Influence of chain rigidity on ion dynamics in polymerized ionic liquids: Insight from high-pressure dielectric studies

Polymerized ionic liquids (PILs) are of great interest in the scientific community due to their potential applications as advanced electrolytes in modern electrochemical devices. Understanding the ion transport mechanism in PILs is critical for designing highly conducting polymer electrolytes. One strategy to bring an essential breakthrough in this issue may be the application of high-pressure techniques. Here, we investigate, over a broad range of temperature and pressure, the ion dynamics of two PILs with different chain rigidity (flexible ethylene oxide vs. rigid vinyl-imidazolium) by using broadband dielectric spectroscopy. The determined pressure coefficient of glass transition temperature and the activation volume of studied PILs indicate that the chain rigidity strongly affects their pressure sensitivity and, thereby, ion dynamics at high-pressure conditions. Additionally, the analysis of high-pressure ion dynamic data using the free-volume-based model established here indicates that the rigid chain significantly reduced the critical volume required for ion hopping and enhanced ion mobility when approaching the glassy state.