SOL-GEL POLYMERIZATION - ANALYSIS OF MOLECULAR MECHANISMS AND THE EFFECT OF HYDROGEN

The polymerization of silicic acid molecules (H4SiO4) was simulated us ing classical molecular dynamics with multibody potentials. The mechan isms involved in the condensation process were analyzed. Although a co ndensation mechanism was observed in the simulations which corresponds to the mechanism commonly assumed, additional mechanisms not previous ly presented were also observed. The advancement of polymerization was found to depend on the non-bridging oxygens' coordination with hydrog en, the number of bridging oxygens around five-coordinated silicons an d atomic momentum. The results show consistency with the chemistry des cribed for the acid catalyzed sol-gel process where hydrogen acts as t he catalyst and chains form before rings.