Non-Eqilibrium Dynamics of Anisotropic Particles Open Up Novel Actuation Strategies

The persistent fascination in locomotion at the mesoscale arises from the time reversibility of motion patterns in overdamped systems. To study the principles of locomotion via cyclic patterns, dispersed magnetic particles and subsequent self-assembled clusters are versatile systems. They rotate via alignment in a time-dependent field, which can be used for controlled actuation. The challenge is to transform field-driven rotation into an effective translation. To date, most examples of magnetic actuation (and other cyclic movers) exploit hydrodynamic coupling between rotation and translation. Here, we present a novel locomotion strategy that exploits internal interactions in multi-component objects. We study self-assembled clusters of magnetic particles that exhibit an off-center dipole moment. By theoretical modeling and in experiments with magnetic Janus particles, we demonstrate that the interaction between such anisotropic particles in the cluster breaks time reversibility. Using the same experimental particle system, we realize various modes of motion - ranging from stirrers to steerable movers with helical or directed path - depending on the magnetic configuration of a cluster.