Electrokinetic and surface charge characteristics of microporous membranes used in aqueous filtration

Abstract

The electrical characteristics of nylon 66, charge-modified nylon 66 and PVDF filter membranes were investigated using the electrophoretic and streaming potential techniques. Characterization of surface charge density of nylon based membranes were performed by acid/base titration. The adsorption of an anionic dye was used to determine the charge density of positive sites on the N66 Posidyne membrane. The results show that the isoelectric point (IEP) of N66 Posidyne and Zetapor (E-grade) occurred at pH 7.6 and 6.2, respectively. The point of zero charge (PZC) of E-grade Zetapor occurred at a much higher pH value than the IEP, indicating inhomogeneity in the extent of charge modification in pore walls and on the external surface. Using the dye adsorption test, the charge density of positive sites on N66 Posidyne was calculated to be approximately 9.5 μcoulombs/cm² at a solution of pH of 5.1, which is in agreement with the surface charge density using the acid/base titration.