Application of PC-SAFT and DGT for the Prediction of Self-Assembly

Abstract

The self-assembly of a surfactant in water is a complex procedure. The classical thermodynamic model for aqueous solutions of a nonionic surfactant, originally developed by Nagarajan and Ruckenstein, includes four contributions for aqueous solutions of a nonionic surfactant. These contributions were calculated using correlations based on experimental data, which were available at that time. The most important contribution is the so-called transfer term for modeling the hydrophobic effect. In this work, we first suggest replacing the original term based on experimental vapor–liquid equilibrium data by the n-alkane activity coefficient at infinite dilution in water calculated with PC-SAFT. The second term in the original model describes the newly formed interface during the self-assembly. This contribution requires the interfacial tension of n-alkane + water mixtures, which was originally calculated using combining rules based on the surface tensions of pure water and pure n-alkane. The second new suggestion of this work is to replace this combining rule by the interfacial tension of n-alkane + water mixtures obtained from PC-SAFT combined with the density gradient theory. The impact of these modifications on the predicted physical properties of surfactant solutions is studied for aqueous solutions of n-octyl-β-d-glucopyranoside (C8G1) as a representative surfactant for the family of sugar surfactants.