ABSTRACT
Amphoteric cross-linked polymer networks contain both positively and negatively fixed charge groups chemically bound to the polymer chains. Most physico-chemical applications of these polymer networks concern their swelling behavior when immersed in an electrolyte bath, especially in the case of polymer hydrogels [1,2]. It is also possible to prepare amphoteric membranes which show ion-exchange properties [3-12]. Early studies on amphoteric membranes were carried out by Sollner [13-15] and Weinstein and Caplan [16-18], who considered charge-mosaic membranes on the basis of the Nonequilibrium Thermodynamics formalism developed by Kedem and Katchalsky [19]. Amphoteric polymer membranes composed of weak polyelectrolytes where the charged groups are randomly distributed along the axial direction rather than on the normal plane of the membrane have been considered more recently by Yamauchi and co-workers [20,21] and by Tanioka and co-workers [22-24]. The membrane potential and piezodialysis properties of these membranes [22-24] were found to be very sensitive to the external pH and then the membranes could be of potential use for biochemical sensors and pHcontrolled drug delivery systems.
