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

TL;DR

This study explores the complex behaviors and interactions of active colloidal dumbbells and trimers under electric fields, revealing new motion patterns and hierarchical self-assembly processes in artificial active matter.

Contribution

It provides the first detailed experimental analysis of shape-dependent active colloid interactions, including orbiting, flipping, and excited states in dumbbell and trimer systems.

Findings

Dumbbells exhibit activity-dependent spinning, orbiting, and collision-induced self-assembly.

Hierarchical self-assembly of tetramers and hexamers with rotational excited states.

Trimers show a novel flipping motion leading to honeycomb-like trajectories.

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.