Oligomerization in silica sols

An empirical potential containing two- and three-body terms for silica-water interactions is proposed, with the oxygen-oxygen interaction treated identically in both the water and vitreous silica subsystems. The structures of water, H₂O dimers, H₂O trimers, and the H₄SiO₄-H₂O complex obtained by molecular dynamics simulations are in reasonable agreement with X-ray diffraction of water and ab initio calculations of molecules. Simulations of monomeric silicic acid sols provide a microscopic description of water producing oligomerization. The intermediate activation complexes are found to involve ionized monomers and pentacoordinate silicon.