ELECTROKINETIC INVESTIGATIONS OF CHARGED POROUS MEMBRANES

Asymmetric ultrafiltration membranes were prepared from fully aromatic polyamides differing in the diamine monomers of the polymeric backbon e and from polysulfone. Nanofiltration membranes were made from polysu lfone and polyethersulfone. The polysulfone as well as the polyethersu lfone were chemically modified to change the surface charges of the me mbranes that were made from these polymers. This means neutral, positi vely as well as negatively charged membranes could be employed for the measurements. The surface properties of the membranes as a function o f pH were determined by measuring the streaming potential in a perpend icular and horizontal mode. Applying proteins the values of the stream ing potential changed depending on the original charges of the membran es as well as on the pH of the solution. The values shifted to either higher or lower absolute values. Thus, characterization of unused and used membranes can be carried out by electrokinetic measurements. This was also demonstrated using a membrane fitted out with invertase. The zeta potential of nanofiltration membranes, however, was only evaluat ed from the results obtained with the horizontally run cell. (C) 1998 Elsevier Science B.V. All rights reserved.