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

In the present paper the distribution of phosphomolybdic acid (PMoA, H3PMo12O40) 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 Å. 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.