Electric Double Layer Composed of an Antagonistic Salt in an Aqueous Mixture

Local Charge Separation and Surface Phase Transition

Syunsuke Yabunaka, Akira Onuki

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

We examine an electric double layer containing an antagonistic salt in an aqueous mixture, where the cations are small and hydrophilic but the anions are large and hydrophobic. In this situation, a strong coupling arises between the charge density and the solvent composition. As a result, the anions are trapped in an oil-rich adsorption layer on a hydrophobic wall. We then vary the surface charge density σ on the wall. For σ>0 the anions remain accumulated, but for σ<0 the cations are attracted to the wall with increasing |σ|. Furthermore, the electric potential drop Ψ(σ) is nonmonotonic when the solvent interaction parameter χ(T) exceeds a critical value χc determined by the composition and the ion density in the bulk. This leads to a first-order phase transition between two kinds of electric double layers with different σ and common Ψ. In equilibrium such two-layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.

Original languageEnglish
Article number118001
JournalPhysical Review Letters
Volume119
Issue number11
DOIs
Publication statusPublished - Sep 11 2017

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polarization (charge separation)
salts
anions
cations
oils
adsorption
electric potential
ions
interactions

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Cite this

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