Aggregation Dynamics of Active Spinning Superparamagnetic Particles in Dense Passive Media

Active matter systems exhibit emergent non-equilibrium dynamical phenomenon which is driven by the activity-induced effective interactions between active particles or units. Here we study aggregation dynamics of many active spinning superparamagnetic particles, spinners, embedded in a dense complex 2D colloidal monolayer of passive particles. Utilizing coarse grained Lattice-Boltzmann simulations and experiments we observed that the aggregation of dynamics of active spinning particles resemble classical 2D Cahn-Hilliard coarsening. The spinners will aggregate and display Cahn-Hilliard coarsening when the passive monolayer is dense enough so that it behaves elastically and when the spinner activity exceeds a minimum activity threshold. For the concentrations investigated here the cluster size scaling is independent of the number of active units. We also observe a critical cluster size which maximizes spinner aggregation by minimizing viscous drag through the dense passive monolayer while maximizing the stress applied on the passive medium. In simulations, we can create ternary mixtures of co-rotating, counter-rotating, and passive particles. The aggregation behavior of such mixtures show distinct aggregates of co and counter-rotating spinners.