Network growth in the flocculation of concentrated colloidal silica dispersions

We have used small-angle X-ray scattering (SAXS) and oscillatory shear rheo metry to study the salt-induced flocculation of a concentrated colloidal si lica dispersion in water. The SAXS results provided qualitative confirmatio n of a primary contact coordination shell and barrier as predicted by the D LVO model. The results are consistent with an irreversible, but volume-cons erving, growth of a network of interparticle contacts. The activation energ y for network growth turns out to be substantially greater than the barrier in the pair potential predicted by the DLVO model, and this difference is ascribed to the importance of multiparticle interactions. The storage modul us of the gel (reflecting the long-range structure) continued to evolve lon g after changes in the local structure could no longer be distinguished, bu t ultimately it also converged to a quasi-stationary state. Disruption of t he gel network by shear had no detectable effect on the local structure, bu t caused a dramatic reduction in the moduli which subsequently recovered fo llowing different kinetics than in the initial growth process.