Characterization of Novel Weak Amphoteric Charged Membranes Using ζ-Potential Measurements: Effect of Dipolar Ion Structure

Abstract

Weak amphoteric charged membranes were prepared by the radiation-induced graft copolymerization of the weakly charged poly(ethylene glycol) derivatives onto high-density polyethylene porous membranes. In this study, two kinds of amphoteric charged membranes, which are the amphoteric ion-pair side chain type and the mixed grafted chain type, were prepared and then characterized using the ζ-potential measurements. For the amphoteric ion-pair type membrane, the ζ-potential/pH profile showed a plateau in the range of pH 6−11 which was characteristic of the dipolar ion structure of an amphoteric ion-pair. On the other hand, the ζ-potential for the mixed grafted chain type membrane showed an intermediate pH dependence between the separate positively charged chain- and negatively charged chain-grafted membranes. The apparent surface charge density on these membranes was obtained from the ζ-potential. For the amphoteric ion-pair side chain type membrane, the experimental results could be explained by the theoreti...