(383c) Non-Reciprocal Interactions between Active and Passive Colloids

Non-reciprocal interactions are common among living organisms, where the symmetry of Newton’s third law of action-reaction is broken. Despite its ubiquity in the self-organization of living matter, non-reciprocity in the assembly of synthetic building blocks remains unexplored. Here, we form non-equilibrium assemblies of motile active particles and Brownian passive particles by overlapping interactions with directed self-propulsion. We use a dispersion containing isotropic passive and metal-patched active particles as models to experimentally demonstrate the assembly process. Application of an external alternating current (ac) electric field generates concurrent dipolar and hydrodynamic forces between the particles which we evaluate using high-speed microscopy. Our findings reveal the critical roles of particle anisotropy, relative particle orientation, and the field characteristics on the metastable assembly of clusters and their motility. The study establishes the principle of leveraging non-reciprocity in active matter as a tool for guided assembly of structures with long-term metastability and non-equilibrium dynamics.