Using 29Si MAS-NMR we investigate the effect of pH on the final connectivity distribution of the silicon atoms in the Stöber particles. Our data suggest that the fraction of the silicon atoms that are ully-connected decreases as the ammonia concentration is increased. This suggests a more negative first shell substitution effect in the precipitated phase (liquid droplet) if condensation reactions are irreversible. A simple model is developed to describe the condensation kinetics in the precipitated phase and the results support the negative first shell substitution effect. These findings challenge the notion of a positive first shell substitution effect in alkaline conditions.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Materials Chemistry