Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical
Ke Ma1, Jan Forsman2, Clifford E Woodward1
1School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Canberra at the Australian Defence Force Academy, Canberra ACT 2600, Australia.
The Journal of Chemical Physics
|May 10, 2015
Summary
Ion pairing in ionic liquids has subtle effects on electrical double layers near surfaces. While short-range structures remain unchanged, long-range properties like capacitance are impacted, especially at low potentials.
Area of Science:
- Physical Chemistry
- Materials Science
- Electrochemistry
Background:
- Room temperature ionic liquids (RTILs) are crucial in electrochemical applications.
- Ion pairing in RTILs influences their bulk and interfacial properties.
- Understanding ion pairing is key to optimizing RTIL-based devices.
Purpose of the Study:
- To investigate the impact of ion pairing on the electrical double layer structure.
- To analyze the effects of ion association on surface forces and differential capacitance.
- To determine how the degree of ion pairing influences interfacial properties of RTILs.
Main Methods:
- Utilized a coarse-grained model for the aromatic ionic liquid [C4MIM(+)][BF4 (-)].
- Incorporated ion pairing as an equilibrium associating species.
- Employed classical density functional theory to model confined ionic liquids.
Main Results:
- Short-range interfacial structure remained largely unaffected by ion pairing, even at 100% association.
- Long-range properties, including surface forces and differential capacitance, were significantly influenced by ion pairing.
- Observed effects on capacitance align with explanations for anomalous temperature dependencies.
Conclusions:
- Ion pairing's influence on RTIL interfacial properties is subtle and primarily affects long-range charge screening.
- Equilibrium properties dependent on charge screening are most sensitive to ion association.
- Directly extracting ion pairing effects from simulations may be challenging due to their subtle nature.
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