Molecular dynamics study of sodium dodecylbenzene sulfonate adsorption on single-walled carbon nanotubes

Stabilizing single-walled carbon nanotubes (SWNTs) monodispersed in diameter and chirality in aqueous media remains elusive. Surfactants have proven useful in deploying ultra-centrifugation techniques for separating carbon nanotubes, but the molecular mechanism responsible for the effectiveness for such technique remains not fully understood. Based on recent molecular simulation results, it appears that the morphology of self-assembled surfactant aggregates on carbon nanotubes strongly affects the effective potential of mean force between pairs of interacting carbon nanotubes. In the present work, the effect of surfactant molecular structure on the properties of aqueous surfactant self-assembled aggregates was investigated using all-atom molecular dynamics simulations. To quantify how the surfactant molecular structure affects self-assembly, sodium dodecyl benzene sulfonate (SDBS) surfactants with the head group located either on the fifth or on the twelfth carbon atom along the dodecyl tail were considered. All simulations were conducted at room conditions for different surface coverages on (6,6), (12,12), and (20,20) SWNTs. The results suggest that the surfactant molecular structure strongly affects the packing of surfactants on the nanotubes, therefore modulating effective nanotube-nanotube interactions. In qualitative agreement with experiments, no strong effects due to nanotube diamerter were observed.