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Network growth in the flocculation of concentrated colloidal silica dispersions

Heiney PA, Butera RJ, Londono JD, Davidson RV, Mazur S

104 (37): 8807-8821 SEP 21 2000
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We have used small-angle X-ray scattering (SAXS) and oscillatory shear rheometry to study the salt-induced flocculation of a concentrated colloidal silica dispersion in water. The SAXS results provided qualitative confirmation of a primary contact coordination shell and barrier as predicted by the DLVO model. The results are consistent with an irreversible, but volume-conserving, growth of a network of interparticle contacts. The activation energy 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 modulus of the gel (reflecting the long-range structure) continued to evolve long after changes in the local structure could no longer be distinguished, but ultimately it also converged to a quasi-stationary state. Disruption of the gel network by shear had no detectable effect on the local structure, but caused a dramatic reduction in the moduli which subsequently recovered following different kinetics than in the initial growth process.

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