Imidazolium-based ionic liquids with different fatty acid anions: phase behavior, electronic structure and ionic...

Area of Science:

• Materials Science
• Physical Chemistry
• Chemical Engineering

Background:

• Ionic liquids (ILs) are salts that are liquid at room temperature, with tunable properties.
• Fatty acid carboxylate anions offer a versatile platform for designing ILs with specific thermal and conductive characteristics.

Purpose of the Study:

• To investigate the thermal phase behaviors of novel 1-alkyl-3-methylimidazolium ionic liquids with varying fatty acid carboxylate anion chain lengths.
• To understand how structural modifications of ILs impact their ionic conductivity.
• To elucidate the interactions between IL cations and anions using computational methods.

Main Methods:

• Synthesis and characterization of a series of 1-alkyl-3-methylimidazolium ionic liquids.
• Differential scanning calorimetry (DSC) and other thermal analysis techniques to study phase transitions.
• Ab initio based Density Functional Theory (DFT) calculations to model ion pair formation and interactions.

Main Results:

• The length of the alkyl chain on the carboxylate anion significantly influences the phase transition temperatures and mesophase stability of the ILs.
• Replacing palmitate with palmitoyl ascorbate or palmitoyl-L-tryptophanate anions leads to a decrease and eventual disappearance of the melting temperature.
• Ionic conductivity is shown to be influenced by the structural modulation of the ILs.
• Computed ion pair formation energies correlate well with experimental observations, aiding in the determination of molecular arrangements in different phases.

Conclusions:

• Structural variations in ionic liquids, particularly the anion's alkyl chain length and functional groups, are critical for controlling thermal properties like melting point and mesophase stability.
• Computational modeling provides valuable insights into the intermolecular forces governing IL behavior, complementing experimental findings.
• These findings enable the rational design of ionic liquids with tailored thermal and conductive properties for diverse applications.