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Interfacial Layering in the Electric Double Layer of Ionic Liquids
J Pedro de Souza1, Zachary A H Goodwin2,3, Michael McEldrew1
1Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Physical Review Letters
|September 25, 2020
Summary
This study introduces a theory for ionic liquids, explaining charge layering at interfaces and bulk structures due to coupled forces. The model accurately predicts ion behavior, matching simulation results.
Area of Science:
- Physical Chemistry
- Materials Science
- Electrochemistry
Background:
- Ions in ionic liquids and concentrated electrolytes exist in crowded, strongly interacting environments.
- This environment leads to discrete charge layers at interfaces and spin-glass structures in the bulk.
Purpose of the Study:
- To propose a simple theory capturing the coupling between steric and electrostatic forces in ionic liquids.
- To predict the formation of discrete charge layers at charged interfaces.
Main Methods:
- Developed a theory coupling steric and electrostatic forces.
- Analyzed the gradient expansion of charge density.
- Compared theoretical predictions with molecular simulations.
Main Results:
- The theory predicts discrete charge layers at charged interfaces.
- Slowly decaying oscillations in charge density with a wavelength of a single ion diameter were observed.
- Quantitative agreement was found between the theory and molecular simulations for differential capacitance and concentration profiles.
Conclusions:
- The proposed theory successfully explains ion behavior in ionic liquids.
- The findings suggest a new structure for partial differential equations governing electrostatic potential at charged interfaces.
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