Surface Reactivity and Leaching of a Sodium Silicate Glass under an Aqueous Environment: A ReaxFF Molecular Dynamics Study
Evidence and attribution¶
Authority of statements
Prose sections below (Summary, Methods, Findings, etc.) are curated summaries of the publication identified by doi, title, and pdf_path in the front matter above. They are not new primary claims by this wiki.
For definitive numerical values, reaction schemes, and interpretations, use the peer-reviewed article (and optional records under normalized/papers/ when present)—not this page alone.
Summary¶
Large-scale ReaxFF MD is used to follow structural and chemical evolution at a sodium silicate glass / water interface, beyond the simpler pure silica–water case. Water attack displaces Na⁺ from nonbridging oxygen (NBO) sites, promotes water dissociation to H⁺/OH⁻, and builds silanol (SiOH) through NBO protonation; protons propagate into the glass by hopping between adjacent NBO sites, so silanol populations grow over the nanosecond trajectories rather than plateauing. Na⁺ leaching is tracked from surface-bound Na–OH-like motifs through a finite residence time before release into bulk water. Seung Ho Hahn and Adri C. T. van Duin provide an atomistic picture of glass corrosion relevant to environmental and biomedical glass uses. The JPCC article emphasizes alkali content as a driver of enhanced hydrolysis relative to vitreous silica alone.
Methods¶
Force-field lineage (A)¶
ReaxFF for Na–Si–O–H glass/water chemistry uses the group’s reactive parametrization appropriate to sodium silicate surfaces in contact with water (trained against QM data in prior van Duin-line work cited in JPCC—see article for references to the underlying parameter set and Supporting Information).
Molecular dynamics protocol (B)¶
Large-scale reactive MD of hydrated sodium silicate slabs with liquid water films: slab construction, water thickness, equilibration, production length, timestep, thermostat/ensemble, and ReaxFF charge equilibration schedules are specified in papers/Hahn_JPC_leaching_2019.pdf (and SI). Analysis tracks time-resolved Na, H, and Si–O speciation across the interface and shallow glass interior, including movies/trajectory figures for ion motion near the surface.
Static QM (C)¶
Not the primary result—the paper positions QM as costly for the length scales targeted and uses ReaxFF MD for reactive sampling.
Reactive MD on glass–water slabs. LAMMPS ReaxFF trajectories in pdf_path use periodic in-plane boundary conditions on sodium silicate slabs contacted by liquid water films (full atom counts, film thickness, timestep, NVT/NPT choice, Berendsen/Nose–Hoover parameters, and production lengths in ns are listed in Computational Methods and SI). Temperature: 300 K (or other K setpoints) for the interfacial runs match the tables in the JPCC article unless the SI specifies a variant. Barostat / pressure: N/A if the summarized leaching study stays constant-volume NVT; confirm any NPT segments in the PDF. External electric field: N/A. Enhanced sampling: N/A.
Findings¶
Mechanisms¶
Ion exchange and acid–base chemistry at nonbridging oxygen (NBO) sites drive continuous surface modification: water displaces Na⁺ from NBO, water dissociation supplies H⁺/OH⁻, NBO protonation builds silanol (SiOH), and protons propagate inward by discrete hopping between adjacent NBO sites—so SiOH populations grow over nanosecond trajectories rather than plateauing. Na⁺ shows finite surface residence as Na–OH-like motifs before release to bulk water.
Limitations vs experiment¶
Nanosecond windows may not reach steady-state altered-layer thicknesses from long-term corrosion experiments.
Outlook¶
The abstract frames ReaxFF MD as supplying physical insight at time/length scales difficult for experiment or first-principles MD alone for these multicomponent glass–water interfaces.
Limitations¶
- Nanosecond MD may not reach steady-state thickness of altered layers seen in long-term experiment.
- ReaxFF for Na–Si–O–H must stay within the fitted composition and condition range validated in related group work.
Wiki prose here is a navigation aid. Definitive numbers, protocol details, and figure-level claims should be taken from the peer-reviewed article at pdf_path (and any Supporting Information cited there), not from this page alone.
Relevance to group¶
Extends the Na/Si/O/H ReaxFF line (see also paper:2018ho-venue-paper SI / main JPCC NaSiOₓ parameterization) toward explicit glass–water reactivity.
Citations and evidence anchors¶
- DOI:
https://doi.org/10.1021/acs.jpcc.9b02940(papers/Hahn_JPC_leaching_2019.pdf).