Wetting in electrolyte solutions

TL;DR

This study uses classical density functional theory on a lattice model to analyze how substrate charge and ionic strength influence wetting transitions in electrolyte solutions, revealing conditions under which wetting behavior changes from second to first order.

Contribution

It provides a detailed theoretical analysis of wetting transitions in electrolyte solutions, highlighting the effects of substrate charge and ionic strength on transition order and temperature.

Findings

Neutral substrates with salt do not change wetting transition order or temperature.

Nonzero substrate charge can convert continuous wetting to first-order upon adding salt.

Increasing substrate charge density lowers the wetting transition temperature.

Abstract

Wetting of a charged substrate by an electrolyte solution is investigated by means of classical density functional theory applied to a lattice model. Within the present model the pure, i.e., salt-free solvent, for which all interactions are of the nearest-neighbor type only, exhibits a second-order wetting transition for all strengths of the substrate-particle and the particle-particle interactions for which the wetting transition temperature is nonzero. The influences of the substrate charge density and of the ionic strength on the wetting transition temperature and on the order of the wetting transition are studied. If the substrate is neutral, the addition of salt to the solvent changes neither the order nor the transition temperature of the wetting transition of the system. If the surface charge is nonzero, upon adding salt this continuous wetting transition changes to first-order within the wide range of substrate surface charge densities and ionic strengths studied here. As the substrate surface charge density is increased, at fixed ionic strength, the wetting transition temperature decreases and the prewetting line associated with the first-order wetting transition becomes longer. This decrease of the wetting transition temperature upon increasing the surface charge density becomes more pronounced by decreasing the ionic strength.