Multifunctional Single-Walled Carbon Nanotube Polycarbonate Composites
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Multifunctional Single-Walled Carbon Nanotube Polycarbonate Composites Jian Chen,†,* Rajagopal Ramasubramaniam,† and Haiying Liu‡ Zyvex Corporation, 1321 North Plano Road, Richardson, Texas 75081, USA. ‡ Department of Chemistry, Michigan Technological University, Houghton, Michigan 49931, USA †
ABSTRACT Uniform single-walled carbon nanotube (SWNT) polycarbonate composites were fabricated using noncovalently functionalized, soluble SWNTs. These composites showed dramatic improvements in the electrical conductivity and mechanical tensile strength at low SWNT loading. We also observed a stress-induced SWNT alignment in polycarbonate film, which is very difficult to achieve with pristine SWNTs. INTRODUCTION Single-walled carbon nanotubes (SWNTs), due to their high-aspect ratio, small diameter, low weight, high-mechanical strength, high thermal and air stability, and high electrical and thermal conductivity, are recognized as the ultimate carbon fibers for high performance, multifunctional composites. Potential property enhancement by well-dispersed SWNTs in polymer matrices include strength, stiffness, electrical and thermal conductivities, thermal stability, solvent resistance, increase in glass transition temperature (Tg), reduction in thermal shrinkage, etc. The remarkable mechanical, electrical, and thermal properties of SWNTs have proven difficult to harness, however, in polymer composites [1-4]. This is largely due to the smooth carbon nanotube surfaces (i.e., sidewalls) that are incompatible with most solvents and polymers, which leads to poor dispersion of nanotubes in the polymer matrix. Nanotube sidewalls are difficult to functionalize without altering the nanotube’s desirable intrinsic properties. Unfunctionalized sidewalls produce poor adhesion between the nanotubes and the polymer matrix. The covalent chemistry of nanotube side-walls can significantly damage or even destroy SWNTs’ intrinsic electrical, thermal and mechanical properties. We have recently developed a versatile and nondamaging chemistry platform to rationally engineer carbon nanotube surfaces, while preserving nearly all of the nanotubes’ intrinsic properties [5,6]. It allows us to engineer specific nanotube surface properties in a straightforward manner. This technology permits excellent solubility of nanotubes in organic solvents, which allows homogeneous dispersion of nanotubes in a polymer matrix, and enables significantly enhanced adhesion between nanotubes and the matrix. We report here that homogeneous nanotube polycarbonate composites can be fabricated using noncovalently functionalized, soluble SWNTs, and that these composites show dramatic improvements in mechanical and electrical conductivity with low SWNT loading.
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EXPERIMENTAL DETAILS SWNTs produced by the high pressure carbon monoxide (HiPco) process were purchased from Carbon Nanotechnologies, Inc. (Lot # R0205), and were solubilized in chloroform with poly(p-phenyleneethynylene) (PPE) (Figure 1) along with vigorous shaking and/or short bath sonication [5,6].
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