LINEAR VISCOELASTIC BEHAVIOR OF AGGREGATED COLLOIDAL DISPERSIONS

The viscoelastic behavior of a depletion-flocculated dispersion of col loidal spheres is investigated at different volume fractions of the sp heres, using a controlled stress and a dynamic rheometer. Combining th e results, we obtain the storage G' and loss G '' moduli over a freque ncy range of 0.02<omega<200 rad/s. The measured G' gradually increases with increasing frequency, while G '' almost remains constant, indica ting a broad spectrum of relaxation times. To describe and explain the observed behavior of the moduli as a function of frequency and volume fraction in terms of microscopic parameters, a microrheological model based on the fractal concept is proposed. Comparing experimental resu lts with model calculations, we find a good agreement between the two, with physically plausible parameter values.