Measuring and predicting Delta(vap)H298 values of ionic liquids.

Area of Science:

• Physical Chemistry
• Materials Science
• Thermodynamics

Background:

• Ionic liquids (ILs) are versatile materials with tunable properties.
• Understanding their thermophysical properties, like enthalpy of vaporization, is crucial for applications.
• Existing models for predicting IL properties often lack broad applicability.

Purpose of the Study:

• To develop a predictive model for the enthalpies of vaporization of ionic liquids.
• To decompose the enthalpy of vaporization into fundamental ionic and molecular contributions.
• To provide accurate estimations for a wide range of ILs.

Main Methods:

• Temperature programmed desorption by mass spectrometry was used to measure enthalpies of vaporization for twelve ILs.
• Enthalpies were decomposed into Coulombic and van der Waals components.
• A universal parameter for anion-cation distance change and individual van der Waals contributions were derived.

Main Results:

• A three-component model for enthalpy of vaporization was established: Coulombic interaction, and van der Waals contributions from anion and cation.
• Universal and individual parameters (R(r), DeltaH(vdw,A), DeltaH(vdw,C)) were determined for various ions.
• The model successfully predicts enthalpies of vaporization for known and fourteen novel ILs.

Conclusions:

• The enthalpy of vaporization of ionic liquids can be accurately predicted using a model based on ionic size, Coulombic forces, and van der Waals interactions.
• This predictive capability facilitates the design and selection of ILs for specific applications.
• The study provides a valuable tool for researchers in ionic liquid chemistry and engineering.