Direct experimental verification of negative deviations from ideal mixing in an archetypal deep eutectic solvent

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Thermodynamics

Background:

• Deep eutectic solvents (DES) are emerging as novel reaction media.
• Understanding solute behavior in DES is crucial for their application.
• Urea-choline chloride is a representative DES with potential industrial uses.

Purpose of the Study:

• To determine the thermodynamic activity of urea in urea-choline chloride DES.
• To investigate the interactions between urea and choline chloride.
• To characterize the mixing thermodynamics in this DES system.

Main Methods:

• Direct tensimetric experiments were performed.
• Knudsen effusion mass spectrometry was employed for measurements.
• Experiments were conducted in the temperature range of 319-343 K.

Main Results:

• Urea activity coefficients ranged from 0.25 to 0.44.
• A significant negative deviation from Raoultian behavior was observed.
• Negative partial enthalpy and entropy of mixing were determined.

Conclusions:

• Strong attractive interactions exist between urea and choline chloride.
• Urea molecules exhibit significant ordering within the DES.
• The findings provide fundamental insights into DES thermodynamics.