Unjamming and reentrant jamming of dense systems in the extreme active limit*

Simulations of dense, athermal assemblies of self-propelled soft particles with infinite persistence time display intriguing mechanical properties as a function of the strength of the active propulsion force and the packing fraction of the system. Applying active propulsion to an initial, passively-jammed state results in unjamming and subsequent flow of the system. We find that there is a threshold force above which the system remains fluid indefinitely but below which the system experiences reentrant jamming, and that this threshold force increases as the density of the system is increased. Interestingly, we find that the average coordination numbers of both fluid and re-jammed states under active propulsion are larger than those of the passively-jammed states for a given packing fraction.

We analyze various network properties over time series of such systems to illuminate the structural differences between packings formed with passive and active constituents, as well as understand the underlying mechanisms of reentrant jamming in this extreme active limit. We also investigate the effect of the magnitude of the active force on jamming behavior.