The Applicability of the Pseudolattice Approach for the Surface Tension of Ionic Liquid Solutions

Recently, the pseudo lattice theory has been used to derive a simple linear correlation for the prediction of the surface tension of pure ionic liquids and their mixtures. That linear equation includes the parameters of coulomb interactions and the short-range interaction between the ions. In this work, a new correlation was derived for the solutions of ionic liquids in molecular solvents. The obtained correlation, predicts that the difference between the experimental surface tension and an approximated surface tension without including ion-solvent interaction, (Δ𝛾) is a function of -5/3 order of molar volume. Δ𝛾 can be calculated by using thermophysical experimental data. The linearity of the plots of Δ𝛾 versus V^-5/3 for mixtures of ionic liquids and solvents (alcohols and water) confirms the applicability of the pseudo lattice theory for these systems. The slope of the obtained lines, Bmix, is a measure of ion-solvent interaction and is independent of the temperature and mole fraction. Finally, an empirical linear relationship between Bmix and pure ionic liquid properties was extracted for each solvent. The equation of the last linear correlation is valuable for approximating 𝐵𝑚𝑖𝑥 and consequently, the surface tension of solutions at a varied range of temperatures and mole fractions.