Electrical Conductivity and Electromagnetic Interference Shielding of Multi-walled Carbon Nanotube Filled Polymer Compos
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Electrical Conductivity and Electromagnetic Interference Shielding of Multi-walled Carbon Nanotube Filled Polymer Composites Yonglai Yang1, Mool C. Gupta1, Kenneth L. Dudley2 and Roland W. Lawrence2 1 Applied Research Center, Old Dominion University, Newport News, VA 23606, U.S.A. 2 Electromagnetics Research Branch, NASA Langley Research Center, Hampton, VA 23681, U.S.A. ABSTRACT Multi-walled carbon nanotube (MWNT) filled polystyrene (PS) composites were synthesized for electromagnetic interference (EMI) shielding applications. SEM images of composites showed the formation of the conducting networks through MWNTs within the PS matrix. The measured DC conductivity of composites increased with increasing MWNT loading, showing a typical percolation behavior. EMI shielding characteristics of MWNT-PS composites were investigated in the frequency range of 8.2-12.4 GHz (X-band). It was observed that the shielding effectiveness (SE) of such composite increased with the increase of MWNT loading. The SE of the composite containing 7 wt% MWNTs could reach more than 26 dB in the measured frequency region. INTRODUCTION Carbon nanotubes, due to their unique nanoscale structures, outstanding mechanical and electrical properties, are recognized as one of the most intriguing nanomaterials in the 21st century [1,2]. In recent years, single-walled and multi-walled carbon nanotubes have been actively pursued in both fundamental and applied research aspects [3-5]. Compared to singlewalled carbon nanotubes, multi-walled carbon nanotubes (MWNTs) are currently receiving more attention for commercial applications, because of easy large-scale production via the chemical vapor deposition synthesis. Electromagnetic interference (EMI) shielding is one of the promising applications of conductive MWNTs filled polymer composites. The conventional EMI shielding materials are common metals and their composites, which have high shielding effectiveness due to the high conductivity and dielectric constant of materials [6]. While metals have good EMI shielding properties, they have disadvantages such as heavy weight, easy corrosion, and poor processing for shielding materials. Due to the desire for lightweight for EMI shielding systems, polymer-based conducting composites are increasingly attractive to supplement the disadvantages of common metals for EMI shielding [7-10]. Carbon materials are very effective to be used as fillers in the polymer composites for EMI shielding, such as carbon black, carbon filaments, carbon fibers, etc [11,12]. It is expected that the use of multi-walled carbon nanotubes as fillers in the polymer composites is attractive for shielding materials due to their small diameter, large aspect ratio, lightweight, high electrical conductivity and mechanical strength. In this study, we report a composite consisting of conductive MWNTs dispersed within an insulating polymer matrix (polystyrene, PS) and investigate its direct current (DC) electrical conductivity and EMI shielding properties in the frequency range of 8.2-12.4 G
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