Prof. Dr. Holger Stark (TU Berlin): Insights into dry and wet active matter

Active matter consists of constituents that consume energy in order to self-propel. It can be found in different environments and, in particular, in the microscopic world of micro-organisms and artificial microswimmers, where inertia is negligible. The talk introduces different features of active matter. In dry active matter the frictional coupling to the surrounding is described by a friction coefficient. We use the resulting system of active Brownian particles to discuss active Szilard engines [1] and perform microrheology of an active bath in order to explore its dynamic properties [2].
Microswimmers initiate hydrodynamic flow fields in their aequous environment through which they interact. For this wet active matter, we performed numerical simulations with the method for multi-particle collision dynamics, where we explore the collective dynamics of elongated model microswimmers [3]. Depending on the swimmer type of neutral rods and pusher/pullers, they exhibit different emergent collective dynamics including active turbulence.
[1] P. Malgaretti and H. Stark, Szilard engines and information-based work extraction for active systems, arXiv:2203.13075 [cond-mat.soft].
[2] M. Knezevic, L.E. Aviles Podgurski, and H. Stark, Oscillatory active microrheology of active suspensions, Sci. Rep. 11, 22706 (2021).
[3] A.W. Zantop and H. Stark, Emergent collective dynamics of pusher and puller squirmer rods: Swarming, clustering, and turbulence, Soft Matter 18, 6179 (2022).