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  Ionic liquids behave as dilute electrolyte solutions

Gebbie, M. A., Valtiner, M., Banquy, X., Fox, E. T., Henderson, W. A., & Israelachvili, J. N. (2013). Ionic liquids behave as dilute electrolyte solutions. Proceedings of the National Academy of Sciences of the USA, 110(24), 9674-9679. doi:10.1073/pnas.1307871110.

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Gebbie, Matthew A.1, Author              
Valtiner, Markus2, Author              
Banquy, Xavier3, Author              
Fox, Eric T.4, Author              
Henderson, Wesley A.4, Author              
Israelachvili, Jacob N.5, 6, Author              
1Materials Department, University of California, Santa Barbara, CA 93116, USA, ou_persistent22              
2Interaction Forces and Functional Materials, Interface Chemistry and Surface Engineering, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society, ou_1863357              
3Department of Chemical Engineering, University of California, Santa Barbara, CA 93106, USA, ou_persistent22              
4Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA, ou_persistent22              
5Department of Chemical Engineering, University of California, Santa Barbara, CA 93106-5080, USA, ou_persistent22              
6Materials Department, University of California, Santa Barbara, CA, USA, ou_persistent22              


Free keywords: Boltzmann distribution; Electrostatic interaction; Interfacial phenomena
 Abstract: We combine direct surface force measurements with thermodynamic arguments to demonstrate that pure ionic liquids are expected to behave as dilute weak electrolyte solutions, with typical effective dissociated ion concentrations of less than 0.1% at room temperature. We performed equilibrium forcedistance measurements across the common ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C(4)mim][NTf2]) using a surface forces apparatus with in situ electrochemical control and quantitatively modeled these measurements using the van der Waals and electrostatic double-layer forces of the DerjaguinLandauVerweyOverbeek theory with an additive repulsive steric (entropic) ionsurface binding force. Our results indicate that ionic liquids screen charged surfaces through the formation of both bound (Stern) and diffuse electric double layers, where the diffuse double layer is comprised of effectively dissociated ionic liquid ions. Additionally, we used the energetics of thermally dissociating ions in a dielectric medium to quantitatively predict the equilibrium for the effective dissociation reaction of [C(4)mim][NTf2] ions, in excellent agreement with the measured Debye length. Our results clearly demonstrate that, outside of the bound double layer, most of the ions in [C(4)mim][NTf2] are not effectively dissociated and thus do not contribute to electrostatic screening. We also provide a general, molecular-scale framework for designing ionic liquids with significantly increased dissociated charge densities via judiciously balancing ion pair interactions with bulk dielectric properties. Our results clear up several inconsistencies that have hampered scientific progress in this important area and guide the rational design of unique, highfree-ion density ionic liquids and ionic liquid blends.


Language(s): eng - English
 Dates: 2013
 Publication Status: Published in print
 Pages: 6
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: ISI: 000320930100031
DOI: 10.1073/pnas.1307871110
 Degree: -



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Title: Proceedings of the National Academy of Sciences of the USA
  Other : Proc. Natl. Acad. Sci. USA
Source Genre: Journal
Publ. Info: National Academy of Sciences
Pages: - Volume / Issue: 110 (24) Sequence Number: - Start / End Page: 9674 - 9679 Identifier: ISSN: 0027-8424
CoNE: https://pure.mpg.de/cone/journals/resource/954925427230