Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

Abstract

Recent development of reactive force fields have enabled molecular dynamics simulations of interactions between silicate glasses and water at the atomistic scale. While multicomponent silicate glasses encompass a wide variety of compositions and properties, one common structural feature in these glasses is the combination of the network structure that is made up of silica tetrahedra linked through corner sharing interspersed with network modifiers like alkali and alkaline‐earth ions that break up the Si–O–Si linkages by forming nonbridging oxygen. In reactions with water, ion exchange between alkali ions in the glass and proton or hydronium in the solution, as well as hydrolysis reaction of the Si–O–Si linkages and subsequent silanol formation, is observed and well documented. We have used a set of recently developed reactive force field to investigate the reactions between water and the surfaces of silica and sodium silicate glasses of different compositions for reactions up to 8 nanoseconds. Our results indicate sodium leaching into water and diffusion of water molecules up to 25 Å into the glass surface. We examined the structural and compositional changes inside the glass and around the diffused ions and use these to explain the rates of silanol formation at the surface. We also observed proton transport in the glass which has an indirect influence on the silanol formation rates. While the surface of the glass was rough to start with, it undergoes further modification into a hydrated gel‐like structure in the glass for up to 5 Å in the higher alkali containing glasses. It was found that the leached sodium ions remain close to the interface and that fragments of silicate network from the surface is capable of dislodging from the bulk glass and enter the aqueous solution. These simulations thus provide insights into the formation and structure of an alteration layers commonly observed in multicomponent silicate glasses corroded in aqueous solutions.

First principles study of the surface of silica and sodium silicate glasses

“…the whole outermost layer is composed by pure Na. These findings are consistent with experimental observations of the surfaces of alkali silicate glasses by using LEIS spectroscopy [10,11,12] as well as with recent findings from classical molecular simulations of sodosilicate glasses with reactive force fields [61]. Upper and lower panels are for Si-O and Si-Si pairs, respectively.…”

Atomic and micro‐structure features of nanoporous aluminosilicate glasses from reactive molecular dynamics simulations

“…The diffuse charge reactive pair potential was initially developed for the simulation of water and silica and recently expanded to sodium silicate-water interactions. 30,31 In the current work, this potential was further extended to include parameters for Ca and Al also. The force field used in the simulation can be described analytically in terms of pair and three-body potentials described below:…”

Reverse osmosis and pervaporation of organic liquids using organosilica membranes: Performance analysis and predictions

“…This phenomenon is highly desired, as the flux increase barely sacrificed rejection during the aging in methanol, which is indicative of the great potential of the BTESA‐100 membrane for real applications. The reason for the changes in the permeating flux and rejection for the BTESA‐100 membrane was likely due to the hydrolytic cleavage of a small portion of the SiOSi bonds within the organosilica network to form SiOH groups induced by the inevitable water molecules in methanol 29,30 . This reaction impacts not only the membrane micropore size and affinity toward methanol but also steric hindrance for larger organic molecules such as toluene and MTBE.…”