EVALUATION OF ELECTROOSMOSIS AND STREAMING POTENTIAL FOR MEASUREMENT OF ELECTRIC CHARGES OF POLYMERIC MEMBRANES

Electrical properties for a range of commercial membranes have been de termined by electroosmosis and streaming potential measurements under identical conditions, For both techniques, the pH range was 3-7 and th e electrolyte used was 10(-3) M KCI at 25 degrees C, as the charges on the membrane are strongly dependent upon the pH and the ionic strengt h of the solution passing through the membrane, For both ultrafiltrati on (UF) and microfiltration (MF) membranes the absolute values of the apparent zeta potential determined from electroosmosis were generally greater than those from streaming potential measurements with a greate r difference at pH less than or equal to 4. The apparent zeta potentia ls obtained from electroosmosis were negative for all membranes studie d, even at pH below the isoelectric point where streaming potentials w ere positive, A substantial increase of the negative zeta potential at low pH (similar to pH 4) was interpreted in terms of the effect of th e applied electric field on distribution of ions and differences in mo bility of ions, particularly H+ compared to the other ions, The magnit ude of the zeta potentials determined from electroosmosis exhibited an apparent difference due to change in orientation of the membrane for asymmetric UF membranes, whereas the streaming potential measurements showed less directional-effect for both UF and MF membranes.