Hydrogen bonding in a mixture of protic ionic liquids: a molecular dynamics simulation study

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Protic ionic liquids (PILs) are salts that are liquid at ambient temperatures and contain acidic protons.
• Hydrogen bonding plays a crucial role in the structure and properties of PILs.
• Understanding hydrogen bonding in PIL mixtures is essential for designing materials with specific functionalities.

Purpose of the Study:

• To investigate the impact of subtle structural differences in anions on hydrogen bonding in PIL mixtures.
• To characterize the formation of hydrogen-bonded aggregates in mixtures of triethylammonium-methylsulfonate (TEAMS) and triethylammonium-triflate (TEATF).
• To correlate hydrogen bond strength with the size and distribution of aggregates.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model and analyze hydrogen bonding interactions.
• The simulations focused on mixtures of TEAMS and TEATF, sharing the triethylammonium cation.
• A combinatorial lattice model was used to predict and explain the observed hydrogen-bonded cluster sizes.

Main Results:

• The triethylammonium cation acts as a hydrogen-bond donor, while the methylsulfonate and triflate anions act as acceptors.
• Replacing a methyl group with a trifluoromethyl group in the anion weakens the hydrogen bond strength.
• These variations in hydrogen bond strength significantly influence the size of hydrogen-bonded aggregates formed in the mixtures.
• The simulated cluster sizes were accurately predicted by a combinatorial lattice model.

Conclusions:

• Hydrogen bond strength is a critical factor governing the self-assembly of aggregates in PIL mixtures.
• Even minor structural modifications in anions can lead to significant changes in macroscopic properties.
• The findings provide insights into the molecular-level mechanisms driving aggregate formation in ionic liquids.
• The developed combinatorial model offers a predictive tool for understanding hydrogen-bonded structures in similar systems.