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Quantifying intermolecular interactions of ionic liquids using cohesive energy densities.
1Department of Chemistry, University of Reading, Reading, UK.
Royal Society Open Science
|January 9, 2018
Summary
Cohesive energy density (ced) quantifies intermolecular forces in ionic liquids (ILs). This study presents new experimental data and analysis for ced in ILs, revealing insights into their unique interactions.
Area of Science:
- Physical Chemistry
- Materials Science
- Thermodynamics
Background:
- Ionic liquids (ILs) present unique challenges for understanding intermolecular interactions due to numerous cation-anion combinations and their ionic nature.
- Cohesive energy density (ced) is a key metric for quantifying intermolecular forces in molecular liquids, typically derived from enthalpy of vaporization.
- Existing methods for assessing IL intermolecular interactions are limited, necessitating novel approaches.
Purpose of the Study:
- To critically analyze experimental challenges and data for determining cohesive energy density (ced) in ionic liquids (ILs).
- To introduce and present experimental data for cedC+A, representing the total intermolecular interaction strength in ILs.
- To explore correlations between different measures of intermolecular interactions in ILs.
Main Methods:
- Analysis of experimental challenges and data for obtaining cohesive energy density (ced) in ionic liquids (ILs).
- Determination of cedIP (based on neutral ion pairs in vapor) for 64 ILs.
- Experimental determination of cedC+A (based on isolated ions in vapor) for ILs.
Main Results:
- Experimental cedC+A for ILs is significantly higher than for most molecular liquids, indicating strong electrostatic interactions.
- Van der Waals interactions play a crucial role in IL volatility due to strong electrostatic interactions within neutral ion pairs.
- Excellent linear correlation observed between cedIP and inverse molecular volume; good correlation between cedIP and IL Gordon parameter.
Conclusions:
- The study provides the first experimental cedC+A, a measure of total intermolecular interaction strength in ILs.
- cedIP is vital for understanding IL intermolecular interactions, despite not capturing the total interaction energy.
- Further research is needed to address remaining challenges in understanding IL intermolecular interactions.
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