Ionic liquids as boundary additives in water-based and PAO lubricants

Wahyu Wijanarko*, Hamid Khanmohammadi, Nuria Espallargas*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


Ionic liquids have been widely discussed as potential lubricants, however, their properties make them also very good potential candidates as lubricant additives (e.g., friction modifiers and anti-wear). In this work, the tribological study of two ionic liquids (tributylmethylphosphonium dimethylphosphate (PP), and 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (BMP)) as lubricant additives has been performed on stainless steel (AISI 316L) exposed to polar (water-glycol) and non-polar (polyalphaolefin) based lubricants under boundary lubricating conditions. The performance of these ionic liquids as lubricant additives has been compared to a classical organic friction modifier (dodecanoic acid (C12)). The water-glycol lubricant formulated with the two ionic liquids showed friction values higher than the same base lubricant formulated with dodecanoic acid, however, opposite results were observed for polyalphaolefin (PAO). A detailed surface chemical analysis using X-ray photoelectron spectroscopy (XPS) revealed differences in the passive/tribofilm thickness and chemical composition of the stainless steel surface tested in all lubricants. In the case of the polar lubricant additivated with ionic liquids, the tribochemical reaction accompanied by a tribocorrosion process led to the formation of an unstable passive/tribofilm resulting in high friction and wear. However, in the absence of tribocorrosion process (polyalphaolefin base lubricant), the tribochemical reaction led to the formation of a stable passive/tribofilm resulting in low friction and wear. A detailed surface and subsurface investigation of the microstructure using scanning electron microscopy equipped with a focused ion beam (SEM-FIB) showed that high wear rates resulted in thicker recrystallization region under the wear track surface. Among all lubricant additives tested in this work, BMP in non-polar lubricant media showed the best tribological performance.

Original languageEnglish
Pages (from-to)1405-1423
Number of pages19
Issue number9
Publication statusPublished - Sept 2022


  • ionic liquids
  • polyalphaolefin (PAO)
  • tribochemistry
  • tribocorrosion
  • tribofilm
  • water lubricant


Dive into the research topics of 'Ionic liquids as boundary additives in water-based and PAO lubricants'. Together they form a unique fingerprint.

Cite this