Interfacial and Bulk Properties of Volatile Amphiphiles and Sodium Dodecyl Sulfate Mixtures

Volatile amphiphiles and surfactant mixtures have gained wide applications in diverse areas of industry, cosmetics, and medicine. The surface tension isotherms, measured at different solute ratios, and data processing, using appropriate theoretical models, provide quantitative information on their bulk and interfacial properties. Here, this approach is applied for mixtures of volatile amphiphile (benzyl acetate, linalool, geraniol, menthol, citronellol) and sodium dodecyl sulfate (SDS). All surface tension isotherms are described by the van der Waals model for a two-component adsorption layer, taking into account the counterion binding in the Stern layer, by varying only one adjustable parameter (interfacial pair interaction energy between adsorbed molecules). Knowing the parameters of the model, we computed various properties of the adsorption layers (adsorptions of different components, occupancy of the Stern layer, and interfacial electrostatic potential). The experimental aqueous solubilities of mixtures are fitted using the regular solution theory to obtain the pair bulk interaction parameter. The mixing of SDS and: (i) benzyl acetate and citronellol is antagonistic; (ii) linalool and geraniol is synergistic; and (iii) menthol is ideal. The reported properties of the volatile amphiphiles and SDS mixtures could be of interest for increasing the range of their applicability in practice.