The microwave region of the dielectric spectrum of hydrated Nafion (R) andother sulfonated membranes

The microwave region (0.045-30 GHz) of the dielectric spectrum is reported here for Nafion(R) 105, 117, and 120 and for PEEK L540, G530, and a blend o f PEEK with 5% PES at various levels of hydration. Our measurements have sh own a strong dependence of the dielectric constant and loss factor of the N afion(R) membranes with water content, The dielectric constant varied from as high as 30 at I GHz in the wettest samples (where up 13 water molecules were associated with each sulfonate group) to only 7, in samples with just 4 waters/SO3- at similar frequencies. In contrast, the PEEK membranes displ ayed a much weaker dependence in the dielectric response with hydration. Am ongst the tested PEEK membranes, the G530 samples exhibited the highest die lectric constant of nearly 20 at 1 GHz for samples possessing 12 water mole cules per fixed site. At similar water contents, the L540 and PEEK + 5% PES membranes exhibited a dielectric constant of only 10. These results sugges t that the water molecules are more tightly bound to the sulfonate groups i n the PEEK membranes than in the Nafion(R) membranes. Finally, the conducti vity of the membranes at various water contents and at frequencies from 1-7 GHz was extracted from the loss factor spectra. When these high frequency conductivities were compared at similar water contents, all of the Nafion(R ) membranes displayed considerably higher values than the PEEK membranes.