A light and X-ray scattering study of the acid catalyzed silica synthesis in the presence of polyethylene glycol

Acid catalyzed silica sol-gel reactions were studied by means of small angl e X-ray scattering (SAXS) and dynamic light scattering (DLS). Emphasis was given as to how different concentrations and molecular weights of polyethyl ene glycol (PEG) influence the fractal dimension (d(f)) and particle size d istribution during and after the sol-gel reaction. From these measurements a reaction mechanism was determined for both stable and phase separated sam ples. The structure the material attained was dependent of the reaction mec hanism. Both high and low concentrations of PEG produced stable reactions. At higher concentrations steric stabilization of the sol occurred. The mech anism for the stable samples was determined to be diffusion limited cluster -cluster aggregation (DLCCA), reaction limited cluster-duster aggregation ( RLCCA) and reaction limited cluster-cluster aggregation with rearrangements , depending on the molecular weight and concentration of PEG and the time o f reaction. Bridging flocculation occurred between the organic and inorgani c polymers in the phase separated samples, but only after the particles had attained a specific size. Lower fractal dimensions were observed for these samples, because the reaction did not follow a percolation growth mechanis m. (C) 2000 Elsevier Science B.V. All rights reserved.