THE EFFECT OF COMPOSITION OF NAFION DEPOSITION SOLUTIONS ON THE DIFFUSIONAL PROPERTIES OF THE FILMS

The properties of Nafion films on electrodes were studied as a functio n of the water content in the deposition solutions (0.7% Nafion in mix ed ethanol/water). The rate of loading and unloading (i.e., ion-exchan ge) of the complex ion Ru(bpy)3(2+), loading into films which were the rmally treated, and penetration of the anion Fe(CN)64- were examined. All these measurements show a nearly linear dependence of the voltamme tric peak currents (for the oxidation of the incorporated ions) on the percentage of water in the deposition solutions. These results lead t o the conclusion that films that are cast from solutions of higher wat er content have more ''open'' structures that allow faster diffusion o f ions. It is also suggested that Ru(bpy)3(2+) exists in the films in two forms: one is strongly bound to the sulfonic groups by ion-pairing , for which the mass-transport mechanism is primarily electron self-ex change (characterized by D(et)). The other is bound to the polymer by weak electrostatic or hydrophobic interactions, for which mass transpo rt proceeds mainly by physical diffusion (D(o)). The two diffusion coe fficients were determined separately in each kind of film, and they bo th show nearly linear dependence on the percent of H2O in the Nafion s olutions from which the films are deposited.