Microstructure-property relations in proton conducting fluorinated polymer composites

This dissertation focuses on the study of solution casted per uorosulfonic acid (PFSA) polymer composites and characterizes their structural, morphological and mechanical properties. The high temperature water retention of new composites with PFSA polymer matrix is investigated based on the structural analysis of such polymers containing sulfuric acid and functionalized solid inorganic additive (FSIA). Unfortunately, at operation temperature above 100 °C, PFSA polymer shows a significant decrease of ionic conductivity and mechanical stability. While the conductivity decrease is due to dehydration caused by low relative humidity of 100 °C, degradation of stiffness is a temperature effect related to the glass transition temperature of PFSA polymer. Attempts to improve properties of PFSA polymer should therefore point in two directions: improvement of ionic conductivity at low relative humidity and increase of stiffness at temperatures more than 80 °C. The attempt is to enable the formation of thin confined different PFSA polymer composites which are prepared with a varying amount of 3-20 weight% of FSIA and with a fixed amount of sulfuric acid (1 wt.%) as additives. The resulting composite has a „hierarchical“ structure with 1-2 µm glass-akes template attached to ~250 nm sized MgF2 nanoparticles embedded in 12-20 µm PFSA polymer ligaments. The combined effect of sulfuric acid and FSIA on the mechanical stability, ionic conductivity, water uptake and thermal stability of the PFSA polymer composites is investigated.