Ion-Specific Bubble Coalescence Dynamics in Electrolyte Solutions

Palliyalil, AC and Mohan, A and Dash, S and Tomar, G (2024) Ion-Specific Bubble Coalescence Dynamics in Electrolyte Solutions. In: Langmuir, 40 (1). pp. 1035-1045.

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Abstract

Bubble coalescence time scale is important in applications such as froth flotation, food and pharmaceutical industries, and two-phase thermal management. The time scale of coalescence is sensitive to the dissolved ions. In this study, we investigate the evolution of a thin electrolyte film between a bubble and a hydrophilic substrate during coalescence. We present a thin-film equation-based numerical model that accounts for the dependence of the surface tension gradient and electric double layer (EDL) on the concentration of ions at the air-liquid interface. The influence of Marangoni stresses and the EDL on the hydrodynamics of drainage determines the coalescence time scale. We show that the electrolytes, such as NaCl, Na2SO4, and NaI retard coalescence, in contrast to HCl and HNO3 that have little effect on the coalescence time scale. We also show that the drainage of the electrolyte films with higher concentrations is retarded due to increased Marangoni stresses at the air-water interface. The slow drainage triggers an early formation of the dimple in the thin film, thus trapping more fluid within, which further decreases the drainage rate. For a hydrophilic substrate, EDL along with van der Waals for a given concentration governs the final dynamics of thin films, eventually resulting in a stable thin layer of the electrolyte between the bubble and the substrate. The stabilizing thickness reduces by an order of magnitude as the NaCl concentration increases from 0.01 to 10 mM. For Na2SO4 solution, the film is stabilized at a smaller thickness due to higher valency cations resulting in higher screening of the EDL repulsion. © 2023 American Chemical Society.

Item Type:	Journal Article
Publication:	Langmuir
Publisher:	American Chemical Society
Additional Information:	The copyright for this article belongs to American Chemical Society.
Keywords:	Air; Coalescence; Electrolytes; Hydrophilicity; Phase interfaces; Sodium chloride; Sodium Iodide; Sodium sulfate; Thin films; Van der Waals forces, Bubble coalescence; Coalescence time; Double layers; Electrolyte solutions; Food industries; Hydrophilic substrate; Marangoni stress; Pharmaceutical industry; Thin-films; Time-scales, Ions, cation; electrolyte; electrolyte solution; ion; water, article; controlled study; dynamics; flotation; hydrodynamics; liquid; surface tension; thickness
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	01 Mar 2024 08:56
Last Modified:	01 Mar 2024 08:56
URI:	https://eprints.iisc.ac.in/id/eprint/83937

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