DISTRIBUTION OF THE MICELLES IN HYDRATED PERFLUORINATED IONOMER MEMBRANES FROM SANS EXPERIMENTS

The analysis of the shape and intensity of small angle neutron scattering (SANS) curves obtained on a perfluorinated ionomer membrane with different water contents suggests a model for the distribution of the hydrated 'micelles' in the perfluorinated matrix. The model describes a locally ordered structure for these micelles with four first neighbours located at a well defined distance embedded in a completely disordered gas of micelles. Only two adjustable parameters are necessary to fit the experimental scattering curves over the whole q range, based on the radial distribution function associated with this locally 'diamond-like' (tetrahedral) structure. It is demonstrated that both the zero angle upturn and the ionomer peak are linked with the ionic domain existence. It is shown that there is no need for long range fluctuations or large scale defects to interpret the zero angle domain. Our model is in reasonably good agreement with all the experimental results for q (q = 4 π sin θ/λ) ranging from 0.02 to 0.26 angstrom-1 and for water contents from 6 to 26% (volume fraction).