Electrokinetic and electrochemical characterisations of a composite polyamide/polysulfone membrane (PAC-1) were carried out by measuring the streaming potential along the membrane surface (polyamide active layer) and the membrane potential at different pHs (3

Here we will analyze the zeta potential versus pH characteristics of an ultrafiltration polysulfone membrane, that will be called here PRI-PSUF This membrane was prepared by phase inversion from casting solutions of polysulfone. The electric potential per unit pressure both through and on the membrane have been evaluated for a constant Cl- concentration with a gradual substitution of protons by sodium cations. It has been seen that the difference in potentials on and through the membrane is almost constant when pH is over 5 when the concentration of protons is very low. This difference can be attributed to diffusion potentials appearing through the membrane due to retention. While, when the fraction of protons is high the potentials through and on the membrane are substantially equal and very low. In order to obtain accurate zeta potentials and the isoelectric point, the streaming potential should be measured on the membrane, when no differences in the surface and inside materials should be expected. These measurements should be conducted at relatively high concentrations of a salt with very similarly mobile anion and cation and then extrapolated to zero protons percentage. All these conditions would warrant an easy calculation of zeta potentials by the simple Smoluchowski equation. (C) 2002 Elsevier Science B.V. All rights reserved.

The pore size distribution of a polysulfone membrane has been obtained from computerised image analysis of scanning force microscopy pictures. The streaming potential on the active layer of this membrane has been measured when it is in contact with aqueous NaCl solutions of different concentrations. Finally, NaCl retention has been taken into account to allow the translation of measured electric potential to the actual streaming potentials through the membrane. It has been shown that it is possible if the diffusion potentials appearing through both the concentration polarisation and the membrane itself are taken into account. By a fitting procedure, the effective transport numbers are obtained, which prove to be adequate not only for high concentrations, when there is no significative electrical double layer overlapping, but also for all the concentrations range used leading to the same streaming potential than measured on the membrane. The so-obtained effective cation transport numbers are not equal to the free solution true transport numbers that are defined when no pressure is applied. They are very similar for the cation and the anion, what should be caused by the applied pressure that should make their mobilities almost equal. Only a little contribution from the diffusion potentials, caused by retention without a relevant separation of the ions, should remain. (C) 2002 Published by Elsevier Science B.V.