Quantifying Adsorbed Dispersant Layers on Single-Wall Carbon Nanotubes in Simple and Complex Environments

Dispersion of single-wall carbon nanotubes (SWCNT) as individual objects in most liquid environments requires the use of an adsorbing dispersing agent such as a small molecule surfactant, dispersant such as DNA, or polymer chain to modulate the interactions with other nanotubes and the solution. The exact structure and density of these dispersing agents controls the stability of the dispersed nanotubes and affects their electronic and optical properties. Importantly, these molecules also enable a variety of separation methods for SWCNTs to purify them from impurities or to select for classes of SWCNTs such as semiconducting or metallic, or even for single species (n,m) structures. In particular, aqueous two-phase extraction using either cosurfactant competition or selective DNA sequences depend on the adsorbed interfacial dispersant layer to determine the achieved separation.<br/><br/>In this talk I will present the use of analytical ultracentrifugation to determine the adsorbed dispersant density on different nanotube species first for single species and surfactants, and then for complex environments including competing surfactants and polymer molecules. The quantification of the bound surfactant quantity and identity as a function of solution concentration on the nanotubes enables the direct testing of separation mechanisms and a measurand for optimization of separation conditions.