A low-viscosity ionic liquid demonstrating superior lubricating performance from mixed to boundary lubrication

abstract This study reports on an ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)i-mide as a promising engine lubricant candidate . This IL has a relatively low viscosity of 4.7 cSt (similarto 0W-10 racing engine oil), a low viscosity–pressure (V–P) coefficient of 6.5 GPa 1 at 100 1C, a highviscosity index of 159, and a high onset decomposition temperature of 472 1C. The ionic liquid deliverssubstantially lower friction in mixed lubrication (ML) and provides better scuffing protection inboundary lubrication (BL) than those of hydrocarbon lubricants with similar viscosities. The low MLfriction is possibly attributed to its low V–P coefficient and a hypothetical multi-layer boundary film atthe interface. In BL, the tribochemical reactions between the IL and the contact surfaces to form aprotective tribo-film are believed to be responsible for the IL’s superior anti-scuffing behavior.Microstructural examination and chemical composition analysis were conducted on the wear scarsfrom both the top surface and the cross section to study the wear mode and characterize the tribo-filmand near-surface structure.& 2012 Elsevier B.V. All rights reserved.

[1]  S. Bair.  The high pressure rheology of some simple model hydrocarbons , 2002 .

[2]  Huaping Xiao,et al.  Film Thickness of Ionic Liquids Under High Contact Pressures as a Function of Alkyl Chain Length , 2011 .

[3]  T. Itoh,et al.  Design of Alkyl Sulfate Ionic Liquids for Lubricants , 2009 .

[4]  Feng Zhou,et al.  Tribological performance of phosphonium based ionic liquids for an aluminum-on-steel system and opinions on lubrication mechanism , 2006 .

[5]  T. E. Tallian,et al.  Ball bearing lubrication: The elastohydrodynamics of elliptical contacts , 1982 .

[6]  Miaofang Chi,et al.  Nanostructure and Composition of Tribo-Boundary Films Formed in Ionic Liquid Lubrication , 2011 .

[7]  Ichiro Minami,et al.  The Tribological Properties of Ionic Liquids Composed of Trifluorotris(pentafluoroethyl) Phosphate as a Hydrophobic Anion , 2008 .

[8]  Takeshi Fukuda,et al.  Lubrication mechanism of concentrated polymer brushes in solvents: effect of solvent viscosity , 2012 .

[9]  Scott Bair,et al.  Pressure-Viscosity Behavior of Lubricants to 1.4 GPa and Its Relation to EHD Traction , 2000 .

[10]  Influence of temperature on PA 6–steel contacts in the presence of an ionic liquid lubricant , 2007 .

[11]  Laigui Yu,et al.  Room-temperature ionic liquids: a novel versatile lubricant. , 2001, Chemical communications.

[12]  Chengfeng Ye,et al.  Polyethylene glycol functionalized dicationic ionic liquids with alkyl or polyfluoroalkyl substituents as high temperature lubricants , 2006 .

[13]  Scott Bair,et al.  High Pressure Rheology for Quantitative Elastohydrodynamics , 2007 .

[14]  J. Shreeve,et al.  Phosphazene-based ionic liquids: synthesis, temperature-dependent viscosity, and effect as additives in water lubrication of silicon nitride ceramics. , 2004, Inorganic chemistry.

[15]  Simon C. Tung,et al.  Automotive tribology overview of current advances and challenges for the future , 2004 .

[16]  Ichiro Minami,et al.  Ionic Liquids in Tribology , 2009, Molecules.

[17]  Farrukh Qureshi,et al.  Accurate Measurements of Pressure-Viscosity Behavior in Lubricants , 2002 .

[18]  S. Bair.  The shear rheology of thin compressed liquid films , 2002 .

[19]  Jun Qu,et al.  Oil-miscible and non-corrosive phosphonium-based ionic liquids as candidate lubricant additives , 2012 .

[20]  John J. Truhan,et al.  Ionic liquids with ammonium cations as lubricants or additives , 2006 .

[21]  A. Pensado,et al.  Pressure–Viscosity Coefficients for Polyalkylene Glycol Oils and Other Ester or Ionic Lubricants , 2011, Tribology Letters.

[22]  María-Dolores Bermúdez,et al.  Ionic Liquids as Advanced Lubricant Fluids , 2009, Molecules.

[23]  L. Rudnick.  Lubricant Additives: Chemistry and Applications , 2007 .

[24]  A. Pensado,et al.  The Pressure–Viscosity Coefficient of Several Ionic Liquids , 2008 .

[25]  Jun Qu,et al.  Ionic Liquids as Novel Lubricants and Additives for Diesel Engine Applications , 2009 .

[26]  K. R. Harris,et al.  Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Hexyl-3-methylimidazolium Hexafluorophosphate and 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide , 2007 .

[27]  Mark A. Nicholls,et al.  Review ofthe lubrication ofmetallic surf aces by zinc dialkyl-dithiophosphates , 2005 .

[28]  Jun Qu,et al.  Tribological characteristics of aluminum alloys sliding against steel lubricated by ammonium and imidazolium ionic liquids , 2009 .

[29]  S. Lawes,et al.  Lubrication of Steel/Steel Contacts by Choline Chloride Ionic Liquids , 2010 .

[30]  P. Blau,et al.  Oxygen Diffusion Enables Anti-Wear Boundary Film Formation on Titanium Surfaces in Zinc-Dialkyl-Dithiophosphate (ZDDP)-Containing Lubricants , 2009 .

[31]  Feng Zhou,et al.  Ionic liquid lubricants: designed chemistry for engineering applications. , 2009, Chemical Society reviews.

[32]  P. Blau,et al.  Antiwear performance and mechanism of an oil-miscible ionic liquid as a lubricant additive. , 2012, ACS applied materials & interfaces.