Effect of long-range repulsive forces on the viscosity of concentrated latices: comparison of experimental data with an effective hard-sphere model

Abstract

The viscosity of concentrated, aqueous latices is enhanced considerably under conditions where the mean particle separation is comparable to the Debye length characterising the range of the electrostatic, interparticle repulsion. A simple interpretation of this behaviour is provided by the idea that the particles have an enhanced excluded volume as a consequence of the long-range repulsion. Three sets of data taken from the literature are compared with a simple model which relies on this idea together with existing correlations for the viscosity of hard-sphere dispersions. The model is shown to reproduce the broad features of two of the sets of data rather well. The correspondence with the third is less satisfactory and possible reasons for this are discussed. The model is also compared with data obtained for non-aqueous latices by Frith, illustrating the effect of an extended steric barrier. The predictions in this case are very sensitive to the assumed form of the steric potential by virtue of the steepness of this. The model correlates the data extremely well nevertheless.