Effect of Ultrasonic Treatment of Nafion® Polymer Solutions on Properties of Membranes Obtained by a Casting Procedure

The paper describes the effect of the processing time (from 1 to 60 min) and power (from 2.7 to 9.4 W) of low-frequency ultrasonic treatment of Nafion® solutions on their viscosity and properties of membranes obtained from them by a casting procedure. The mechanical properties of membranes, their water uptake, and proton conductivity at high and low relative humidity, as well as the selectivity of the cation transfer have been studied. Ultrasonic treatment of solutions leads to a gradual decrease in their viscosity. The values of the break stress and strain of membranes strongly decrease after ultrasonic treatment of polymer solutions. The conductivity of membranes obtained from a polymer solution after a short-time ultrasonic treatment and/or ultrasonic treatment of low power increases up to 40% compared to a membrane obtained from an initial Nafion® solution. A further increase in the prolongation and/or power of treatment leads to a decrease in the water uptake and proton conductivity of membranes. After ultrasonic treatment of polymer solutions, the selectivity of the transfer of cations through membranes decreases. An explanation of the observed changes is proposed. The results obtained show the need to evaluate the effect of ultrasonic action on the properties of polymers and materials obtained from them when choosing conditions for ultrasonic treatment in the process of obtaining hybrid membranes and catalytic inks for membrane-electrode blocks of fuel cells.