Molecular dynamics simulation of the adsorption of sodium dodecyl sulphate on single walled carbon nanotubes in aqueous solution

The separation of carbon nanotubes (CNT) into samples that are monodisperse in diameter and chirality still constitutes a bottleneck for specific applications of this material. According to preliminary experimental results [1], surfactant-assisted separation of CNT is a promising solution of this problem. However, the mechanism for which surfactants help the separation with some specificity, or which surfactants or environmental conditions improve the separation are not yet understood. In this work, we present a multi-ensemble molecular dynamics study of the adsorption of sodium dodecyl sulphate (SDS) on a variety of single walled CNT’s [(m, n) = (6,6), (10,2), (11,0), etc.] in aqueous solution at various temperatures. The adsorption of the dodecyl sulfate anions on the CNT is characterized by their atomic radial distribution with respect to the CNT, distribution of characteristic lengths (radius of gyration), and end-to-end azimuthal angle (which shows the degree of wrapping of the molecule around the CNT). We discuss how these are related to the physical characteristics of the CNT’s in solution.