Dispersions and solutions of single walled carbon nanotubes

Abstract

Large scale exfoliation of single walled carbon nanotubes (SWNTs) has been shown in various media. Debundling of SWNTS has been demonstrated by dilution of nanotube dispersions. On making the initial dispersions, large aggregates (~100s of microns) are removed by a mild centrifugation step resulting in an isotropic phase containing bundles of nanotubes. The root mean square bundle diameter, of bundles in this isotropic phase, has been shown to be concentration dependent. Such debundling has been demonstrated in the solvents N-methyl-2-pyrrolidone (NMP) and for the narcotic drug y- Butyrolactone, sometimes referred to as 'liquid ecstasy'. After centrifugation, the dispersions are stable against sedimentation and further aggregation for a period of weeks at least. Atomic-force-microscopy studies on deposited films reveal that the bundle diameter distribution decreases dramatically as concentration is decreased. Detailed data analysis suggests the presence of an equilibrium bundle number density and that the dispersions self-arrange themselves to always remain close to the dilute/semi-dilute boundary. A population of individual nanotubes is always observed which increases with decreasing concentration until almost seventy percent of all dispersed objects are individual nanotubes at a concentration of 0.004 mg/ml in the NMP dispersions and for y- Butyrolactone forty percent of all dispersed objects are individual nanotubes at a concentration of 6x10'-4 mg/ml. The presence of individual nanotubes in NMP dispersion was confirmed by photoluminescence spectroscopy. Concentration dependence of the photoluminescence intensity confirms that the AFM measurements reflect the diameter distributions in-situ. In addition, Raman spectroscopy confirms the presence of large quantities of individual nanotubes in the deposited films.