Cation folding and the thermal stability limit of the ionic liquid [BMIM⁺][BF₄ ^-] under total vacuum

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Chemistry

Background:

• Ionic liquids (ILs) based on alkylated imidazoles exhibit complex cation conformations.
• Understanding these conformations is crucial for predicting IL properties and behavior.

Purpose of the Study:

• To investigate the bimodal distribution of cation conformations (folded/unfolded) in alkylated imidazole-based ionic liquids.
• To elucidate the effect of temperature on cation conformation and its influence on IL cohesivity and interfacial behavior.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model ionic liquid systems.
• Analysis focused on cation alkyl chain folding, cation-anion interactions, and interfacial structures.

Main Results:

• A bimodal distribution of cation conformations (folded/unfolded) was observed.
• Increasing temperature promotes cation folding, contrary to protein denaturation.
• Folded cations reduce liquid cohesivity by blocking cation-anion interactions.
• An outermost cation layer at the interface, tilted towards it, stabilizes the system transversely.

Conclusions:

• Cation conformation in ionic liquids is temperature-dependent and influences macroscopic properties.
• Interfacial cation arrangements contribute to thermal stability and limit vaporization.
• The findings provide insights into the molecular mechanisms governing ionic liquid behavior.