LMP Seminar

LMP Seminar: Microswimmers: From collective motion under gravity to smart navigation

  • Date: Feb 25, 2020
  • Time: 14:00 - 15:30
  • Speaker: Prof. Dr. Holger Stark
  • Institut für Theoretische Physik, Technische Universität Berlin
  • Location: Max-Planck-Institut für Dynamik und Selbstorganisation (MPIDS)
  • Room: SR 0.79, Am Faßberg 17, Göttingen
  • Host: MPIDS / LMP
  • Contact: golestanian-office@ds.mpg.de
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. Microswimmers interact by their self-generated flow fields and thereby show appealing dynamic patterns as a consequence of the non-equilibrium. A new development in the field is how microswimmers learn to navigate in a complex environment.

Using multi-particle collision dynamics, we simulate squirmer model swimmers and study how they behave under gravity. We find a variety of different phenomena depending on the ratio of swimming to bulk sedimentation velocity. Single squirmers can float or slide above the bottom wall. A collection of squirmers exhibits a very dynamic sedimentation profile with dense layering at the bottom and exponential decay towards the top, where large-scale convective flow arises. When they become bottom-heavy, they exhibit inverted sedimentation, convective rolls and plumes reminiscent of patterns seen in bioconvection, and also spawning clusters. Finally, a single layer of squirmers under strong gravity shows different collective dynamics including “hydrodynamic Wigner fluids” and swarming.

At the end I discuss optimal steering of microswimmers in order to optimize their travel time in a potential landscape and how smart microswimmers with some some internal information processing machinery can use reinforcement learning to perform this task autonomously.
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