Mechanistic Study on Surface Tension of Binary and Ternary Mixtures Containing Choline Chloride, Ethylene Glycol and Water (Components of Aqueous Solutions of a Deep Eutectic Solvent, Ethaline)

Abstract The paper reports the results of the measurement of surface tension in binary liquid mixtures containing choline chloride, ethylene glycol and water and ternary mixtures of ethaline (a eutectic mixture of ethylene glycol and choline chloride, the so-called deep eutectic solvent) with water. The surface tension is determined in a wide range of components’ concentration for the temperatures of 25, 30, 40, 50, 60 and 70 °C. The dependences of surface tension on the concentration of liquids are treated by means of Gibbs adsorption isotherm and linear form of Langmuir adsorption isotherms. The values of the equilibrium constant of adsorption at the interface liquid solution/air as well as the standard adsorption Gibbs energy, enthalpy and entropy are calculated for the binary and ternary mixtures under consideration. The obtained results are interpreted in the light of intermolecular interactions in fluids. Our findings show that ethylene glycol and choline cation interact with each other in the adsorbed surface layer formed at the interface between air and diluted solutions of ethaline.