Study on the structure of polymer electrolyte membrane using small angle X-ray scattering and positron annihilation spectroscopy

Abstract

The structure of poly (styrenesulfonic acid)- grafted poly(ethylene-co- tetrafluoroethylene) polymer electrolyte membrane (ETFE-PEM) was investigated by comparison with those of precursor original ETFE film and styrene-grafted films (grafted-ETFE) using positron annihilation lifetime spectroscopy (PALS) and small angle Xray scattering (SAXS). PALS of these samples indicated that there were two lifetime components, which were assigned to the annihilation of ortho- Positronium (o-Ps). The two types of o-Ps relate to the free volume at sub nanoscale locating in the crystalline and amorphous phases. SAXS profiles of these samples indicated the presence of lamellar stacks andlamellar grains. Sizes of lamellar stacks and lamellar grains varied significantly during the graftingprocess, whereas only change a little bit at sulfonation process and at wet state. A compination of PALS and SAXS allowed us to investigate the structures of ETFEPEMs with scale ranging from several Ångströms to micrometer.