Competitive Binding in Mixed Surfactant Systems for Single-Walled Carbon Nanotube Separation

The separation of single-walled carbon nanotubes (SWNTs) by chirality is of great interest to enable the next generation of optical and optoelectronic devices. Many separation schemes employ the surfactant sodium dodecyl sulfate (SDS), with or without a bile salt surfactant such as sodium cholate (SC). In this study, we observe and explain the effect of these mixed surfactant systems on the hydrogel-based selective adsorption separation method. We find that sodium cholate outcompetes SDS more effectively on smaller diameter tubes and quantify this difference as the sodium cholate concentration is increased and (6,5) separation is diminished. These changes in separation efficiency with surfactant composition are understood using a theoretical model developed previously and predict that surfactant mixtures alter the charge per unit length of specific (n,m) SWNTs, altering the separation. This understanding of the chiral dependence of the surfactant binding will not only enable a greater understanding of surfactant coverage on the SWNT but also pave the path to further control the SWNT separation processes that depend on these surfactants.