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Lubrication Behavior of Water Molecules Confined in TiO2 Nanoslits: A Molecular Dynamics Study
College of Chemical Engineering, State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University.
College of Chemical Engineering, State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
College of Chemical Engineering, State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University.
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Number of Authors: 6
2016 (English)In: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134Article in journal (Refereed) Epub ahead of print
Abstract [en]

Titanium (Ti) metal has been widely used in orthopedic implants, such as knee replacements and fracture fixation devices, where water is the base fluid of the lubricant. In this work, a series of nonequilibrium molecular dynamics have been carried out to investigate the microstructure and lubrication of water molecules confined in TiO2 nanoslits under shearing. The effects of varying slit gap widths (0.8, 1.2, 1.6, and 2.0 nm) and shear velocities (200, 100, 50, and 10 m/s) on the friction coefficients between TiO2 and water molecules were evaluated to shed light on the role of the confined water molecules on lubrication. Simulation results showed that the friction coefficient decreased as the slit width increased. Detailed analysis of water molecules microstructure revealed that water molecules confined in the slits were layered. Typically, all the water molecules in Layer 1 and some water molecules in Layer 2 could reach the sliding velocity of the wall, which were in agreement with the reported mobility of water molecules absorbed on TiO2 nanoparticles via nuclear magnetic resonance. As the width of slit gap increased, the average lifetime of the H-bonds between water molecules within and beyond Layer 1 reduced and the amount of free water increased accordingly, which caused a decrease in the friction coefficient. This understanding can be used to explain at the molecular scale the observation in our previous atomic force microscope experiment in which the higher roughness in TiO2 reflected a lower friction coefficient. 

Place, publisher, year, edition, pages
2016.
National Category
Tribology
Research subject
Machine Elements
Identifiers
URN: urn:nbn:se:ltu:diva-59645DOI: 10.1021/acs.jced.6b00534OAI: oai:DiVA.org:ltu-59645DiVA: diva2:1034043
Available from: 2016-10-11 Created: 2016-10-11 Last updated: 2016-12-03

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Shi, Yijun
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