Electrical Percolation in Carbon Nanotube Dispersions: A Mesoscale Modeling and Experimental Study
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Electrical Percolation in Carbon Nanotube Dispersions: A Mesoscale Modeling and Experimental Study Sameer Sharad Rahatekar1,2, Milo S P Shaffer3, and James A Elliott4 1 Fire Research Division, National Institute of Standards and Technology, 100 Bareau Drive, Mail stop 8665, Gaithersburg, MD, 20899 2 Materials Science and Metallurgy, University of Cambridge, Department of materials Science and Metallurgy, Pembroke Street, Cambridge, CB2 3QZ, United Kingdom 3 Department of Chemistry, Imperial College, London, Imperial College, London, South Kensington, London, SW7 2AZ, United Kingdom 4 Materials Science and Metallurgy, University of Cambridge, Materials Science and Metallurgy, Pembroke Street, Cambridge, CB2 3QZ Abstract: This paper describes our current work on electrical percolation in carbon nanotubes filled thermoplastic polymer fibers. The objective of this work is to develop an understanding of how the electrical properties of the nanotube/polymer composites are affected by processing conditions, orientation of nanotubes, and their loading fraction. In the first part of the work, mesoscale modelling of nanotubes was carried out using a dissipative particle dynamics method. The percolation threshold required to achieve an electrically conductive network of nanotubes within in a polymer fibre was predicted as a function of orientation and aspect ratio of nanotubes using a Monte Carlo method to measure the network impedance. In the second part of this work, X-ray diffraction analyses were carried out to find the degree of alignment of nanotubes in polyamide 12 fibers.
Introduction: The addition of fibrous fillers to polymer matrices improves the properties of composites, such as strength, stiffness, thermal and electrical conductivity, which are generally enhanced by the high aspect ratio of the fibers [1-3]. Electrical conductivity and the viscosity of the suspension is particularly sensitive to the aspect ratio of the conductive fibers used; when dispersed in a matrix, higher aspect ratio fibers achieve percolation at much lower volume fractions than less anisotropic particles [4-6]. This dependence is understood for randomly distributed, and to some extent aligned, straight rigid fibers. However, real systems are additionally influenced by applied fields such as shear force and external electric field, fiber polydispersity, curvature, flexibility, and interaction with the polymer matrix. The work described in this paper is applicable to the general category of conducting fibers dispersed in a non-conducting matrix, and allows studies of both the percolation
behavior and the evolution of the fiber network on which it depends. This study is particularly motivated by a long-standing interest in carbon nanotube filled polymers fibers.
The theoretical study of percolation of fiber like objects has been carried out by various researchers [7-12]. The principal limitation of these studies is that they can not take into account the effect of fiber-fiber interactions or fiber-matrix interactions. Therefor
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