Proton Dynamics at the Water–Silica Interface via Dissociative Molecular Dynamics

Abstract

A robust and accurate dissociative potential that reproduces the structural and dynamic properties of bulk and nanoconfined water, and proton transport similar to ab initio calculations in bulk water, is used for reactive molecular dynamics simulations of the proton dynamics at the silica/water interface. The simulations are used to evaluate the lifetimes of protonated sites at the interfaces of water with planar amorphous silica surfaces and cylindrical pores in amorphous silica with different densities of water confined in the pores. In addition to lifetimes, the donor/acceptor sites are evaluated and discussed in terms of local atomistic structure. The results of the lifetimes of the protonated sites, including H 3 O + , SiOH, SiOH 2 + , and Si−(OH + )−Si sites, are considered. The lifetime of the hydronium ion, H 3 O + , is considerably shorter near the interface than in bulk water, as are the lifetimes of the other protonated sites. The results indicate the beneficial effect of the amorphous silica surface in enhancing proton transport in wet silica as seen in electrochemical studies and provide the specific molecular mechanisms.

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

“…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.…”

“…The behavior of water in contact with amorphous silica (a‐silica) surfaces and penetration into the subsurface has garnered significant interest over many decades . In general, water has been shown to weaken silica in tension via stress corrosion cracking at a stress less than the normal fracture stress.…”

“…In order to address this question at a molecular level, molecular dynamics computer simulations using a robust, transferrable reactive interatomic potential has been used to address the effect of molecular water vs hydroxyls in amorphous silica on volume in comparison to dry silica.…”

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

“…use of a reactive potential is critical for analyzing all the reactions and material transport inside the glass and solution. Recent improvements of reactive MD force fields have allowed for several advances in the modeling of silica‐water interactions . In one of the most recent studies of sodium silicate hydration with the ReaxFF, leaching of sodium into water and accumulation at the interface of the leached Na + ions was observed along with proton transport inside the glass in the first nanosecond of reaction.…”

“…Recent improvements of reactive MD force fields have allowed for several advances in the modeling of silica-water interactions. [33][34][35][36][37][38] In one of the most recent studies of sodium silicate hydration with the ReaxFF, 39 leaching of sodium into water and accumulation at the interface of the leached Na + ions was observed along with proton transport inside the glass in the first nanosecond of reaction. Another recent study with the same ReaxFF potential studied the continuation of these simulations for a longer time (3 ns) and for different temperatures.…”