortex pattern is obtained in the two circles for weak activity. In binary-passage system, long single-passage system, and short single-passage system, ferromagnetic vortices (FMV), uncorrelated vortices (UV), and anti-ferromagnetic vortices (AFMV) can be obtained, respectively. For intermediate activity, a regular periodic oscillation of the rod number n r in one circle can be seen clearly. For strong activity, mixing of high- and low-frequency oscillation is observed. The amplitude of the rod current in the passage I p follows the relation , where F a denotes the self-propelled force.