Attempts to control depletion in the surfactant-assisted stabilization of single-walled carbon nanotubes

Single-walled carbon nanotubes were stabilized by an anionic surfactant, sometimes in mixture with a nonionic one (Triton TX-100), and/or in presence of salt. The stabilizing activity of sodium dodecylsulfate is poor, with occurrence of phase separation at moderate surfactant content; even lower is the one ascribed to TX-100. We quantified the stabilization in terms of surface coverage by the adsorbing species; the effect is counteracted by the presence of micelles present in the surrounding medium. A chemical approach accounted for the competition between surface adsorption and micelle formation. Destabilization of the dispersions is due to unbalanced osmotic effects and is related to depletion. The above phenomenon occurs when the volume fraction of micellar aggregates reaches a certain threshold, whose value is related to micelle size. Depletion was avoided by selecting the maximum possible amounts of sodium dodecylsulfate, NaCl and/or Triton TX-100. In mixed systems the stabilization is active for longer times compared to dodecylsulfate, although depletion occurs at lower surfactant content. (C) 2013 Elsevier B.V. All rights reserved.