The surface potential explains ion specific bubble coalescence inhibition

TL;DR

This study proposes that the electrostatic surface potential created by specific ion combinations influences bubble coalescence inhibition by modulating the Gibbs-Marangoni pressure, providing a new explanation for ion-specific effects.

Contribution

The paper introduces a generalized Gibbs-Marangoni pressure model incorporating electrostatic surface potential, explaining ion-specific bubble coalescence inhibition.

Findings

Electrostatic surface potential reduces Gibbs-Marangoni pressure in mixed electrolytes.

Ion combinations with differing surface propensities dampen surface tension effects.

The mechanism explains the ion-specific behavior in bubble coalescence inhibition.

Abstract

Hypothesis: Some ions can prevent bubbles from coalescing in water. The Gibbs-Marangoni pressure has been proposed as an explanation of this phenomenon. This repulsive pressure occurs during thin film drainage whenever surface enhanced or surface depleted solutes are present. However, bubble coalescence inhibition is known to depend on which particular combination of ions are present in a peculiar and unexplained way. This dependence may be explained by the electrostatic surface potential created by the distribution of ions at the interface, which will alters the natural surface propensity of the ions and hence the Gibbs-Marangoni pressure. Calculations: A generalised form of the Gibbs-Marangoni pressure is derived for a mixture of solutes and a modified Poisson-Boltzmann equation model is used to calculate this pressure for five different electrolyte solutions made up of four different ions. Findings: Combining ions with differing surface propensities, i.e., one enhanced and one depleted, creates a significant electrostatic surface potential which dampens the natural surface propensity of these ions, resulting in a reduced Gibbs-Marangoni pressure, which allows bubble coalescence. This mechanism explains why the ability of electrolytes to inhibit bubble coalescence is correlated with surface tension for pure electrolytes but not for mixed electrolytes.