VISCOELASTIC BEHAVIOR OF CONCENTRATED SPHERICAL SUSPENSIONS

Experimental results on the linear viscoelastic behavior of concentrat ed suspensions are presented. The materials studies were prepared by d ispersing submicron silica spheres at volume fractions phi ranging fro m 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 zer o frequency viscosity eta0 and the limiting high-frequency viscosity e ta(infinity)' for all particle radii studied were essentially identica l to results previously obtained for suspensions having hard sphere in teractions. 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 m ean 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 cons tant. We also found that at sufficiently high frequencies, G' has a pl ateau, G(infinity), that is given by kT/a3 times a function of phi.