Exploration of Aqueous Two-Phase Systems for Single-Wall Carbon Nanotube Separations via Automated Fluorescence Titration

C.M. Sims, T. Hicks, J.A. Fagan
National Institute of Standards and Technology,
United States

Keywords: carbon nanotube, CNT, fluorescence, automation, separation, metrology


The exceptional optical, thermal, and electronic properties of single-wall carbon nanotubes (SWCNTs) have enabled their use across a broad range of applications, including biotherapeutics, sensors, and digital logic. However, the full realization of these properties, and thus, SWCNT technology development, requires the isolation of each (n,m) specie from commercially synthesized mixtures. While surfactant-controlled aqueous two-phase extraction (ATPE) is an effective and scalable liquid-phase processing method for these isolations, the vast parameter space complicates the development and optimization of the ATPE method for isolating individual (n,m) species and their handed enantiomers. Towards this, we recently advanced an automated fluorescence-based spectroscopy titration method, which offers significant advances in the throughput and resolution in determining extraction conditions for SWCNTs that does not rely on the performance of experimental separations. Here, we use this new method to quantitatively determine the effects of several ATPE solution parameters on SWCNT extraction conditions. Specifically, the effect of salt addition to the ATPE system was explored, where the identity of the cation was shown to greatly affect the surfactant concentrations necessary for (n,m) extraction, while the identity of the anion was observed to have little effect. In addition, multi-surfactant mixtures of varying ratios were also evaluated, with initial results showing promise for identifying new ATPE mixtures that could better isolate difficult to separate (n,m) species and their handed enantiomers. Altogether, these results provide valuable insights towards new and unique types of ATPE-based SWCNT separations.