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Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach.

Ma, Ke; Forsman, Jan LU and Woodward, Clifford E (2015) In Journal of Chemical Physics 142(17).
Abstract
We explore the influence of ion pairing in room temperature ionic liquids confined by planar electrode surfaces. Using a coarse-grained model for the aromatic ionic liquid [C4MIM(+)][BF4 (-)], we account for an ion pairing component as an equilibrium associating species within a classical density functional theory. We investigated the resulting structure of the electrical double layer as well as the ensuing surface forces and differential capacitance, as a function of the degree of ion association. We found that the short-range structure adjacent to surfaces was remarkably unaffected by the degree of ion pairing, up to several molecular diameters. This was even the case for 100% of ions being paired. The physical implications of ion... (More)
We explore the influence of ion pairing in room temperature ionic liquids confined by planar electrode surfaces. Using a coarse-grained model for the aromatic ionic liquid [C4MIM(+)][BF4 (-)], we account for an ion pairing component as an equilibrium associating species within a classical density functional theory. We investigated the resulting structure of the electrical double layer as well as the ensuing surface forces and differential capacitance, as a function of the degree of ion association. We found that the short-range structure adjacent to surfaces was remarkably unaffected by the degree of ion pairing, up to several molecular diameters. This was even the case for 100% of ions being paired. The physical implications of ion pairing only become apparent in equilibrium properties that depend upon the long-range screening of charges, such as the asymptotic behaviour of surface forces and the differential capacitance, especially at low surface potential. The effect of ion pairing on capacitance is consistent with their invocation as a source of the anomalous temperature dependence of the latter. This work shows that ion pairing effects on equilibrium properties are subtle and may be difficult to extract directly from simulations. (Less)
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author
organization
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type
Contribution to journal
publication status
published
subject
in
Journal of Chemical Physics
volume
142
issue
17
publisher
American Institute of Physics
external identifiers
  • pmid:25956113
  • wos:000354258200036
  • scopus:84929081358
ISSN
0021-9606
DOI
10.1063/1.4919314
language
English
LU publication?
yes
id
d8805a32-5b3a-42dd-ae89-78d78a82ecde (old id 5453712)
date added to LUP
2015-06-16 09:47:19
date last changed
2017-10-08 03:18:31
@article{d8805a32-5b3a-42dd-ae89-78d78a82ecde,
  abstract     = {We explore the influence of ion pairing in room temperature ionic liquids confined by planar electrode surfaces. Using a coarse-grained model for the aromatic ionic liquid [C4MIM(+)][BF4 (-)], we account for an ion pairing component as an equilibrium associating species within a classical density functional theory. We investigated the resulting structure of the electrical double layer as well as the ensuing surface forces and differential capacitance, as a function of the degree of ion association. We found that the short-range structure adjacent to surfaces was remarkably unaffected by the degree of ion pairing, up to several molecular diameters. This was even the case for 100% of ions being paired. The physical implications of ion pairing only become apparent in equilibrium properties that depend upon the long-range screening of charges, such as the asymptotic behaviour of surface forces and the differential capacitance, especially at low surface potential. The effect of ion pairing on capacitance is consistent with their invocation as a source of the anomalous temperature dependence of the latter. This work shows that ion pairing effects on equilibrium properties are subtle and may be difficult to extract directly from simulations.},
  articleno    = {174704},
  author       = {Ma, Ke and Forsman, Jan and Woodward, Clifford E},
  issn         = {0021-9606},
  language     = {eng},
  number       = {17},
  publisher    = {American Institute of Physics},
  series       = {Journal of Chemical Physics},
  title        = {Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach.},
  url          = {http://dx.doi.org/10.1063/1.4919314},
  volume       = {142},
  year         = {2015},
}