Title: Magnetocapillary self-assemblies: locomotion and micromanipulation along a liquid interface,
Abstract: This paper presents an overview and discussion of magnetocapillary
self-assemblies. New results are presented, in particular concerning the
possible development of future applications. These self-organizing structures
possess the notable ability to move along an interface when powered by an
oscillatory, uniform magnetic field. The system is constructed as follows. Soft
magnetic particles are placed on a liquid interface, and submitted to a
magnetic induction field. An attractive force due to the curvature of the
interface around the particles competes with an interaction between magnetic
dipoles. Ordered structures can spontaneously emerge from these conditions.
Furthermore, time-dependent magnetic fields can produce a wide range of dynamic
behaviours, including non-time-reversible deformation sequences that produce
translational motion at low Reynolds number. In other words, due to a
spontaneous breaking of time-reversal symmetry, the assembly can turn into a
surface microswimmer. Trajectories have been shown to be precisely
controllable. As a consequence, this system offers a way to produce microrobots
able to perform different tasks. This is illustrated in this paper by the
capture, transport and release of a floating cargo, and the controlled mixing
of fluids at low Reynolds number.