A comparison between streaming potential and membrane potential measured across single charged and bipolar membranes

Pressure-induced (streaming) potential and membrane potential across two ion-exchanger membranes (one positively charged and another negatively charged) have been measured with the membranes in contact with NaCl solutions at different salt concentrations. Membrane permselectivity was calculated from membrane potential and lower values were obtained for the cation-exchanger membrane. For comparison, measurements with a bipolar membrane obtained by a series association of both single-charged membranes has also been made. The influence of electrical asymmetry of bipolar membranes in both electrical potentials was studied by reversing the direction of pressure and concentration gradients. Results show that the streaming potential coefficient depends on salt concentration for the bipolar membrane, while for both ion-exchanger membranes, it is practically constant within the range of concentration studied (5×10 M5C510 M). Membrane potential values for the bipolar membrane show a higher influence of the anion exchange sublayer. In both types of measurements, differences due to the opposite directions of the external gradients across the bipolar membrane were obtained. © 2001 Elsevier Science B.V. All rights reserved.