Large Populations of Individual Nanotubes in Surfactant-Based Dispersions without the Need for Ultracentrifugation

Abstract

Stable dispersions of single-walled carbon nanotubes have been produced using the surfactant sodium dodecylbenzene sulfonate (SDBS). Atomic force microscopy analysis shows that, on dilution of these dispersions, the nanotubes exfoliate from bundles, resulting in a concentration-dependent bundle diameter distribution which saturates at D rms ≈ 2 nm for concentrations, C NT < 0.05 mg/mL. The total bundle number density increases with concentration, saturating at ∼6 bundles per μm3 for C NT > 0.05 mg/mL. As the concentration is reduced the number fraction of individual nanotubes grows, approaching 50% at low concentration. In addition, partial concentrations of individual SWNTs approaching 0.01 mg/mL can be realized. These values are far superior to those for solvent dispersions due to repulsion stabilization of the surfactant-coated nanotubes. These methods facilitate the preparation of high-quality nanotube dispersions without the need for ultracentrifugation, thus significantly increasing the yield of dispersed nanotubes.

Liquid‐Phase Exfoliation of Nanotubes and Graphene

“…[88] This behaviour is very similar to that displayed by a number of solvents including NMP. The main differences are that higher nanotube concentrations are achieved using surfactants compared to all solvents (except CHP) and that the D rms v. C NT curve for the surfactant dispersions was shifted to higher concentrations (by a factor of ~7 compared to NMP).…”

“…To test this we prepared a stock dispersion of surfactant-stabilised nanotubes by adding nanotubes (C NT =1mg/ml) to an aqueous SDBS solution (C SDBS =5 mg/ml). [88] This was then mildly centrifuged to give a dispersion with C NT =0.28 mg/ml. We note that the surfactant concentration generally needs to be above the critical micelle concentration (CMC, ~0.7 mg/mL for SDBS) [52,89] and the surfactant concentration needs to substantially exceed the nanotube concentration [79,82,88] to achieve stable dispersions.…”

“…[88] This was then mildly centrifuged to give a dispersion with C NT =0.28 mg/ml. We note that the surfactant concentration generally needs to be above the critical micelle concentration (CMC, ~0.7 mg/mL for SDBS) [52,89] and the surfactant concentration needs to substantially exceed the nanotube concentration [79,82,88] to achieve stable dispersions. This stock solution was then diluted to varying degrees by mixing with an aqueous SDBS solution (C SDBS =5 mg/ml) to create a dilution series, sonicating after every dilution.…”

Liquid Phase Production of Graphene by Exfoliation of Graphite in Surfactant/Water Solutions

“…We disperse graphite in surfactant-water solutions in a manner similar to surfactant aided nanotube dispersion [12][13][14][15][16][17] . By TEM analysis we demonstrate significant levels of exfoliation including the observation of a number of graphene monolayers.…”

Sonication-assisted dispersion of carbon nanotubes in aqueous solutions of the anionic surfactant SDBS: The role of sonication energy

“…These results indicated that an insufficient supply of sonication energy could lead to the insufficient dispersion of CNTs, and dispersed CNT particles that are not small enough [12,13], while excessive sonication energy would not be economical. In previous studies, the sonication energies (E) applied to disperse CNTs in surfactant solutions ranged from 320 to 50400 J/mL, with the sonication time (t) ranging from 5 to 120 min (Table 1) [11,12,[15][16][17][18][19][20]. It is therefore necessary to examine the role of the sonication energy in surfactant-assisted CNT dispersion, to facilitate the effective use of energy in the industrial applications of CNTs.…”