Thermodynamic Study of Amine-Based Deep Eutectic Solvents with H 2 O

High Resolution Image Download MS PowerPoint Slide The densities and viscosities of ([C n mimCl][MEA] + H 2 O) systems ( n = 2, 4, 6) were measured over 288.15–323.15 K, and the enthalpies of mixing were determined at 298.15 and 308.15 K. Density data showed nonmonotonic composition dependence with extrema near x DES ≈ 0.4–0.5, and negative excess molar volumes indicated enhanced molecular packing. Viscosity increased sharply at low DES content and more gradually toward pure DESs, exhibiting S-shape deviation profiles that reflect structural rearrangements in both DES-rich and H 2 O-rich regions. Negative enthalpies of mixing confirmed exothermic mixing due to strong DES–H 2 O interactions, and the data were well correlated by the NRTL model. The coincidence of extrema in density and enthalpy of mixing, together with viscosity transitions, suggests the formation of complexes among the DES constituents and H 2 O, probably leading to compact ternary DES-like microstructures. Further comparative analysis revealed that H 2 O addition reorganizes the hydrogen-bond network, forming extensive MEA–H 2 O associations. These findings offer molecular-level insights for the rational design of DES-based solvents for CO 2 capture and related separation processes.