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Title: Phosphonium-Organophosphate Ionic Liquids as Lubricant Additives: Effects of Cation Structure on Physicochemical and Tribological Characteristics

Abstract

In our previous work we suggest great potential for a phosphonium-organophosphate ionic liquid (IL) as an antiwear lubricant additive. In this study, a set of five ILs were carefully designed and synthesized, with identical organophosphate anions but dissimilar phosphonium cations, to allow systematic investigation of the effects of cation alkyl chain length and symmetry on physicochemical and tribological properties. Symmetric cations with shorter alkyl chains seem to increase the density and thermal stability due to closer packing. On the other hand, either higher cation symmetry or longer alkyl moieties induce a higher viscosity, though the viscosity index is dependent more on molecular mass than on symmetry. While a larger cation size generally increases an IL’s solubility in nonpolar hydrocarbon oils, six-carbon seems to be the critical minimum alkyl chain length for high oil miscibility. Both the two ILs, that are mutually oil miscible, have demonstrated promising lubricating performance at 1.04% treat rate, though the symmetric-cation IL moderately outperformed the asymmetric-cation IL. Moreover, characterizations on the tribofilm formed by the best-performing symmetric-cation IL revealed the film thickness, nanostructure, and chemical composition. Our results provide fundamental insights for future molecular design in developing oil-soluble ILs as lubricant additives.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Shell Projects and Technology (US), Houston, TX (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V); USDOE Office of Science (SC), Workforce Development for Teachers and Scientists (WDTS)
OSTI Identifier:
1185558
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 6; Journal Issue: 24; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; gas-to-liquid oil; ionic liquid; lubricant antiwear additive; oil solubility; organophosphate; phosphonium

Citation Formats

Barnhill, William C., Qu, Jun, Luo, Huimin, Meyer III, Harry M., Ma, Cheng, Chi, Miaofang, and Papke, Brian L. Phosphonium-Organophosphate Ionic Liquids as Lubricant Additives: Effects of Cation Structure on Physicochemical and Tribological Characteristics. United States: N. p., 2014. Web. doi:10.1021/am506702u.
Barnhill, William C., Qu, Jun, Luo, Huimin, Meyer III, Harry M., Ma, Cheng, Chi, Miaofang, & Papke, Brian L. Phosphonium-Organophosphate Ionic Liquids as Lubricant Additives: Effects of Cation Structure on Physicochemical and Tribological Characteristics. United States. https://doi.org/10.1021/am506702u
Barnhill, William C., Qu, Jun, Luo, Huimin, Meyer III, Harry M., Ma, Cheng, Chi, Miaofang, and Papke, Brian L. 2014. "Phosphonium-Organophosphate Ionic Liquids as Lubricant Additives: Effects of Cation Structure on Physicochemical and Tribological Characteristics". United States. https://doi.org/10.1021/am506702u. https://www.osti.gov/servlets/purl/1185558.
@article{osti_1185558,
title = {Phosphonium-Organophosphate Ionic Liquids as Lubricant Additives: Effects of Cation Structure on Physicochemical and Tribological Characteristics},
author = {Barnhill, William C. and Qu, Jun and Luo, Huimin and Meyer III, Harry M. and Ma, Cheng and Chi, Miaofang and Papke, Brian L.},
abstractNote = {In our previous work we suggest great potential for a phosphonium-organophosphate ionic liquid (IL) as an antiwear lubricant additive. In this study, a set of five ILs were carefully designed and synthesized, with identical organophosphate anions but dissimilar phosphonium cations, to allow systematic investigation of the effects of cation alkyl chain length and symmetry on physicochemical and tribological properties. Symmetric cations with shorter alkyl chains seem to increase the density and thermal stability due to closer packing. On the other hand, either higher cation symmetry or longer alkyl moieties induce a higher viscosity, though the viscosity index is dependent more on molecular mass than on symmetry. While a larger cation size generally increases an IL’s solubility in nonpolar hydrocarbon oils, six-carbon seems to be the critical minimum alkyl chain length for high oil miscibility. Both the two ILs, that are mutually oil miscible, have demonstrated promising lubricating performance at 1.04% treat rate, though the symmetric-cation IL moderately outperformed the asymmetric-cation IL. Moreover, characterizations on the tribofilm formed by the best-performing symmetric-cation IL revealed the film thickness, nanostructure, and chemical composition. Our results provide fundamental insights for future molecular design in developing oil-soluble ILs as lubricant additives.},
doi = {10.1021/am506702u},
url = {https://www.osti.gov/biblio/1185558}, journal = {ACS Applied Materials and Interfaces},
issn = {1944-8244},
number = 24,
volume = 6,
place = {United States},
year = {2014},
month = {11}
}

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Cited by: 42 works
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Works referenced in this record:

Global energy consumption due to friction in passenger cars
journal, March 2012


Functional Room-temperature Ionic Liquids as Lubricants for an Aluminum-on-Steel System
journal, May 2004


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journal, April 2010


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journal, January 2009


Imidazolium Ionic Liquids As Antiwear and Antioxidant Additive in Poly(ethylene glycol) for Steel/Steel Contacts
journal, March 2010


Antiwear Performance and Mechanism of an Oil-Miscible Ionic Liquid as a Lubricant Additive
journal, February 2012


Comparison of an oil-miscible ionic liquid and ZDDP as a lubricant anti-wear additive
journal, March 2014


Ionic Liquids as Antiwear Additives in Base Oils: Influence of Structure on Miscibility and Antiwear Performance for Steel on Aluminum
journal, November 2013


Ionic Liquids Based on Phosphonium Cations As Neat Lubricants or Lubricant Additives for a Steel/Steel Contact
journal, July 2014


Effects of 1-hexadecyl-3-methylimidazolium ionic liquids on the physicochemical characteristics and cytotoxicity of phosphatidylcholine vesicles
journal, September 2013


Detecting the onset of localized scuffing in a pin-on-twin fuel-lubricated test for heavy-duty diesel fuel injectors
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Nanostructure and Composition of Tribo-Boundary Films Formed in Ionic Liquid Lubrication
journal, May 2011


Works referencing / citing this record:

New dimensions in salt–solvent mixtures: a 4th evolution of ionic liquids
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Physicochemical and tribophysical properties of trioctylalkylammonium bis(salicylato)borate (N888n-BScB) ionic liquids: effect of alkyl chain length
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Tribotronic control of friction in oil-based lubricants with ionic liquid additives
journal, January 2016


Ionic Liquid Additives for Mixed and Elastohydrodynamic Lubrication
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Impact of Lubricant Oil Additives on the Performance of Pd-Based Three-Way Catalysts
journal, September 2019


Controlled Friction Behaviors of Porous Copper/Graphite Storing Ionic Liquid through Electrical Stimulation
journal, December 2017


Understanding Spectroscopic Features of Trihexyltetradecylphosphonium Chloride
journal, April 2016


Tribological Improvement Using Ionic Liquids as Additives in Synthetic and Bio-Based Lubricants for Steel–Steel Contacts
journal, November 2019