Formation and Disruption of Hydrogen Bond in 1-Ethyl-3-methylimidazolium Ethylsulfate and Glycerol Binary Mixtures: A Molecular Perspective

This study focuses on the hydrogen bonding interactions that govern the physicochemical properties of the binary mixtures of 1-ethyl-3-methylimidazolium ethylsulfate ([C₂mim]C₂H₅SO₄) and glycerol. Various thermodynamic properties of [C₂mim]C₂H₅SO₄ and glycerol mixtures were investigated by using density and viscosity across a range of compositions and temperatures, while structural properties were explored by using temperature-dependent near-infrared (NIR) spectroscopy, two-dimensional (2D) correlation spectroscopy, and principal component analyses (PCA). In order to better understand hydrogen bonding interactions, both analyses were employed. The NIR spectroscopic analysis shows the presence of various types of hydrogen-bonded clusters in the structure of glycerol and a strong hydrogen bond between the hydrogen of the imidazole ring and the oxygen of ethylsulfate anions. In the binary mixtures, hydrogen-bonded clusters of glycerol were sustained upon addition of [C₂mim]C₂H₅SO₄ up to a mole fraction of 0.6. Further addition of [C₂mim]C₂H₅SO₄ causes breakdown of the cluster of glycerol and forms solvated ions of [C₂mim]C₂H₅SO_4. The variation of excess molar volume, dynamic viscosity deviation, excess molar Gibbs free energy of activation, and thermodynamic activation parameters also show transitions at this particular composition. Hence, the dynamic interaction between the formation and disruption of hydrogen bonds in these compounds controls the thermodynamic properties, which is the key factor to apply this binary system in various fields.