Dispersion of carbon nanotubes with SDS surfactants: a study from a binding energy perspective

Dispersion of carbon nanotubes with sodium dodecyl sulfate (SDS) surfactant is reported by molecular mechanics simulations from an energy perspective. The interaction energy of carbon nanotubes in a tube bundle is first calculated to estimate the force sufficient to separate it from the bundle. The binding energy between increasing numbers of SDS molecules with a carbon nanotube is next estimated to identify the threshold number of surfactant molecules for a possible dispersion. With the help of ultrasonication, a sufficient number of SDS molecules are found to penetrate into an initial gap between a single tube and other nanotubes in the bundle. Owing to further congregation of the surfactants at the gap site, the gap becomes enlarged until complete dispersion. In addition to the dispersion observation in view of the interaction and binding energy perspectives, four congregation processes were identified to reveal the aggregation morphologies of SDS surfactants on the surface of carbon nanotubes as well as the effect of diameter of a carbon nanotube on the adsorption density.