MODIFICATION OF ION-EXCHANGE MEMBRANE-SURFACE BY PLASMA PROCESS .2. MONOVALENT CATION PERMSELECTIVE MEMBRANE FROM PERFLUOROSULFONATE CATION-EXCHANGE MEMBRANE

The monovalent cation perm-selectivity of a perfluorosulfonate cation-exchange membrane, Nafion® 117, was enhanced by depositing an ultra-thin anionic exchange layer on its surface. The anion exchange layer was prepared by plasma polymerization of 4-vinylpyridine followed by quaternization with 1-bromopropane. The resulting layers were about 0.2 μm thick, pinhole-free, and of uniform thickness. The influence of the plasma parameter of polymerization pressure on the deposition rate, membrane resistance, and monovalent cation transference number were investigated. The monovalent cation perm-selectivity of the plasma-modified Nafion membrane was determined by measuring tFe, the transference number of Fe2+ through the membrane, in the Li+-Fe2+ system. Plasma-modified Nafion membranes exhibited a high lithium ion perm-selectivity. This perm-selectivity was enhanced with decreasing polymerization pressure at the cost of high membrane resistance. © 1990.