Magnetocapillary self-assemblies: locomotion and micromanipulation along a liquid interface

TL;DR

This paper reviews magnetocapillary self-assemblies that can move and manipulate objects on liquid interfaces using magnetic fields, highlighting their potential for microrobotics and fluid control at microscopic scales.

Contribution

It introduces new experimental results on the dynamic behaviors and controllability of magnetocapillary self-assemblies for micromanipulation.

Findings

Self-assemblies can spontaneously form ordered structures.

Dynamic magnetic fields induce controllable translational motion.

Assemblies can perform tasks like cargo transport and fluid mixing.

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.