Improving Electrical Conductivity and Thermal Properties of Polymers by the Addition of Carbon Nanotubes as Fillers
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Conductivity and Thermal Properties of Polymers by the Addition of Carbon Nanotubes as Fillers Karen I. Winey, Takashi Kashiwagi, and Minfang Mu
Abstract The remarkable electrical and thermal conductivities of isolated carbon nanotubes have spurred worldwide interest in using nanotubes to enhance polymer properties. Electrical conductivity in nanotube/polymer composites is well described by percolation, where the presence of an interconnected nanotube network corresponds to a dramatic increase in electrical conductivity ranging from 10–5 S/cm to 1 S/cm. Given the high aspect ratios and small diameters of carbon nanotubes, percolation thresholds are often reported below 1 wt%, although nanotube dispersion and alignment strongly influence this value. Increases in thermal conductivity are modest (⬃3 times) because the interfacial thermal resistance between nanotubes is considerable and the thermal conductivity of nanotubes is only 104 greater than the polymer, which forces the matrix to contribute more toward the composite thermal conductivity, as compared to the contrast in electrical conductivity, ⬎1014. The nanotube network is also valuable for improving flame-retardant efficiency by producing a protective nanotube residue. In this article, we highlight published research results that elucidate fundamental structure–property relationships pertaining to electrical, thermal, and/or flammability properties in numerous nanotube-containing polymer composites, so that specific applications can be targeted for future commercial success.
Introduction Carbon nanotubes possess three important characteristics relative to the numerous available fillers: phenomenal electrical conductivity, nanoscopic size, and high aspect ratio. This combination of properties can lead to electrical percolation at low concentrations and has naturally spurred considerable activity in producing value-added polymer nanocomposites. Electrical percolation occurs when the filler has an electrical conductivity vastly higher than the polymer matrix. The higher
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electrical conductivities that are available in nanotube/polymer composites are being explored for a variety of potential applications, including housings for cell phones and computers, lightning-strike protection for airplanes, actuators, chemical sensors, photovoltaic devices (solar cells), electrical interconnects for plastic electronics, printable circuit wiring, transparent conductive coatings, and electromagnetic interference shielding. In fact, the first major commercial product from
Hyperion Catalysis International that used multiwall carbon nanotubes (MWNTs) provides improved electrical conductivity that facilitates electrostatic coating for painting automobile bumpers.1 A variety of potential applications are also being developed that require higher thermal conductivities, including heat exchangers and heat dissipation materials for electronics packaging. This article provides a brief synopsis of fundamental research in polymer nanocomposites containing carbon nanotubes focusing
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