Dresden 2017 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 51: Microswimmers III (Joint Session BP/DY)

BP 51.1: Vortrag

Donnerstag, 23. März 2017, 11:15–11:30, ZEU 250

A single squirmer under gravity — •Felix Rühle and Holger Stark — Inst. für Theor. Physik, TU Berlin, 10623 Berlin

A simple yet versatile model for many microswimmers is the widely studied spherical squirmer [1]. In this contribution we include a gravitational force acting on a single swimmer. In experiments this setup has yielded fascinating non-equilibrium structure formation such as floating rafts formed by active emulsion droplets [2] or dancing Volvox algae [3]. While theoretical and numerical studies for microswimmers under gravity do exist  [4,5], they usually do not account for full hydrodynamics, which need to be included in the presence of surfaces.

In our study we observe a rich phenomenology depending on gravitational strength and on squirmer type: Swimmers are caught at the wall or completely escape from its influence, or they float at a finite distance from the bottom wall, both permanently and recurrently. We reproduce and explain these findings, which we obtained in MPCD simulations, using analytical calculations, which include wall-induced linear and angular velocities in the near and far field [6].

[1] J. R. Blake, J. Fluid Mech.  46, 199 (1971).

[2] C. Krüger et al., EPJE 39, 64 (2016).

[3] K. Drescher et al., Phys. Rev. Lett.  102, 168101 (2009).

[4] M. Enculescu and H. Stark, Phys. Rev. Lett. 107, 058301 (2011); K. Wolff, A. M. Hahn and H. Stark, EPJE 36(4), 1 (2013).

[5] B. ten Hagen et al. Nat. Comm. 5, 4829 (2014).

[6] J. S. Lintuvuori et al., Soft Matter 12, 7959 (2016)

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