Equivalent weight and crystallinity effects on water content and proton conductivity in bis[(perfluoroalkyl)sulfonyl]imide-based ionomers

Abstract

Water content and ionic conductivity data were acquired as a function of relative humidity for representative samples of a novel series of perfluorinated ionomers based on bis[(perfluoroalkyl)sulfonyl]imide. The humidity dependence of both water content and ionic conductivity correlates strongly with ionomer equivalent weight (EW); the higher EW ionomer (1205 g equiv-1) exhibited a much sharper drop in water content and ionic conductivity with diminished humidity than did the lower EW ionomer (1095 g equiv-1). This drop in water content and ionic conductivity at low humidity correlates with X-ray diffraction measurements which indicate a higher poly(tetrafluoroethylene)-like crystallinity in the higher EW ionomer.