The collective transport of the self-propelled rods (SPRs) is studied by dissipative particle dynamics simulations. Two types of channels (channel I and channel II) are taken into account for various rod concentrations. It is found that in channel I-the asymmetric corrugated channel with periodically varying width, some SPRs are trapped at the corners and form the hedgehog clusters. Other SPRs aggregate at the bottleneck and lead to a traffic jam. Consequently, channel I is inefficient for the directional SPR transport in the case of finite concentration. To achieve efficient collective particle transport, channel II-the channel with constant width and arrays of asymmetric obstacles within it, which can avoid the traffic clogging and hedgehog aggregate is suggested. It is found that the swimmer-obstacle interaction gives rise to the directional motion, the spacing between obstacles can avoid the formation of the hedgehog clusters. The high-efficiency directional collective motion of the SPRs is acquired in channel II. Overall, our simulation study offers an efficient approach for directional collective motion of SPRs.

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.

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