(Invited, Digital Presentation) Determining Surfactant Layer Composition on an (n,m) SWCNT at Extraction Conditions in Aqueous Two-Phase Extraction

Abstract

Surfactant-controlled aqueous two-polymer phase extraction is a sensitive method for separating specific (n,m) structures of single-walled carbon nanotubes (SWCNTs). Using empirically determined values for the overall surfactant compositions that enable differential extraction, it is possible to isolate many (n,m) species across a broad diameter range from < 0.8 nm to > 1.5 nm, however, researching new methods requires extensive new separation experiments. To overcome this barrier, we recently advanced a fluorescence-based methodology for determining extraction conditions for specific (n,m) species SWCNTs and their enantiomers that does not rely on the performance of separations, and can be performed at well controlled environmental conditions with orders of magnitude less nanotube sample. This method is based on the finding that the change in the nature of the extraction is directly correlated with a dramatic change in fluorescence intensity of the particular (n,m) structure. Using analytical ultracentrifugation, we have now orthogonally determined the density of the bound surfactant on specific nanotube (n,m)s below, near, and above the surfactant concentrations yielding the extraction change, as well as for the two co-surfactants separately. These results enable evaluation of the hypothesis that the fluorescence and extraction conditions changes are the result of a change in the composition of the dominant adsorbed surfactant at a specific composition ratio.