Exploring the "friction modifier" phenomenon: Nanorheology of n-alkane chains with polar terminus dissolved in n-alkane solvent

Marina Ruths, Hiroko Ohtani, Michael L. Greenfield, Steve Granick

Research output: Contribution to journalArticlepeer-review

Abstract

Dilute solutions of two polar end-functionalized linear alkanes (1-hexadecylamine and palmitic acid), each dissolved in tetradecane, were confined between two mica surfaces and investigated using a surface forces apparatus modified to study shear nanorheology. These two solutions showed similar nanorheological properties that differed from those observed for pure n-alkanes. In static measurements, a "hard wall", rather than an oscillatory force, was observed as a function of film thickness. The polar alkane component formed a weakly adsorbed single layer at each mica surface, disrupting the layered structures found in neat n-tetradecane. In dynamic experiments at low shear amplitude, the storage modulus G′ exceeded the loss modulus G″ at low frequencies; above some characteristic frequencies G″ increased such that G′ ≈ G″, indicating significantly more energy loss through viscous modes at higher frequency. When the amplitude was varied at fixed frequency, no stick-slip was observed and the limiting value of the shear stress at high effective shear rate was an order of magnitude less than for unfunctionalized n-alkanes at similar loads. Together, these results show that the addition of a small amount of polar alkane component, by disrupting the layered structures that would have been formed in the neat n-alkane, is effective in suppressing static friction and reducing kinetic friction in the boundary lubrication regime.

Original languageEnglish (US)
Pages (from-to)207-214
Number of pages8
JournalTribology Letters
Volume6
Issue number3-4
StatePublished - Dec 1 1999

Keywords

  • Friction modifiers
  • Molecular tribology
  • Nanorheology
  • Surface forces apparatus
  • Thin film lubrication

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Mechanical Engineering

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