IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Tribology Wednesday Sessions
       Session TR+SS-WeM

Invited Paper TR+SS-WeM7
The Effect of Packing Density on the Friction of Alkane Monolayers

Wednesday, October 31, 2001, 10:20 am, Room 132

Session: Fundamentals of Tribology & Adhesion
Presenter: J.A. Harrison, United States Naval Academy
Authors: J.A. Harrison, United States Naval Academy
P.T. Mikulski, United States Naval Academy
Correspondent: Click to Email
Hydrocarbon materials have traditionally been used to prevent the friction and wear of mechanical components in sliding contact. One important example of this is the use of oil in conventional combustion engines. The advent of chemical vapor deposition technology has piqued interest in the use of solid hydrocarbons as lubricants in systems such as microelectromechanical devices. A detailed knowledge of the molecular-scale mechanisms responsible for lubrication would be invaluable in the design of novel solid lubricants. We are using molecular dynamics to examine the atomic-scale phenomena governing the tribology of hydrocarbon-containing systems. Because liquid hydrocarbons and boundary layer lubricants, such as self-assembled monolayers, are to be studied, the potential energy function must include intermolecular interactions. The new adaptive intermolecular reactive empirical bond-order potential (AIREBO)@footnote 1@ can simulate reactive and non-reactive processes in a wide range of environments, including graphite, liquid hydrocarbons, and self-assembled monolayers. We have conducted extensive simulations that have examined the friction of alkane monolayers attached to diamond surfaces or model self-assembled monolayer systems. We have examined friction as a function of packing density, chain length,@footnote 2@ and sliding direction. Recent AFM results of Perry and coworkers@footnote 3@ unambiguously demonstrate that decreasing the packing density, or the disorder of the film, increases the friction. Simulations reproduce this trend and provide an atomic-scale explanation for this observation. *Supported by ONR and AFOSR. . @FootnoteText@ @footnote 1@ S. J. Stuart, A. B. Tutein, and J. A. Harrison, J. Chem. Phys. 112, 6472-6486 (2000). @footnote 2@ A. B. Tutein, S. J. Stuart, and J. A. Harrison, Langmuir 16, 291-296 (2000); Ibid. , J. Phys. Chem. B 103, 11357-11365 (1999). @footnote 3@ Lee et al., Langmuir 16 2220 (2000).