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We theoretically study the effect of external deformation on activatedstructural relaxation and elementary aspects of the nonlinear mechanicalresponse of glassy hard sphere fluids in the context of the nonequilibriumversion of the Elastically Collective Nonlinear Langevin Equation (ECNLE)theory. ECNLE theory describes activated relaxation as a coupled local-nonlocalevent involving local caging and longer range collective elasticity, with thelatter becoming more important with increasing packing fraction. The centralnew question is how this physical picture, and the relative importance ofcaging versus elasticity physics, depends on external stress, strain and shearrate. Theoretical predictions are presented for deformation induced enhancementof mobility, onset of relaxation speed up at remarkably low values of stress,strain or dimensionless shear rate, thinning of the structural relaxation timeand viscosity with apparent power law exponents, a non-vanishing activationbarrier in the shear thinning regime, a Herschel-Bulkley form of ratedependence of the steady state shear stress, exponential growth of dynamicyield stresses with packing fraction, and reduced dynamic fragility andheterogeneity under deformation. The results are contrasted with experimentsand simulations, and qualitative or better agreement is found. An overarchingconclusion is that deformation strongly reduces the importance of longer rangecollective elastic effects for most, but not all, physical questions, withstress-dependent dynamic heterogeneity phenomena being qualitatively sensitiveto collective elasticity. Overall, nonlinear rheology is a more local cagescale problem than quiescent relaxation, albeit with deformation-modifiedactivated processes still important.

journal of chemical physics online/the journal of chemical physics/journal of chemical physics

The Role of Collective Elasticity on Activated Structural Relaxation,  Yielding and Steady State Flow in Hard Sphere Fluids and Colloidal  Suspensions Under Strong Deformation