VISCOELASTIC BEHAVIOR OF CONCENTRATED SPHERICAL SUSPENSIONS

Experimental results on the linear viscoelastic behavior of concentrated suspensions are presented. The materials studies were prepared by dispersing submicron silica spheres at volume fractions phi ranging from 0.3 to 0.6, in a highly viscous liquid. The response to oscillatory shearing was determined over a wide range of frequency, omega. The zero frequency viscosity eta0 and the limiting high-frequency viscosity eta(infinity)' for all particle radii studied were essentially identical to results previously obtained for suspensions having hard sphere interactions. In this range of concentrations, the frequency dependence of the dynamic moduli, G' and G'' - omegaeta(infinity)', appears to be described by universal functions of omegatau(w) where tau(w) is the mean longest relaxation time proportional to a characteristic (Peclet) time defined as tau(p) = a2/6D(s)(phi). Herein a denotes the particle radius and D(s)(phi) is a phi dependent short-time self-diffusion constant. We also found that at sufficiently high frequencies, G' has a plateau, G(infinity), that is given by kT/a3 times a function of phi.