Journal of Electroanalytical Chemistry 464 (1999) 222 – 229 Convective electrodiffusion processes through graft-modified charged porous membranes R. Telaranta a , J.A. Manzanares b , K. Kontturi a, * a Laboratory of Physical Chemistry and Electrochemistry, Helsinki Uniersity of Technology, PO Box 6100, FIN-02015 HUT, Finland b Department of Thermodynamics, Faculty of Physics, Uniersity of Valencia, E-46100 Burjassot, Spain Received 31 August 1998; received in revised form 15 December 1998 Abstract Convective diffusion and electrophoresis across a charged porous membrane showing variable permeability properties were studied. The membrane used was prepared by grafting poly(acrylic acid) (PAA) onto a porous polyvinylidene fluoride (PVDF) membrane. The degree of grafting was selected to be relatively low, 18 wt%, to compromise between the ion selectivity and hydraulic permeability of the membrane. The possible electric field induced effects on the membrane permselectivity were examined after the membrane had been characterized by convective diffusion and concentration cell potential measurements. The measured electrophoresis data, however, could be modelled using the extended Teorell – Meyer – Sievers theory, which indicates that the membrane studied shows no variable permeability behaviour with respect to a weak applied external electric field. This conclusion was also further confirmed by separation experiments carried out with ternary salt solutions. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Variable permeability membranes; Convective separation processes; Membrane electrochemistry 1. Introduction Charged porous membranes prepared by radiation [1]or plasma induced [2] graft-copolymerization of dif- ferent monomers into porous films is an emerging field in membrane science which is receiving increasing at- tention. The grafting method is very attractive from the point of view of membrane preparation, and enables easy control of the membrane properties through the degree of grafting [3,4]. More importantly, the perme- ability of the grafted membranes is sensitive to their environment, as are biological membranes, and can be controlled by changes in temperature [5], pH [6,7], salt concentration [8] and by applying an external electric field [9,10]. This behaviour is explained by the confor- mational changes of the polyacid groups attached to the membrane pore walls, which affect the transport properties by opening or closing the pores [11 – 13]. In previous studies [3,10,13], we prepared variable permeability membranes (VPM) by grafting poly(- acrylic acid) (PAA) onto porous polyvinylidene fluoride (PVDF) membranes and found that their mechanical permeability changed by several orders of magnitude when the ionic strength and the pH of the permeate was varied. Since the VPM behaviour enables the control of mechanical permeability and permselectivity, the use of this kind of membrane in convective electrodiffusion processes becomes appealing. Continuous convective electrophoresis in porous membranes has been studied extensively in our laboratory as a separation method for small ions [14–16] and charged proteins [17]. The use of the PVDF/PAA VPM for this application re- quires knowledge of its permselective properties in cur- rent-driven processes. Moderate changes in the membrane permselectivity due to the effect of an elec- * Corresponding author. Fax: +358-451-2580. 0022-0728/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0022-0728(99)00025-X