The effect of ambient humidity on the electrical response of ion-migration-based polymer sensor with various cations

Abstract

A water-based ionic polymer–metal composite (IPMC) sensor, induced by ion migration, is a promising alternative to natural sensing systems. Focusing on water effects, this paper investigated the voltage responses of Au-Nafion IPMC at multiple fixed levels of ambient humidity under a small step bending deformation. The voltage includes two processes: a fast rising and a subsequent slow decay. As the relative ambient humidity decreases, the peak voltage first increases and then decreases because the mass storage capacity of IPMC, related to the compressed state of a polymer network, reaches the optimum at a moderate water content (30 ∼ 90%RH), whereas the proportion of decay related to hydration effect decreases as the level of relative humidity is decreased. The detailed physics has been revealed qualitatively based on transport theory, and a fitting equation has been proposed to approximate the general electrical response.