C.M. Sims, J.A. Fagan
National Institute of Standards and Technology,
Keywords: carbon nanotube, CNT, analytical ultracentrifugation, surface chemistry, purification, metrology
Summary:The exceptional optical, thermal, and electronic properties of single-wall carbon nanotubes (SWCNTs) have enabled their use across a broad range of applications, including photonics, biomedicine, and sensors. However, the full realization of these properties, and thus, SWCNT technology development, requires the isolation of each (n,m) specie from commercially synthesized mixtures, which contain multiple individual species. Aqueous two-phase extraction (ATPE) is an effective, yet still developing, liquid-phase processing method for these isolations, with control usually achieved by competing two or more dispersants against the nanotube surface. However, validation of the surface competition model in ATPE has not been directly demonstrated. Here, we present the use of analytical ultracentrifugation to determine the adsorbed dispersant density on different nanotube species, first for single species and surfactants, and then for complex environments including competing surfactants and polymer molecules. The quantification of the bound surfactant quantity and identity as a function of solution concentration on the nanotubes enables direct testing of the surface competition model and separation mechanisms, and also provides a measurand for optimization of SWCNT separation conditions using ATPE.