Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 38: Computational Physics of Soft Matter I

CPP 38.10: Talk

Wednesday, March 18, 2015, 12:30–12:45, C 264

Collective Motion of Spherical Microswimmers in a Quasi-2D Geometry — •Maurice Maurer, Andreas Zöttl, and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, D-10623 Berlin

The collective motion of microorganisms and artificial microswimmers exhibits interesting dynamic structure formation on length scales much larger than the size of an individual particle.

Experiments with self-propelled colloids in a quasi-2D geometry show dynamic clustering behavior and phase separation due to hydrodynamic interactions. Motivated by these experiments, we numerically investigate the collective behavior of spherical model swimmers [1]. Using domain decomposition and the message passing interface (MPI), we developed a highly scalable parallel version of multi-particle collision dynamics - a particle-based solver of the Navier-Stokes equations.

Here we study squirmers, which mimic the propulsion mechanism of active emulsion droplets and ciliated microorganisms like volvox algae by a surface velocity field. Furthermore, we simulate active Janus particles, the surfaces of which are only partly active. For low densities the colloids show gas-like behavior while at high densities crystalline structures emerge. Only for neutral squirmers and Janus particles almost fully covered by the active region, we observe that structural order increases steeply at a critical density, indicating a non-equilibrium phase transition. Finally, we also show how system size and reducing the colloidal degrees of freedom influence our findings.

[1] A. Zöttl and H. Stark, Phys. Rev. Lett. 112, 118101 (2014).