Glassy behavior in collections of frictional particles

Surface roughness is a common feature of particles in colloidal liquids, vibrated grains, geomechanical flows, and molecular liquids. While the static structural properties of jammed packings of frictional particles are well understood, the impact of surface roughness on their dynamic properties has not been described quantitatively. We carry out discrete element method simulations of dense liquids composed of particles with tunable surface roughness in 2D using the geometric asperity model. We calculate the timescales for the structural relaxation of the translational and rotational degrees of freedom. From the rapid growth of the respective structural relaxation times, we estimate the packing fractions at which these timescales diverge as a function of the surface roughness. In line with existing experimental results, we find that the translational motion generally freezes out at lower packing fractions compared to the rotational motion, resulting in a rotator regime at intermediate packing fractions.