Strongly protocol-dependent jamming of frictional cohesive grains

Using molecular dynamics simulations, we examine how the structure of marginally jammed systems of grains with varying degrees of friction and cohesion depends on the protocol with which these systems are prepared.  We compare results for systems with four types of intergrain interactions: (1) no friction or cohesion, (2) friction but no cohesion, (3) cohesion but no friction, and (4) both cohesion and friction.  The final packing fractions (φ_J) of systems prepared by beginning with a dilute state and then ramping the pressure (to a fixed, small P_final) range from ~.64 for system (1) to ~.35 for system (4).  Critically, while these φ_J are almost independent of the pressure ramp rate R_P for systems (1-3), φ_J in system (4) decreases substantially with decreasing R_P .  We show that this effect arises from friction slowing down the rearrangement dynamics of weakly-cohesively-bound clusters that form prior to jamming, which in turn leads to the formation of stable voids in the final jammed solids whose size increases with decreasing R_P.