@article {1105, title = {Parallel cylindrical water nanochannels
in Nafion fuel-cell membranes}, journal = {Nature Materials},
volume = {7}, number = {1}, year = {2008}, month = {Jan}, pages
= {75-83}, type = {Article}, abstract = {The structure of the
Nafion ionomer used in proton-exchange membranes of H-2/O-2 fuel
cells has long been contentious. Using a recently introduced
algorithm, we have quantitatively simulated previously published
small-angle scattering data of hydrated Nafion. The
characteristic {\textquoteright}ionomer peak{\textquoteright}
arises from long parallel but otherwise randomly packed water
channels surrounded by partially hydrophilic side branches,
forming inverted-micelle cylinders. At 20 vol\% water, the water
channels have diameters of between 1.8 and 3.5 nm, with an
average of 2.4 nm. Nafion crystallites (similar to 10 vol\%),
which form physical crosslinks that are crucial for the
mechanical properties of Nafion films, are elongated and
parallel to the water channels, with cross-se