Self-assembled inverted micelles stabilize ionic liquid domains in supercritical CO2

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Molecular aggregation, crucial for microemulsion formation, is challenging to study experimentally.
• Ionic liquid-in-carbon dioxide (IL-in-CO(2)) microemulsions are of interest but their formation mechanisms require detailed investigation.

Purpose of the Study:

• To elucidate the atomic-level self-aggregation process in IL-in-CO(2) microemulsions.
• To provide a detailed understanding of the structural and energetic properties governing microemulsion stability.
• To identify key interactions responsible for the stability of IL-in-CO(2) systems.

Main Methods:

• Utilized advanced computer simulations to model the entire self-aggregation process of IL-in-CO(2) microemulsions.
• Analyzed structural and energetic properties at the atomic level.
• Validated simulation results against experimental small-angle neutron scattering (SANS) data.

Main Results:

• Provided direct evidence for stable IL droplets within a continuous CO(2) phase, stabilized by amphiphilic surfactants.
• Microstructure of nanodroplets from simulations showed excellent agreement with SANS data.
• Demonstrated that guanidium acetate-based IL-in-CO(2) microemulsions are more stable than imidazolium hexafluorophosphate-based ones.
• Identified IL anion-headgroup interactions as the primary driver of microemulsion stability, with cations playing a secondary role.

Conclusions:

• The study offers a detailed atomic-level insight into IL-in-CO(2) microemulsion formation and stability.
• Findings challenge existing hypotheses by emphasizing the dominant role of anion-headgroup interactions.
• The understanding gained can guide the design of novel surfactants for improved IL uptake in CO(2), relevant for carbon capture technologies.