Effect of Ionic Composition on Physicochemical Properties of Mono-Ether Functional Ionic Liquids

Area of Science:

• Materials Science
• Physical Chemistry
• Organic Chemistry

Background:

• Functional ionic liquids (FILs) offer tunable properties for specific applications.
• Ether-functionalized FILs are effective solvents for organic compounds and enzymatic reactions.
• Ionic composition significantly impacts FIL solubility and physicochemical properties.

Purpose of the Study:

• To synthesize and characterize novel mono-ether group (ME) functionalized ionic liquids based on imidazole.
• To systematically investigate the influence of cationic structure and anion type on the physicochemical properties of ME-FILs.
• To understand the structure-property relationships for designing tailor-made FILs.

Main Methods:

• Cationic functionalization and anionic exchange reactions for FIL synthesis.
• Characterization using Nuclear Magnetic Resonance (NMR), mass spectrometry, and Thermogravimetric Analysis (TGA).
• Systematic evaluation of density, viscosity, ionic conductivity, electrochemical window, and thermal properties.

Main Results:

• Viscosity and heat capacity increase with larger cationic volumes; 2-alkyl substitution on imidazolium significantly enhances viscosity.
• Density and conductivity decrease with larger cationic volumes for a fixed anion ([NTf2]−).
• For ME-FILs with the same cation, property order varies by anion: density ([NTf2]− > [PF6]− > [BF4]−), viscosity ([PF6]− > [BF4]− > [NTf2]−), and conductivity ([NTf2]− ≈ [BF4]− > [PF6]−).

Conclusions:

• Both cationic structure and counter anion collectively dictate the physicochemical properties of ME-FILs.
• ME-FILs exhibit tunable properties, broad electrochemical windows, and defined thermal transitions.
• The findings provide a basis for designing specific ME-FILs for targeted applications.