Advanced electrokinetic characterization of composite porous membranes

The effect of the streaming current flowing through the porous structure of composite membranes during tangential electrokinetic measurements was investigated. It was shown that neglecting this additional path for streaming current may have dramatic implications in the interpretation of the experimental data and on the determination of the membrane zeta potential. Experimental measurements of both streaming current and electrical conductance were performed with two different composite polymer membranes. By following the procedure proposed by Yaroshchuk and Luxbacher (ref. 17 in the present work) it was possible to determine separately the zeta potential of the membrane surfaces and that of their underlying porous structures. This experimental procedure was shown to provide useful information about the efficiency of the functionalization of an ultrafiltration polyethersulfone membrane by positively charged 4-benzyltriphenylphosphonium groups, notably that the chemical modification primarily occurs in the porous substructure of the membrane rather than on its external surface.