Activated complex model and surfactant reorganization during SWCNT separations on hydrogels

Hydrogels can efficiently separate metallic and semiconducting single-wall carbon nanotube (SWCNT) species at high rates by selective adsorption in a column configuration, but mechanistic details remain unclear. We examined the temperature dependence of SWCNT adsorption in an operating column using a model that considers the formation of an activated complex. The enthalpy and entropy changes associated with formation of the activated complex were determined. Due to a high sensitivity to protonation doping, large diameter pulsed laser vaporization tubes provided an opportunity to probe details of the adsorption mechanism. In contrast to the prevailing view in the literature, we conclude that the surfactant environment surrounding the nanotube is substantially reorganized upon adsorption and that adsorption also occurs within gel pores. Our findings provide new mechanistic insights that should assist in the development of improved separation methods.