INTEGRAL SWELLING FREE-ENERGIES OF ALKALINE-EARTH IONIC FORMS OF PERFLUOROSULFONATE EXCHANGER MEMBRANES (NAFION-117) AND DOWEX 50WX8 CATIONITES IN AQUEOUS-MEDIUM

Water uptake (n(w)) by the Mg2+, Ca2+, Sr2+, and Ba2+ ionic forms of N afion-117 exchanger membrane as well as Dowex 50WX8 resin has been inv estigated as a function of water activity (a(w)). The isotherms constr ucted reveal appreciable differences for each ionic form, larger water uptake being seen for Nafion-117 particularly at low water activities ; Thus much larger integral free energy changes on water sorption (Del ta G(sw)) have been found for Nafion-117 compared to that for Dowex 50 WX8, Mg2+ form revealing a factor of two while Ba2+ form Delta G(sw) i nvolves a factor closer to three. Analysis further shows that the diff erences between the two exchangers emanate due to different hydration behaviour of each cation caused by different exchanger morphologies an d ionic concentrations. Preliminary data obtained on the alkaline eart h ion/H+ exchanges appear to support above conclusions.