Computer modeling of water adsorption on silica and silicate glass fracture surfaces

Molecular dynamics (MD) has been used to simulate water adsorption behavior on glass fracture surfaces. Energy minimization techniques were developed to obtain energy distributions of surface adsorption sites as well as a breakdown of site energies by site type. MD physisorption simulations were used to illustrate the role of the high-energy sites in the initial adsorption of water molecules onto the surface. It is shown that the strongest adsorption sites are associated with defects in the network, and not with modifier species. The modifier species also introduce water adsorption sites, but they are weaker than those associated with the network defects. Finally, surface hydroxylation is shown to greatly reduce the strength of fracture surface defect sites with respect to physisorption of water.