Dynamics in Quaternary Ionic Liquids with Non-Flexible Anions: Insights from Mechanical Spectroscopy

The present work investigates how mechanical properties and ion dynamics in ionic liquids (ILs) can be affected by ILs' design while considering possible relationships between different mechanical and transport properties. Specifically, we study mechanical properties of quaternary ionic liquids with rigid anions by means of Dynamical Mechanical Analysis (DMA). We are able to relate the DMA results to the rheological and transport properties provided by viscosity, conductivity, and diffusion coefficient measurements. A good agreement is found in the temperature dependence of different variables described by the Vogel-Fulcher-Tammann model. In particular, the mechanical spectra of all the measured liquids showed the occurrence of a relaxation, for which the analysis suggested its attribution to a diffusive process, which becomes evident when the ion dynamics are not affected by the fast structural reorganization of flexible anions on a local level.

Automated summary

This study investigates the impact of ionic liquid (ILs) design on the mechanical properties and ion dynamics of ILs, while considering the relationships between different mechanical and transport properties. The mechanical properties of quaternary ILs with rigid anions are studied using Dynamical Mechanical Analysis (DMA), and the results are compared with rheological and transport properties measured through viscosity, conductivity, and diffusion coefficient measurements. The temperature dependence of different variables is well described by the Vogel-Fulcher-Tammann model. The occurrence of a relaxation process in the mechanical spectra of all measured liquids is attributed to a diffusive process when the ion dynamics are not affected by fast structural reorganization of flexible anions at a local level.