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Effects of Water on Tribochemical Wear of Silicon Oxide Interface: Molecular Dynamics (MD) Study with Reactive Force Field (ReaxFF)

Summary

ReaxFF molecular dynamics is used to model atomistic processes at a sliding interface between fully hydroxylated amorphous silica and oxidized silicon, with varying interfacial water from dry to submonolayer to monolayer-like conditions. The simulations address how water enables or suppresses interfacial mixing, Si–O–Si bridge formation, and atom transfer that accompany tribochemical wear. The study is motivated by MEMS and silica tribology contexts where humidity swings change wear rates without obvious macroscopic lubricant films. Langmuir framing ties the shear-driven chemistry to humidity-controlled adhesion and wear in silicon oxide contacts common in MEMS reliability studies.

Methods

This slug points at a reduced-size PDF (papers/Yeon_Langmuir_2016_reduced.pdf) for the same Langmuir article as [[2016yeon-venue-la5b04062]] (DOI 10.1021/acs.langmuir.5b04062). Methods match the VOR page: Engine / code: LAMMPS; ReaxFF (Fogarty Si/O/water); 3.19 × 3.19 × 7.0 nm\(^3\) periodic cell; ensemble: NVT; thermostat: Nose–Hoover; timestep: 0.25 fs; normal load: 1 GPa on the top rigid slab; shear: 10 m/s for 1 ns; interfacial water: 0 / 20 / 50 / 100 molecules; temperatures: 300 / 500 / 700 K (Simulation Methods in the issue PDF).

2 — Force-field training. N/A — literature ReaxFF parametrization.

3 — Static QM. N/A — not used.

4 — Replica / enhanced sampling. N/A — not used.

Findings

  • Without water, interfacial mixing begins with dehydroxylation followed by Si–O–Si bridges linking the two surfaces, with substantial atom transfer across the interface during sliding.
  • With submonolayer water, water dissociation opens additional pathways to form Si–O–Si bridges and sustain cross-interface atom transfer.
  • When interfacial water is sufficient for a full monolayer, atom transfer is strongly reduced because interfacial silicon sites are terminated by hydroxyls rather than forming as many interfacial Si–O–Si bridge bonds.
  • The authors argue the simulations clarify how humidity and water coverage modulate tribochemical wear of silicon oxide interfaces at the atomistic level.

Limitations

Reduced PDF may omit SI figures present in the full file; use [[2016yeon-venue-la5b04062]] for archival completeness. Idealized planar contacts omit asperity statistics and third-body debris relevant to MEMS wear maps.

Relevance to group

Penn State collaboration on ReaxFF for silica tribochemistry and MEMS-relevant interfaces. The humidity-dependent atom-transfer story here is frequently cited alongside later group papers on silica wear, so maintaining consistent terminology around “submonolayer” versus “monolayer-like” coverage helps cross-linking within the wiki graph.

Citations and evidence anchors

  • DOI: 10.1021/acs.langmuir.5b04062; volume/pages per the issue PDF on [[2016yeon-venue-la5b04062]].
  • Text-aligned pointers: normalized/extracts/2016yeon-venue-la5b04062-2_p1-2.txt