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 sc attering in the q range of 7 10(-3) Angstrom (-1) to 0.4 Angstrom (-1). Ext ernal conditions were varied: counterions, electrolyte concentration, tempe rature, and pretreatment of membranes. The nanostructure of Nation exhibits a sensivity that depends on the parameters considered: changing counterion s and concentration leads to a reversible local reorganization of the hydro philic cavities, whereas changing temperature and pretreatment leads to a i rreversible reorganization on a larger scale. The mean variation of the rad ius of the hydrophilic cavities versus these parameters is about 10%. The i nterface between hydrophobic and hydrophilic phases appears to be sharp exc ept when the temperature exceeds 60 degreesC. (C) 2001 John Wiley & Sons, I nc.