Mechanisms of Intermolecular Interactions and Molecular Dynamics in Anionic and Nonionic Surfactant Microemulsions

This study investigates the molecular interactions and self-assembly behaviors in microemulsions formed by alkanes, alcohols, a nonionic surfactant (C12E5), and anionic surfactants (SDBS, SDS). Utilizing quantum mechanical weak interaction analysis and molecular dynamics simulations, we explore the weak interaction forces, thermal stability, and conformation of surfactant molecules at the interface membrane. Radial distribution function (RDF) and molecular polar surface area (MPSA) analyses reveal how hydrophilic group structures influence water molecules, while reduced density gradient (RDG) diagrams provide insights into microscopic interactions. Molecular dynamics simulations demonstrate that the surfactant concentration significantly affects the interaction energies between microemulsion components. As the surfactant concentration increases, the interaction energies between pentanol, water, and alkanes also increase. Specifically, C12E5 shows a gradual decrease in the interaction energy between water and pentanol at higher concentrations, with only a 1.79% increase at 9% concentration compared to a 65.03 and 23.38% decrease for SDBS and SDS, respectively. These findings suggest that C12E5 contributes to a more stable microemulsion system, while anionic surfactants lead to more pronounced energy fluctuations and structural changes in the interface membrane. This work establishes a comprehensive framework for analyzing weak interactions and microemulsion formation, offering valuable insights into the molecular mechanisms that govern the surfactant behavior in microemulsion systems.