Dynamics and Interactions of Quincke Roller Clusters: from Orbits and Flips to Excited States

Abstract: Active matter systems may be characterised by the conversion of energy into active motion, e.g. the self-propulsion of microorganisms. Artificial active colloids form models which exhibit essential properties of more complex biological systems but are amenable to laboratory experiments. While most experimental models consist of spheres, such as Janus particles, active particles of different shapes are less understood. In particular, interactions between such active colloidal "molecules" are largely unexplored. Here, we investigate the motion of active colloidal molecules and the interactions between them. We focus on self-assembled dumbbells and trimers powered by an external electric field. For dumbbells, we observe an activity-dependent behaviour of spinning, circular and orbital motion. Moreover, collisions between dumbbells lead to the hierarchical self-assembly of tetramers and hexamers, both of which form rotational excited states. On the other hand, trimers exhibit a novel type of flipping motion that leads to trajectories reminiscent of a honeycomb lattice.