PROBING THE DYNAMICS OF THE SILICA NANOSTRUCTURE FORMATION AND GROWTHBY SAXS

The formation of colloidal silica particles from tetraethyl orthosilic ate in several low molecular weight alcohols under base-catalyzed cond itions is investigated by small-angle X-ray scattering technique. We m easured the changes of the radius of gyration and the fractal dimensio n as a function of time during growth. We find that, after an inductio n period, the first particles to form in the solution are mass fractal s characterized by their polymeric, open structure. Interestingly, the se mass fractals are sizable and could be considered the primary parti cles. Indeed by undergoing continuous intraparticle densification and further smoothing of the interface, they turn later into the usual com pact, nonfractal, stable structures. The stages of growth and transfor mation, though continuous, cannot be accounted for by the growth model s proposed so far.