High quality dispersions of functionalized single walled nanotubes at high concentration

Single walled nanotubes are difficult to disperse in solvents, with dispersion quality limited by nanotube bundling at high concentration. We quantitatively study dispersions of singlewall nanotubes, functionalized with the bulky molecules PABS, PEG, and ODA, in common solvents. TGA measurements coupled with AFM analysis of deposited nanotubes shows almost complete coverage of the functionalities along the nanotube body. The best solvents are characterized by Hildebrand solubility parameters that are close to those of the functional groups. At low concentration, the dispersions contain predominately individual functionalized SWNTs as evidenced by root-mean-square bundle diameters of ∼ 3-4 nm. This can be compared with the measured diameter of individual functionalized nanotubes of ∼ 3 nm. These nanotubes display very weak concentration dependent aggregation when dispersed in common solvents. Root-mean-square bundle diameters of only ∼ 5-6 nm were observed at concentrations as high as 1 mg/mL. This translates into > 100 bundles per cubic micron of solvent, much higher than observed in other systems. These results have practical implications for the production of well dispersed polymer-nanotube composites that would be expected to display high interfacial stress transfer.