Arresting Active Spinning Particle Coarsening in Passive Media via Actuation Protocols

Active matter systems are unique in the rich non-equilibrium dynamical behavior that emerges such as flocking, lanning, swarming, and vortexting. Such emergent behavior has been previously observed in complex hybrid active-inactive systems with in-plane rotating magnetic particles; where active particle attraction is induced by the activity of the particles and the mechanical properties of the passive media. When continuously actuated these active particles will aggregate and coarsen. We present a novel approach which allows the control of coarsening behavior and resultant characteristic domain size via modulation of the activity actuation protocol. By tuning the frequency at which the rotational direction of the active spinning magnetic particles is changed, either clockwise or counter-clockwise, the system can exhibit microphase separation behavior distinct from the macrophase separation of active and passive particles. Changing the rotational direction is effectively equivalent to reversing the torque and unloading the stress in the system. This limits the ability of active particle clusters to attract, can arrest the coarsening behavior, and decrease the characteristic domain size. Thus, allowing control of the structure of these hybrid active-inactive systems.