Spinning ferrofluid microscopic droplets

E. Janiaud^1,2 - F. Elias¹ - J.-C. Bacri^1,2 - V. Cabuil³ - R. Perzynski¹

¹ Laboratoire des Milieux D?sordonnés et Hétérogènes, Universit? Paris 6, case 78, 4 place Jussieu, 75252 Paris cedex 05, France
² Universit? Paris 7, Unit? de Formation et de Recherche de Physique, case 70.08, 2 place Jussieu, 75251 Paris cedex 05, France
³ Laboratoire des Liquides Ioniques et des Interfaces Chag?s, Universit? Paris 6, case 0063, 4 place Jussieu, 75252 Paris cedex 05, France

Abstract
We investigate experimentally the behaviour of microscopic ferrofluid droplets under the effect of a rotating external magnetic field. Depending on the system control parameters, the drops adopt fascinating shapes, like starfish, rod-like or pancake shapes, co-rotating with the external field, but also creeping snakes, swirling loops and rings. We describe these structures and classify them in a phase diagram. With simple arguments, we discuss the droplet dynamics and morphology in each phase. Fig. 11, Refs. 22.