A SANS determination of the influence of external conditions on the nanostructure of nafion membrane

We have studied the structure of nafion membranes by small-angle neutron scattering in the q range of 7 10−3 Å−1 to 0.4 Å−1. External conditions were varied: counterions, electrolyte concentration, temperature, and pretreatment of membranes. The nanostructure of Nafion exhibits a sensivity that depends on the parameters considered: changing counterions and concentration leads to a reversible local reorganization of the hydrophilic cavities, whereas changing temperature and pretreament leads to a irreversible reoganization on a larger scale. The mean variation of the radius of the hydrophilic cavities versus these parameters is about 10%. The interface between hydrophobic and hydrophilic phases appears to be sharp except when the temperature exceeds 60 °C.