Origin of the Surfactant‐Dependent Redox Chemistry of Single‐Wall Carbon Nanotubes

Abstract The redox chemistry of single‐walled carbon nanotubes (SWCNTs) was examined by using optical absorption spectroscopy measurements in the presence of sodium dodecyl sulfate (SDS) and its analog surfactants, that is, sodium 1‐undecanesulfonate (SUS) and sodium dodecylbenzenesulfonate (SDBS). Redox reactions of the SWCNTs were observed in the SDS and SUS solutions, whereas such reactions were suppressed in the SDBS solution. Molecular dynamics simulations were performed to investigate the assembly of the surfactants around an SWCNT. SDS and SUS were shown to primarily form single layers on the SWCNT and certain solvent‐exposed areas, whereas SDBS predictably densely coated the SWCNTs. The results suggest that the SDBS layer on the SWCNT surfaces prevents charge‐transfer reactions; in contrast, the sparse layers of SDS and SUS allow the redox chemistry through the charge‐transfer reactions. Interestingly, a positively charged SWCNT as a model for the oxidized SWCNT showed an increase in the number of surfactant molecules around the SWCNT in the SDS and SUS solutions owing to electrostatic interaction, which is related to the chirality‐dependence of the SWCNT colloidal stability.