Colloids and Surfaces A: Physicochem. Eng. Aspects 443 (2014) 129–134 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects jo ur nal ho me page: www.elsevier.com/locate/colsurfa Bubbling potential as a measure of the charge of gas bubbles in aqueous environment Tajana Preoˇ canin ∗ , Filip ˇ Supljika, Matija Lovrak, Josip Barun, Nikola Kallay Division of Physical Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia h i g h l i g h t s • Bubbles cause changes in electrical potential of the electrodes with a ceramic plug. • Effect is dynamic caused by collision and interception of bubbles and plug surface. • Bubbling potential provides informa- tion on the isoelectric point of the gas bubbles. • Bubbling potential may be recal- culated to -potentials using the Gouy–Chapman theory. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 4 September 2013 Received in revised form 17 October 2013 Accepted 4 November 2013 Available online 10 November 2013 Keywords: Gas/water interface Bubbles Bubbling potential Electrokinetics Electrokinetic -potential a b s t r a c t 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 infor- mation on the isoelectric point of the gas bubbles, and may be recalculated to -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 10 nm. 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. Measure- ment of bubbling potential is fast and reproducible and may be used as a useful tool for examination of gas/water interfaces. © 2013 Elsevier B.V. All rights reserved. 1. Introduction It was shown earlier [1] that introduction of bubbling into aque- ous electrolyte system cause changes in the potential of a reference ∗ Corresponding author. Tel.: +385 1 46 06 154; fax: +385 1 46 06 131. E-mail addresses: tajana@chem.pmf.hr (T. Preoˇ canin), fsupljika@chem.pmf.hr (F. ˇ Supljika), matija.lovrak@gmail.com (M. Lovrak), jbarun8472@hotmail.com (J. Barun), nkallay@chem.pmf.hr (N. Kallay). electrode equipped with salt bridge separated with ceramic porous plug. The potential of other electrodes (the potential of which is determined by reversible redox equilibrium), as well as of glass electrode (the potential of which is determined by the ion exchange equilibrium) is not affected by bubbling [1]. In order to under- stand the origin of this phenomenon several various experiments were performed. It was previously suggested [2] that the effect might be attributed to the so-called sedimentation potential. The sedimentation potential, i.e. Dorn effect [3], is an electrode poten- tial difference between two electrodes mounted at two different 0927-7757/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfa.2013.11.002