Dispersing Individual Single-Wall Carbon Nanotubes in Aqueous Surfactant Solutions below the cmc

Dispersions of single-wall carbon nanotubes (SWCNTs) in surfactant solutions below the critical micelle concentration (cmc) have been studied theoretically and experimentally. Dissipative particle dynamics (DPD) simulations of a coarse-grained model predict that surfactant adsorption on small diameter tubes is dominated by aggregation of the surfactant molecules into adsorbed micelles at C approximate to 0.3C(cmc). We also find that the surfactant adsorption is nearly complete at a concentration of around C approximate to 0.5C(cmc). Further increase of the surfactant concentration has only minor effects on the radial density of surfactant headgroups, indicating that SWCNT may be fully stabilized in solutions below the cmc. SWCNT dispersions in solutions of anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS) below the cmc show a significant fraction of dispersed individual tubes and small bundles, in agreement with the model calculations.