Preparation of monodisperse silica particles: Control of size and mass fraction

We extend the work of Stober, Fink and Bohn (J. Colloid Interfac Sci. 26 (1968) 62) to establish the ranges of reagent concentrations which result in the precipitation of monodisperse silica particles from ethanol solutions containing ammonia, water, and tetraethyl orthosilica. A correlation is presented which can be used to predict final particle sizes over concentrations of 0.1-0.5 M TEOS, 0.5–17.0 M H2O and 0.5-3 M NH3. The maximum particle size achievable for these conditions at 25°C is ⋍ 800 nm and near the maximum, monodispersity is difficult to maintain. The effects of reaction temperature are studied and particle size distributions are analyzed. A seeded growth technique for preparing larger particles and/or increasing solids mass fraction up to a theoretical limit of ⋍ 24 wt% of silica is described.