Molecular Dynamics Simulation of the Structure and Hydroxylation of Silica Glass Surfaces

The surface structure of silica glasses has been simulated using molecular dynamics. The surface hydroxyl concentration was estimated to be 4.5/nm², based on surface defect statistics. Hydroxyl-silica potentials were developed and used to study the hydroxylation of silica surface. It is found that the energy of chemisorption of water declines in the sequence: three coordinated silicon (Si³) and non-bridging oxygen (NBO) on separate sites, Si³ and NBO on combined sites, two- and three-membered rings. Partial hydroxylation of the most reactive sites, which leads to an OH coverage of 2.5/nm², was studied. Structural relaxation after hydroxylation was observed.