Sodium dodecyl sulfate at water-hydrophobic interfaces: a simulation study.

Using molecular dynamics simulations, we have studied the water-vapor and water-oil (decane) interfaces of aqueous solutions of sodium dodecyl sulfate (SDS). The water-vapor interface is often used as a model for water-oil (hydrophobic) interfaces, yet we observe that the behavior of amphiphilic DS(-) ions at these two interfaces is very different. Specifically, on a water-vapor interface, SDS forms aggregates at low coverages, while it is homogeneously distributed on the water-oil interface. Two decane parametrizations resulted in dramatically different conformations: decane parametrized based on a GROMOS force field "froze", while decane parametrized with a TraPPE force field remained liquid at 300 K. The calculated effective second-order susceptibilities and nonlinear sum frequency scattering intensities of DS(-) ions at the "frozen" decane-water agree well with experimental data of DS(-) ions at the hexadecane droplet-water interface. This suggests that the orientation of longer alkane molecules is predominantly parallel to the interface and that, at low coverages, DS(-) ions follow the orientation of oil molecules.

Citation

Robert Vácha, Sylvie Roke. Sodium dodecyl sulfate at water-hydrophobic interfaces: a simulation study. The journal of physical chemistry. B. 2012 Oct 4;116(39):11936-42

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PMID: 22998553

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