SURFACE CHARACTERIZATION OF POLY(ACRYLONITRILE) MEMBRANES GRAFT-POLYMERIZED WITH IONIC MONOMERS AS REVEALED BY ZETA-POTENTIAL MEASUREMENT

Anionic and cationic monomers were graft-polymerized onto poly(acrylon itrile) (PAN) membrane surfaces. The graft polymerization was initiate d by an oxidation-reduction system at 25 degrees C. Grafted PAN membra ne surfaces yielded FT-IR/ATR spectra clearly different from that of a n unmodified PAN membrane, because of the presence of the graft chains . zeta potentials of the pore surfaces of the grafted PAN membranes we re obtained from streaming potential measurements. The surface propert ies are discussed with respect to a single site dissociation model, wh ich is based on the protonation and deprotonation of charged surface g roups. In this study, we obtained some characteristic parameters of th e pore surfaces from the theoretical fits using the site dissociation model. This approach gives direct insight into the pore surface proper ties of the membrane. The results could be well explained by an ion-pa iring effect in terms of different charge characteristics between memb ranes having hydrophobic or hydrophilic graft chains: charge groups of hydrophobic graft chains are likely to form ion pairs with counterion s from the external solution. The local dielectric constant surroundin g ion pairs plays an important role in the surface effective charge co ncentration.