(594b) Mixed-Surfactant Adsorption on Single-Walled Carbon Nanotubes: Insights from Molecular Simulations

Single-walled carbon nanotubes (SWCNTs) present unique mechanical, electrical, and optical properties but many difficulties exist in the practical application of this material. The main barrier to more widespread use is the need to separate and purify the heterogeneous mixtures (in terms of size and chirality) produced during synthesis. Numerous attempts have been made to design methods to efficiently separate particular SWCNT chiralities, but such techniques have yet to demonstrate success beyond the bench scale. These approaches usually involve a two-step process – first dispersion of the SWCNT material in aqueous solution via the use of either small-molecule or polymeric surfactants followed by manipulation of the dispersed mixture via some external action (centrifugation, phase separation, etc.). Recently, via near-infrared fluorescence emission measurements, it has been shown that varying the relative amounts of deoxycholate (DOC) and dodecyl sulfate (SDS) results in a sharp transition in the two-phase partitioning behavior of the dispersed SWCNTs. Furthermore, the location of this transition appears to be different for each SWCNT chirality. We shed light on the nature of this transition by using molecular simulations to investigate competitive adsorption in multi-surfactant systems. Resulting packing motifs are then compared across a range of relative surfactant concentrations. Free energy perturbation is also used to determine the relative solvation energies of these complexes. This work will be used to help design separation protocols that allow for the sequential extraction of specific SWCNT chiralities.