Integral swelling free energies of alkaline earth ionic forms of perfluorosulphonate exchanger membranes (Nafion-117) and Dowex 50WX8 cationites in aqueous medium

Abstract

<span style="font-size:11.0pt;line-height:115%; font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "times="" new="" roman";mso-fareast-theme-font:minor-fareast;mso-hansi-theme-font:="" minor-latin;mso-bidi-font-family:arial;mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="">Water uptake (<i>n</i>_w) by the Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ionic forms of Nafion-117 exchanger membrane as well as Dowex 50WX8 resin has been investigated as a function of water activity (<i>a</i>_w). The isotherms constructed reveal appreciable differences for each ionic form, larger water uptake being seen for Nation-117 particularly at low water activities. Thus much larger integral free energy changes on water sorption (ΔG_sw) has been found for Nation-117 compared to that for Dowex 50WX8, Mg²⁺ form revealing a factor of two while Ba²⁺ form ΔG_sw involves a factor closer to three. Analysis further shows that the differences between the two exchangers emanate due to different hydration behaviour of each cation caused by different exchanger morphologies and ionic concentrations. Preliminary data obtained on the alkaline earth ion/H⁺ exchanges appear to support above conclusions.</span>