From Solvent-Free to Dilute Electrolytes: Essential Components for a Continuum Theory.

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Highly concentrated electrolytes and ionic liquids exhibit unique phenomena (self-assembly, underscreening) not explained by current mean-field models.
• Existing models fail to capture distinct behaviors observed in concentrated electrolyte systems, necessitating new theoretical frameworks.

Purpose of the Study:

• To develop a self-consistent spatiotemporal continuum framework for ternary mixtures of ions and solvent.
• To model phenomena in highly concentrated electrolytes and ionic liquids, including self-assembly, transport, and electrical screening.

Main Methods:

• Developed a free energy functional incorporating short- and long-range interactions.
• Implemented an energy dissipation mechanism based on Onsager's relations.
• Utilized a spatiotemporal framework for a ternary composition (ions and solvent).

Main Results:

• The model successfully describes multiple bulk and interfacial morphologies at steady-state.
• Demonstrated the importance of dynamic processes in morphology emergence, alongside free energy interactions.
• Provided insights into transport mechanisms beyond Stokes-Einstein-Smoluchowski relations.

Conclusions:

• The new framework qualitatively recovers experimental observations of nonmonotonic electrical screening length in ionic liquid/organic solvent mixtures.
• The model offers a robust approach for understanding complex behaviors in highly concentrated electrolyte systems.
• Highlights the critical role of dynamics in conjunction with interactions for emergent properties.