Collective Dynamics of Active Colloidal Rings

Living systems are spectacular examples of spatiotemporally organized structures, and the collective motion of such entities features a multitude of novel and fascinating phenomena which are not attainable by the equilibrium counterpart^1,2. To understand the coordinated motion of active shape- deforming agents, we computationally study the collective dynamics of active Brownian colloidal rings in 2D^3,4. The combination of excluded-volume interactions, shape deformation, and self- propulsion leads to several distinct dynamic states as a function of activity and packing fraction of rings. Our analyses uncover that the collective dynamics gets enhanced with increasing activity for a fixed packing fraction. Surprisingly, the dynamics displays a non-monotonic behavior with increasing packing fraction, initially, the dynamics slows down and then again becomes faster for a fixed activity due to the activity-induced deformation driven dynamic clustering of the active rings. They form larger clusters at small activities and smaller clusters but larger in numbers at higher activities as well as at higher packing fractions. Though dynamic, the clustering is absent in the passive case. This may also indicate the absence of motility induced phase separation (MIPS)⁵ in case of active rings in 2D.

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