Interfacial Structure and Evolution of the Water-Silica Gel System by Reactive Force-Field-Based Molecular Dynamics Simulations
JM Rimsza and JC Du, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 11534-11543 (2017).
Nanoporous silica gel structures and associated interfaces formed on the surface of silicate and borosilicate glasses play an important role in understanding the dissolution mechanisms of these glasses. Interfacial models that consist of bulk silica, nanoporous hydrated silica gel, and bulk water were constructed and their evolution was studied to understand the water-glass reaction fronts using the Reactive Force Field (ReaxFF)-based molecular dynamics simulations. The short and medium-range structures of the gel and the interfaces as well as water diffusion and silica dissolution behaviors were studied in detail. It was found that the gel region exhibited an increase in Si-O network connectivity with time, consistent with recent NMR results, due to cross-linking of siloxane bonds in the gel and the dissolution of less connected SiO4 groups into the water region. Higher network connectivity of the silica gel can regulate transport of ions and plays the role of passivation. Dissolved silica clusters in water experienced an initial sharp increase and then reached equilibrium concentration at longer time. The development of realistic multiphase nanoporous silica gel interfacial models provides insights into understanding glass- dissolution mechanisms, especially the residual dissolution rate and long-term corrosion behaviors of multicomponent borosilicate glasses.
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