Stiff liquid marbles, soft liquid marbles, many liquid marbles

Ferrofluid liquid marbles, or ferromarbles, are magnetically responsive drops encased in a non-wetting powder. This powder shells allows the drops to move on a surface without any liquid-surface contact. In this talk, we demonstrate how to actuate a ferromarble with a rotational magnetic field, and show that these marbles can move in three distinct ways: rocking, rolling, and hopping. We model the rolling motion of a rigid ferromarble (where its shape remains undeformed) as a rolling ellipsoid, and predict the transition from rolling to hopping. As the marble becomes more and more deformable, the model fails to capture its motion. However, soft ferromarbles exhibit new behaviors which enable new functionalities. We additionally study the collective behavior of our ferromarbles, and show that when they interact, they can work together to accomplish tasks beyond the ability of a single ferromarble.