Temperature-Dependent Frictional Behavior of MoS<sub>2</sub> in Humid Environments: Insights from Water Molecule Adsorption and DFT Analyses
Bibliographic record
Abstract
This study investigates the temperature-dependent frictional behavior of MoS 2 in humid environments within the context of a long-standing debate over increased friction due to oxidation processes or molecular adsorption. By combining sliding friction experiments and density functional theory (DFT)-based first-principles simulations, it aims to clarify the role of water molecule adsorption in influencing frictional properties of MoS 2, addressing the challenge of identifying interfacial bonding behavior responsible for friction in such conditions. Sliding experiments revealed that magnetron-sputtered MoS 2 exhibits a reduction in the coefficient of friction (COF) with an increase in temperature from 25 to 100 °C under 20 and 40% relative humidity. This change in the COF obeys the Arrhenius law, presenting an energy barrier of 0.165 eV, indicative of the temperature-dependent nature of these frictional changes and suggests a consistent frictional mechanism. DFT simulations showed that H 2 O molecules are adsorbed at MoS 2 vacancy defects with adsorption energies ranging from −0.56 to −0.17 eV, which align with the experimentally determined energy barrier. Adsorptive interactions, particularly the formation of stable H···S interfacial hydrogen bonds at defect sites, increase the interlayer adhesion and impede layer shearing. TEM analysis confirms that although MoS 2 layers align parallel to the sliding direction in humid conditions, the COF remains at 0.12, as opposed to approximately 0.02 in dry air. This demonstrates that parallel layer alignment does not notably decrease the COF, underscoring humidity’s significant role in MoS 2 ’s COF values, a result also supported by the Arrhenius analysis. The reversibility of the physisorption process, demonstrated by the recovery of the COF in high-temperature humid environments, suggests its dynamic nature. This study yields fundamental insights into MoS 2 interfaces for environments with variable humidity and temperature, crucial for demanding tribological applications.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".