Structure and Friction of Stearic Acid and Oleic Acid Films Adsorbed on Iron Oxide Surfaces in Squalane

Michael Doig, Chris P. Warrens, Philip J. Camp*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The structure and friction of fatty acid surfactant films adsorbed on iron oxide surfaces lubricated by squalane are examined using large-scale molecular dynamics simulations. The structures of stearic acid and oleic acid films under static and shear conditions, and at various surface coverages, are described in detail, and the effects of unsaturation in the tail group are highlighted. At high surface coverage, the measured properties of stearic acid and oleic acid films are seen to be very similar. At low and intermediate surface coverages, the presence of a double bond, as in oleic acid, is seen to give rise to less penetration of lubricant in to the surfactant film and less layering of the lubricant near to the film. The kinetic friction coefficient is measured as a function of shear rate within the hydrodynamic (high shear rate) lubrication regime. Lubricant penetration and layering are observed to be correlated with friction coefficient. The friction coefficient with oleic acid depends only weakly on surface coverage, while stearic acid admits more lubricant penetration, and its friction coefficient increases significantly with decreasing surface coverage. Connections between film structure and friction are discussed.

Original languageEnglish
Pages (from-to)186-195
Number of pages10
JournalLangmuir
Volume30
Issue number1
Early online date24 Dec 2013
DOIs
Publication statusPublished - 14 Jan 2014

Keywords

  • MOLECULAR-DYNAMICS SIMULATION
  • KINETIC-FRICTION
  • STATIC FRICTION
  • OIL INTERFACE
  • ROCK FRICTION
  • BRUSH LAYERS
  • FATTY-ACIDS
  • SHEAR
  • FORCES
  • SLIP

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