Berlin 2018 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: Active Matter I (joint session DY/CPP/BP)

CPP 9.4: Talk

Monday, March 12, 2018, 10:45–11:00, BH-N 243

Collective dynamics of squirmers confined to a surface by strong gravity — •Jan-Timm Kuhr, Felix Rühle, Johannes Blaschke, and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, Hardenberg Str. 36, 10623 Berlin, Germany

External fields acting on microswimmers are of paramount importance for collective phenomena like bioconvection. In previous work we explored the individual [1] and collective [2] dynamics of squirmer model swimmers under moderate gravity by MPCD simulations. Here, we turn to strong gravity, where microswimmers form a single layer at the bottom surface, while interacting hydrodynamically in 3D.

We find various intriguing phenomena depending on the swimmer type (neutral, pusher, and puller) and area density: Formation of pairs, chains and other metastable bound states, but also collective swarming parallel to the surface.

Neutral squirmers at low area densities repel each other by their self-generated flow fields and thereby arrange in strongly disturbed hexagonal lattices reminiscent of 2D crystals subject to intense fluctuations. For higher densities attractive interactions become important and give rise to pair and chain formation. We characterize these distinct emergent states, compare to melting of 2D colloids, and explore the flow fields, which create hexagonal lattices.
[1] F. Rühle et al., accepted at New J. Phys.
J.-T. Kuhr, J. Blaschke, F. Rühle, and H. Stark, Soft Matter 13, 7548 (2017).