FORMATION OF COLLOIDAL SILICA PARTICLES FROM ALKOXIDES

The growth of solution-derived monodisperse silica particles was studied by cryogenic transmission electron microscopy (cryo-TEM) in order to provide direct observation of the growth mechanism in colloidal particle formation from alkoxides. The silica particles were grown from tetraethoxysilane solutions using n-propanol and ethanol as solvents with an ammonia catalyst. A range of water concentrations was used. The reacting solutions were cryogenically fast-frozen at various times in the reaction and the samples were directly observed in the TEM. The results indicate that low density particles are seen initially, and these undergo a collapse to form the colloidally stable seed for further growth. Nuclear magnetic resonance was also used to follow the particle formation in order to test this growth model. Continued growth is postulated to occur by addition of small, low density particles to the growing seed, surmised from a lack of dense small particles and no evidence for aggregation of larger particles in the cryo-TEM results.