Control of colloidal cohesive states in active chiral fluids

Abstract

Ensembles of suspended spinning particles in liquids form a distinct category of active matter systems known as chiral fluids. Recent experimental instances of dense chiral fluids have comprised of spinning colloidal magnets powered by an external rotating magnetic field. These particles interact through both magnetic and hydrodynamic forces, organizing collectively into circulating clusters characterized by unidirectional edge flows. Here, we externally drive the collective behavior of spinning colloids by leveraging diffusiophoretic interactions among the geometrically anisotropic particles. We show that these nanoscale interfacial flows lead to the formation of bound states between spinning colloids that are stabilized through near-field hydrodynamic and chemical interactions. At a collective level, we demonstrate that added diffusiophoretic interactions cause a loss in structural cohesion of the circulating clusters and promote expansion, while preserving global cluster inter-connectivity. The expanded cluster state is characterized by the formation of a dynamic interconnected network promoted by axi-asymmetric interactions around particles with attractive dipolar interactions dominating along the direction of the magnetic moment. This process is observed to be entirely reversible, offering external control over the emergent dynamics in dense chiral fluids, paving the way for new self-organization routes in chiral fluids and broader forms of active matter. Chiral active systems are composed of spinning constituent particles that self-organize into complex structures through hydrodynamic interactions. The authors develop methods to control these self-organized structures by introducing additional chemical interactions between spinning particles.