Membrane potential of bipolar membranes prepared by plasma-induced grafted polymerization on porous polyolefin

The membrane potential of a bipolar membrane prepared by plasma-induced grafted polymerization on porous polypropylene was measured. The membrane potentials were plotted as a function of the logarithmic or reciprocal solution concentration on the low concentration side of the cells. If the high concentration side is against the positively charged surface, the membrane potential monotonically decreases with a concentration increase. On the other hand, the membrane potential has a maximum if the high concentration side is against the negatively charged surface. As the concentration increases, both membrane potentials gradually approach each other. These are theoretically explained using the Donnan potentials of both surfaces and diffusion potential in the membrane where the intermediate part between the two surfaces is supposed to be neutral. The calculated result is in good agreement with the experimental one. (C) 1997 Elsevier Science B.V.