Insights into Interfacial Water Structuring at the Nafion Surface by T1-Weighted Magnetic Resonance Imaging

T1-weighted magnetic resonance images of water in the surroundings of a Nafion surface allowed the identification of the presence of a low-mobility zone (LMZ), 60 μm thick, consisting of water molecules structured in a hydrogen-bonding network, promoted by the presence of the acidic protons on the surface of the sulphonated polymer. In parallel, the exclusion zone (EZ) was assessed by observing in optical microscopy the distribution of microspheres suspended in the medium in contact with the Nafion membrane. It was found that the LMZ and the EZ do not correspond: in fact, the former is thinner and more stable over time than the latter and they behave differently when ions are present in the medium in which Nafion is immersed.