Desorption followed with radioisotopes and membrane potentials in perfluorinated vinyl4pyridine and quaternary ammonium membranes

Abstract

A radiotracer technique used to follow desorption and exchange processes with vinyl4pyridine (V4P) and quaternary ammonium membranes (QAM) allowed one to compare the properties of these two types of membranes and to point out the deprotonation process in V4P membranes. Exchange capacities obtained with this technique were compared with those obtained by microanalysis titration of nitrogen from V4P exchange sites. The deprotonation process enabled one to explain the important differences obtained with the two methods. With radiotracers we could set up a new technique to determine the p K a of these membranes. This work was completed by measuring swelling ratios and membrane potentials in uncross-linked and cross-linked V4P and QAM membranes. These measurements allowed one to study the cross-linking and hydration effects with NaCl and HCl solutions and to point out the importance of the deprotonation process in water and in NaCl solutions. Potential measurements show for these two types of membranes an important loss of permselectivity in concentrated HCl or NaCl solutions.