An atomistic model for perÑuorinated ionomer membranes (PIMs), in particular NaÐon materials, is presented and used in conjunction with NVT molecular dynamics simulations to investigate the dynamic and conÐgurational properties of these polymers. It is found that the electrostatic term in the force Ðeld is responsible for the formation of an apparently phase separated morphology which is selectively conductive, favouring the passage of cations. SpeciÐcally, the mobility of ions is found to be D3.2 times greater H 3 Ot han that of OH~ions, under the application of an external electric Ðeld. This phenomenon is shown to be consistent with a jump di †usion model of ion transport in PIMs. There is also evidence for the existence of water in two distinct environments in the simulations : both tightly bound to ion exchange groups, and more loosely associated with the Ñuorocarbon matrix.

The hydrolysis of Nafion ® † precursor material to a perfluorosulfonate ion exchange membrane has been studied in situ at the surface of a sample using atomic force microscopy (AFM), and in the bulk using a combination of small and wide-angle X-ray scattering. The AFM results show that there is a rapid and significant change in the surface morphology of the sample during the first 12 min after the introduction of aqueous hydroxyl ions, provided that an appropriate swelling agent is used. After this point there is little change in surface morphology, although bulk swelling of the sample continues. The wide-angle X-ray scattering results indicate a significant drop in the degree of crystallinity of fluorocarbon matrix from 14±1% to 7±1% on hydrolysis, as a result of the bulk structural reordering necessary to accommodate the formation of ionic clusters. Ionic clustering is confirmed by the appearance of a characteristic small-angle X-ray peak. However, the peak forms towards the end of the hydrolysis process, and subsequently coarsens, suggesting that the formation of ionic clusters is a slow process compared to the rate of hydrolysis. It is confirmed that an appropriate water/solvent mixture is necessary to achieve an efficient conversion of precursor to membrane. AFM images of the precursor surface, when water alone is used, show no signs of structural change.