The eutectic point in choline chloride and ethylene glycol mixtures

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Choline chloride (ChCl) and ethylene glycol (EG) mixtures are widely recognized as model deep eutectic solvents (DES).
• Accurate phase diagrams are crucial for understanding and utilizing DES properties.

Purpose of the Study:

• To precisely determine the phase behavior and eutectic point of the ChCl-EG mixture.
• To construct an extended phase diagram for this paradigmatic DES.

Main Methods:

• Experimental measurement of phase transitions over a broad composition range.
• Analysis of thermal properties to identify phase boundaries.

Main Results:

• The eutectic point was identified at -28 ± 1 °C with a ChCl mole fraction between 0.01 and 0.02.
• A cold-crystallization event was observed at -65 °C, distinct from the eutectic point.
• The determined eutectic temperature is shallower than predicted by ideal solution theory.

Conclusions:

• The established eutectic composition for ChCl-EG DES was inaccurate.
• The observed cold-crystallization may have been previously misidentified as the eutectic point.
• This revised phase diagram offers a more accurate understanding of ChCl-EG DES behavior.