Molecular dynamics computer simulations of condensed phase interfaces with silicate glasses

The effects of interface formation on the surface structure of silicate glasses were studied using the classical molecular dynamics (MD) computer simulation technique. Interatomic potential functions were utilized which have been previously shown to accurately simulate silicate glasses and their surfaces. Condensed phase interfaces with glasses were formed by a simulated deposition and film growth of model metal atoms on a sodium alumino-silicate (NAS) glass surface. In addition, interfaces between a model crystalline metal and silica glass were created by a low temperature joining of the constituent surfaces. Low temperature separation of the crystal from the glass allowed analysis of remnant effects of interface formation on the glass surface structure. Elevated temperature atomic behavior at these interfaces was also simulated.;Deposition onto the NAS glass surface was compared to previous simulations where a simpler potential was used to govern adsorbate interactions. Qualitatively, the change in adsorbate potential had no effect on the NAS surface structural response. Of particular interest was an observed shift in the siloxane bond angle distribution for atoms within 5A of the glass surface. This shift was to a higher concentration of siloxane bond angles between 125;Structural changes in the glass surfaces caused by low temperature approach of a crystal are also described. Most notably, a similar shift in the siloxane bond angle distribution as was seen during deposition and film growth was observed at close approach. Analysis of the glass surface structure after removal of the crystal showed that some of the siloxane bond angle shift remained. This permanent change in the glass surface was further probed by allowing water to react with the surface. Comparison of these simulations with similar ones performed prior to interface formation revealed an increased concentration of reaction sites after interface formation and removal.;In an independent set of simulations, the model crystal/silica glass interfaces were subjected to elevated temperatures. The behavior observed was compared to high temperature simulations of the pure surface of the crystal. A reduction in the temperature where roughening of the crystal surface and subsequent melting occurs was seen when the crystal was interfaced with the silica glass. Further data presented indicate this effect to be largely a result of the excess volume inherent at the surface of an oxide glass.