Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 600, Issue -, Pages 338-343Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2021.04.144
Keywords
Electrolyte solution; Gibbs-Marangoni stress; Air-water interface; Poisson-Boltzmann equation; Surface pressure; Surface forces
Categories
Funding
- Australian Research Council (ARC) [DE200100794, DP200102573]
- Australian Research Council [DP200102573, DE200100794] Funding Source: Australian Research Council
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This study investigates the mechanism of ions preventing bubble coalescence in water, finding that the Gibbs-Marangoni pressure explains this phenomenon, and the distribution of ions and surface potential affect this pressure, thereby impacting the ability of bubble coalescence.
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 coales-cence inhibition is known to depend on which particular combination of ions are present in a peculiar and unexplained way. This dependence can be explained by the electrostatic surface potential created by the distribution of ions at the interface, which will alter 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 the modified Poisson-Boltzmann equation 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. (c) 2021 Elsevier Inc. All rights reserved.
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