  Inhibition of bubble coalescence in electrolyte solutions enables the
formation of oceanic whitecaps and affects the heat and mass transfer in many
bubble related engineering processes. For different electrolytes, the ability
to inhibit bubble coalescence correlates to the ion specificity at the air
water interface at an abnormal cation-anion pair relationship, rather than the
typically expected cation or anion series that was widely reported in
atmospheric, bio- and chemical processes. Here we show that the inhomogeneous
interfacial flow, at a different electrolyte concentration from the solution
because of the surface specificity of both cation and anion, contributes to the
bubble coalescence inhibition behavior in electrolyte solutions. The
interfacial flow, achieved with the mobile air-water interface, contributes to
the continuous change of electrolyte concentration within the liquid film
formed between two colliding bubbles, thereby resulting in a concentration
gradient of electrolytes between the thin film and the bulk solution. The
electrolyte concentration gradient, hence surface tension gradient, becomes
significant to resist film thinning when the film thickness reaches tens of
nanometers. The retarded film thinning between two bubbles and delayed bubble
coalescence were experimentally captured by high-speed interferometry and
quantitatively explained by the proposed electrolyte transportation model. This
finding clearly highlights the coupled effect of interfacial flow and ion
specificity, and shows important implications for improved understanding of
ocean waves, for future development of colloidal science in high concentration
electrolyte solutions that is critical for biology, and benefits many applied
fields like water splitting and mineral extraction.
