Developments in the non-newtonian rheology of glass forming systems
An extensive simulation study using homogeneous shear NEMD of a soft-sphere model covering a wide scaling range of density/thermal energy/shear rate is reported. The model results relate to molecular fluids in the glassy region and to dense colloidal suspensions.
All the common non-Newtonian flow phenomena, dilatancy and shear thickening, shear thinning, structural ordering effects, shear flocculation, normal pressure effects, normal diffusivity differences, and associated time-dependent phenomena viscoelasticity, thixotropy, rheopexy and Bingham plasticity (yield stress effects), can be seen to occur in certain density-shear rate-time domains and relate to a characteristic phase diagram. Many of these non-Newtonian effects involve phase transitions and two-phase behaviour and are described by shear perturbations of the static system at thermodynamic equlibrium or metastable equilibrium.
In the glass transition region both the particle pressures and diffusivities are highly anisotropic; under shear flow the fluid may become vitreous in either of the two directions normal to flow. This gives rise to shear-induced kinetic glass-transition-like effects which dominate the rheology at high packing density and high shear rates.
KeywordsShear Rate High Shear Rate Weissenberg Number Dense Suspension Percolation Transition
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