Viscosity on Conversion of Microgel to Sol

When microgel is formed from extremely small particles at low concentration at low pH, it may disperse and form a sol when the pH is raised above 7. This occurs only if the salt concentration in the system is less than about 0.2-0.3 N, that is, the critical coagulation concentration. Otherwise the growing particles remain aggregated and become further cemented together as a precipitate. 

When the pH is raised, there is particle growth as chain segments dissolve and silica is deposited around branch points, eventually forming irregularly shaped, separate particles. At the same time the specific surface area of the silica is greatly diminished. 

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