Coarse-Grained Model of the Sodium Dodecyl Sulfate Anionic Surfactant Based on the MDPD--Martini Force Field

Abstract

The sodium dodecyl sulfate (SDS) surfactant is widely used in various applications, such as household products (e.g., shampoos, toothpaste, detergents, and cleaning products) and food manufacturing (e.g., emulsifiers). To investigate its properties via computer simulation, various models have been developed, including coarse-grained (CG) models that are suitable for capturing a surfactant's self-assembly and fundamental properties for aqueous systems with a surfactant, such as surface tension. Here, we present a CG model for SDS/water systems for many-body dissipative particle dynamics (MDPD), which is based on the MDPD--Martini force field (FF). In the model, charged groups, namely, the SDS sulfate headgroup and the sodium cation, are explicitly modeled following the standard mapping of the Martini force field for molecular dynamics (MD), while the remaining interactions have been obtained from previous MDPD--Martini models for lipid systems, thus demonstrating their transferability. Various relevant system properties, such as the coherent scattered intensity and surfactant distribution at the liquid--vapor surface, are investigated, and results are compared to those obtained by MD simulations and experiments at different surfactant concentrations. Our findings indicate that MDPD--Martini models can offer a credible alternative to MD--Martini models for systems with explicit charges as shown here for SDS. Moreover, MDPD--Martini models reproduce nicely the experimental surface tension isotherm, in contrast to MD simulations. In view of the transferability of the MDPD--Martini interactions, the model parameters of this study can be tested and used to simulate a wider range of soft-matter systems.