Streaming potential through multilayer membranes

The fundamental and practical importance of electrokinetic characterization of porous membranes is now well recognized. However, not enough attention has focused on the fact that the most practically interesting membranes hav e a multilayer structure. Then, standard electrokinetic methods, such as st reaming potential measurement performed through these multilayer membranes, lead to a global signal that does not necessarily reflect the electrokinet ic behavior of the skin layer that rules the membrane selectivity. of The r elative influence of membrane layers with different physical (pore length, porosity, pore radius) and electrical (zeta potential) properties on tire g lobal streaming potential arising across a two-layer membrane is studied. E ach porous layer plays a role in the streaming potential process, but in a wide range of length fraction of support layer the skin layer contributes m ore than the support layer to the global signal. The contribution of the sk in layer increases as its porosity and pore radius decrease, but is little affected by its zeta potential. Nevertheless, in many practical situations, the support layer is likely to play a nonnegligible role on the global sig nal due to its huge thickness with respect to the skin layer. Therefore, el ectrokinetic measurements performed with multilayer membranes should be int erpreted carefully.