Regensburg 2019 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 32: Active matter II (joint session BP/CPP/DY)

BP 32.2: Vortrag

Freitag, 5. April 2019, 09:45–10:00, H11

Dynamics of bottom-heavy squirmers — •Felix Ruehle and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, Germany

The self-propulsion of biological or synthetic microswimmers is often influenced by a gravitational field [1,2], where a density mismatch leads to sedimentation and an offset center of mass triggers reorientation along the direction of gravity so that they swim upwards [2]. Combining these passive effects with the non-equilibrium properties of active motion creates novel and interesting dynamics, both in dense and dilute suspensions [3]. In particular, a large variety of dynamical behaviours has been observed for the squirmer microswimmer model [4,5].

In this contribution we focus on bottom-heavy squirmers and determine their state diagram, depending on the gravitational force and acting torque. For strong gravitational forces we observe conventional sedimentation, whereas the density profile is inverted for weaker forces. Additionally, we find stable convective plumes for neutral squirmers that become metastable as the torque increases. We also observe spawning clusters at the bottom if the sedimentation velocity almost equalizes the swimming speed. Spawning clusters and continuous plumes do not occur for pusher and puller type swimmers.