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Tetra-branched tetra-cationic ionic liquids: Effects of spacer and tail structure on physical properties
Ikeda, Taichi
, p. 1218 - 1225 (2020)
Electrolytes are key materials that support information society because they are included in most electronic devices, e.g., batteries, supercapacitors, fuel cells, and electrochromic devices. Ionic organic compounds, such as ionic liquids, have attracted increasing attention due to their designability and non-volatility. In this study, ten tetra-branched tetra-cationic ionic liquids, which consisted of a pentaerythritol-based core, alkylene or ethylenedioxy spacers, imidazolium cationic units, and short alkyl tails, were synthesized. The physical properties of the tetra-cations, including their glass transition and thermal decomposition temperatures, densities, viscosities, and ionic conductivities, were investigated. The tetra-cations were analyzed to determine the effects of the spacer and tail structure on these physical properties. The spacer unit located between the pentaerythrityl core and cationic unit was confirmed to be the key for improving ionic conductivity. A maximum ionic conductivity of 2.8 x 10-4 S/cm (25 °C under anhydrous conditions) and a minimum viscosity of 1.6 Pa-sec (25 °C) were observed. While the physical values of the tetra-cationic ionic liquids are close to those of di-cationic ionic liquids, their structure-property relationship is similar to that of poly-cations rather than di-cations.
