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HH4.11.1

Characterization of Single-walled Carbon Nanotube Fibers and Correlation with Stretch Alignment Michelle Chen1, Csaba Guthy1, Juraj Vavro1, John E. Fischer1, Stéphane Badaire2, Cécile Zakri2, Philippe Poulin2, Vincent Pichot3 and Pascale Launois3 1

Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104-6272 USA 2 Centre de Recherche Paul Pascale-CNRS, Av. Schweitzer, 33600 Pessac France 3 Laboratoire de Physique des Solides (UMR CNRS 8502), Bât. 510, Université de Paris Sud, 91405 Orsay France Abstract Structural, electrical and thermal methods are applied to characterize single-walled carbon nanotube (SWNT) fibers with post-extrusion stretching as the independent variable. HiPco SWNTs are dispersed in water using sodium dodecyl sulfate (SDS), and then co-extruded with polyvinyl alcohol (PVA)/water through a long syringe into a rotating water/PVA coagulation bath. Partial axial alignment is thereby achieved, and further enhanced by applying tension to the flexible green fibers in the coagulation bath. Our findings include: (1) X-ray diffraction shows that the full width at half maximum (FWHM) of the Bragg peaks decreases from 55 (asextruded) to less than 30 degrees by 80% elongation. That is, SWNT alignment increases linearly with stretch (up to 80%). (2) In resistivity at room temperature vs. stretch ratio, result shows an initial rapid decrease followed by saturation; essentially all the improvement in electronic transport is obtained once alignment reached 40o FWHM. (3) Annealing in hydrogen at 1000oC is performed to drive out PVA, to improve inter-tube and inter-bundle contacts, and to heal damage on the tube walls. Such annealing is found to increase conductivity by at least 4 orders of magnitude. (4) Below 25 K, resistivity vs. temperature of the annealed fiber is wellrepresented by Coulomb gap variable range hopping (CG-VRH). It is rationalized that the Coulomb interactions in disordered systems open a gap at the Fermi energy. Above 25 K, the thermal energy is greater than the Coulomb gap, so thermal activation is more probable than correlated electron hops. (5) Finally, a measurable thermal conductivity is observed as stretch alignment increases. Introduction Single-walled carbon nanotube (SWNT) fibers are a macroscopic realization of the unique 1D nano-scale SWNT characteristics. Nanotube fibers can be spun by the injection of a SWNT suspension through an orifice into a co-flowing stream of a coagulating solution [1,2,3]. This process aligns the carbon nanotubes in the fiber. The resultant fibers offer promise for elements with high strength, light weight, and high thermal and electrical conductivity at a lower cost than other nanotube forms [4]. Studies have shown that the mechanical [5,6], electrical and thermal [7] properties depend on the SWNT alignment. The mechanical property (Young’s modulus) of SWNT fiber with respect to stretch ratio have been studied by Vigolo et al. [6] and shown that the alignment is further improved by post synthesis stret