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Center for Nonlinear Studies |
We explore phase separation and kinetic arrest in a model active colloidal system consisting of self-propelled, hard-core particles with non-convex shapes. The passive limit of the model, namely cross-shaped particles on a square lattice, exhibits a first order transition from a fluid phase to a solid phase with increasing density. Quenches into the two-phase coexistence region exhibit an aging regime. The non-convex shape of the particles eases jamming in the passive system and leads to strong inhibition of rotations of the active particles. Using numerical simulations and analytical modeling, we quantify the non-equilibrium phase behavior as a function of density and activity. If we view activity as the analog of attraction strength, the phase diagram exhibits strong similarities to that of attractive colloids, exhibiting both aging, glassy states and gel-like arrested states. We present a hydrodynamic theory of the non-equilibrium phases, which is exact in the limit of infinite persistence time of the self-propulsion direction. A remarkable feature of the theory is its ability to predict the length scales that characterize the morphology of the arrested, gel states, which agree well with our numerical simulations in the infinitely persistent limit. The predictions remain qualitatively valid for finite persistence times.
Host: Cristiano Nisoli