title: Self-propulsion of pure water droplets by spontaneous Marangoni-stress-driven motion.
abstract: We report spontaneous motion in a fully biocompatible system consisting of pure water droplets in an oil-surfactant medium of squalane and monoolein. Water from the droplet is solubilized by the reverse micellar solution, creating a concentration gradient of swollen reverse micelles around each droplet. The strong advection and weak diffusion conditions allow for the first experimental realization of spontaneous motion in a system of isotropic particles at sufficiently large Péclet number according to a straightforward generalization of a recently proposed mechanism [S. Michelin, E. Lauga, and D. Bartolo, Phys. Fluids 25, 061701 (2013); S. Michelin and E. Lauga, J. Fluid Mech. 747, 572 (2014)]. Experiments with a highly concentrated solution of salt instead of water, and tetradecane instead of squalane, confirm the above mechanism. The present swimming droplets are able to carry external bodies such as large colloids, salt crystals, and even cells.
authors.affiliation: EC2M, UMR Gulliver 7083 CNRS, ESPCI ParisTech, PSL Research University, 10 rue Vauquelin, 75005 Paris, France.
authors.forename: Ziane
authors.initials: Z
authors.lastname: Izri
authors.affiliation: EC2M, UMR Gulliver 7083 CNRS, ESPCI ParisTech, PSL Research University, 10 rue Vauquelin, 75005 Paris, France.
authors.forename: Marjolein N
authors.initials: MN
authors.lastname: van der Linden
authors.affiliation: LadHyX, Département de Mécanique, Ecole Polytechnique, CNRS, 91128 Palaiseau, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Michelin
authors.affiliation: EC2M, UMR Gulliver 7083 CNRS, ESPCI ParisTech, PSL Research University, 10 rue Vauquelin, 75005 Paris, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Dauchot