Use of electrophoretic mobility and streaming potential measurements to characterize electrokinetic properties of ultrafiltration and microfiltration membranes

The electrophoretic mobility of mineral oxide particles and the streaming potential of UF and MF inorganic membranes both depend on the electrical charge distribution at the oxide-solution interface. They are related to the zeta potential. The aim of this work is to evaluate experimentally how measuring the electrophoretic mobility and streaming potential complement each other for understanding the physical-chemical phenomena linked to filtration. We investigated the effect of pH and ionic strength on electrophoretic mobility and streaming potential values. The isoelectric point (i.e.p.) determined by microelectrophoretic measurements on zirconia particles obtained by membrane scraping is different from the i.e.p. obtained from pure zirconia powder. The i.e.p. obtained from scraped particles is the i.e.p. obtained from streaming potential measurements. Zeta potential values calculated from measurements using both techniques are compared to ascertain the accuracy of the conditions of validity of the Helmoltz-Smoluchowski relation for the streaming potential and zeta potential. Well-known inadequacies of this relation stem from double layer overlapping, the conductivity in the pores, etc. A correction factor, between zero and one is calculated. It is related to the zeta potential obtained from electrophoretic mobility measurements. (C) 1998 Elsevier Science B.V.