Interaction‐Driven Assembly Pathways in Heterogeneous Active Microrobotic Systems

ABSTRACT

Active microrobotic swarms are promising platforms for programmable matter, yet how competing interactions govern self‐organization in heterogeneous active systems remains unclear. Here, we investigate interaction‐controlled self‐assembly in heterogeneous populations of light‐powered α‐Fe ₂ O ₃ /Au microrobots with distinct morphologies, magnetic responses, and photocatalytic activities. We show that magnetic dipole–dipole interactions drive a reversible colloidal polymerization process in which individual microrobots behave as active monomers that assemble into dynamic chain‐like architectures. Quantitative analysis of pairwise trajectories enables direct extraction of magnetic dipole moments from active dynamics, in excellent agreement with independent magnetometry measurements, establishing a general strategy to probe interparticle interactions in active matter. Upon light activation, the emergence of phoretic interactions competes with magnetic attraction, destabilizing colloidal polymers and promoting a transition toward disordered clustered states. In heterogeneous populations, the imbalance between magnetic and phoretic interactions generates non‐random assembly pathways, where cubic microrobots preferentially act as nucleation centers that recruit peanut‐shaped microrobots into hybrid aggregates through a colloidal copolymerization mechanism. By tuning the relative strength of competing interactions, the assembly pathway can be selectively programmed, enabling controlled transitions between dispersed, polymeric, and clustered states. Beyond elucidating assembly rules of heterogeneous active matter, these mechanisms enable the efficient phoretic trapping of dispersed nano/microplastics.