Thermodynamical and structural properties of imidazolium based ionic liquids from molecular simulation

Area of Science:

• Computational Chemistry
• Materials Science
• Physical Chemistry

Background:

• Ionic liquids (ILs) are tunable solvents with diverse applications.
• Understanding their structural properties is crucial for designing new materials.
• Accurate and efficient simulation methods are needed for IL research.

Purpose of the Study:

• To determine thermophysical properties (density, heat of vaporization) and structural information for 1-alkyl-3-methylimidazolium-based ILs ([amim][Cl] and [amim][BF4]).
• To evaluate the accuracy and computational efficiency of a united atom model for IL simulations.
• To analyze the influence of anion type, cation size, and temperature on IL local structure.

Main Methods:

• Molecular dynamics (MD) simulations were performed.
• A united atom (UA) model was employed, extending existing models for imidazolium cations ([emim(+)], [bmim(+)], [hmim(+)]) and using established parameters for the chloride anion ([Cl(-)]).
• Radial distribution functions (RDFs) and spatial distribution functions (SDFs) were used to analyze local structure.

Main Results:

• The UA model provided reasonable predictions for IL properties with reduced computational cost compared to all-atom models.
• Simulations revealed temperature-dependent tail aggregations in ILs with increasing side chain length.
• Structural analysis showed influence of anion, cation size, and temperature on local ordering.

Conclusions:

• The united atom model is a computationally efficient and accurate approach for simulating imidazolium-based ionic liquids.
• Tail aggregation increases with alkyl chain length and temperature, impacting IL structure.
• This study provides valuable insights into the structure-property relationships of ILs.