29Si-NMR, conductimetry, and photon correlation spectroscopy are used to monitor the temporal profile of intermediate concentrations in Stober synthesis (i.e., ammonia-catalyzed hydrolysis of tetraethoxysilane in a batch reactor). Extreme models of the process are assessed by examining the effect of initial composition on these transients (over a wider range of composition than attempted previously). The trends with initial composition suggest that the nucleation is rate-limited by the hydrolysis of the singly hydrolyzed monomer, the product of which probably phase separates. Moreover, the trends are consistent with the aggregation model discussed by G.H. Bogush and C.F. Zukoski (J. Colloid Interface Sci. 142, 1, 19 (1991) and by M.T. Harris (Ph.D. dissertation, Univ. of Tennessee, 1992). The trends are not consistent with a growth model without aggregation.
Bibliographical noteFunding Information:
We acknowledge the use of characterization facility of the Center for Interfacial Engineering at the University of Minnesota and support from the Office of Naval Research and the Office of Basic Energy Sciences, Material Sciences Division, U.S. Department of Energy. We also thank Dr. Arun N. Sathyagal for clarification of the figures.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films
- Colloid and Surface Chemistry