Mixing and unmixing induced by active camphor particles

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