LOCAL AND LONG-RANGE STRUCTURE OF WATER IN A PERFLUORINATED IONOMER MEMBRANE

We have measured the H-H and O-H correlations within nickel-substituted amorphous Nafion membrane using a novel combination of small- and wide-angle neutron scattering. Diffraction patterns were measured over a momentum transfer range of 0.03-20 angstrom-1 for three isotopic water mixtures. From the partial structure factors atom-atom radial distribution functions for H-H and O-H from 1 to 100 angstrom were obtained by Fourier inversion. The local water structure is similar to that of bulk water. On a larger scale atom-atom correlations show that the average radius of aqueous domains is 18.5 angstrom with a mean separation of 70 angstrom. The shapes of the atom-atom radial distribution functions are consistent with the water being located in a continuous network.