Attainment of a High Concentration of Salt Ions Near a Metallic or Dielectric Wall in a Salt Solution as a result of Electrical Image Forces Near the Wall

TL;DR

This paper investigates how electrical image forces near metallic or dielectric walls can lead to high salt ion concentrations at surfaces, considering barriers like solvation energy and screening effects that influence ion accumulation.

Contribution

It introduces a theoretical analysis of ion concentration near walls due to electrical image forces, accounting for solvation barriers and screening effects in salt solutions.

Findings

Electrical image forces can attract ions to walls, increasing local concentration.

Solvation energy barriers can prevent ion accumulation unless overcome by screening or thermal activation.

Conditions for ion precipitation near surfaces are identified based on dielectric properties and ion concentration.

Abstract

Electrical image potentials near a metallic or a dielectric wall of higher dielectric constant than that of the solution are attractive, and therefore, can concentrate salt ions near the wall. It has recently been observed that near a metallic surface, ions in room temperature ionic liquids precipitate (but not near a nonmetallic surface). It will be argued that a likely reason for why precipitation of ions in salt water, as a result of electrical image forces, has not as yet been observed is the existence of an energy barrier near a solid surface, resulting from the decrease of ion solvation as a result of the large decrease of the dielectric constant of water normal to a solid wall within a short distance from the wall. We will explore the conditions under which ions are able to get past this barrier and concentrate at a solid wall, either as a result of a reduction of this barrier caused by screening at high ion concentration or as a result of thermal activation over this solvation energy potential barrier.