Significance of electrically induced shear stress in drainage of thin aqueous films.

We develop a novel model of drainage of microscale thin aqueous film separating a gas bubble and a solid wall. In contrast to previous studies, the electrostatic effects are accounted for not only in the normal but also in the shear stress balance at the liquid-gas interface. We show that the action of the tangential component of the electric field leads to potentially strong spatially variable shear stress at the deforming charged interface. This previously overlooked effect turns out to be essential for correctly estimating the long-time drainage rates. Comparison of time-dependent fluid interface shapes predicted by our model with the experimental data is discussed.

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.