Bubbling potential as a measure of the charge of gas bubbles in aqueous environment

Abstract

Gas bubbles in aqueous environment cause changes in electrical potential of the electrodes containing a ceramic porous plug. It was found that collision and interception of bubbles and porous plug surface are responsible for the observed phenomenon. In the course of collision bubble approaches porous plug surface to a certain distance within diffuse layer of air/water interface. At that distance the electrostatic potential of gas bubble affects the electrode potential. Reversible redox electrodes cannot serve as a bubbling indicator electrode due to relaxation of the electrode reactions. Bubbling potential is defined as the difference of indicator electrode potential in presence and absence of bubbles. It provides information on the isoelectric point of the gas bubbles, and may be recalculated to ζ-potentials using the Gouy–Chapman theory. For that purpose, the distance between electrokinetic slip plane and plane of bubble contact with porous plug surface should be known. This distance was estimated to be between 6 and 10nm. As electrokinetic potential, the bubbling potential is also significantly reduced by increasing electrolyte concentration, which is markedly more pronounced for counterions of higher charge. The effect of pH and several various electrolytes on argon bubbles was examined and discussed. Measurement of bubbling potential is fast and reproducible and may be used as a useful tool for examination of gas/water interfaces.