Hybridization of Nafion Membranes by the Infusion of Functionalized Siloxane Precursors

Polysiloxane-modified hybrid membranes were prepd. by introducing in a pre-swelled com. Nafion membrane a sol-gel precursor soln., consisting of a pre-hydrolyzed mixt. of tetraethoxysilane and a mercaptan functionalized organoalkoxysilane. The structure of the polysiloxane network was changed by altering the ratio of the two silane components within the precursor soln. The mercaptosilane modifier was used to provide an addnl. source of acidic Bronsted sites through the oxidization of the mercaptan groups to sulfonic acid groups. The phys. and chem. properties of the hybrid membranes were examd. by TGA, FT-IR and SEM-EDS anal. The water vapor sorption and proton cond. characteristics were evaluated at 40, 60 and 70° and with water activity in the region of 0.4-1. The polysiloxane network alters the water vapor sorption mechanism of the Nafion membrane, resulting in an increase in the equil. amt. of water absorbed in the middle range of water activity (0.4-0.6). At the same time, the increased water sorption capability produced a concomitant increase in ionic cond. at low water activities.