Implications of multiscale modeling on sensing predictions in Nafion

Multiscale modeling is used to investigate mechanical stiffness of ionic polymers and the subsequent implications for electromechanical sensing. Unlike the more common empirical and gray box approaches this study presents the hypothesis of streaming current as the fundamental, underlying mechanism responsible for sensing. The approach accommodates the observation that both stiffness and sensing response can be affected by cation type and hydration level. Rotational isomeric state (RIS) theory is used to predict the conformation of the hydrophobic backbone of a Nafion, 1200 equivalent weight (EW) in lithium and sodium forms. The RIS method generates crosslink-to-crosslink chain lengths to assess material multiscale stiffness. Both the stiffness and sensing predictions are compared to experiment for validation. It is observed that the multiscale stiffness does not necessarily evolve in concert with the global stiffness. However, the implications are consistent with, and offer an explanation of, experimentally observed water uptake and sensing phenomena