TLtunable2006 - Tunable friction behavior of oriented...

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Unformatted text preview: Tunable friction behavior of oriented carbon nanotube films P.L. Dickrell a, *, S.K. Pal b , G.R. Bourne a , C. Muratore c , A.A. Voevodin c , P.M. Ajayan b , L.S. Schadler b and W.G. Sawyer a a Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA b Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA c Air Force Research Laboratory, Wright Patterson AFB, OH 45433, USA Received 16 June 2006; accepted 25 September 2006 Measured friction coefficients of carbon nanotubes vary widely from l <0.1– l >1.0 [1–6], while theoretical studies suggest intrinsically high friction coefficients, approaching unity [7]. Here we report that measured friction coefficients of MWNT films are strong functions of surface chemistry and temperature, but are not dependent on the presence of water vapor. We hypothesize that the origin of the temperature dependence arises from the interaction of the surface chemical groups on the nanotubes [8–12] and rubbing counterface. The friction coefficient of individual films can be easily tuned by changing the surface temperature and chemistry of either the countersurface or the nanotubes, we have demonstrated the ability to create and control high and low friction pairs through plasma treatments of the nanotube films with argon, hydrogen, nitrogen, and oxygen. This behavior is completely reversible, and when coupled with the superior strength, thermal, and electrical properties of nanotubes, provides a versatile tunable, multifunctional tribological system. KEY WORDS: carbon nanotubes, coefficient of friction, micro-tribology, engineered surfaces A schematic of the MWNT film grown with a vertical orientation is shown in figure 1 (a). Scanning electron microscopy images of a free edge of the vertical film are shown in figures 1(b)–1(d). The vertically aligned film was grown by a chemical vapor deposition (CVD) pro- cess using ferrocene and xylene precursors [13]. Fol- lowing CVD growth, the MWNT films are cleaned using an oxygen plasma treatment. The vertically aligned MWNT films are approximately 65 l m thick and 5% dense. The MWNTs were vertically aligned, with the last few micrometers from the top surface the films entan- gled and intertwined as shown in figures 1(b)–1(d). A sample of transversely orientated nanotubes was also prepared by mechanically removing the vertical MWNTs, sonicating in acetone and dispersing onto an identical quartz substrate. After drying, this transversely oriented nanotube film was found to be approximately 5 l m thick and was comprised of a distributed ensemble of entangled nanotubes oriented in plane with the quartz substrate (figure 1(e) and 1(f))....
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.

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TLtunable2006 - Tunable friction behavior of oriented...

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