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Active motion of biological and artificial microswimmers is relevant in the real world, in microfluidics, and biological applications but also poses fundamental questions in non-equi- librium statistical physics. Mechanisms of single microswimmers either designed by nature or in the lab need to be understood and a detailed modeling of microorganisms helps to explore their complex cell design and their behavior. It also motivates biomimetic approaches. The emergent collective motion of microswimmers generates appealing dynamic patterns as a consequence of the non-equilibrium.
In this talk I review some of our work modeling biological microswimmers such as E. coli and the African trypanosome, the causative agent of the sleeping sickness, but also explain the mechanism how an active emulsion droplet moves. Using simpler model microswimmers called squirmers, I will demonstrate the richness of their emerging collective behavior. Hydrodynamic simulations with multi-particle collision dynamics show exponential sedimentation profiles under gravity with superimposed large-scale convection. Sedimentation becomes inverted for bottom-heavy microswimmers reminiscent of algae and also convective plumes and spawning clusters occur. Finally, self-phoretic active colloids are able to sense their environment and perform chemotactic motion mimicking a mechanism important in bacterial systems.
Prof. Holger Stark (Institut für Theoretische Physik, Technische Universität Berlin)
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