(357d) Modulation of Thermodynamically-Stable Surfactant Structures for Selective Desorption of Single Wall Carbon Nanotubes
Over the past decade, the post-synthetic separation of single wall carbon nanotubes (SWCNTs) has been studied with great interest. The most promising techniques include the selective adsorption of SWCNTs onto hydrogel stationary phases and aqueous two-phase extraction. While several researchers have successfully achieved separation of the semiconducting fractions by (n,m) type by manipulating the selective adsorption of the nanotubes, these processes often require multiple columns or experimental conditions that are difficult to control. However, the high-fidelity desorption of SWCNTs would provide a simpler approach that minimizes dilution and provides higher yields. Here we report the selective desorption of a wide range of single-chirality (n,m) fractions in a single column packed with agarose gel. High-purity fractions of (n,m) nanotubes are obtained with high yield once a specific ratio of sodium dodecyl sulfate (SDS)/sodium deoxycholate (DOC) co-surfactant solution is used. In the selective desorption from hydrogels, the co-surfactant structure surrounding the SWCNTs has been shown to play an important role in the separation. The elution of only one (n,m) type at a specific co-surfactant ratio while other types are exposed to more surfactant suggests that each (n,m) type forms a thermodynamically-stable surfactant structure in the co-surfactant solution. These thermodynamic equilibrium states result in entropy-driven desorption at specific co-surfactant ratios, enabling high-fidelity separations of a single (n,m) type in a single column. Moreover, the differences between the co-surfactant ratios needed to separate two (n,m) species can sometime be very small. The separation can be obtained under a wide variety of co-surfactant background concentrations. An improved separation sensitivity can be achieved at higher background concentrations.