Hidden Thermoreversible Actuation Behavior of Nafion and Its Morphological Origin

Recent morphological characterization of Nafion as correlated to its proton transport properties has led to the conclusion that the structural ordering in the ionic phase of Nafion may be quite similar to liquid crystalline polymers. Liquid crystalline polymers, on the other hand, are well-known for their thermoreversible actuation (or two-way shape memory) behavior. This has motivated us to design and conduct thermomechanical experiments to probe Nafion's potential liquid crystalline characteristics from the standpoint of thermoreversible actuation. Our experimental results surprisingly revealed the thermoreversible actuation behavior of Nafion, buried alongside the irreversible creep behavior commonly observed for some polymers. As such, the current study provides evidence supporting Nafion's structural similarity to liquid crystalline polymers.