TY - JOUR KW - Temperature KW - Water KW - Films KW - Conductivity KW - Degradation KW - Nafion membranes KW - Structure/property KW - Saxs/waxs KW - Hygrothermal aging KW - Ion-exchange capacity KW - PFSA ionomers KW - Transport properties KW - Relative-humidity KW - Molecular-origins KW - Ionomers AU - Shouwen Shi AU - Thomas J Dursch AU - Colin Blake AU - Rangachary Mukundan AU - Rodney L Borup AU - Adam Z Weber AU - Ahmet Kusoglu AB -

Perfluorosulfonic-acid (PFSA) membranes are widely used as the solid electrolyte in electrochemical devices where their main functionalities are ion (proton) conduction and gas separation in a thermomechanically stable matrix. Due to prolonged operational requirements in these devices, PFSA membranes’ properties change with time due to hygrothermal aging. This paper studies the evolution of PFSA structure/property relationship changes during hygrothermal aging, including chemical changes leading to changes in ion-exchange capacity (IEC), nanostructure, water-uptake behavior, conductivity, and mechanical properties. Our findings demonstrate that with hygrothermal aging, the storage modulus increases, while IEC and water content decrease, consistent with the changes in nanostructure, that is, water- and crystalline-domain spacings inferred from small- and wide-angle X-ray scattering (SAXS/WAXS) experiments. In addition, the impact of aging is found to depend on the membrane's thermal prehistory and post-treatments, although universal correlations exist between nanostructural changes and water uptake. The findings have impact on understanding lifetime, durability, and use of these and related polymers in various technologies.

BT - Journal of Polymer Science Part B: Polymer Physics DA - 10/2015 DO - 10.1002/polb.23946 IS - 5 N2 -

Perfluorosulfonic-acid (PFSA) membranes are widely used as the solid electrolyte in electrochemical devices where their main functionalities are ion (proton) conduction and gas separation in a thermomechanically stable matrix. Due to prolonged operational requirements in these devices, PFSA membranes’ properties change with time due to hygrothermal aging. This paper studies the evolution of PFSA structure/property relationship changes during hygrothermal aging, including chemical changes leading to changes in ion-exchange capacity (IEC), nanostructure, water-uptake behavior, conductivity, and mechanical properties. Our findings demonstrate that with hygrothermal aging, the storage modulus increases, while IEC and water content decrease, consistent with the changes in nanostructure, that is, water- and crystalline-domain spacings inferred from small- and wide-angle X-ray scattering (SAXS/WAXS) experiments. In addition, the impact of aging is found to depend on the membrane's thermal prehistory and post-treatments, although universal correlations exist between nanostructural changes and water uptake. The findings have impact on understanding lifetime, durability, and use of these and related polymers in various technologies.

PY - 2015 SP - 570 EP - 581 ST - J. Polym. Sci. Part B: Polym. Phys. T2 - Journal of Polymer Science Part B: Polymer Physics TI - Impact of hygrothermal aging on structure/function relationship of perfluorosulfonic-acid membrane VL - 54 ER -