Impact of water on the charge transport of a glass-forming ionic liquid

TL;DR

This study investigates how water uptake affects the glassy dynamics and ionic conductivity of an ionic liquid, revealing that water accelerates cation reorientation and increases conductivity, mainly by lowering the glass transition temperature.

Contribution

It provides a detailed analysis of water's impact on the dielectric and thermal properties of a typical ionic liquid, highlighting changes in fragility and decoupling phenomena.

Findings

Water increases ionic conductivity and accelerates cation reorientation.

Higher water content lowers the glass transition temperature.

Fragility of the ionic subsystem varies with water content.

Abstract

Using dielectric spectroscopy and differential scanning calorimetry, we have performed a detailed investigation of the influence of water uptake on the translational and reorientational glassy dynamics in the typical ionic liquid 1-Butyl-3-methyl-imidazolium chloride. From a careful analysis of the measured dielectric permittivity and conductivity spectra, we find a significant acceleration of cation reorientation and a marked increase of the ionic conductivity for higher water contents. The latter effect mainly arises due to a strong impact of water content on the glass temperature, which for the well-dried material is found to be larger than any values reported in literature for this system. The fragility, characterizing the non-Arrhenius glassy dynamics of the ionic subsystem, also changes with varying water content. Decoupling of the ionic motion from the structural dynamics has to be considered to explain the results.