Anomalous diffusion, structural relaxation and shear thinning in glassy hard spherefluids

Abstract

The stochastic nonlinear Langevin equation theory of the single-particle dynamics ofglassy hard sphere fluids and suspensions has been applied to address severalissues raised by recent experimental and simulation studies. The theoreticallypredicted degree of non-Fickian behaviour at intermediate times, and the slowstructural relaxation component of the small wavevector incoherent dynamic structurefactor, are compared quantitatively with recent measurements and reveal goodagreement. A roughly power law growth, with a common exponent, of the classic andalternative non-Gaussian parameter amplitudes with mean alpha relaxation timeis predicted, and qualitative similarities with a multi-point susceptibility thatquantifies dynamic heterogeneity effects are noted. The nonlinear rheology version ofthe theory has been quantitatively applied to explain recent measurements ofshear-induced acceleration of the single-particle relaxation time on the local cage scale.The resulting no adjustable parameter calculations are in remarkable agreementwith the experimental observations for the absolute magnitude, volume fractiondependence and fractional power law scaling aspects of the shear thinning phenomenon.