Achieving electrical percolation in polymer-carbon nanotube composites
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Achieving electrical percolation in polymer-carbon nanotube composites Sameer S. Rahatekar, M. Hamm, Milo S. P. Shaffer1, James A. Elliott Macromolecular Materials Laboratory, Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QE 1 Department of Chemistry, Imperial College, South Kensington, London, SW7 2AZ, UK. ABSTRACT The addition of carbon nanotubes (CNTs) to a polymer matrix is expected to yield improvements in both mechanical and electrical properties. The focus of this paper is to give a snapshot of our current work on CNT-filled thermoplastic polymer textile fibers and the enhancement of their electrical properties. The challenge is to determine the type and size of nanotubes that are most effective for a given application, and how they should be dispersed or modified to interact with the polymer. The objective of this work is to develop an understanding of how the processing methods and properties of nanotube polymer composites are related to the geometry of the nanotubes used, their orientation, and their loading fraction. It will then be possible to design desired composite properties by controlling the relevant process variables. The research described in this paper primarily involves mesoscale simulations (dissipative particle dynamics) of packed assemblies of oriented CNTs suspended in a polymer matrix. Computer simulations have been carried out to study the effect of processing conditions, aspect ratio of CNTs and effect of electric field on electrical conductivity. The percolation threshold required to achieve an electrically conductive polymer-CNT fiber can be predicted for given set of process variables. The model predictions are compared with the predictions of classical percolation theory, and with experimental data from measurements of bulk resistivity from CNTs dispersed in thermoplastic polymers. INTRODUCTION There is an increasing worldwide demand for novel polymer materials with improved physical and mechanical properties for applications ranging from the aerospace sector to high performance textiles. Due to their remarkable intrinsic properties, the addition of carbon nanotubes to polymer matrices is expected to yield benefits in a number of areas such as strength, stiffness, thermal and electrical conductivity, and maximum operating temperature. Furthermore, the small size of nanotubes yields a high quality surface finish, and may permit easier recycling of the composite materials. The dimensions of the nanotubes also enable uniform filling of thin composite sections and one of the most appealing prospects is that of the nanofiber-reinforced fiber. However, development of these nanocomposite materials is in its infancy, with many issues remaining to be solved. Although considerable efforts have been applied to the atomistic and quantum mechanical modelling of carbon nanotubes and fullerenes, comparatively little work has been published on the behaviour of assemblies of nanotubes within a composite material. Most work has looked
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