Microstructural Modeling of Electrical Behavior in CNT Polymer Composites
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Microstructural Modeling of Electrical Behavior in CNT Polymer Composites S. Xu, O. Rezvanian, K. Peters, and M.A. Zikry Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695 ABSTRACT A three-dimensional (3D) carbon nanotube (CNT) resistor network computational model was developed to investigate the electrical conductivity, and current and thermal flow in polymer composites with randomly dispersed CNTs. A search algorithm was developed to determine conductive paths for 3D CNT arrangements and to account for electron tunneling effects. By coupling Maxwell specialized finite-element (FE) formulation with Fermi-based tunneling resistance, specialized FE techniques were then used to obtain current density evolution for different CNT/polymer dispersions and tunneling distances. These computational approaches address the limitations of percolation theories that are used to estimate electrical conductivity of CNTs. The predictions indicate that tunneling distance significantly affects 3D electrical conductivity and thermal distributions. INTRODUCTION Carbon nanotubes (CNTs) have the potential to be used in many new technological applications including electrically conductive polymer composite, due to their high electrical conductivity and large aspect ratios [1]. Among the various conductive fillers for polymer matrices, CNTs have significant advantages over the other fillers, since CNTs have superior intrinsic conductivities (105-108 S m-1), high compatibility with polymer matrices, and large tunable aspect ratios [2]. Improvements in electrical and thermal properties of CNT polymer composites have indicated that CNTs can have complex three-dimensional (3D) conducting paths throughout the composite structure [3]. The electrical behavior of a conductive polymer composite comprised of insulating polymers and conducting fillers is commonly described by percolation theory. In the classical percolation theory, the conducting fillers are either connected or disconnected [4, 5]. It has been shown that this classical geometrical percolation theory cannot fully explain the electrical conductive behavior of CNT-filled polymer composites [6, 7], where the fillers do not physically touch each other and the electrical connectedness is established through tunneling between the conducting fillers [8]. However, the classical percolation behavior has been widely applied to understand and predict conductivity in composite systems [4], and the limitations have been discussed for different applications [7, 8]. In 3D CNT networks in polymer composites, current leakage through tunneling can play a dominant role in the overall electrical conductivity of the composites. Therefore, a better understanding of the electrical conduction mechanism and how tunneling works in different CNT arrangements, can be essential in designing CNT polymer composites with self-sensing capabilities. Recent computational efforts to simulate the electrical behavior of CNT polymer composites have used resistor network pe
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