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Title: Ionic liquids composed of phosphonium cations and organophosphate, carboxylate, and sulfonate as lubricant antiwear additives

Oil-soluble phosphonium-based ionic liquids (ILs) have recently been reported as potential ashless lubricant additives. This study is to expand the IL chemistry envelope and to achieve fundamental correlations between the ion structures and ILs’ physiochemical and tribological properties. Here we present eight ILs containing two different phosphonium cations and seven different anions from three groups: organophosphate, carboxylate, and sulfonate. The oil solubility of ILs seems largely governed by the IL molecule size and structure complexity. When used as oil additives, the ranking of effectiveness in wear protection for the anions are: organophosphate > carboxylate > sulfonate. All selected ILs outperformed a commercial ashless anti-wear additive. Surface characterization from the top and the cross-section revealed the nanostructures and compositions of the tribo-films formed by the ILs. Some fundamental insights were achieved: branched and long alkyls improve the IL’s oil solubility, anions of a phosphonium-phosphate IL contribute most phosphorus in the tribofilm, and carboxylate anions, though free of P, S, N, or halogen, can promote the formation of an anti-wear tribofilm.
 [1] ;  [2] ;  [2] ;  [3] ;  [3] ;  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Texas A & M Univ., College Station, TX (United States)
  2. Cytec Industries Inc., Woodland Park, NJ (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Additional Journal Information:
Journal Volume: 30; Journal Issue: 44; Journal ID: ISSN 0743-7463
American Chemical Society
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ionic liquids; lubricant additives; phosphonium; carboxylate; oil-solubility