Ionic Conduction and Dielectric Response of Poly(imidazolium acrylate) Ionomers

Abstract

We use X-ray scattering to investigate morphology and dielectric spectroscopy to study ionic conduction and dielectric response of imidazolium-based single-ion conductors with two different counterions [hexafluorophosphate (PF6–) or bis(trifluoromethanesulfonyl)imide (F3CSO2NSO2CF3– = Tf2N–)] with different imidazolium pendant structures, particularly tail length (n-butyl vs n-dodecyl). A physical model of electrode polarization is used to separate ionic conductivity of the ionomers into number density of conducting ions and their mobility. Tf2N– counterions display higher ionic conductivity and mobility than PF6– counterions, as anticipated by ab initio calculations. Ion mobility is coupled to polymer segmental motion, as these are observed to share the same Vogel temperature. Ionomers with the n-butyl tail impart much larger static dielectric constant than those with the n-dodecyl tail. From the analysis of the static dielectric constant using Onsager theory, there is more ionic aggregation in ionomers with the n-dodecyl tails than in those with the n-butyl tails, consistent with X-ray scattering, which shows a much stronger ionic aggregate peak for the ionomers with dodecyl tails on their imidazolium side chains.