DESORPTION FOLLOWED WITH RADIOISOTOPES AND MEMBRANE-POTENTIALS IN PERFLUORINATED VINYL4PYRIDINE AND QUATERNARY AMMONIUM MEMBRANES

A radiotracer technique used to follow desorption and exchange process es with vinyl4pyridine (V4P) and quaternary ammonium membranes (QAM) a llowed one to compare the properties of these two types of membranes a nd to point out the deprotonation process in V4P membranes. Exchange c apacities obtained with this technique were compared with those obtain ed by microanalysis titration of nitrogen from V4P exchange sites. The deprotonation process enabled one to explain the important difference s obtained with the two methods. With radiotracers we could set up a n ew technique to determine the pK(a) of these membranes. This work was completed by measuring swelling ratios and membrane potentials in uncr oss-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 deprotonatio n 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.