Thermodynamic properties of TPAC-EG deep eutectic solvents: A study based on the IGC method with molecular simulations

Abstract

The study of thermodynamic properties and intermolecular interactions in deep eutectic solvents (DES) is an important innovative step in the development of DES. This research focuses on the synthesis of DES using a 1:2 M ratio of tetrapropylammonium chloride and ethylene glycol. Inverse gas chromatography (IGC) techniques are used to investigate DES of thermodynamics in the temperature range of 303.15–333.15 K. Additionally, molecular dynamics (MD) simulations and density functional theory (DFT) are used to explore intermolecular interactions in DES at both molecular and atomic levels. The research findings yield crucial insights, including the successful determination of infinite dilution activity coefficients, Flory-Huggin’s interaction parameters, solubility parameters, and Abraham solvation parameters of DES through IGC techniques. A careful study of the temperature-dependent trends in these parameters is provided. Analyses of structural properties, including radial distribution functions, hydrogen bond counts, and thermal fluctuation indices, reveal that, at experiments temperatures, the amount and nature of intermolecular hydrogen bonds in binary mixtures are the main factors influencing the thermodynamic properties of DES. Finally, based on DFT calculations, a quantitative assessment of the molecular interaction mechanisms of DESs at the atomic level confirms the predominant role of hydrogen bonding in DES formation, with multicenter hydrogen bonds characterized by stronger hydrogen bond strengths emerging as the primary type.