The effect of surface roughness on the adhesion of solid surfaces for systems with and without liquid lubricant

V. N. Samoilov, Ion Marius Sivebæk, B. N. J. Persson

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Abstract

We present molecular dynamics results for the interaction between two solid elastic walls during pull-off for systems with and without octane (C8H18) lubricant. We used two types of substrate-flat and corrugated-and varied the lubricant coverage from similar to1/8 to similar to4 ML (monolayers) of octane. For the flat substrate without lubricant the maximum adhesion was found to be approximately three times larger than for the system with the corrugated substrate. As a function of the octane coverage (for the corrugated substrate) the pull-off force first increases as the coverage increases from 0 to similar to1 ML, and then decreases as the coverage is increased beyond monolayer coverage. It is shown that at low octane coverage, the octane molecules located in the substrate corrugation wells during squeezing are pulled out of the wells during pull-off, forming a network of nanocapillary bridges around the substrate nanoasperities, thus increasing the adhesion between two surfaces. For greater lubricant coverages a single capillary bridge is formed. The adhesion force saturates for lubricant coverages greater than 3 ML. For the flat substrate, during pull-off we observe discontinuous, thermally activated changes in the number n of lubricant layers (n-1-->n layering transitions), whereas for the corrugated substrate these transitions are "averaged" by the substrate surface roughness.
Original languageEnglish
JournalJournal of Chemical Physics
Volume121
Issue number19
Pages (from-to)9639-9647
ISSN0021-9606
DOIs
Publication statusPublished - 2004

Bibliographical note

Copyright (2004) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

Keywords

  • SOLVATION FORCES
  • LONG-RANGE ELASTICITY
  • ATOMIC-SCALE
  • THIN-FILMS
  • LAYERING TRANSITION
  • INTERFACIAL PROCESSES
  • BIOLOGICAL-SYSTEMS
  • MOLECULAR-DYNAMICS
  • CONFINED FILMS
  • KINETIC FRICTION

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