Magnetocapillary Swimmers: a Self-Assembled System to Study Locomotion, Transport Cargoes and Mix Fluids.*

Because of capillary forces, small objects floating on a liquid tend to aggregate. Combined with a magnetic induction field, this effect can be used to assemble soft-ferromagnetic spheres into tunable structures. When they are exposed to oscillating magnetic fields, these assemblies spontaneously move along the interface. This is due to a breaking of time-reversal symmetry in their adopted shapes. These structures are conceptually simple, chemically inert, and spontaneously form without direct intervention or complex microfabrication process. Therefore, they offer a very wide range of possibilities, from the experimental study of the basic physical principles of locomotion, to the development of complex tasks such as cargo transport and fluid mixing.