In an aqueous colloidal silica suspension, there is negative charge on the surface of the particles, which stabilizes the dispersion against flocculation by causing electrostatic repulsion. The addition of salt solution leads to destabilization of the kinetically stable system and lead to aggregation and gelation.

Effects of particle concentration and ionic strength on the irreversible gelation of aqueous colloidal silica particles (Ludox) are studied by dynamic light scattering (DLS) and rheological measurements and by both Stokesian and Brownian dynamics simulation. After destabilization of the system, hydrodynamic radius r was measured through DLS, which grows exponentially. The growth curves all fall onto a master curve for different salt and solid compositions. The increase in r indicates the aggregation of the colloidal particles and clusters. Approaching the gel point, < r > goes to infinity, apparently because the particles form a space-filling network. The storage modulus G' and loss modulus G'' increase and become measurable by rheometric methods as the gel forms; both increase over hours as the gel becomes stronger, while the linear viscoelastic region of the gel shrinks to a smaller range. Through the combination of methods, we can determine the gel point. Static light scattering results are applied to determine the fractal dimension.

Stokesian and Brownian Dynamics simulation techniques are applied to study the relationship between microstructure and mechanical properties of the colloidal gel, with a focus on understanding the role of hydrodynamics in combination with a short range attractive force and long range repulsive force. The simulations mimic the evolution of particle aggregation and gelation, and rheological properties, G' and G'' and viscosity, are calculated.