The wetting behavior of aqueous imidazolium based ionic liquids: a molecular dynamics study

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Aqueous ionic liquids (ILs) offer tunable properties, but their structure-property relationships require deeper investigation.
• Understanding IL behavior at interfaces is crucial for applications in materials science and nanotechnology.

Purpose of the Study:

• To investigate the wetting behavior of aqueous imidazolium-based ILs on a graphite surface.
• To elucidate the effects of anion type ([BF4]- vs. [NTF2]-) and IL concentration on interfacial properties.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model aqueous ILs ([EMIM]+ cation with [BF4]- or [NTF2]- anions) at varying concentrations (0-50 wt%) on graphite.
• Contact angle measurements, density profiling (z and r directions), and an orientation order parameter were used to analyze droplet characteristics.

Main Results:

• Increasing IL concentration decreased the contact angle, indicating enhanced wetting.
• IL adsorption at the graphite interface led to water depletion near the surface.
• The hydrophobic [NTF2]- anion drove IL adsorption, while the hydrophilic [BF4]- anion kept ILs in the droplet bulk.

Conclusions:

• Anion hydrophobicity, water-anion hydrogen bonding, and interfacial tensions significantly influence the wetting behavior of aqueous ILs.
• The study provides insights into the interfacial behavior of ILs, crucial for designing IL-based materials and processes.