Electric Fields Applied to Surfactant Molecules for Enhancing Removal of Hydrocarbons from a Solid Surface: A Molecular Dynamics Study

Abstract

Desorption of decane molecules from a graphite surface using sodium dodecyl sulfate surfactants (SDS) with and without the presence of electric fields has been investigated. Different constant electric field strengths, E Z = ±1, ±2, ±3, ±4, ±5, and ±6 V/nm were applied perpendicular to the interface and removal of decane molecules was analyzed. It is observed that positive fields keep alkanes next to the surface whereas negative fields help desorption of the hydrocarbon chains. Moreover, weak negative electric fields do not have much influence on the SDS molecules, whereas strong electric fields have significant effects on the surfactant headgroups and consequently on the decane molecules attached to the SDS tails. Simulations were carried out for different water models, SPC/E, TIP4P/ϵ, and a polarizable one as well as a united and all-atom models for the surfactant molecules, and no significant differences were found in the results. By analysis of different properties, such as the radius of gyration and diffusion coefficients, it is noted that the complete alkane desorption started at electric field values around E Z ≈ −3 and −4 V/nm.