Hybrids of perfluorosulfonic acid ionomer and silicon oxide by sol-gel reaction from solution: Morphology and thermal analysis

NAFION®/silicon oxide hybrids were prepared from solution by hydrolysis/polycondensation of alkoxy silanes. Transparent, but brittle films were obtained when TEOS was used as the inorganic polymer precursor, showing a lamellar structure by transmission electron microscopy. Part of the TEOS was substituted by TMDES to increase the film flexibility. For substitution higher than 10% phase separation was clearly observed by scanning and transmission electron microscopy. The thermal analysis of NATION® and hybrids with different inorganic contents showed two main endothermic transitions, one assigned to the NAFION® ionic clusters and the other to the melting of the perfluorinated matrix. The cluster transition temperature decreases as the TEOS content increases up to 50 wt%, but than increases as the TEOS content reaches 80 wt%.