Characterization of nafion® membranes by transmission electron microscopy

Nafion® membranes were examined by transmission electron microscopy (TEM). Both solution casting and positive staining techniques were employed. The staining of solution-cast Nafion® membrane by RuO₄ vapor led to good image contrast so that the ionic cluster domains in the membrane could be clearly observed. The TEM micrographs indicated the presence of three phases: ionic cluster phase, an organic matrix phase and an interfacial phase. The spherical ionic clusters were surrounded by the interracial phase and were uniformly distributed across the membrane; the average size of the clusters was found to be 25 to 50 Å. The staining mechanism was investigated by analyzing the ruthenium content of stained membranes by X-ray fluorescence spectroscopy and by comparing the FTIR spectra of stained and unstained membranes. It was concluded that the staining reaction involved the oxidation of absorbed water by RuO₄ vapor to give RuO₂ microparticles.