Abstract
Phys. Rev. Research 2, 013260 (2020) We explore phase separation and kinetic arrest in a model active colloidal
system consisting of self-propelled, hard-core particles with nonconvex 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 nonconvex 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
nonequilibrium 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. The two types of dynamically
arrested states, glasses and gels, are distinguished by the appearance of
density heterogenities in the latter. In the infinitely persistent limit, we
show that a coarse-grained model based on the asymmetric exclusion process
quantitatively predicts the density profiles of the gel states. The predictions
remain qualitatively valid for finite rotation rates. Using these results, we
classify the activity-driven phases and identify the boundaries separating
them.