Thermodynamic Study of Amine-Based Deep Eutectic Solvents with H₂O

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Deep eutectic solvents (DES) are emerging as tunable solvent platforms.
• Understanding the physical properties and interactions of DES with other components is crucial for their application.
• Water's influence on DES structure and properties requires detailed investigation.

Purpose of the Study:

• To investigate the thermophysical properties (density, viscosity, enthalpy of mixing) of ([CnmimCl]-[MEA] + H2O) systems.
• To elucidate the molecular interactions and structural rearrangements occurring upon water addition to DES.
• To provide insights for the design of DES-based solvents for CO2 capture.

Main Methods:

• Measurement of densities and viscosities across a temperature range (288.15–323.15 K).
• Determination of enthalpies of mixing at different temperatures (298.15 and 308.15 K).
• Analysis of composition dependence and correlation using the NRTL model.

Main Results:

• Nonmonotonic density dependence with extrema observed, indicating enhanced molecular packing.
• Viscosity showed sharp increases at low water content, with S-shape deviation profiles.
• Negative enthalpies of mixing confirmed exothermic DES-H2O interactions, suggesting complex formation and ternary microstructure development.
• Water addition reorganized hydrogen-bond networks, promoting MEA-H2O associations.

Conclusions:

• The study reveals complex formation between DES constituents and water, leading to compact ternary structures.
• Water significantly influences the hydrogen-bond network and solvent properties.
• Findings provide molecular-level understanding for optimizing DES solvents in separation processes like CO2 capture.