Anomalous Small-Angle X-Ray Scattering Characterization of Composites Based on Sulfonated Poly(ether ether ketone), Zirconium Phosphates, and Zirconium Oxide

The morphology and distribution of zirconium oxide and zirconium phosphates in a matrix of sulfonated poly(ether ether ketone) (SPEEK) were investigated with anomalous small-angle X-ray scattering (ASAXS) and electron microscopy. ASAXS revealed that ZrO₂ was distributed in the SPEEK matrix in the form of nanoparticles smaller than 13 Å. A decrease in the conductivity suggested that the sulfonic groups were bound to the zirconium oxo species at the particle surface. Furthermore, two kinds of membranes containing zirconium phosphate were investigated. In one case, the phosphate was directly dispersed in the polymer solution for the casting of the membrane. In the other case, the phosphate was previously treated with n-propyl ammonium and polybenzimidazole. From ASAXS data, the fractal dimension could be estimated. Mass-fractal behavior was confirmed for the SPEEK membrane containing previously exfoliated zirconium phosphate, with aggregates of 6.3-165 Å. Surfacefractal behavior was detected for membranes with untreated phosphates, with aggregates of 6.4-185 Å. The untreated phosphates caused an increase in the permeability, without changing the proton conductivity much.