Microstructure of BAM® membranes:: A small-angle neutron scattering study

BAM(R) membranes which are sulfonated trifluorostyrene-based polymers, were studied in the swollen state using small-angle neutron scattering (SANS) and over an extended angular range. Sulfonic acid and water contents are significantly larger compared to Nafion and the ionomer peak characteristic of the nanophase separation is located at larger angles. The peak position scales as the polymer volume fraction to the power -0.8. These results were interpreted as being indicative of a connected network of relatively small rod-like particles whose connectivity decreases as water content increases. The membranes, neutralized with protonated and deuterated ammonium ions, were studied in D2O and H2O. The counterion condensation in the proton-conducting membrane is confirmed and the data analysis reveals that the rods are composed of a perfluorinated core (R = 4Angstrom) and a phenyl ring shell (R = 2.5Angstrom).