Surface Tension of Aqueous Solutions of Electrolytes: Relationship with Ion Hydration, Oxygen Solubility, and Bubble Coalescence.

The surface tension of aqueous solutions of simple inorganic electrolytes (36 in total) have been measured by the maximum bubble pressure method as a function of electrolyte concentration up to 1 M. In most cases the surface tension increased, however in a minority of cases, certain combinations of cations and anions had a negligible effect or decreased surface tension. Results were analysed in terms of surface tension/electrolyte concentration gradients (d(Deltagamma)/dc) and this parameter was found to correlate with the entropies of ion hydration, Jones-Dole viscosity coefficients and dissolved oxygen gradients. Calculation of Gibbs surface deficiencies for selected electrolytes were carried out using the raw surface tension data. Discussion of the surface tension/electrolyte concentration gradients was extended to the mechanism of inhibition of bubble coalescence by electrolytes. The Gibbs-Marangoni effect did not provide a satisfactory explanation for the inhibition of coalescence for all electrolytes and from the present study we suggest that dissolved gas (microbubble) gradients between macroscopic bubbles plays an important role in the coalescence process.