The link between ion specific bubble coalescence and Hofmeister effects is the partitioning of ions within the interface

Specific ion effects are ubiquitous in soft matter systems and are most readily observed at high salt concentrations where long-range electrostatic forces are screened. In biological systems, ion-specificity is universal and is necessary to introduce the complexity required to carry out the processes of life. Many specific ion effects fall within the Hofmeister paradigm, whereby the strengths of action of the anions and cations follow a well-defined order, independent of the counterion. In contrast, specific ion effects evident in bubble coalescence inhibition depend on the combination of ions, and this phenomenon can be codified using simple ion-combining rules not evident in the Hofmeister systems. Here we show that these disparate specific ion effects have the same origin: They result from the variation in ion affinity for the solution interface. Equilibrium affinities explain Hofmeister effects, whereas we argue that the cation/anion combination controls bubble coalescence inhibition because of dynamic interfacial processes occurring at the more deformable gas-water interface.