Interplaying Ion Transport and Structure of Polymerized Ionic Liquids

In this study, correlation between nanoscale organization and ion transport of 1,2,3-triazole based polymerized ionic liquids (PILs) was investigated using wide-angle X-ray scattering (WAXS) and broadband dielectric spectroscopy (BDS). The dc ionic conductivity of PILs was correlated with the glass temperature transition (Tg) in which the low Tg system exhibited higher dc conductivity. A comparison of the WAXS and BDS results indicates mobile ion volume and chemical structure of the pendant groups controlled structural heterogeneity and ion conduction of the studied PILs. The normalized heterogeneity length extracted from X-ray scattering spectra is considered as a criterion for the structural packing. For the polycation samples, larger TFSI–mobile ion results in a higher packed structure than small Cl–anion, and polyanion (PVBSO3C4MIm) samples. The estimation of the characteristic ion diffusion lengths from the activation energies of the dc conductivity below Tg measured by BDS is quantitatively correlated to the ion-ion correlation lengths and structural heterogeneity obtained from nanostructure analysis using WAXS. This suggests that increasing the spatial heterogeneity of the PILs lead to a reduction in activation energy barriers of long-range ion motions. These results highlight the role of spatial heterogeneity in designing efficient polymerized ionic liquids.