Dresden 2017 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 45: Microswimmers (joint session BP/DY)
DY 45.1: 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].
[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)