LINEAR VISCOELASTICITY OF CONCENTRATED HARD-SPHERE DISPERSIONS

The viscoelastic behaviour of model near hard-sphere continuous potent ial r-36 dispersions have been determined using Brownian dynamics simu lations in a hydrodynamics-free approximation. Two methods were used t o obtain the real and imaginary components of the complex shear viscos ity, eta' and eta'', respectively: first, calculating a time correlati on function under no-shear conditions using a Green-Kubo formula; seco ndly applying finite-strain amplitude oscillatory shear cycles in the linear response limit to the contents of the BD cell. We find that the normalized stress autocorrelation function can be approximated very w ell by a two-parameter stretched exponential over the complete volume fraction range. The state dependence of the derived spectrum of relaxa tion times is determined. As for experimental systems the complex visc osity scales with a 'longest' relaxation time, in dimensionless form, D0tau1/a2, where a is the radius of the particle and D0 is the self-di ffusion coefficient in the zero-density limit. Also in the intermediat e-frequency regime 40 < a2omega/D0 < 400 we find that both the real an d imaginary parts of the complex shear viscosity decay as approximatel y omega-1/2 in agreement with experiment and theory. The Newtonian vis cosities obtained using eta'(omega --> 0) agree well with the predicti ons of the Krieger-Dougherty equations. The product of the Newtonian v iscosity and the long-time self-diffusion coefficient increases linear ly with volume fraction for most of the fluid range.