(727c) Characterizing Salt Effects on Adsorbed Interfacial Surfactant and Hydration Layers Around Single Wall Carbon Nanotubes Using Analytical Ultracentrifugation

Characterization of the interfacial layer structure on dispersed nanoparticles is of great interest, but is typically challenging, especially for anisotropic or polydisperse particle populations. For example, for single wall carbon nanotubes (SWCNTs), the success and efficiency of various dispersion and purification methods are believed to be strongly dependent on the characteristics of the bound layer of dispersant (such as small molecule surfactant(s) or DNA) both in the amount of bound dispersant as well as the specific structure it forms at the nanotube surface. However, only limited direct measurements of the differences in the bound layers on well-resolved SWCNT populations have been reported. To study the structure of the adsorbed surfactant layer, we utilize analytical ultracentrifugation (AUC). AUC is a powerful technique which allows for simultaneous sampling of the entire population distribution of a solute (e.g. proteins, DNA, particles), and through varying experimental parameters can be utilized to resolve the density and radial distribution of adsorbed surfactants and associated water at various solution conditions. In this work we report direct measurement of the hydration changes of the surfactactant SWCNT complex with added salt, and identify conditions at which the addition influences the structure of the adsorbed surfactant. These changes lend context to literature effects on the addition of salt to SWCNT separations, and identify hydration differences as the primary effect of salt addition rather than changes to the adsorbed surfactant number.