Transport-structural parameters of perfluorinated membranes Nafion-117 and MF-4SK

The concentration dependences of the electroconductivity of membranes Nafion-117 and MF-4SK are studied in salt solutions under identical experimental conditions. The results are compared with nanostructural characteristics of Nafion-117 measured independently by the AFM and quasi-elastic neutron scattering methods. The role played by internal interfaces between hydrophobic and water-cluster microphases of Nafion during the membrane transition from the Na+ form to the form of tetraalkylammonium ions is determined. It is established that the specific adsorption of organic ions makes the water clusters disintegrate and the elasticity of side segments diminish; as a result, the polymer film's conductivity "switches off." This morphological effect is used for interpreting the fact that the conducting and hydrophilic properties of perfluorinated membranes substantially depend on their conditioning prior to measurements. It is shown that expanding the membranes reduces the differences between the electroconductivity and structural organization of specimens of different brands with close values of the exchange capacity