Lubrication Behavior of Water Molecules Confined in TiO2 Nanoslits: A Molecular Dynamics Study

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• 作者：Yudan Zhu ; Yumeng Zhang ; Yijun Shi ; Xiaohua Lu ; Jiahui Li ; Linghong Lu
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2016
• 出版时间：December 8, 2016
• 年：2016
• 卷：61
• 期：12
• 页码：4023-4030
• 全文大小：480K
• ISSN：1520-5134

文摘

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.