C.M. Sims, J.A. Fagan
National Institute of Standards and Technology,
Keywords: SWCNT, carbon nanotube, separation, fluorescence
Summary:Full realization of the optical, thermal, or electronic properties of specific single-wall carbon nanotube (SWCNT) (n,m) species requires the isolation of each specie from commercially synthesized mixtures, which contain several individual species. Aqueous two-polymer phase extraction (ATPE) is an effective, yet still developing, separation method for enriching or isolating single species of SWCNTs, with control of individual SWCNT specie isolation usually achieved by competing two or more surfactants against the nanotube surface. However, methods for rapidly determining the aqueous surfactant concentration conditions that yield upper or lower polymer phase extraction for specific (n,m) species of SWCNTs in ATPE separations are a missing component limiting quicker development and optimization of the ATPE technique. Here, we demonstrate the use of near-infrared fluorescence emission from single-phase dispersions of multiple SWCNT specie mixtures to determine these partition coefficient conditions without performing ATPE separations. This new methodology enables rapid quantitative determination of partitioning conditions for individual (n,m) species and their handed enantiomers, while using dramatically less material and without ambiguity of mass transfer limitations or interfacial adsorption present when conducting the ATPE separation itself. This methodology also enables swifter investigation of complicating factors such as temperature, polymer composition, and surfactant chemistry; variations of which are shown to strongly affect the amount of surfactant necessary to cause (n,m) extraction using the ATPE method. These results provide additional insight into the underlying mechanisms behind ATPE-based SWCNT separations, towards further development and optimization of the ATPE method.