Electric double layer composed of an antagonistic salt in an aqueous mixture: Local charge separation and surface phase transition

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. % while the cations are expelled from it. We then vary the surface charge density $\sigma$ on the wall. For $\sigma >0$ the anions remain accumulated, but for $\sigma <0$ the cations are attracted to the wall with increasing $|\sigma |$. Furthermore, the electric potential drop $\Psi (\sigma )$ is nonmonotonic when the solvent interaction parameter $\chi (T)$ exceeds a critical value ${\chi }_c$ 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 $\sigma$ and common $\Psi$. In equilibrium such two layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.

arXiv comment8 Pages, 8 Figs, accepted for Phys. Rev. Lett

References in corpus (11)

• Steric Effects in Electrolytes: A Modified Poisson-Boltzmann Equation
• Ion-Specific Hydration Effects: Extending the Poisson-Boltzmann Theory
• Onion structures induced by hydrophilic and hydrophobic ions in a binary mixture
• Phase-separation in ion-containing mixtures in electric fields
• Charged colloids in an aqueous mixture with a salt
• Mesoscale phenomena in solutions of 3-methylpyridine, heavy water, and an antagonistic salt
• Structure Formation due to Antagonistic Salts
• Solvation Effects in Phase Transitions in Soft Matter
• The interaction between colloids in polar mixtures above Tc
• Tuning colloid-interface interactions by salt partitioning
• Recent advances in liquid mixtures in electric fields

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