A modification of Schmutzer’s model is proposed for the interface between aqueous electrolyte solution|hydrophobic phase. Image and hydration forces are explicitly modeled. The thickness of the ion free layer at the surface is calculated from the thicknesses of the hydrophobic gap and the hydration shell of the ion [1-3]. This model (without adjustable parameters) is used for the calculation of the interfacial tension of systems where the hydrophobic phase is air [1,2], oil or solution of alcohol in oil [3]. It is in good agreement with the experimental data, except for the case where large ions are present (due to the neglected van der Waals and hydrophobic forces). The Hofmeister effect on the interfacial tension of salts of the same valence type is explained with the ion-specific bulk activity coefficient. The interfacial tension of aqueous electrolyte|solution of alcohol in oil is lower than that of an electrolyte solution|oil interface due to the adsorption of alcohol which shifts the Gibbs surface.
Schmutzer’s model predicts also the surface Δc-potential of brines [2]. The addition of salt to the water lowers its dielectric permittivity e; since c ~ 1/e, the surface potential c becomes more negative than that of pure water (i.e., Δc<0). For a series of electrolytes, the order of Δc at given concentration follows the order of the electrolyte-specific dielectric permittivity.
1. R. Slavchov, J. Novev, J. Colloid Interface Sci. 387 (2012) 234.
2. R. Slavchov, J. Novev, T. Peshkova, N. Grozev, J. Colloid Interface Sci. 403 (2013) 113.
3. R. Slavchov, T. Peshkova, J. Colloid Interface Sci., submitted.
tatyana_peshkova@abv.bg
