Studying homogeneity and zeta potential of membranes using electroacoustics

Abstract

Abstract The goal of this paper is to show that electroacoustic spectroscopy can be used as a viable means for characterizing membranes. A novel set-up was designed for performing these experiments with a standard electroacoustic zeta potential probe typically used for measuring ζ-potential in concentrated dispersions. Calculation of zeta (ζ) potential from the measured signal was performed with a newly derived electroacoustic theory that takes into account overlap of double layers in the membrane pores (nano-filtration membrane NF 270 manufactured by Dow Chemicals). Several titrations were performed: two salt titrations with potassium chloride and copper sulfate, and pH titration in several solutions of KCl. In all these experiments, changes in ionic environment caused changes in the ζ-potential within the pores of the membrane, as was measured by changes in electroacoustic current. In all cases the results were consistent with theoretical expectations based on prior research and knowledge of ion effects on ζ-potential. Lastly, differences in electroacoustic signal from one area of the membrane to the next (all of the same material) shed some light into the homogeneity of the membrane itself.