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Interfacial structure and structural forces in mixtures of ionic liquid with a polar solvent
Samuel W Coles1, Alexander M Smith2, Maxim V Fedorov3
1Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, UK. susan.perkin@chem.ox.ac.uk.
Faraday Discussions
|September 22, 2017
Summary
Ionic liquids mixed with solvents exhibit complex interfacial behavior. Simulations and experiments reveal a switch from charge-oscillatory to charge-monotonic structures at interfaces, influencing forces.
Area of Science:
- Chemical Physics
- Materials Science
- Electrochemistry
Background:
- Ionic liquids (ILs) are frequently used in mixtures with neutral molecular solvents.
- Understanding the chemical physics of these high-concentration electrolytes at interfaces is crucial but challenging.
- Interfacial behavior in IL-solvent mixtures dictates their performance in various applications.
Purpose of the Study:
- To correlate structural forces measured at interfaces with molecular dynamics (MD) simulations.
- To establish an experimental method for determining effective surface charge on mica in ILs.
- To investigate the relationship between interfacial structure and solvation forces in IL-solvent mixtures.
Main Methods:
- Experimental measurement of structural forces using mica surfaces in IL-solvent mixtures.
- Molecular dynamics simulations of IL-solvent mixtures with fixed-charge surfaces.
- Development of a procedure to quantify effective surface charge on mica in ILs.
- Phase diagram construction in composition-surface charge space.
Main Results:
- A structural crossover was identified, transitioning from charge-oscillatory to charge-monotonic interfacial structures.
- Solvent layering becomes dominant at the crossover point.
- Simulations support the experimental inference of this structural crossover.
- A phase diagram illustrates distinct regions of charge-oscillatory and charge-monotonic interfacial structures.
Conclusions:
- The study successfully links experimental force measurements with MD simulations for IL-solvent mixtures.
- A novel method for determining effective surface charge on mica in ILs was presented.
- The findings reveal a composition- and charge-dependent switch in interfacial structure, impacting solvation forces.
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