3. Physico-chemical aspects of sol-gel polymerization

From a physico-chemical point of view, the changes likely to occur during polymerization are very significant, particularly in terms of macroscopic properties during the transition from sol to gel, then to aged gel and finally to xerogel. The most striking properties concerned are, of course, mechanical properties, but also optical properties (variation in refractive index), conductance, porosity, etc., the latter being highly dependent on the nature of the synthesis process.

In general, the sol-gel polymerization process can be summarized as shown in figure 4 . The solution containing the monomers leads to the sol, which then gels to...