Perfluorinated and sulfonated proton exchange membranes: Effect of supercritical fluid processing on ion exchange capacity and proton conductivity

Abstract

The present work has processed Nafion® and sulfonated polystyrene-isobutylenestyrene (SIBS) with supercritical fluid (SCF) carbon dioxide at a 40°C and 200 bar with the aid of ten co-solvents of different size and polarity. The goal of the investigation was to morphologically re-arrange the sulfonic acid groups to maintain the proton conductivity, while also re-arranging the CO2-phillic perfluorinated groups to block the methanol for crossing over. Measured ion exchange capacities (IEC) of the processed samples showed an increase, supporting our hypothesis, but very sensitive to the co-solvent selected. In addition, density results confirmed the membrane integrity. The last stage of this investigation has been studying the proton conductivity to have a better description of the orientation arrangement of the molecules. These results coupled with thermogravimetric, swelling, and dynamic mechanical analysis can provide a better picture of the structure property relation of these complex heterogeneous polymers.