Electrolyte solutions at heterogeneously charged substrates

TL;DR

This paper uses classical density functional theory to analyze how heterogeneous charged surfaces influence electrolyte solution densities, revealing long-range effects and dependence on interaction patterns and distributions.

Contribution

It provides analytic expressions for fluid density profiles near chemically and electrically nonuniform walls, considering explicit solvent and ion-solvent interactions.

Findings

Density profiles are highly sensitive to interaction type and distribution.

Heterogeneity effects extend over long ranges due to Debye length.

Analytic formulas describe influence of various surface patterns.

Abstract

The influence of a chemically or electrically heterogeneous distribution of interaction sites at a planar substrate on the number density of an adjacent fluid is studied by means of classical density functional theory (DFT). In the case of electrolyte solutions the effect of this heterogeneity is particularly long ranged, because the corresponding relevant length scale is set by the Debye length which is large compared to molecular sizes. The DFT used here takes the solvent particles explicitly into account and thus captures phenomena, inter alia, due to ion-solvent coupling. The present approach provides closed analytic expressions describing the influence of chemically and electrically nonuniform walls. The analysis of isolated \delta-like interactions, isolated interaction patches, and hexagonal periodic distributions of interaction sites reveals a sensitive dependence of the fluid density profiles on the type of the interaction, as well as on the size and the lateral distribution of the interaction sites.