The role of sodium dodecyl sulfate concentration in the separation of carbon nanotubes using gel chromatography

Gel chromatography has been demonstrated as an effective method for generating separated fractions of metallic and semiconducting carbon nanotubes when starting with a heterogeneous dispersion in sodium dodecyl sulfate (SDS). The influence of the surfactant concentration in this process has been examined here for chromatographic separation using a dextran-based gel as the stationary phase. Decreasing the concentration of SDS from 4 to 0.5 wt.% caused a gradual increase in the adsorption of semiconducting nanotubes to the gel in a species-selective manner, with low concentrations of SDS (around 0.5%) found to provide the best semiconductor-metal separation. Elution using a stepwise concentration gradient was able to produce fractions of reduced diameter population from the polydisperse HiPCO starting material, where a good correlation between the concentration of elution and local bond curvature for each nanotube species was observed. Since bleaching of optical absorbance through protonation in the presence of dissolved oxygen was found to mask the presence of nanotubes with large diameters, it was deemed necessary to reverse the protonation effect through hydroxide addition in order to detect these species in optical measurements of nanotube dispersions.