On the Influence of Solvent and Ultrasonic Treatment on Properties of Cast Nafion® Membranes

The effect of the nature of the solvent on the properties of Nafion membranes obtained from them by casting procedure has been discussed on examples of polar protic (water) and aprotic (N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA)) liquids. The water uptake and proton conductivity of Nafion membranes obtained from an aqueous dispersion are higher than those obtained from dispersions in DMF and DMA; however, their mechanical properties and stability are usually low. Short time ultrasonic (US) treatment of Nafion dispersions in DMF and DMA results in increase in conductivity of membranes and decrease in its activation energy. This is due to the improvement of the membrane microstructure as a result of the deagglomeration of macromolecules. The presence of water in Nafion dispersions upon US treatment leads to increase in their viscosity and loss of a large number of functional sulfo groups. As a result, the conductivity of the membranes decreases. To level these processes, it is advisable to use aprotic liquids or mixtures with a low water content for Nafion polymer. An explanation of the influence of the nature of the dispersing liquid and US treatment on the properties of Nafion membranes from the point of view of the morphology of the polymer in the dispersion and in the membrane has been proposed.