title: Ratio of effective temperature to pressure controls the mobility of sheared hard spheres.
abstract: Using molecular dynamics simulations, we calculate fluctuations and responses for steadily sheared hard spheres over a wide range of packing fractions φ and shear strain rates γ[over ̇], using two different methods to dissipate energy. To a good approximation, shear stress and density fluctuations are related to their associated response functions by a single effective temperature T(eff) that is equal to or larger than the kinetic temperature T(kin). We find a crossover in the relationship between the relaxation time τ and the the nondimensionalized effective temperature T(eff)/pσ(3), where p is the pressure and σ is the sphere diameter. In the solid response regime, the behavior at a fixed packing fraction satisfies τ ̇γ∝exp(-cpσ(3)/T(eff)), where c depends weakly on φ, suggesting that the average local yield strain is controlled by the effective temperature in a way that is consistent with shear transformation zone theory. In the fluid response regime, the relaxation time depends on T(eff)/pσ(3) as it depends on T(kin)/pσ(3) in equilibrium. This regime includes both near-equilibrium conditions where T(eff)≃T(kin) and far-from-equilibrium conditions where T(eff)≠T(kin). We discuss the implications of our results for systems with soft repulsive interactions.
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Haxton
mesh_terms: D003102:Colloids / Q000737:chemistry*; D003198:Computer Simulation; D004058:Diffusion; D008956:Models, Chemical; D008958:Models, Molecular; D009038:Motion; D054118:Nanospheres / Q000737:chemistry* / Q000648:ultrastructure*; D011312:Pressure; D013696:Temperature
chemical_list: D003102:Colloids