Effect of charge regulation on the stability of electrolyte films

The stability of a thin liquid film of an electrolyte on a solid substrate is investigated. In the framework of the Debye-Hückel approximation, we show that the commonly used approximation of fixed potential at the solid-liquid interface does not lead to predictions of film rupture. To reconcile the model with experimental observations, we consider the constant charge density approximation for the solid substrate and then proceed to systematically investigate the effects of charge regulation based on a linear relationship between charge density and potential. Stability criteria are formulated in terms of charge regulation parameters and electrolyte properties, resulting in different types of stability diagrams. Critical thickness below which the film ruptures is shown to decrease as the charge regulation at the solid-liquid interface becomes stronger.