Streaming Potential Hypothesis for Ionic Polymer Transducers in Sensing: Roles of Ionomer State and Morphology

Abstract

To date, consensus has not been reached on the underlying physical mechanism responsible for the experimentally observed sensing response of ionic polymer transducers, sometimes referred to as ionic polymer-metal composites. It is understood that a robust hypothesis will be able to accommodate a range of experimental observations. Moreover, because the actual morphology of ionic polymers is (a) an open topic and (b) expected to vary, a robust sensing hypothesis should additionally be decoupled from any particular morphological assumption. Explored here is the streaming potential hypothesis. As per this hypothesis, the magnitude of the predicted electromechanical response will vary with assumed morphology, but will always exist. This study demonstrates scenarios including predicting the evolution of sensing with diluent and cation variations for two morphological propositions. Specifically, sensing predictions are offered for a Nafion-based sensor (a) exchanged with lithium versus sodium cations, (b) imbued with water versus ionic liquid diluents, and (c) each of these cases is considered for a parallel circular cylindrical channel morphology versus a spherical cluster morphology. Both candidate morphologies correctly predict higher sensitivity for the lithium exchanged and water imbued cases.