Thermal and Mechanical Behaviors of Nafion Thin Film in Hydrated State

Abstract

Nafion is a Teflon(PTFE) based polymer which is characterized by a good separation between hydrophobic domain (back bone) and hydrophilic domain (ionic cluster). High conductivity to cations and water of Nafion. Nafion is being used to electrolyte or ionomer binder of electrode in PEMFC (Proton Exchange Membrane Fuel Cell), IPMC (Ionic Polymer Metal Composite) actuator, and bio-sensor. However, it is commonly occurred the lack of performance and durability due to differences in behavior between the Nafion thin film and adjacent materials in long range operating cycles. In previous studies, however, experiments were conducted on various substrates, and behaviors of Nafion film are effected greatly type of substrate as their thickness decreases. Thus, in this study, the test is quantitative measurement that the effect of the substrate is eliminated by conducting an assessment on water. As the thickness decreased under 60nm, Nafion is constructed from the ion group dominant structure to back bone dominant structure, resulting in increased thermal expansion at low temperature and Young’s modulus, decreased α-transition temperature, elongation at break, and tensile strength. Hydration growth as the thickness decreases causes mechanical properties to weak. However, Young’s modulus in hydrated state was increased as thickness decrease because confinement effect of backbone is more dominant.