Computational Prediction of the Adsorption Equilibrium for Ionic Surfactants at the Electrified Oil/Water Interface

In a previous study (Somekawa et al., Langmuir 2019, 35, 11345-11350) a non-Bornian solvation model was successfully applied to computational prediction of the adsorption equilibrium for nonionic surfactants at the oil (O)/water (W) interface. In this study, the method was extended to the adsorption of ionic surfactants at the polarized O/W interface. In this extension, the electrostatic potential of an ionic surfactant in the electric double layer formed at the O/W interface was taken into account together with the chemical potential estimated using the non-Bornian solvation model. The calculation results clearly showed that a cationic surfactant (hexadecyltrimethylammonium ion) was adsorbed at the nitrobenzene/W interface, when the interfacial potential was negative. This prediction was consistent with the previous experimental observation using electrocapillary measurements.

Automated summary

In this study, a non-Bornian solvation model was extended to predict the adsorption equilibrium of ionic surfactants at the polarized oil/water interface. The calculation results showed that a cationic surfactant was adsorbed at the nitrobenzene/water interface when the interfacial potential was negative, consistent with previous experimental observations.