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

Journal Article · · ACS Applied Materials and Interfaces
DOI:https://doi.org/10.1021/am506702u· OSTI ID:1185558
 [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)
+ Show Author Affiliations

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.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Organization:
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)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1185558
Journal Information:
ACS Applied Materials and Interfaces, Vol. 6, Issue 24; ISSN 1944-8244
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 130 works
Citation information provided by
Web of Science

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Cited By (11)

New dimensions in salt–solvent mixtures: a 4th evolution of ionic liquids journal January 2018
Physicochemical and tribophysical properties of trioctylalkylammonium bis(salicylato)borate (N888n-BScB) ionic liquids: effect of alkyl chain length journal January 2017
Tribotronic control of friction in oil-based lubricants with ionic liquid additives journal January 2016
Ionic Liquid Additives for Mixed and Elastohydrodynamic Lubrication journal April 2018
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
Understanding Tribofilm Formation Mechanisms in Ionic Liquid Lubrication journal August 2017
Nano- and Macroscale Study of the Lubrication of Titania Using Pure and Diluted Ionic Liquids journal April 2019
Tribological Bench and Engine Dynamometer Tests of a Low Viscosity SAE 0W-16 Engine Oil Using a Combination of Ionic Liquid and ZDDP as Anti-Wear Additives journal September 2015

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
gas-to-liquid oil
ionic liquid
lubricant antiwear additive
oil solubility
organophosphate
phosphonium