(142b) Characterizing the Differences in Adsorbed Surfactant and Hydration Layers Around Single Species Metallic and Semiconducting Single-Wall Carbon Nanotubes with Analytical Ultracentrifugation

Authors: 
Lam, S., National Institute of Standards and Technology
Fagan, J. A., National Institute of Standards and Technology

Over the past decade, numerous methods have emerged for the dispersion and liquid phase purification of single-wall carbon nanotubes (SWCNTs). The success and efficiency of the dispersion and purification methods, however, 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. However, only limited direct measurements of the differences in the bound layers on well-resolved SWCNT populations have been reported. Thus, it is important to elucidate the structure of the adsorbed surfactant and hydration shells around different single species SWCNTs and surfactant-SWCNT complexes, respectively, to quantitatively address the differences in structure that drive differential separation. To study the structure of the adsorbed surfactant layer, we utilize analytical ultracentrifugation (AUC) to resolve the density and radial distribution of adsorbed bile salt surfactants (sodium deoxycholate, sodium cholate) and sodium dodecyl sulfate on different species of SWCNTs at various solution conditions. In our AUC experiments, we use nanotubes which have been both chirality and length sorted, giving us a population of particles which not only have a narrow length and diameter distribution, but also unique optical transitions and, in theory, unique interactions with surfactants. In this work, we measure and compare the anhydrous and buoyant radii around multiple semiconducting and metallic SWCNT species dispersed in sodium deoxycholate and provide direct measurements of the effects of adding co-surfactant to the observed sedimentation.