Stability of Concentrated Colloids: The Controlling Parameters.

A theoretical framework has been developed for predicting and explaining the colloidal stability of concentrated dispersions. It is based on multiparticle interaction models for the electrical double layer (EDL) and van der Waals (vdW) interactions. An asymmetric cell model is used for estimating EDL interaction energy from the solution of the Poisson-Boltzmann equation. The unretarded vdW interaction energy is calculated via Hamaker's method, adopting the pairwise-additivity approach. Various dispersion parameters are investigated for their effects on the flocculation energy barrier. These include volume fraction, size, and surface potential of particles, as well as the ionic strength of the dispersing medium. The results show several new trends borne out of multiparticle interaction effects. A maximum in the energy barrier is predicted as a function of salinity, contrasting the monotonic dependence from the classical DLVO theory. This salinity dependence of the energy barrier provides the first comprehensive explanation of reported experimental findings on stability and rheological properties of concentrated dispersions. Other predictions include the occurrence of flocculation at a secondary minimum and the particle-size dependent variation of suspension stability with particle volume fraction. Copyright 1998 Academic Press.