Electroviscous effects, streaming potential, and zeta potential in polycarbonate track-etched membranes

Electroviscous effects and streaming potentials were measured for various t rack-etched ultrafiltration and microfiltration membranes at a number of sa lt concentrations, using both LiCl and KCl electrolytes. A calculation prog ram was developed that calculates zeta potentials from this experimental da ta, using electrokinetic flow theory and a numerical solution of the Poisso n-Boltzmann equation. It was demonstrated, both experimentally and by calculation, that the elect roviscous effect for negatively charged membranes is larger when employing LiCl solutions than when employing KCl solutions. This effect is absent for positively charged membranes and can thus be used for determination of the sign of the membrane charge. It was found that zeta potentials calculated from electroviscosity data wer e al ways higher than those calculated from streaming potential data. This indicates that the electrokinetic theory underpredicts the electroviscous e ffect; It was also found that at low salt concentrations and small pore siz es (kappa r(p) < 1.5) it was not possible to calculate the zeta potential f rom streaming potential or electroviscous effect. This may be caused by the fact that some assumptions made in electrokinetic flow theory lose their v alidity under these conditions. (C) 2000 Elsevier Science B.V. All rights r eserved.