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

¹ Condensed Matter Science and Technology Institute, School of Instrumentation Science and Engineering, Harbin Institute of Technology - Harbin 150080, China
² Key Lab of Ultra- precision Intelligent Instrumentation ( Harbin Institute of Technology), Ministry of Industry and Information Technology - Harbin 150080, China
³ Department of Physics, Tianjin University Renai College - Tianjin 301636, China
⁴ School of Physics and Electronics, Shandong Normal University - Jinan 250014, China

^(a) zhengjiawang@hit.edu.cn
^(b) nkhjh@mail.nankai.edu.cn

Received: 10 August 2020
Accepted: 28 October 2020

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 $I_{p}{\sim}F_{a}$ , where F_a denotes the self-propelled force.