Morphology Transitions of SDS Coatings on Single-Walled Carbon Nanotubes

The morphologies of sodium dodecyl sulfate (SDS) coatings adsorbed on single-walled carbon nanotubes (SWCNTs) were investigated through molecular dynamics (MD) computations. Simulations covering a range of nanotube diameters and SDS concentrations showed regimes giving three different SDS morphologies, characterized as ordered, random, and micellar. In the ordered structures, which were formed at the lowest SDS concentrations, nanotubes were coated with a partial monolayer of SDS molecules whose alkyl tails were aligned parallel to the nanotube axis. Higher SDS concentrations gave the random coating morphology with a partial monolayer of more closely packed and poorly aligned adsorbed molecules. At the highest concentrations, spheroidal micellar clusters of SDS formed on the nanotube surface. The morphologies were quantitatively characterized by computed distribution functions of the SDS alkyl chain orientation and radius of gyration. A machine learning method was also applied to determine the aggregation numbers of SDS micelles in these colloidal systems.