C.M. Sims, J.A. Fagan
National Institute of Standards and Technology,
Keywords: carbon nanotube, CNT, separation, fluorescence, photoluminescence, surfactant
Summary:Full realization of the optical, thermal, or electronic properties of specific single-wall carbon nanotube (SWCNT) (n,m) species requires the extraction of each specie from commercially synthesized mixtures. Aqueous two-polymer phase extraction (ATPE) is a scalable, liquid-phase processing method for isolating individual (n,m) species of single-wall carbon nanotubes (SWCNTs) from multiple specie mixtures, with partitioning control usually achieved by competing two or more surfactants against the nanotube surface. Here, we quantitatively determined the effects of systematic variations in surfactant chemistry on SWCNT extraction conditions in ATPE using a recently developed near-infrared fluorescence emission monitoring method. Specifically, variations in alkyl surfactant tail length and anionic head group chemistry were observed to strongly affect the amount of surfactant necessary to cause extraction of nanotube species in ATPE extraction. Substitution of different di-hydroxy bile salts is also shown to greatly affect the surfactant concentrations necessary for (n,m) extraction. In addition, distinct surfactant ratios were found to extract specific (n,m) SWCNTs, supporting a hypothesized competitive adsorption mechanism model of SWCNT sorting. These results provide valuable insights into the underlying mechanisms behind ATPE-based SWCNT separations, towards further development and optimization of the ATPE method for isolating individual (n,m) species and their handed enantiomers.