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The collective behavior of self-propelled particles (SPPs) under the combined effects of a circularly patterned substrate and circular confinement is investigated through coarse-grained molecular dynamics simulations of polarized and disjoint ring polymers. The study is performed over a wide range of values of the SPPs packing fraction ϕover ¯, motility force F₃, and area fraction of the patterned region. At low packing fractions, the SPPs are excluded from the system's center and exhibit a vortical motion that is dominated by the substrate at intermediate values of F₃. This exclusion zone is due to the coupling between the driving force and torque induced by the substrate, which induces an outward spiral motion of the SPPs. For high values of F₃, the SPPs exclusion from the center is dominated by the confining boundary. At high values of ϕover ¯, the substrate pattern leads to reversals in the vorticity, which become quasiperiodic with increasing ϕover ¯. We also found that the substrate pattern is able to separate SPPs based on their motilities.
Wen et al. (Fri,) studied this question.