Excess volumes of mixtures consisting of deep eutectic solvents by the Prigogine-Flory-Patterson theory

Deep Eutectic Solvents are complex solvents whose properties are challenging to understand and to model. In this study, the Prigogine-Flory-Patterson (PFP) theory was used, for the first time in literature, to estimate excess molar volumes of different systems consisting of Deep Eutectic Solvents (DESs). Twelve different systems, consisting of Ethaline + DMSO, Ethaline + water, Reline + water, Reline + methanol, Reline + ethanol, Glycine + water, Glycine + methanol, Glycine + ethanol, Glycine + isopropanol, Maline + water, Tegaline + water, and Glucoline + water were investigated in the full range of concentrations and within wide ranges of temperature, at atmospheric pressure. Excess molar volume is a complicated thermodynamic property because it depends not only on the shape, size, and chemical nature of each pure component in the mixture, but also on all of the binary and higher order interactions of the components in the mixture. The Prigogine-Flory-Patterson theory is one of the very few theoretical models for estimating excess molar volume. Because of the thermodynamic background of the PFP theory, which divides the excess molar volume into three different molecular interaction contributions, the results of this model in mixtures involving DESs can be valuable for a rough interpretation of the molecular interactions of such complex mixtures at a microscopic scale. In order to avoid the correlative aspect of the PFP theory, a generalized relation was proposed for the interaction parameter of the theory covering all temperatures. The resulting model, with a total AARD% of 14.6% and agreement between the predicted trends and the corresponding experimental trends, indicated the capability and suitability of the PFP theory in estimating excess molar volumes of such complex and non-ideal mixtures consisting of DESs.