Insights into the\nIntermolecular Interactions of Monoethanolamine–<i>p</i>‑Hydroxyanisole DES Aqueous Solution through Volumetric\nand Viscometric Properties

Deep eutectic solvents (DESs) have been increasingly\nstudied due\nto their wide application in many fields, such as metal treatment,\nextraction and separation, chemical synthesis, refinement of biological\nand natural components, and gas absorption. Water, as an abundant,\nenvironmentally friendly, and low-cost resource, can effectively regulate\nthe structure and thermodynamic properties of DES; thus, it is important\nto study the effect of water on DESs. In this work, DESs with different\nwater contents composed of monoethanolamine (MEA) and <i>p</i>-hydroxyanisole (MEHQ) in various mole ratios (1.0000:1.0000 to 5.0000:1.0000)\nwere successfully prepared, and the density and viscosity were measured\nat temperatures ranging from 293.15 to 323.15 K using a U-shaped vibrating\ntube densitometer and a falling ball viscometer. Intermolecular interactions\nin DES aqueous solutions were investigated by using volumetric and\nviscometric properties: excess molar volume, thermal expansion coefficient,\nviscosity deviation, viscous flow activation energy, and excess Gibbs\nactivation energy. The effect of the water content on the structure\nof DES could be roughly classified into three zones: the zone of structural\nintegrity of DES, the zone of partial destruction of DES, and the\nzone of freeing of DES components.