Abstract
Ion conducting capability is often imparted to polymeric materials through short polyether side-chains, and yet the impact of this graft polymer architecture on ion solvation and conduction has not been fully explored. Here, we use a combination of impedance spectroscopy, vibrational spectroscopy, and atomistic molecular dynamics (MD) to compare the conductivity, ionic interactions, and polymer dynamics in a series of graft polyether electrolytes. We find that in poly[(oligo ethylene oxide)methyl ether methacrylate] (POEM), a widely used graft polymer electrolyte, the ionic conductivity drops more than an order of magnitude as the side-chain length is decreased from nine ethylene oxide (EO) units to three. This difference in conductivity is unexplained by differences in the calorimetric glass transition temperature (Tg), which varies only slightly with side-chain length. Through vibrational spectroscopy and MD simulations we demonstrate that both linear and graft polyethers solvate Li+ions effectively and dissociate them from large counterions, irrespective of side-chain length. Li+ions do, however, show preferential solvation by EO units far from the methacrylate backbone. Similarly, EO units far from the backbone show enhanced segmental dynamics, while those near the immobile methacrylate group move substantially more slowly, as quantified by bond vector autocorrelation relaxation times. This heterogeneity in both ion solvation and local segmental relaxation explains variation in ion conductivity where material-averaged properties such asTgand number of free ions fail to do so. Importantly, the ionic conductivity is dictated primarily by the segmental mobility of the EO units which form effective solvation sites, rather than system-wide dynamics.
| Original language | English |
|---|---|
| Pages (from-to) | 9937-9951 |
| Number of pages | 15 |
| Journal | Journal of Materials Chemistry A |
| Volume | 9 |
| Issue number | 15 |
| DOIs | |
| State | Published - 21 Apr 2021 |
| Externally published | Yes |
Bibliographical note
Funding Information:We gratefully acknowledge support by the U.S. Department of Energy (DOE), Basic Energy Sciences, Materials Sciences and Engineering Division. This work made use of the Pritzker Nanofabrication Facility, which receives partial support from the SHyNE Resource, a node of the National Science Foundation's National Nanotechnology Coordinated Infrastructure (NSF ECCS-2025633). This work made use of the shared facilities at the University of Chicago Materials Research Science and Engineering Center, supported by National Science Foundation under award number DMR-2011854. Parts of this work were carried out at the So Matter Characterization Facility of the University of Chicago. The simulations were completed on computational resources provided by the University of Chicago Research Computing Center. MAW acknowledges support from Princeton University.
Funding Information:
We gratefully acknowledge support by the U.S. Department of Energy (DOE), Basic Energy Sciences, Materials Sciences and Engineering Division. This work made use of the Pritzker Nanofabrication Facility, which receives partial support from the SHyNE Resource, a node of the National Science Foundation's National Nanotechnology Coordinated Infrastructure (NSF ECCS-2025633). This work made use of the shared facilities at the University of Chicago Materials Research Science and Engineering Center, supported by National Science Foundation under award number DMR-2011854. Parts of this work were carried out at the Soft Matter Characterization Facility of the University of Chicago. The simulations were completed on computational resources provided by the University of Chicago Research Computing Center. MAW acknowledges support from Princeton University.
Publisher Copyright:
© The Royal Society of Chemistry 2021.
