, Volume 7, Issue 6, pp 625–636 | Cite as

Molecular behaviors in thin film lubrication—Part three: Superlubricity attained by polar and nonpolar molecules

  • Xiangyu Ge
  • Tobias Halmans
  • Jinjin LiEmail author
  • Jianbin LuoEmail author
Open Access
Research Article


In thin-film lubrication (TFL), generally, the viscosity of the lubricant and its coefficient of friction (CoF) increase. Finding a method to reduce the CoF in TFL is a significant challenge for tribologists. In the present work, we report a robust superlubricity attained by using polyalkylene glycols (PAGs, polar molecules) and poly-α-olefins (PAOs, nonpolar molecules) as lubricants on steel/steel friction pairs that have been pre-treated by wearing-in with polyethylene glycol aqueous solution (PEG(aq)). A steady superlubricity state with a CoF of 0.0045 for PAG100 and 0.006 for PAO6 could be maintained for at least 1 h. Various affecting factors, including the sliding velocity, normal load, and viscosity of the lubricants, were investigated. Element analysis proved that composite tribochemical layers were deposited on the worn region after the treatment with PEG(aq). These layers were formed by the tribochemical reactions between PEG and steel and composed of various substances including oxides, iron oxides, FeOOH, and Fe(OH)3, which contributed to the superlubricity. In addition to the tribochemical layers, ordered layers and a fluid layer were formed by the PAGs and PAOs during the superlubricity periods. All the three types of layers contributed to the superlubricity, indicating that it was attained in the TFL regime. Accordingly, a mechanism was proposed for the superlubricity of the PAGs and PAOs in the TFL regime in this work. This study will increase the scientific understanding of the superlubricity in the TFL regime and reveal, in the future, the potential for designing superlubricity systems on steel surfaces for industrial applications.


thin film lubrication superlubricity PEG PAG PAO 



This work was financially supported by National Natural Science Foundation of China (Nos. 51775295, 51405256, and 51527901).


  1. [1]
    Reynolds O. On the theory of lubrication and its application to Mr. Beauchamp Tower's experiments, including an experimental determination of the viscosity of olive oil. Phil Trans R Soc Lond177: 157–234 (1886)Google Scholar
  2. [2]
    Hardy W B, Doubleday I. Boundary lubrication–The paraffin series. Proc R Soc A: Math, Phys Eng Sci100(707): 550–574 (1922)CrossRefGoogle Scholar
  3. [3]
    Grubin A N, Vinogradova I E. Fundamentals of the hydrodynamic theory of lubrication of heavily loaded cylindrical surfaces. In Investigation of the Contact of Machine Components. Ketova K F, Ed. Moscow: Central Scientific Research Institute for Technology and Mechanical Engineering, 1949.Google Scholar
  4. [4]
    Lugt P M, Morales–Espejel G E. A review of elastohydrodynamic lubrication theory. Tribol Trans54(3): 470–496 (2011)CrossRefGoogle Scholar
  5. [5]
    Spikes H A. Sixty years of EHL. Lubr Sci18(4): 265–291 (2006)CrossRefGoogle Scholar
  6. [6]
    Zhang J, Meng Y G. Boundary lubrication by adsorption film. Friction3(2): 115–147 (2015)CrossRefGoogle Scholar
  7. [7]
    Luo J B, Wen S Z, Huang P. Thin film lubrication. Part I. Study on the transition between EHL and thin film lubrication using a relative optical interference intensity technique. Wear194(1–2): 107–115 (1996)CrossRefGoogle Scholar
  8. [8]
    Ma L R, Luo J B. Thin film lubrication in the past 20 years. Friction4(4): 280–302 (2016)CrossRefGoogle Scholar
  9. [9]
    Gao M, Li H, Ma L, Gao Y, Ma L, Luo J. Molecular behaviors in thin film lubrication, Part two: Direct observation of the molecular orientation near the solid surface. Friction (submitted)Google Scholar
  10. [10]
    Luo J B, Shen M W, Wen S Z. Tribological properties of nanoliquid film under an external electric field. J Appl Phys96(11): 6733–6738 (2004)CrossRefGoogle Scholar
  11. [11]
    Liang H, Guo D, Luo J B. Film forming behavior in thin film lubrication at high speeds. Friction6(2): 156–163 (2018)CrossRefGoogle Scholar
  12. [12]
    Krupka I, Hartl M, Liška M. Thin lubricating films behaviour at very high contact pressure. Tribol Int39(12): 1726–1731 (2006)CrossRefGoogle Scholar
  13. [13]
    Liang H, Guo D, Luo J B. Experimental investigation of lubrication film starvation of polyalphaolefin oil at high speeds. Tribol Lett56(3): 491–500 (2014)CrossRefGoogle Scholar
  14. [14]
    Damiens B, Venner C H, Cann P M E, Lubrecht A A. Starved lubrication of elliptical EHD contacts. J Tribol126(1): 105–111 (2004)CrossRefGoogle Scholar
  15. [15]
    Qiao Y, Zhang S, Liu Y, Ma L, Luo J. Molecular behaviors in thin film lubrication, Part one: Film formation for different polarities of molecules. Friction (submitted)Google Scholar
  16. [16]
    Li J J, Zhang C H, Deng M M, Luo J B. Investigation of the difference in liquid superlubricity between water–and oil–based lubricants. RSC Adv 5(78): 63827–63833 (2015)Google Scholar
  17. [17]
    Zeng Q F, Eryilmaz O, Erdemir A. Superlubricity of the DLC films–related friction system at elevated temperature. RSC Adv 5(113): 93147–93154 (2015)CrossRefGoogle Scholar
  18. [18]
    Li J J, Gao T Y, Luo J B. Superlubricity of graphite induced by multiple transferred graphene nanoflakes. Adv Sci5(3): 1700616 (2018)CrossRefGoogle Scholar
  19. [19]
    Xu J, Li J J. New achievements in superlubricity from international workshop on superlubricity: Fundamental and applications. Friction3(4): 344–351 (2015)CrossRefGoogle Scholar
  20. [20]
    Zeng Q F, Yu F, Dong G N. Superlubricity behaviors of Si3N4/DLC films under PAO oil with nano boron nitride additive lubrication. Surf Interface Anal45(8): 1283–1290 (2013)CrossRefGoogle Scholar
  21. [21]
    Zeng Q F, Dong G N, Martin J M. Green superlubricity of Nitinol 60 alloy against steel in presence of castor oil. Sci Rep6: 29992 (2016)CrossRefGoogle Scholar
  22. [22]
    Chen Z, Liu Y H, Zhang S H, Luo J B. Controllable superlubricity of glycerol solution via environment humidity. Langmuir29(38): 11924–11930 (2013)CrossRefGoogle Scholar
  23. [23]
    Tortora A M, Veeregowda D H. Effects of two sliding motions on the superlubricity and wear of self–mated bearing steel lubricated by aqueous glycerol with and without nanodiamonds. Wear386–387: 173–178 (2017)CrossRefGoogle Scholar
  24. [24]
    Li H, Wood R J, Rutland M W, Atkin R. An ionic liquid lubricant enables superlubricity to be “switched on” in situ using an electrical potential. Chem Commun50(33): 4368–4370 (2014)CrossRefGoogle Scholar
  25. [25]
    Ge X Y, Li J J, Zhang C H, Wang Z N, Luo J B. Superlubricity of 1–ethyl–3–methylimidazolium trifluoromethanesulfonate ionic liquid induced by tribochemical reactions. Langmuir34(18): 5245–5252 (2018)CrossRefGoogle Scholar
  26. [26]
    Li J J, Zhang C H, Luo J B. Superlubricity behavior with phosphoric acid–water network induced by rubbing. Langmuir27(15): 9413–9417 (2011)CrossRefGoogle Scholar
  27. [27]
    Ge X Y, Li J J, Zhang C H, Luo J B. Liquid superlubricity of polyethylene glycol aqueous solution achieved with boric acid additive. Langmuir34(12): 3578–3587 (2018)CrossRefGoogle Scholar
  28. [28]
    Ding M, Lin B, Sui T Y, Wang A Y, Yan S, Yang Q. The excellent anti–wear and friction reduction properties of silica nanoparticles as ceramic water lubrication additives. Ceram Int44(12): 14901–14906 (2018)CrossRefGoogle Scholar
  29. [29]
    Li J J, Zhang C H, Deng M M, Luo J B. Investigation of the difference in liquid superlubricity between water–and oil–based lubricants. RSC Adv5(78): 63827–63833 (2015)CrossRefGoogle Scholar
  30. [30]
    Dowson D, Higginson G R. Elasto–Hydrodynamic Lubrication. Oxford (UK): Pergamon Press, 1977.zbMATHGoogle Scholar
  31. [31]
    Guilminot E, Dalard F, Degrigny C. Mechanism of iron corrosion in water–polyethylene glycol (PEG 400) mixtures. Corros Sci44(10): 2199–2208 (2002)CrossRefGoogle Scholar
  32. [32]
    Soltani T, Lee B K. A benign ultrasonic route to reduced graphene oxide from pristine graphite. J Colloid Interface Sci486: 337–343 (2017)CrossRefGoogle Scholar
  33. [33]
    Espinosa T, Sanes J, Bermúdez M D. New alkylether–thiazolium room–temperature ionic liquid lubricants: surface interactions and tribological performance. ACS Appl Mater Interfaces8(28): 18631–18639 (2016)CrossRefGoogle Scholar
  34. [34]
    Wang H Z, Song Z H, Qiao D, Feng D P, Lu J J. Tribological behavior of Si3N4/Ti3SiC2 contacts lubricated by lithiumbased ionic liquids. Adv Mater Sci Eng2014: 863230 (2014)Google Scholar
  35. [35]
    Song Z H, Liang Y M, Fan M J, Zhou F, Liu W M. Lithium–based ionic liquids as novel lubricant additives for multiply alkylated cyclopentanes (MACs). Friction1(3): 222–231 (2013)CrossRefGoogle Scholar
  36. [36]
    Amann T, Gatti F, Oberle N, Kailer A, Rühe J. Galvanically induced potentials to enable minimal tribochemical wear of stainless steel lubricated with sodium chloride and ionic liquid aqueous solution. Friction6(2): 230–242 (2018)CrossRefGoogle Scholar
  37. [37]
    Luo J B, Huang P, Wen S, Li L K Y. Characteristics of liquid lubricant films at the nano–scale. J Tribol121(4): 872–878 (1999)CrossRefGoogle Scholar
  38. [38]
    Biresaw G, Sharma B K, Bantchev G B, Kurth T L, Doll K M, Erhan S Z, Kunwar B, Scott J W. Elastohydrodynamic properties of biobased heat–bodied oils. Ind Eng Chem Res53(42): 16183–16195 (2014)CrossRefGoogle Scholar
  39. [39]
    Zhang C H, Zhao Y C, Björling M, Wang Y, Luo J B, Prakash B. EHL properties of polyalkylene glycols and their aqueous solutions. Tribol Lett45(3): 379–385 (2012)CrossRefGoogle Scholar
  40. [40]
    Wang H D, Liu Y H, Li J J, Luo J B. Investigation of superlubricity achieved by polyalkylene glycol aqueous solutions. Adv Mater Interfaces3(19): 1600531 (2016)CrossRefGoogle Scholar
  41. [41]
    Xiao H P, Guo D, Liu S H, Lu X C, Luo J B. Experimental investigation of lubrication properties at high contact pressure. Tribol Lett40(1): 85–97 (2010)CrossRefGoogle Scholar

Copyright information

© The author(s) 2018

Open Access: This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors and Affiliations

  1. 1.State Key Laboratory of TribologyTsinghua UniversityBeijingChina
  2. 2.RWTH Aachen UniversityAachenGermany

Personalised recommendations