Active matter or self-propelled systems have been attracting growing attention in biological systems such as swimming bacteria as well as artificial swimmers such as self-driven colloids. These systems exhibit interesting effects including an activity-induced self clustering that occurs even when all pairwise particle-particle interactions are repulsive. Due to the size scale of the active particles, tailored landscapes can be created for the particles by means of optical trapping. Using large scale simulations we examine an active matter system of self-propelled disks moving in confined geometries and in quasi-1D periodic and asymmetric saw-tooth landscapes. The system forms a dense cluster when the trapping sites are large, but still exhibits modes of motion along the edges of the clusters. We discuss how these effects could be related to a mechanical version of topological protection. For periodic quasi-1D traps we find that there can be a 1D ordering of the disks with motion occurring along only one dimension. For asymmetric substrates we find an active matter ratchet effect similar that observed previously; however, when strong interactions between the particles are introduced, we find that it is possible to obtain a reversal of the ratchet effect in which the net flow is in the direction opposite to the easy-flow direction of the substrate asymmetry. The ability to produce a reversal of the active ratchet effect suggests that it may be possible to set up a landscape in which different species of active matter particles move in opposite directions.
Charles M. Reichhardt, Cynthia J. Reichhardt, and Danielle McDermott, "The dynamics of active matter on ordered and disordered substrates
(Conference Presentation)," Proc. SPIE 9922, Optical Trapping and Optical Micromanipulation XIII, 99221H (Presented at SPIE Nanoscience + Engineering: August 31, 2016; Published: 11 November 2016); https://doi.org/10.1117/12.2238868.5161456702001.
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