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BP: Fachverband Biologische Physik

BP 30: Active Matter IV (joint session DY/BP/CPP)

BP 30.10: Talk

Thursday, March 21, 2024, 12:30–12:45, BH-N 334

Stationary particle currents in sedimenting active matter wetting a wall — •Matthieu Mangeat, Shauri Chakraborty, Adam Wysocki, and Heiko Rieger — Saarland University, Saarbrücken, Germany

Recently it was predicted, on the basis of a lattice gas model, that scalar active matter would rise against gravity up a confining wall in spite of repulsive particle-wall interactions [PRL 124, 048001 (2020)]. We confirm this prediction with sedimenting active Brownian particles (ABPs) in a box and elucidate the mechanism leading to the formation of a meniscus rising above the bulk of the sedimentation region. The height of the meniscus increases algebraically with the activity, and the formation of the meniscus is determined by a stationary circular particle current centered at the base of the meniscus. The origin of these vortices can be traced back to the confinement of the ABPs in a box: already the stationary state of non-interacting ABPs without gravitation displays highly symmetric circular currents. Gravitation distorts this vortex configuration downward, leaving two major vortices at the two side walls, with a strong downward flow along the walls. Repulsive interactions between the ABPs change this situation only as soon as motility induced phase separation (MIPS) sets in and forms a dense, sedimented liquid region at the bottom, which pushes the center of the vortex upwards towards the liquid-gas interface. Self-propelled particles therefore represent an impressive realization of scalar active matter that forms stationary particle currents being able to perform visible work against gravity, which we predict to be observable experimentally.

Keywords: active Brownian particles; active sedimentation; stationary currents; capillary action