Regensburg 2022 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 50: Active Matter 5 (joint session DY/BP/CPP)
DY 50.6: Vortrag
Freitag, 9. September 2022, 11:15–11:30, H18
Odd viscosity and active turbulence of hydrodynamic microrotors — •Joscha Mecke1, Yongxiang Gao2, Dirk G.A.L. Aarts3, Alberto Medina1, Gerhard Gompper1, and Marisol Ripoll1 — 1Institute of Biological Information Processing, Forschungszentrum Jülich, Germany — 2Institute for Advanced Study, Shenzhen University, China — 3Department of Chemistry, University of Oxford, UK
Suspensions of rod-like silica colloids with a ferromagnetic head are considered in a rotating magnetic field applied parallel to a substrate. The magnetic moment is oriented perpendicular to the rod axis which implies a non-equilibrium vertical orientation to the substrate and synchronous spinning in the rotating field. We combine experiments and simulations to study the collective properties of these rotors. The hydrodynamic flows generated by the colloid rotations induce a cascade of translational motions in the neighbouring colloids. Thus, the rotors can be regarded as active matter with transport coefficients varying with local configuration and thus rotor density. The competition between hydrodynamic and steric interactions renders the translational dynamics non-monotonous in rotor density. The ensemble dynamics shows the emergence of eddies of various sizes reminiscent of turbulence. Furthermore, the rotor fluid is a realisation of a chiral active fluid with odd viscosity, that manifests itself in stress forces orthogonal to the direction of shear. In vortex flow, the stress acts like an effective pressure leading to density-vorticity correlations. Our experimental and numerical results are found to be in agreement.