(61f) Non-Reciprocal Interactions between Active and Passive Colloids in Ac Electric Fields

Living organisms often exhibit non-reciprocal interactions that trigger unique forms of self-organization. The combination of reciprocal and non-reciprocal interactions between synthetic building blocks remains largely unexplored. Here, we form out-of-equilibrium assemblies of non-motile isotropic passive and metal-patched motile active particles by overlapping bulk interactions with directed self-propulsion. An external alternating current (ac) electric field generates concurrent dipolar and induced-charge electrophoretic forces5 between the particles which we evaluate using microscopy. The interaction force measurements allow us to determine the degree of reciprocity in interactions, which is tunable by designing the active particle and its trajectory. While linearly-propelled active particles evade assembly with passive particles, helically propelled active particles form active-passive clusters with dynamic reconfiguration and long-lived metastability. Large clusters display programmable stability and reconfigurability by controlling the fraction of active particles. The study establishes principles of integrating reciprocal and non-reciprocal interactions in guided colloidal assembly of reconfigurable metastable structures.