SAXS/WAXS characterization of proton-conducting polymer membranes containing phosphomolybdic acid

Abstract

In the present paper the distribution of phosphomolybdic acid (PMoA,H 3PMo12O40) dispersed in sulfonated poly(ether ether ketone),SPEEK, was investigated by simultaneous small/wide-angle X-ray scattering SAXS/WAXS technique. The hydrolysis and condensation of 3-aminopropyltrimethoxysilane or zirconium tetrapropylate in these polymeric matrices were used to produce poly(3-aminopropyl silsesquioxane) or ZrO2,as nano-fillers. Contrary to previous results reported for membranes containing phosphotungstic acid,the PMoA coalesced into mass-fractal structure,with fractal-dimension 1.85. The largest fractal aggregate was about 524 A˚ . Moreover,WAXS curves evidenced the crystallization of this heteropolyacid during the casting process. No changes concerning the distribution of PMoA were observed in the membranes containing SPEEK,PMoA and the poly(3-aminopropyl silsesquioxane). On the other hand,no crystallization of the heteropolyacid was observed in the membranes containing ZrO2,although denser surface fractal-like structures constituted by the heteropolyacid were observed.