Rheological studies on dispersions of uniform colloidal spheres: II. Dispersions in nonaqueous media

Abstract

The study of aqueous dispersions of uniform colloidal spheres (I in this series) was extended to nonaqueous dispersions. These were prepared from aqueous crosslinked polystyrene latexes by two-stage solvent exchange dialysis, with methanol as intermediate solvent. Non-Newtonian relative viscosities η r were measured in benzyl alcohol and m-cresol at volume fractions φ up to 0.50, for particle diameters from 0.15 to 0.43 μ. A single rheological equation η r = f( φ, τ r ) was found to apply to nonaqueous dispersions in both media, and to aqueous dispersions the interparticle coulombic and van der Waals' forces of which are negligible. Here τ r = τa 3 kT is a reduced shear stress, in which r is the actual shear stress, a the particle radius, k Boltzmann's constant, and T the absolute temperature. The experimentally observed functional form of f was well fitted by Krieger and Dougherty's (1) modification of the Williamson equation, using their expression for the dependence on concentration of the high-and low-shear limiting viscosities.