Mixed lubrication with C18 fatty acids: Effect of unsaturation

Sophie Loehle, Christine Matta, Clotilde Minfray, Thierry Le Mogne, Jean Michel Martin, Raphaele Iovine, Yukiko Obara, Ryuji Miura, Akira Miyamoto

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

In this paper, the lubrication mechanism of fatty acids is revisited with a new approach combining experimental and computational chemistry studies. The lubricating properties of single and mixtures of stearic, oleic and linoleic acids in a synthetic Poly-Alpha-Olefin base oil (PAO4) on iron oxide surface are investigated under mixed boundary regime with temperatures from 50 °C up to 150 °C. Low friction coefficient (about 0.055) with no visible wear is reported in the presence of single stearic acid at high temperature. This lubricating behavior is inhibited in the presence of unsaturated fatty acids highlighting an anti-synergic effect of a saturated/unsaturated mixture, especially at 150 °C. To understand the anti-synergic effect and the adsorption mechanism of these molecules, molecular dynamic (MD) and quantum chemistry simulations are performed to evaluate their diffusion coefficient in PAO4 and their adsorption mechanism on iron oxide at different temperatures. MD simulation results show a faster diffusion toward the surface for unsaturated fatty acids than for saturated fatty acid at all the studied temperatures. This means that unsaturated molecules arrive and mainly adsorb before stearic acid on the surface leading to a tribological behavior of the mixture characteristic of the unsaturated molecule. Computational chemistry suggests that all fatty acids (saturated and unsaturated) adsorption mechanism is due to the chemisorption of the carboxylic group on iron oxide surface with no desorption up to 150 °C.

Original languageEnglish
Pages (from-to)319-328
Number of pages10
JournalTribology Letters
Volume53
Issue number1
DOIs
Publication statusPublished - 2014 Jan 1

Keywords

  • Computational chemistry
  • Fatty acids
  • High temperature
  • Mixed lubrication regime

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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  • Cite this

    Loehle, S., Matta, C., Minfray, C., Mogne, T. L., Martin, J. M., Iovine, R., Obara, Y., Miura, R., & Miyamoto, A. (2014). Mixed lubrication with C18 fatty acids: Effect of unsaturation. Tribology Letters, 53(1), 319-328. https://doi.org/10.1007/s11249-013-0270-3