Thermal Development of Free Volumes in Nafion Membrane

Abstract

In this work we employed positron lifetime spectroscopy for investigation of the thermal development of free volumes in H + Nafion membrane over a broad range of temperatures from -150 to 150• C. Positron lifetime studies were combined with differential scanning calorimetry. Size distribution of free volumes was determined from ortho-positronium contribution to positron lifetime spectra. Our investigations revealed that the mean size of free volume holes strongly increases with temperature. On the other hand, the width of the size distribution and the positronium yield decreases with temperature. Transition temperatures corresponding to a change in the slope of the temperature dependence of ortho-positronium lifetime were identified. Results of positron lifetime spectroscopy agree well with the curve obtained by differential scanning calorimetry.

Positron annihilation spectroscopy studies of implanted polymer membranes

“…• The third irradiation step-blue graph, cumulative implantation fluence value of 7 × 10 16 ions/cm 2 ; a change appears, the curve by PAS as mentioned in literature. [15][16][17][18] Nafion CDBS spectra can be seen in Figure 5 The Nafion membrane has PTFE backbone and side chain terminated with sulfonic group through two ether bonds. 20 Aggregation of hydrophilic sites, sulfonic groups, forms clusters and such clusters are connected each other with channels where hydrated proton can be transferred, which is known as a cluster-network model and is most widely referenced, though other models have been proposed.…”

“…The phenomena described in the case of polyethylene are also present in the case of Nafion, but to a lesser extent and at different implantation fluence. The Nafion membrane was extensively studied by PAS as mentioned in literature 15‐18 …”

“…The PAS measurements were performed on the non-implanted membranes and then after 2 × 10 16 ions/cm 2 implantation steps up to10 17…”