Mixing and unmixing induced by active camphor particles

Clément Gouiller, Florence Raynal, Laurent Maquet, Mickaël Bourgoin, Cécile Cottin-Bizonne, Romain Volk, and Christophe Ybert
Phys. Rev. Fluids 6, 014501 – Published 27 January 2021

Abstract

In this experimental study, we report on the mixing properties of interfacial colloidal floaters (glass bubbles) by chemical and hydrodynamical currents generated by self-propelled camphor disks swimming at the air-water interface. Despite reaching a statistically stationary state for the glass bubbles distribution, those floaters always remain only partially mixed. This intermediate state results from a competition between (i) the mixing induced by the disordered motion of many camphor swimmers and (ii) the unmixing promoted by the chemical cloud attached to each individual self-propelled disk. Mixing/unmixing is characterized globally using the standard deviation of concentration and spectra, but also more locally by averaging the concentration field around a swimmer. Besides the demixing process, the system develops a “turbulentlike” concentration spectra, with a large-scale region, an inertial regime, and a Batchelor region. We show that unmixing is due to the Marangoni flow around the camphor swimmers, and is associated to compressible effects.

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  • Received 13 September 2020
  • Accepted 4 January 2021

DOI:https://doi.org/10.1103/PhysRevFluids.6.014501

©2021 American Physical Society

Physics Subject Headings (PhySH)

Fluid DynamicsCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Clément Gouiller1, Florence Raynal2, Laurent Maquet1, Mickaël Bourgoin3, Cécile Cottin-Bizonne1, Romain Volk3, and Christophe Ybert1

  • 1ILM, Univ Lyon, Univ Lyon 1, CNRS, F-69622 Villeurbanne Cedex, France
  • 2LMFA, Univ Lyon, Centrale Lyon, INSA Lyon, Univ Lyon 1, CNRS, F-69134 Écully, France
  • 3Laboratoire de Physique, Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, F-69342 Lyon, France

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Vol. 6, Iss. 1 — January 2021

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