Fabrication of solution grown C60 fullerene nanotubes with tunable diameter.

Transmission electron micrographs of fullerene nanotubes grown in solution of C60-saturated pyridine and isopropyl alcohol cooled at 5 degrees C, 10 degrees C, and 15 degrees C show systematic variation of the outer and inner diameters with growth temperature. Calculated mean values of outer diameters are 471 nm, 432 nm, and 405 nm while the inner diameters are 224 nm, 193 nm, and 185 nm for nanotubes grown at 5 degrees C, 10 degrees C and 15 C, respectively. Plots of the outer and inner diameters show that tubular structure forms when the outer diameter of the nanofibers is greater than 200 nm and that the wall thickness is not constant. The formation of thicker nanotubes at lower temperature is possibly related to the solubility of C60 molecules and the nature of the solvents used. It has been suggested that fullerene nanotubes are composed of C60 aggregates forming pearl-chain like structures and bonded by van der Waals forces. This means that thicker nanotubes formed at cooler temperature have more incorporation of C60 molecules along their walls indicating less solubility of C60. This result follows the common experience that for organic solutes in organic solvents, the solubility increases on warming. Hence, abundant C60 molecules may have remained during incubation at 5 degrees C. Moreover, increased solubility in higher temperatures may have also been induced by relatively weak van der Waals forces bonding the C60 molecules together.