BPCPPDYSOE21 – scientific programme
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BP: Fachverband Biologische Physik
BP 10: Posters DY - Fluid Physics, Active Matter, Complex Fluids, Soft Matter and Glasses (joint session DY/BP)
BP 10.19: Poster
Monday, March 22, 2021, 14:00–16:30, DYp
Bistable vortices formed by active particles with retarded interactions - Experiment — •Xiangzun Wang1, Pin-Chuan Chen2, Viktor Holubec2,3, Klaus Kroy2, and Frank Cichos1 — 1Molecular Nanophotonics Group, Peter Debye Institute for Soft Matter Physics, Universität Leipzig, 04103 Leipzig, Germany — 2Institute for Theoretical Physics, Universität Leipzig, 04103 Leipzig, Germany — 3Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, 18000 Prague, Czech Republic
Rotating formations of living species are frequently observed in nature from bacterial systems and insects to larger animals like fish or birds. The ubiquity of this behavior suggests universal underlying principles. One could be related to inevitable delays caused by sensimotoric feedback. We explore experimentally the influence of a delayed interaction between individual self-thermophoretic microswimmers on their collective behaviour. Our microswimmers are gold nanoparticle decorated melamine resin colloids, which are propelled by self-thermophoresis due to a local heating of the gold nanoparticles with a focused laser. Using a feedback algorithm we are able to introduce time-delayed virtual interactions with other particles or targets. We find for a single swimmer attracted to an immobilized particle, a transition from a diffusive to a rotating state with two possible rotation directions. This behavior is captured by a simple theoretical model (see companion contribution). This bifurcation is also observed in ensembles of multiple particles where the rotational phase of the ensemble is synchronized by particle collisions.