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Unformatted text preview: Thermal properties and percolation in carbon nanotube-polymer composites P. Bonnet, D. Sireude, B. Garnier, and O. Chauvet a ! Institut de Matériaux Jean Rouxel, UMR 6502 and Laboratoire de Thermocinetique de Nantes, UMR 6607 CNRS—Universite de Nantes, BP 32229, 44322 Nantes cedex 3, France s Received 7 September 2007; accepted 25 October 2007; published online 14 November 2007 d Thermal properties of single walled carbon nanotube s SWNT d /polymethylmetacrylate composite thick films have been investigated at room temperature. The introduction of , 7% SWNT into the polymer matrix enhances the thermal conductivity of the composite by 55% while the electrical conductivity increases by several orders of magnitude. Despite this difference, we show that the s moderate d enhancement of the thermal conductivity is quantified by the percolation of the SWNT network. A thermal conductivity of the SWNT network of , 55 W/m K is estimated. © 2007 American Institute of Physics . f DOI: 10.1063/1.2813625 g The unique physical properties of single walled carbon nanotubes s SWNT d suggest important mechanical reinforce- ment and electrical or thermal conductivity enhancement of SWNT based composites, of interest for potential applications. 1 – 3 In the case of thermal properties, the en- hancements are often less than expected 4 or from what can be extrapolated from the electrical transport properties. The quality of the SWNT dispersion in the matrix and the homo- geneity of the composite or tube purity may be responsible for these poor properties. 5 More fundamental reasons are also evoked such as the role of Kapitza contact resistances or tube-end transport. 6 There is still a debate whether the en- hancement should be described within the percolation concept 7 , 8 or by making use of effective medium approaches. 9 In this paper, we investigate the thermal properties of SWNT/polymethylmetacrylate s PMMA d composites. The thermal conductivity of the composites increases by 55% for 7% SWNT loading. This enhancement is described within the percolation concept and its rather low magnitude comes from the intrinsic thermal conductivity of the SWNT net- work which is found to be close to 55 W/m K. The SWNT/PMMA nanocomposite films have been ob- tained with nanotubes produced by electric arc discharge s GDPC, Montpellier d and polymethylmetacrylate s Aldrich, MW: 120 000 g/mol d . Raman spectroscopy shows that the average tube diameter is close to 1.5 nm. The SWNTs are dispersed in dimethylformamide s DMF d s 0.75 mg/ml d and sonicated for 2 h. The dispersion is mixed with PMMA and the SWNT/PMMA ratio is adjusted for a final SWNT vol- ume fraction f in the solid phase between 0.1% and 7.4% assuming that DMF is fully removed and that the films are dense. The mixture is sonicated for 2 h and stirred for ho- mogenization at 50 °C. This treatment increases the viscos- ity of the dispersion which, in turn, limits the SWNT aggre- gation before the solvent evaporation. The DMF evaporationgation before the solvent evaporation....
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This note was uploaded on 03/18/2012 for the course PHYSICS 303 taught by Professor Ihn during the Spring '12 term at Swiss Federal Institute of Technology Zurich.
- Spring '12
- Applied Physics