Nano- and macroscale study of the lubrication of titania using pure and diluted ionic liquids

Peter K. Cooper, Joe Staddon, Songwei Zhang, Zachary M. Aman, Rob Atkin, Hua Li

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Titanium is a strong, corrosion-resistant light - weight metal which is poised to replace steel in automobiles, aircraft, and watercraft. However, the titanium oxide (titania) layer that forms on the surface of titanium in air is notoriously difficult to lubricate with conventional lubricants, which restricts its use in moving parts such as bearings. Ionic liquids (ILs) are potentially excellent lubricants for titania but the relationship between IL molecular structure and lubricity for titania remains poorly understood. Here, three-ball-on-disk macrotribology and atomic force microscopy (AFM) nanotribology measurements reveal the lubricity of four IL lubricants: trioctyl(2-ethylhexyl)phosphonium bis(2 ethylhexyl)phosphate (P8,8,8,6(2) BEHP), trihexyl(tetradecyl)phosphonium bis(2 ethylhexyl)phosphate (P6,6,6,14 BEHP), trihexyl(tetradecyl)phosphonium bis(2,4,4 trimethylpentyl)phosphinate (P6,6,6,14 (iC8)2PO2), and trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide (P6,6,6,14 TFSI). The macrotribology measurements demonstrated that friction decreased in P6,6,6,14 TFSI by four times (μ = 0.13) compared to in hexadecane, even at 60 °C and loads up to 10 N. On the other hand, P8,8,8,6(2) BEHP reduced friction most effectively in the AFM nanotribology measurements. The results were interpreted in terms of the lubrication regime. The lower viscosity of P6,6,6,14 TFSI coupled with its good boundary lubrication made it the most effective IL for the macrotribology measurements, which were in the mixed lubrication regime. Conversely, the cation structure the P8,8,8,6(2) BEHP allowed it to adsorb strongly to the surface and minimized energy dissipation in the nanotribology measurements, although its high bulk viscosity inhibited its performance in the mixed regime. These results reinforce the importance of carefully selecting IL lubricants based on the lubrication regime of the sliding surfaces.

Original languageEnglish
Article number287
JournalFrontiers in Chemistry
Volume7
Issue numberAPR
DOIs
Publication statusPublished - 1 Jan 2019

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Ionic Liquids
Nanotribology
Lubrication
Lubricants
Titanium
Atomic force microscopy
Bearings (structural)
Phosphates
Viscosity
Friction
Imides
Steel
Molecular structure
Automobiles
Cations
Energy dissipation
Metals
Aircraft
titanium dioxide
Corrosion

Cite this

@article{f0dede98e7cd44e1aaf32f94c5652bdd,
title = "Nano- and macroscale study of the lubrication of titania using pure and diluted ionic liquids",
abstract = "Titanium is a strong, corrosion-resistant light - weight metal which is poised to replace steel in automobiles, aircraft, and watercraft. However, the titanium oxide (titania) layer that forms on the surface of titanium in air is notoriously difficult to lubricate with conventional lubricants, which restricts its use in moving parts such as bearings. Ionic liquids (ILs) are potentially excellent lubricants for titania but the relationship between IL molecular structure and lubricity for titania remains poorly understood. Here, three-ball-on-disk macrotribology and atomic force microscopy (AFM) nanotribology measurements reveal the lubricity of four IL lubricants: trioctyl(2-ethylhexyl)phosphonium bis(2 ethylhexyl)phosphate (P8,8,8,6(2) BEHP), trihexyl(tetradecyl)phosphonium bis(2 ethylhexyl)phosphate (P6,6,6,14 BEHP), trihexyl(tetradecyl)phosphonium bis(2,4,4 trimethylpentyl)phosphinate (P6,6,6,14 (iC8)2PO2), and trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide (P6,6,6,14 TFSI). The macrotribology measurements demonstrated that friction decreased in P6,6,6,14 TFSI by four times (μ = 0.13) compared to in hexadecane, even at 60 °C and loads up to 10 N. On the other hand, P8,8,8,6(2) BEHP reduced friction most effectively in the AFM nanotribology measurements. The results were interpreted in terms of the lubrication regime. The lower viscosity of P6,6,6,14 TFSI coupled with its good boundary lubrication made it the most effective IL for the macrotribology measurements, which were in the mixed lubrication regime. Conversely, the cation structure the P8,8,8,6(2) BEHP allowed it to adsorb strongly to the surface and minimized energy dissipation in the nanotribology measurements, although its high bulk viscosity inhibited its performance in the mixed regime. These results reinforce the importance of carefully selecting IL lubricants based on the lubrication regime of the sliding surfaces.",
keywords = "Atomic Force Microscopy, Friction mechanism, Light-weight metal, Lubrication, Nanotribology, Titanium",
author = "Cooper, {Peter K.} and Joe Staddon and Songwei Zhang and Aman, {Zachary M.} and Rob Atkin and Hua Li",
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Nano- and macroscale study of the lubrication of titania using pure and diluted ionic liquids. / Cooper, Peter K.; Staddon, Joe; Zhang, Songwei; Aman, Zachary M.; Atkin, Rob; Li, Hua.

In: Frontiers in Chemistry, Vol. 7, No. APR, 287, 01.01.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Nano- and macroscale study of the lubrication of titania using pure and diluted ionic liquids

AU - Cooper, Peter K.

AU - Staddon, Joe

AU - Zhang, Songwei

AU - Aman, Zachary M.

AU - Atkin, Rob

AU - Li, Hua

PY - 2019/1/1

Y1 - 2019/1/1

N2 - Titanium is a strong, corrosion-resistant light - weight metal which is poised to replace steel in automobiles, aircraft, and watercraft. However, the titanium oxide (titania) layer that forms on the surface of titanium in air is notoriously difficult to lubricate with conventional lubricants, which restricts its use in moving parts such as bearings. Ionic liquids (ILs) are potentially excellent lubricants for titania but the relationship between IL molecular structure and lubricity for titania remains poorly understood. Here, three-ball-on-disk macrotribology and atomic force microscopy (AFM) nanotribology measurements reveal the lubricity of four IL lubricants: trioctyl(2-ethylhexyl)phosphonium bis(2 ethylhexyl)phosphate (P8,8,8,6(2) BEHP), trihexyl(tetradecyl)phosphonium bis(2 ethylhexyl)phosphate (P6,6,6,14 BEHP), trihexyl(tetradecyl)phosphonium bis(2,4,4 trimethylpentyl)phosphinate (P6,6,6,14 (iC8)2PO2), and trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide (P6,6,6,14 TFSI). The macrotribology measurements demonstrated that friction decreased in P6,6,6,14 TFSI by four times (μ = 0.13) compared to in hexadecane, even at 60 °C and loads up to 10 N. On the other hand, P8,8,8,6(2) BEHP reduced friction most effectively in the AFM nanotribology measurements. The results were interpreted in terms of the lubrication regime. The lower viscosity of P6,6,6,14 TFSI coupled with its good boundary lubrication made it the most effective IL for the macrotribology measurements, which were in the mixed lubrication regime. Conversely, the cation structure the P8,8,8,6(2) BEHP allowed it to adsorb strongly to the surface and minimized energy dissipation in the nanotribology measurements, although its high bulk viscosity inhibited its performance in the mixed regime. These results reinforce the importance of carefully selecting IL lubricants based on the lubrication regime of the sliding surfaces.

AB - Titanium is a strong, corrosion-resistant light - weight metal which is poised to replace steel in automobiles, aircraft, and watercraft. However, the titanium oxide (titania) layer that forms on the surface of titanium in air is notoriously difficult to lubricate with conventional lubricants, which restricts its use in moving parts such as bearings. Ionic liquids (ILs) are potentially excellent lubricants for titania but the relationship between IL molecular structure and lubricity for titania remains poorly understood. Here, three-ball-on-disk macrotribology and atomic force microscopy (AFM) nanotribology measurements reveal the lubricity of four IL lubricants: trioctyl(2-ethylhexyl)phosphonium bis(2 ethylhexyl)phosphate (P8,8,8,6(2) BEHP), trihexyl(tetradecyl)phosphonium bis(2 ethylhexyl)phosphate (P6,6,6,14 BEHP), trihexyl(tetradecyl)phosphonium bis(2,4,4 trimethylpentyl)phosphinate (P6,6,6,14 (iC8)2PO2), and trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide (P6,6,6,14 TFSI). The macrotribology measurements demonstrated that friction decreased in P6,6,6,14 TFSI by four times (μ = 0.13) compared to in hexadecane, even at 60 °C and loads up to 10 N. On the other hand, P8,8,8,6(2) BEHP reduced friction most effectively in the AFM nanotribology measurements. The results were interpreted in terms of the lubrication regime. The lower viscosity of P6,6,6,14 TFSI coupled with its good boundary lubrication made it the most effective IL for the macrotribology measurements, which were in the mixed lubrication regime. Conversely, the cation structure the P8,8,8,6(2) BEHP allowed it to adsorb strongly to the surface and minimized energy dissipation in the nanotribology measurements, although its high bulk viscosity inhibited its performance in the mixed regime. These results reinforce the importance of carefully selecting IL lubricants based on the lubrication regime of the sliding surfaces.

KW - Atomic Force Microscopy

KW - Friction mechanism

KW - Light-weight metal

KW - Lubrication

KW - Nanotribology

KW - Titanium

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DO - 10.3389/fchem.2019.00287

M3 - Article

VL - 7

JO - Frontiers in Chemistry

JF - Frontiers in Chemistry

SN - 2296-2646

IS - APR

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