On the Regular Behavior of a Binary Mixture of Ionic Liquids

Area of Science:

• Physical Chemistry
• Materials Science
• Spectroscopy

Background:

• Ionic liquids (ILs) are salts that are liquid below 100°C, with tunable properties.
• Understanding the thermodynamic and structural behavior of IL mixtures is crucial for their applications.
• Binary mixtures of 1-ethyl-3-methylimidazolium dicyanamide and tributyl(methyl)ammonium dicyanamide were chosen for this study.

Purpose of the Study:

• To characterize the thermodynamic and structural properties of binary ionic liquid mixtures.
• To determine if these mixtures conform to the regular solution theory.
• To investigate the local environment around the dicyanamide anion using Raman spectroscopy.

Main Methods:

• Measurement of excess properties: excess enthalpy (H^E) and excess volume (V^E).
• Viscosity measurements across varying compositions.
• Raman spectroscopy to analyze the dicyanamide anion's symmetric stretching mode (ν_s(C≡N)).

Main Results:

• The studied ionic liquid mixtures exhibit positive excess volumes (V^E > 0) and excess enthalpies (H^E > 0).
• Viscosity data correlates with the observed positive excess enthalpy.
• Raman spectra analysis shows changes in peak frequency and bandwidth of the ν_s(C≡N) mode, consistent with concentration fluctuations.

Conclusions:

• The combination of thermodynamic and spectroscopic data supports classifying the studied ionic liquid mixture as a regular solution.
• The findings validate the application of regular solution theory to these IL mixtures.
• The study provides a framework for applying regular solution equations to other binary ionic liquid mixtures.