From a eutectic mixture to a deep eutectic system via anion selection: Glutaric acid + tetraethylammonium halides

Area of Science:

• Physical Chemistry
• Materials Science

Background:

• Understanding structure-property relationships is crucial for designing eutectic mixtures.
• The melting point depression in binary eutectic mixtures is influenced by various components.

Purpose of the Study:

• To investigate the influence of the anion on the solid-liquid (S-L) phase behavior in glutaric acid + tetraethylammonium salt mixtures.
• To explore structure-property relationships for melting point depression in these binary eutectic systems.

Main Methods:

• Experimental evaluation of S-L phase behavior for glutaric acid with tetraethylammonium chloride, bromide, and iodide.
• Inter- and extrapolation of data using Gibbs energy of mixing models.
• Fitting experimental data to a Redlich-Kister expansion with Flory entropy.

Main Results:

• The eutectic point shifts to lower temperatures and higher salt content as the anion's ionic radius decreases.
• Eutectic depth correlates with the anion's ionic radius.
• Salt fusion properties were inaccessible due to thermal decomposition.

Conclusions:

• Anion type and size are critical design parameters for the liquid window of deep eutectic solvents.
• This study provides insights into tailoring eutectic mixture properties by anion selection.