High frequency shear modulus of polymerically stabilized colloids

Rheological measurements on concentrated colloidal dispersions at high frequencies probe interactions at small separations and provide the most direct link between the shear modulus and the pair potential. For colloids stabilized with a grafted polymer layer, others have extracted the pair potential from measurements of the high frequency shear modulus via a molecular theory, which does not account for hydrodynamic interactions. Here we apply a nonequilibrium theory that includes the repulsion between polymer layers and its effect on the equilibrium structure, while accounting for flow of the suspending fluid within the layer in evaluation of the hydrodynamics. Predictions with a simple approximation for the hydrodynamic interactions, which interpolates between the lubrication and far field limits, are compared with the molecular theory. We also demonstrate qualitative agreement with experimental data and assess over what range of effective volume fractions neglect of hydrodynamic interactions permits data to be inverted to obtain an interaction potential. (C) 1998 The Society of Rheology. [S0148-6055(98)00402-7].