De Barros Bouchet, M. I. and Matta, C. and Le-Mogne, Th. and Martin, J. Michel and Zhang, Q. and Goddard, W., III and Kano, M. and Mabuchi, Y. and Ye, J. (2007) Superlubricity mechanism of diamond-like carbon with glycerol. Coupling of experimental and simulation studies. Journal of Physics: Conference Series, 89 . Art. No. 012003. ISSN 1742-6596 http://resolver.caltech.edu/CaltechAUTHORS:BARjpcs07
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We report a unique tribological system that produces superlubricity under boundary lubrication conditions with extremely little wear. This system is a thin coating of hydrogen-free amorphous Diamond-Like-Carbon (denoted as ta-C) at 353 K in a ta-C/ta-C friction pair lubricated with pure glycerol. To understand the mechanism of friction vanishing we performed ToF-SIMS experiments using deuterated glycerol and 13C glycerol. This was complemented by first-principles-based computer simulations using the ReaxFF reactive force field to create an atomistic model of ta-C. These simulations show that DLC with the experimental density of 3.24 g/cc leads to an atomistic structure consisting of a 3D percolating network of tetrahedral (sp3) carbons accounting for 71.5% of the total, in excellent agreement with the 70% deduced from our Auger spectroscopy and XANES experiments. The simulations show that the remaining carbons (with sp2 and sp1 character) attach in short chains of length 1 to 7. In sliding simulations including glycerol molecules, the surface atoms react readily to form a very smooth carbon surface containing OH-terminated groups. This agrees with our SIMS experiments. The simulations find that the OH atoms are mostly bound to surface sp1 atoms leading to very flexible elastic response to sliding. Both simulations and experiments suggest that the origin of the superlubricity arises from the formation of this OH-terminated surface.
|Additional Information:||© 2007 IOP Publishing Limited. Accepted papers received: 12 November 2007. Published online: 29 November 2007. We would like to dedicate this paper to the memory of Dr. Michael Gardos who was instrumental in stimulating our research toward how fundamental chemistry of surfaces plays a role in friction and wear. International Conference on Science of Friction, Irago, Aichi, Japan, 9–13 September 2007, Journal of Physics: Conference Series 89 (2007) http://www.iop.org/EJ/toc/1742-6596/89/1|
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|Deposited On:||29 Nov 2007|
|Last Modified:||26 Dec 2012 09:46|
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