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 $\sigma$ 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 $\mathrm{\Psi }(\sigma )$ 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 $\mathrm{\Psi }$. In equilibrium such two-layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.

中文翻译：

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水溶液中的拮抗盐组成的双电层：局部电荷分离和表面相变

我们研究了在水性混合物中含有拮抗盐的双电层，其中阳离子小且亲水，而阴离子大且疏水。在这种情况下，电荷密度和溶剂组成之间会产生强耦合。结果，阴离子被捕获在疏水壁上的富油吸附层中。然后我们改变表面电荷密度$\sigma$在墙壁上。为了$\sigma >0$ 阴离子仍然积累，但是对于 $\sigma <0$ 随着阳离子的增加，阳离子被吸引到墙壁上 $|\sigma |$。此外，电势下降$\mathrm{\Psi }（\sigma ）$ 当溶剂相互作用参数为非单调时 $\chi （Ť）$ 超过临界值 ${\chi }_C$由组成和整体中的离子密度决定。这会导致两种具有不同电双层的双电层之间发生一阶相变$\sigma$ 和普通的 $\mathrm{\Psi }$。在平衡中，这样的两层区域可以共存。在这些现象中，有限离子尺寸引起的空间效应至关重要。