The molar surface quasi-Gibbs energy and its application to the binary mixtures of 1-(2-methoxyethyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide [MOEMIM][NTf2] with methanol and ethanol

Abstract

The IL (ionic liquid) 1-(2-methoxyethyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide [MOEMIM][NTf2] was prepared and confirmed by 1H NMR (1H nuclear magnetic resonance) spectroscopy and 13C NMR (13C nuclear magnetic resonance) spectroscopy. The density and surface tension for the binary mixtures of [MOEMIM][NTf2] with methanol and ethanol were measured across the entire range of mole fraction (x1 = 0.0000–1.0000) at T = (288.15–318.15) K. The average molar volumes of the binary mixtures were calculated from the experimental density, which increased with the increase of mole fraction and temperature. The excess molar volumes, VmE, were obtained and fitted by Redlich–Kister equation. The interaction between ionic liquid and alcohol is the strongest efficient packing and/or attractive interaction at the minimum point. The lower the temperature was, the smaller the absolute value of excess molar volume was. The new function – the molar surface quasi-Gibbs energy of mixtures was obtained by us in this work. On a basis of molar surface quasi-Gibbs energy of mixtures, a new Eӧtvӧs equation was obtained of mixtures and applied to binary mixtures of [MOEMIM][NTf2] with alcohols. The absolute value of the slope of the new Eötvös equation is the mole surface entropy, s, and the intercept is the molar surface enthalpy, h, which is temperature-independent. The deviation of molar surface quasi-Gibbs energy, Δgs, of mixtures for [MOEMIM][NTf2] with methanol and ethanol were calculated. Δgs was well fitted by Redlich–Kister equation. In terms of Redlich–Kister’s parameters, Ai, a new method for estimating the surface tension, γ, with any component of the mixtures is proposed and the estimated values, γ (est.), are in good agreement with the corresponding experimental ones, γ(exp.).