Pore size distribution effects on electrokinetic phenomena in semipermeable membranes

Electrokinetic phenomena occurring in charged ultrafiltration membranes can significantly influence the transport characteristics of these membranes. Theoretical calculations have been performed to evaluate the effects of different log-normal pore size distributions on the solvent flow rate, the induced streaming potential, and the membrane zeta potential. The solvent flow rate increased with an increase in the breadth of the pore size distribution, with this effect being much more pronounced for pressure-driven flow than for electrically-driven flow. The streaming potential induced by the convective fluid flow significantly alters the flow profiles through the membrane due to the very different dependence of the pressure-driven and counter-electroosmotic flow on the pore radius. This causes a relatively large negative (reverse) flow to develop through the smallest pores in the distribution. The membrane zeta potential was also a function of the pore size distribution, even for membranes having the same hydraulic permeability and surface charge density. These results provide important insights into the effects of different pore size distributions on membrane transport and on the proper interpretation of these electrokinetic phenomena.