Curvature effects on the adsorption of aqueous sodium-dodecyl-sulfate surfactants on carbonaceous substrates: structural features and counterion dynamics.

The effect of substrate curvature on surfactant self-assembly has been studied using all-atom molecular-dynamics simulations. We studied aqueous sodium-dodecyl-sulfate (SDS) surfactants on graphite, on the outer surface of single walled carbon nanotubes (SWNTs) and within SWNTs. Our results reveal that although the chemical nature of the substrates is constant, the self-assembled structures change significantly as the curvature varies. For example, at large surface density, SDS surfactants yield micellar structures on graphite, layered self-assemblies outside SWNTs, and cylindrical lamellar structures inside SWNTs. Changes in substrate curvature as well as surfactant surface density affect significantly surfactant orientation and, more importantly, headgroup-headgroup distribution, headgroup-counterion packing, and counterion residence time next to the headgroups.