Correlations between classical molecular dynamics and DFT calculations for interfacial properties of different type surfactants in decane-water systems


José G. Cisneros, Miguel Fernández, and Fernando Ruette


1Laboratorio de Química Computacional, Centro de Química “Dr. Gabriel Chuchani”, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado 21827, Caracas 1020-A, Venezuela.



Abstract:

Properties of different types of surfactants (DHPD (nonionic), HBS-1 (anionic), HFA+ (cationic); and, b-HBS-2 (gemini)) were evaluated with DFT quantum chemical (QC) methods. In addition, simulations of these surfactants in decane-water interface at different surfactant concentrations were performed with classical molecular dynamics (MD). Surfactant QC properties, such as head group charge, total dipole moment (TDM), the principal component of the dipolar moment (PCDM), and solvation energies (SE) were evaluated. Correlations between QC properties with MD results of the simulated systems were analyzed considering: snapshots, density profiles, radial distribution function (RDF), interface thickness (IFTh), interface formation energy (IFE), and interfacial tension (IFT), at different area per molecule (APM). The results shows that the IFT order is nonionic > anionic > cationic > gemini. Correlations between IFT with APM, IFTh, and IFE were observed. Likewise, correlations of IFT with surfactant QC properties: IFT decreases, in general, with the increase of head group charge, PCDM, and SE in water (SEW) and oil (SEO). These correlations can be interpreted as an interplay of the following forces: repulsive, attractive, steric hindrance, hydrogen bonds, and dispersion attractions between surfactant tail with decane. This study displays correlations between the intrinsic properties of surfactants and their behavior at the decane-water interface, which may be useful to formulate compounds with improved tensoactive capabilities.