Saturation of surfactant structure at the single-walled carbon nanotube surface.

Density gradient ultracentrifugation (DGU) and fluorescence spectroscopy are used to probe the limiting behaviors of the dynamic response of surfactant structure at the single-walled carbon nanotube (SWNT) surface to reorganizing forces, including changes in surfactant concentration and electrolyte screening. DGU results indicate that, as surfactant (sodium dodecyl sulfate, SDS) concentration is increased, SDS adsorbed on metallic SWNTs becomes limited in its ability to reorganize before SDS adsorbed on semiconducting species. A diameter-dependent enhancement is observed in photoluminescence intensities from semiconducting SWNTS upon initial titration with NaCl.

Electrolyte tuning of surfactant interfacial behavior for enhanced density-based separations of single-walled carbon nanotubes.

We study the interfacial behavior between the straight-chain alkyl surfactant sodium dodecyl sulfate (SDS) and single-walled carbon nanotubes (SWNTs) as a function of added electrolytes, including NaCl. We observe an increase in photoluminescence intensity and narrowing of spectral line widths with electrolyte addition, indicating a change in SDS aggregation number that leads to a pronounced volume change in the nanotube/SDS composite structure. By tuning the interfacial dynamics through NaCl addition and temperature change, we demonstrate that this volume change can be used to yield diameter-dependent separation of metallic and semiconducting SWNTs, without the use of any additional cosurfactant, through density gradient ultracentrifugation.