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Exploring nanoscale lubrication mechanisms of multilayer MoS2 during sliding: the effect of humidity

Exploring nanoscale lubrication mechanisms of multilayer MoS2 during sliding: the effect of humidity
Exploring nanoscale lubrication mechanisms of multilayer MoS2 during sliding: the effect of humidity

Solid lubricants have received substantial attention due to their excellent frictional properties. Among others, molybdenum disulfide (MoS2) is one of the most studied lubricants. Humidity results in a deterioration of the frictional properties of MoS2. The actual mechanism at the nanoscale is still under debate, although there are indications that chemical reactions are not likely to occur in defect-free structures. In this study, we performed nonequilibrium molecular dynamics simulations to study the frictional properties of multilayer MoS2 during sliding in the presence of water. Moreover, we also investigated the effect of sliding speed and normal load. We confirmed earlier results that a thin layer of water organizes as a solidified, ice-like network of hydrogen bonds as a result of being confined in a two-dimensional fashion between MoS2. Moreover, we found that there exists an energy-driven, rotational dependence of the water network atop/beneath MoS2. This orientational anisotropy is directly related to the dissipative character of MoS2 during sliding. Finally, three distinct frictional regimes were identified, two for a thin layer of water and one for bulk water. In the case of a thin layer and low coverage, water represents a solid-like contaminant, causing high energy dissipation. For a thin layer and high coverage, water starts to act as a solid-like lubricant, reducing dissipation during sliding. Finally, a regime where water acts as a liquid lubricant, characterized by a clear velocity dependence was found.

friction, humidity, hydrogen bond network, molecular dynamics simulations, molybdenum disulfide, tribology, water
2296-2646
Claerbout, Victor E.P.
a4f7382e-cb6f-483d-9378-073307b7fe23
Nicolini, Paolo
80726840-4adf-44ea-a1dd-a77f9cb1e72d
Polcar, Tomas
c669b663-3ba9-4e7b-9f97-8ef5655ac6d2
Claerbout, Victor E.P.
a4f7382e-cb6f-483d-9378-073307b7fe23
Nicolini, Paolo
80726840-4adf-44ea-a1dd-a77f9cb1e72d
Polcar, Tomas
c669b663-3ba9-4e7b-9f97-8ef5655ac6d2

Claerbout, Victor E.P., Nicolini, Paolo and Polcar, Tomas (2021) Exploring nanoscale lubrication mechanisms of multilayer MoS2 during sliding: the effect of humidity. Frontiers in Chemistry, 9, [684441]. (doi:10.3389/fchem.2021.684441).

Record type: Article

Abstract

Solid lubricants have received substantial attention due to their excellent frictional properties. Among others, molybdenum disulfide (MoS2) is one of the most studied lubricants. Humidity results in a deterioration of the frictional properties of MoS2. The actual mechanism at the nanoscale is still under debate, although there are indications that chemical reactions are not likely to occur in defect-free structures. In this study, we performed nonequilibrium molecular dynamics simulations to study the frictional properties of multilayer MoS2 during sliding in the presence of water. Moreover, we also investigated the effect of sliding speed and normal load. We confirmed earlier results that a thin layer of water organizes as a solidified, ice-like network of hydrogen bonds as a result of being confined in a two-dimensional fashion between MoS2. Moreover, we found that there exists an energy-driven, rotational dependence of the water network atop/beneath MoS2. This orientational anisotropy is directly related to the dissipative character of MoS2 during sliding. Finally, three distinct frictional regimes were identified, two for a thin layer of water and one for bulk water. In the case of a thin layer and low coverage, water represents a solid-like contaminant, causing high energy dissipation. For a thin layer and high coverage, water starts to act as a solid-like lubricant, reducing dissipation during sliding. Finally, a regime where water acts as a liquid lubricant, characterized by a clear velocity dependence was found.

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Accepted/In Press date: 31 May 2021
Published date: 24 June 2021
Additional Information: Funding Information: This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic through the e-INFRA CZ (ID: 90140). The publication has received funding from the European Union’s Horizon 2020 research and innovation program under the grant agreement No. 721642: SOLUTION. PN acknowledges the support of the Czech Science Foundation through the project 16-11516Y. TP acknowledges the support of the project Novel nanostructures for engineering applications (No. CZ.02.1.01/0.0/ 0.0/16_026/0008396).
Keywords: friction, humidity, hydrogen bond network, molecular dynamics simulations, molybdenum disulfide, tribology, water

Identifiers

Local EPrints ID: 454498
URI: http://eprints.soton.ac.uk/id/eprint/454498
ISSN: 2296-2646
PURE UUID: 5b1e5ddb-bd8e-42ff-8843-932cecb58e4f
ORCID for Tomas Polcar: ORCID iD orcid.org/0000-0002-0863-6287

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Date deposited: 14 Feb 2022 17:37
Last modified: 18 Mar 2024 03:19

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Contributors

Author: Victor E.P. Claerbout
Author: Paolo Nicolini
Author: Tomas Polcar ORCID iD

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