Scheme 1.

Mechanism of silica nucleation, seed development, and particle growth. (A) represents a new approach to control the particle development as a function of phasing out TEOS precursor from ethanol solution by supersaturating the reaction medium with water. Addition of excess water will immediately moves TEOS from solution phase to emulsion thus stopping the particle growth immediately. The phased out TEOS then can be removed by either simple pipetting, centrifugation, or both. (B) depicts the hydrolysis and condensation of TEOS taking place in solution phase. TEOS hydrolyzed to all its probabilistic derivatives which later condense to form oligomeric species followed by formation of primary seeds. The condensate oligomers will further precipitate over the seed contributing to the particle growth.