Keywords: carbon nanotube, nanocomposite, electrical property, strain sensor.

Carbon nanotubes (CNTs) of high aspect ratio possess excellent electrical conductivity. Therefore, with a small amount of CNTs, which are dispersed in insulating polymers, it is possible to produce nanocomposites with high electrical conductivity. This kind of conductive CNT/polymer nanocomposite can be applied to various fields, such as highly sensitive strain sensors, electromagnetic interference materials, etc. Generally, with the gradual increase of CNTs filled into an insulating polymer, at a specified volume fraction of CNTs, the electrical conductivity of composites will suddenly increase remarkably due to the formation of a complete electrically conducting path connected by CNTs. This process is called as percolation process.

Until now, there have been some studies on the electrical properties of this new nanocomposite [1,2,3,4,5,6]. However, there has been no numerical model or theoretical study, which evaluates electrical behavior of composites at and after the percolation threshold. In the present work, a 3D numerical model for predicting the behavior of electrical conductivity in polymers filled by CNTs is proposed. A new nanocomposite is made from a kind of epoxy and multi-walled carbon nanotubes (MWCNTs). The experimental measurements have been performed to obtain the electrical properties of this new nanocomposite. The present experimental results with many other experimental results are used to verify the proposed numerical model. The verified numerical model is then used to obtain a general percolation theory. Also, this numerical model is extended by considering the tunnel effect for predicting the resistance change of nanocomposites under the prescribed strains. Finally, a highly sensitive strain sensor is made from this nanocomposite, which is employed to show its ability on the strain measurement in the bending test of a cantilever beam. Both numerical and experimental results demonstrate that the present new strain sensor is much more sensitive than the traditional strain gauges.

1

Z. Ounaies, C. Park, K.E. Wise, E.J. Siochi and J.S. Harrison, "Electrical properties of single wall carbon nanotube reinforced polyimide composites", Composite Science & Technology, 63, 1637-1646, 2003. doi:10.1016/S0266-3538(03)00067-8

2

E. Kymakis and G.A.J. Amaratunga, "Electrical properties of single-wall carbon nanotube-polymer composite films", Journal of Applied Physics, 99, 084302, 2006. doi:10.1063/1.2189931

3

E.B. Kilbride, J.N. Coleman, J. Fraysse, P. Fournet, M. Cadek, A. Drury, S. Hutzler, S. Roth and W.J. Blau, "Experimental observation of scaling laws for alternating current and direct current conductivity in polymer-carbon nanotube composite thin films", Journal of Applied Physics, 92, 4024-4030, 2002. doi:10.1063/1.1506397

4

C.A. Martin, J.K.W. Sandler, M.S.P. Shaffer, M.K. Schwarz, W. Bauhofer, K. Schulte and A.H. Windle, "Formation of percolating networks in multi-wall carbon-nanotube-epoxy composites", Composite Science & Technology, 64, 2309-2316, 2004. doi:10.1016/j.compscitech.2004.01.025

5

J. Sandler, M.S.P. Shaffer, T. Prasse, W. Bauhofer, K. Schulte and A.H. Windle, "Development of a dispersion process for carbon nanotubes in an epoxy matrix and the resulting electrical properties", Polymer, 40, 5967-5971, 1999. doi:10.1016/S0032-3861(99)00166-4

6

J.K.W. Sandler, J.E. Kirk, I.A. Kinloch, M.S.P. Shaffer and A.H. Windle, "Ultra-low electrical percolation threshold in carbon-nanotube-epoxy composites", Polymer, 44, 5893-5899, 2003. doi:10.1016/S0032-3861(03)00539-1

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