Water behavior in perfluorinated ion-exchange membranes

The water molecules in acid and salt forms of perfluorinated sulfocation membranes (MF-4SK) have been investigated by employing nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC) techniques. The mobility parameters, correlation time and activation energy of water molecules were estimated from the results of the temperature dependence of¹H relaxation time and compared with water self-diffusion coefficients obtained with pulsed field gradient NMR. The NMR data showed no frozen unbound water in membranes at low water content with an amount of water molecules per sulfonate groupn being comparable to the cationic hydration numberh _o, whereas DSC thermograms showed peaks which are usually interpreted as a water fusion phenomenon in the membranes. The diffusion mechanism of water molecules below 260 K is different from that above 300 K due to additional hydrogen bonds in water clusters at the low-temperature region.