Surface modification of ion exchange membrane (Nafion™) -: The enhancement of cation selectivity by plasma polymerization process

An ultra-thin anionic exchange layer containing -NH2 and -CONH2 was deposited on the surface of Nafion(TM) membrane. This layer was deposited from ethylene and ammonia using a glow-discharge plasma polymerization technique. The SEM, ATR(attenuated total reflection) spectra and XPS(X-ray photoelectron spectroscopy) showed that the resulted plasma polymers containing -NH2 and -CONH2 was about 0.5 mum thick. The proton perm-selectivity of plasma-modified Nafion(TM) membrane was expressed by t(Cu), the transference number of the Cu2+ ion through the membrane which was determined by using NafionTM membrane as the separator in a typical two-compartment cell (0.25 mol/L CuCl2- 0.5mol/L HCl / plasma-modified Nafion(TM) membrane / 1 mol/L HCl), Pretreatment of the Nafion(TM) membrane by oxygen sputtering enhanced the adhesion of plasma polymer onto its surface. The plasma-treated membrane exhibited a high perm-selectivity and its resistance in 1 mol/L HCl was only a little bit higher than Nafion(TM) membrane (<0.5 Ohm . cm(2)).