Experimental Thermophysical Properties and Temperature Dependence of Four Non-Ionic Deep Eutectic Solvents

Deep eutectic solvents (DESs) have emerged as promising alternatives to conventional solvents due to their tunable properties and potential environmental benefits. While most studies focus on ionic DESs, nonionic DESs remain less explored. In this work, four nonionic deep eutectic solvents (DESs) are prepared using diethylene glycol dimethyl ether or isoquinoline as hydrogen-bond acceptors (HBA) and cyclohexanecarboxylic acid, nonanoic acid, or 1-naphthylamine as hydrogen-bond donors (HBD) at specific molar ratios. Their fundamental thermophysical properties, including density, viscosity, surface tension, electrical conductivity, and melting point, are systematically measured over the temperature range of 303.15–343.15 K. The temperature dependence of all measured properties is quantitatively analyzed using appropriate empirical or Arrhenius-type correlations. The results provide insights into the influence of molecular composition on nonionic DES behavior, expanding the experimental database and highlighting their potential as low-viscosity, tunable, and versatile solvents for chemical engineering applications.