When  h<1, there is less possibility of forming infinite network because of the presence of few   M-OH groups for cross linking and gelation. If excess amount of water is present, that is h>m, extensively cross linked gel can be formed. For a given amount of water another way to control the process is to control the rate of addition of water.

The pH of the system affects the relative rate of hydrolysis and condensation. Fig. 3 compares the rates of hydrolysis and condensation of tetra ethyl ortho silicate (TEOS), a very widely used precursors, as a function of pH. Under acidic conditions, hydrolysis occurs at a faster rate than condensation and the resulting gel is weakly branched. Under basic conditions, the reverse occurs and the resulting gel is highly branched and contains colloidal aggregates. Subsequently, dried and heat treated samples have different surface functions and pore structures.  

Fig. 3. Schematic diagram showing effect of relative rates of hydrolysis and condensations reactions on gel structure.