Selective coalescence of bubbles in simple electrolytes

Stjepan Marčelja*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    70 Citations (Scopus)

    Abstract

    Simple ions in electrolytes exhibit different degrees of affinity for the approach to the free surface of water. This results in strong ion-specific effects that are particularly dramatic in the selective inhibition of bubble coalescence. I present here the calculation of electrostatic interaction between free surfaces of electrolytes caused by the ion accumulation or depletion near a surface. When both anion and cation are attracted to the surface (like H+ and Cl- in HCl solutions), van der Waals attraction facilitates approach of the surfaces and the coalescence of air bubbles. When only an anion or cation is attracted to the surface (like Cl - in NaCl solutions), an electric double layer forms, resulting in repulsive interaction between free surfaces. I applied the method of effective potentials (evaluated from published ion density profiles obtained in simulations) to calculate the ionic contribution to the surface-surface interaction in NaCl and HCl solutions. In NaCl, but not in HCl, the double-layer interaction creates a repulsive barrier to the approach of bubbles, in agreement with the experiments. Moreover, the concentration where ionic repulsion in NaCl becomes comparable in magnitude to the short-range hydrophobic attraction corresponds to the experimentally found transition region toward the inhibition of coalescence.

    Original languageEnglish
    Pages (from-to)13062-13067
    Number of pages6
    JournalJournal of Physical Chemistry B
    Volume110
    Issue number26
    DOIs
    Publication statusPublished - 6 Jul 2006

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