Manipulation of Cohesive States in Colloidal Chiral Fluids

Chiral fluids composed of spinning colloidal particles are an emerging topic in active matter systems, exhibiting distinct self-organizing and emergent behaviors. A typical synthetic chiral fluid involves rotating colloidal magnets, where magnetic and hydrodynamic forces between particles give rise to circulating clusters with unidirectional edge flows. In this work, we incorporate additional diffusiophoretic interactions to externally influence the collective behavior of spinning colloids. The system is composed of ellipsoidal hematite microparticles suspended in H2O2. Under an external rotating magnetic field, phase separation into circulating clusters, a characteristic of chiral fluids, is observed. However, UV light exposure triggers the decomposition of H2O2 on the hematite surface, introducing diffusiophoretic forces that disrupt the structural cohesion of the clusters. This chemical interaction expands the circulating clusters to a limited degree while preserving their overall interconnectivity. The expansion observed is fully reversible, with clusters reverting to their original cohesive state once UV illumination ceases. Incorporating chemically-driven interactions into chiral fluids opens up new possibilities for self-organization, both in these systems and in broader active colloidal systems.