Classical Molecular Dynamics and DFT Calculations for Interfacial Properties of the Water‐Decane Systems Using Different Types of Surfactants

ABSTRACT Simulations of surfactants with different charges (DHPD [nonionic], HBS − [anionic], HFA + [cationic], and Bis‐HBS 2− [gemini]) in water‐decane interfaces were performed with classical molecular dynamics (MD) at different concentrations. Properties of isolated surfactants were calculated using DFT quantum chemical (QC) methods, with and without considering the incorporation of solvent effects in the molecular simulation. Qualitative properties (snapshots and density profiles) were analyzed for the highest area per molecule ( APM ). Interfacial tension ( IFT ), interfacial thickness ( IFTh ), interface formation energy ( IFE ), and hydrogen bond number ( HBN ), at different area APM , were evaluated using MD. The IFT follows the order: nonionic > anionic > cationic > gemini. Qualitative results showed correspondence of IFT with the width of the water region in snapshots, the height, and the area of density profiles for surfactant heads and tails. A schematic representation of different molecular interactions at the interface explains the IFT change. Correlations between IFT and IFTh , IFE , and HBN were also observed at different APMs . Surfactant QC calculations for head group charge, total dipole moment, the principal component of dipole moment, and solvation energies in water and decane were carried out. Relationships of IFT with calculated surfactant QC properties were found.