VISCOELASTICITY OF CONCENTRATED DISPERSIONS

A statistical dynamic theory is presented to describe the effects of relaxation of the microstructure, frequency, and volume fraction (phi) on the complex shear viscosity of concentrated colloidal dispersions. On the basis of a fluid lattice model, the relationship between the memory function and relaxation spectrum is derived, and the limits of shear viscosity at low and high frequencies are determined. In addition to the pair interactions, the many body interactions at higher phi are included in the analysis. We calculate the viscoelastic behavior of disperse systems ranging from dilute, to semidilute, to concentrated dispersions. The theory reveals that the viscoelastic effect is negligible in dilute and semidilute suspensions, but is dominant in concentrated dispersions.