Role of the hydrogen bond lifetimes and rotations at the water/amorphous silica interface on proton transport

Lentz, Jesse; Garofalini, Stephen H.

doi:10.1039/c9cp01994d

Cited by 27 publications

(26 citation statements)

References 88 publications

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“…The simulations also show proton transfers involving water molecules adjacent to the glass surface and surface sites, with formation of H 3 O + ions. The lifetimes of H 3 O + ions in bulk water are consistent with that observed experimentally and in ab‐initio calculations of such species; their lifetimes adjacent to the glass surface are much shorter‐lived and the proton transfer mechanisms are the same as those seen in ab‐initio calculations …”

Section: Introductionsupporting

confidence: 82%

“…43 The simulations also show proton transfers involving water molecules adjacent to the glass surface and surface sites, with formation of H 3 O + ions. The lifetimes of H 3 O + ions in bulk water are consistent with that observed experimentally and in ab-initio calculations of such species 44 ; their lifetimes adjacent to the glass surface are much shorter-lived 45 and the proton transfer mechanisms are the same as those seen in ab-initio calculations. 10,13,20,43 Simulations with this potential also showed proton transfer from an H 3 O + ion in bulk water via formation of Eigen and Zundel complexes that resulted in the proton transferring while in the Zundel complex, with an energy barrier of 0.8 kcal/mole, 44 consistent with ab-initio calculations that showed a value of 0.6 kcal/mole 46 at the same 2.4 Å O-O spacing as the simulations.…”

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confidence: 83%

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Molecular mechanism of the expansion of silica glass upon exposure to moisture

2019

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Molecular dynamics simulations show that the expansion of silica glass occurs by the presence of the hydroxyl (SiOH) groups present in the glass as opposed to intact water (H2O) molecules, providing an accurate molecular description of the experimentally observed volume changes in silica glass exposed to water. Using a robust and accurate reactive potential, the simulations show that the expansion is caused by the rupture of siloxane (Si–O–Si) linkages in the glass via reactions with water molecules, forming SiOHs. Such reactions remove smaller rings and form larger rings, with a decrease in the overall number of rings smaller than a prescribed large ring size in comparison to dry glasses. This change in ring structure overcomes the inherently stronger hydrogen bonding in the glasses containing SiOH in comparison to the glasses containing predominantly intact H2O molecules. This stronger H‐bonding of the SiOH also causes a shift to lower frequencies in the high‐frequency OH vibrational spectrum for the silanols, as shown in previous ab‐initio calculations. This introduces a question about assuming the lower frequency part of the high‐frequency peak is only due to intact H2O molecules. A slight decrease in volume occurred in the glasses containing the largest concentration of intact H2O molecules. There is no change in the ring size distribution between the H2O glasses and dry glasses. Rather, the slight decrease in volume in the H2O system is caused by a decrease in siloxane bond angles caused by the formation of H‐bonds between the H2O molecules and the glass O in the siloxane cages surrounding the H2O molecules.

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Section: Introductionsupporting

confidence: 82%

supporting

confidence: 83%

Molecular mechanism of the expansion of silica glass upon exposure to moisture

2019

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“…The overall conductivity in sodium silicates is also affected by the water content, compositions and the diffusion of Na + ions . The present results of increased proton transfer frequencies indicate that the lifetime of protons involved in silanols is higher than those on water molecules and highly conductive glasses . The increase in frequencies with composition indicates that the activation energy for conductivity in silicates will be lowered with increasing Na 2 O content in the glass …”

Section: Resultsmentioning

confidence: 60%

“…Interactions between water and amorphous silicates always involve the dissociation of water and formation of silanols which result in the reorganization of the glass network and the transport of glass components into the solution . In Molecular Dynamics (MD) simulations, the modeling of dissociation of water and reaction with silicates is a critical component simulating glass‐water interactions . While the transport of glass components into solution can be modeled with nonreactive force fields .…”

Section: Introductionmentioning

confidence: 99%

“…28,29 In Molecular Dynamics (MD) simulations, the modeling of dissociation of water and reaction with silicates is a critical component simulating glass-water interactions. 27,30 While the transport of glass components into solution can be modeled with nonreactive force fields. 31,32 use of a reactive potential is critical for analyzing all the reactions and material transport inside the glass and solution.…”

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confidence: 99%

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

Mahadevan

2020

J Am Ceram Soc

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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.

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