Correlation of properties with preferred orientation in coagulated and stretch-aligned single-wall carbon nanotubes

We report structure-property correlations in single wall carbon nanotube (SWNT) fibers, among electrical, thermal and chemical parameters with respect to stretch-induced preferential SWNT alignment along the fiber axis. Purified HiPco tubes are dispersed with the aid of an anionic surfactant and coagulated in the co-flowing stream of an adsorbing polymer. The fibers are then dried, rewetted under tensile load and redried to improve the alignment. Complete removal of the polymer was assured by annealing in hydrogen at 1000oC. The degree of alignment was determined by x-ray scattering from individual fibers using a 2-dimensional detector. The half width at half maximum (HWHM) describing the axially symmetric distribution of SWNT axes decreases linearly from 27.5o in the initial extruded fiber to 14.5o after stretching by 80%. The electrical resistivity ρ at 300 K decreases overall by a factor ~4 with stretching, for both as-spun composite and polymer-free annealed fibers. However, the temperature dependence ρ(T) is markedly different for the two, implying different electron transport mechanisms with and without the polymer. Thermal conductivity also improves with increasing alignment, while the absolute values are limited by the disordered network of finite length tubes and bundles. Comparisons are made with results from similar fibers spun from oleum, and with magnetically aligned buckypapers.