(Invited) New Methods to Probe the Surfactant Structure Surrounding Swcnts

The surfactant structure surrounding single walled carbon nanotubes (SWCNTs) plays an important role in their separation by nearly any method. However, characterizing the structure of these molecular layers remains difficult. The structure of the surfactant or other molecules around the SWCNTs could also have important implications in toxicology and drug delivery. While changes to the local environmental surrounding SWCNT can be observed by photoluminescence (PL), it does not directly probe the surfactant or its structure. Here we describe how proton NMR and Pulsed Field Gradient NMR can monitor the interaction of surfactant with the SWCNTs. By combining PL and Proton NMR analysis, we aim to understand the formation and morphology of surfactant structures that form around SWCNTs, especially differences that exist for metallic and semiconducting species. We find that the observed critical micelle concentration (CMC) is dependent on the SWCNT loading. In some cases, the observed CMC is actually below the surfactant-only solution. The ultimate goal is to learn how to control these structures around SWCNTs to influence their interaction with biological materials and other surfaces.