ELECTRON-MICROSCOPY INVESTIGATION OF THE MICROSTRUCTURE OF NAFION FILMS

Transmission electron microscopy (TEM) and transmission electron diffraction were used to study the microstructure of recast Nafion films. Zero-loss bright-field (BF) images were obtained, as well as Dage SIT low-light images (minimum specimen damage) and specific sulfur imaging. The results show a nonrandom distribution of the -SO3- groups in the polymer film,,primarily as similar to 5 nm clusters. Electron diffraction of deposited Nafion films shows the existence of single crystals, randomly distributed in the film, with an average distance of several microns. The diffraction pattern indicates an orthorhombic crystal structure which is similar to that of polyethylene (PE). The calculated d-spacings of the corresponding lattice planes for the two polymers are also quite close, suggesting similarity in their crystal structures. This result indicates that the fluorocarbon backbone of Nafion is in the form of a linear zigzag chain as in PE and nota twisted chain as in polytetrafluroethylene (PTFE), despite the similarity in the chemical composition of Nafion and PTFE.