Mechanism for the complex micellar system of sodium dodecyl sulfate/octylphenol ethoxylate OPE9 to solubilize methane

Abstract

Surfactant solutions are widely used in solubilizing methane, but there is a lack of research on the optimum ratios of surfactant solutions and their mechanism. In this study, surfactants sodium dodecyl sulfate (SDS) and octylphenol ethoxylate OPE9 (Triton X-100) were selected to better understand the mechanism of the surfactant solution to solubilize methane from a microscopic aspect. The mixed SDS and Triton X-100 solution was proven greater at methane solubilization than a single-component SDS, because it generated a higher number of micelles with hydrophobic cores. When the SDS–to–Triton X-100 concentration ratio was 1:4, the lowest critical micelle concentration, the strongest interaction between SDS and Triton X-100, the maximum absolute value of Gibbs free energy, and the maximum value of viscosity were observed. This indicated that the solution was most likely to generate micelles with a hydrophobic environment and that these micelles were favorable for the methane solubilization. This solution also showed a greater uniformity of micelles, a smaller micelle particle size, and a relatively compact micelle structure. It was deduced that methane stays longer in the micelle core of this structure, which can facilitate methane solubilization. The optimum SDS–to–Triton X-100 ratio to solubilize methane was shown to be 1:4.