Charge Transport and Dynamics in Imidazolium Chloroaluminate Ionic Liquids

Ion dynamics and charge transport in 1-alkyl-3-methylimidazolium chloroaluminate ionic liquids were investigated over broad temperature and frequency ranges by broadband dielectric spectroscopy and differential scanning calorimetry. The timescale of ion dynamics, as captured by the imaginary component of the complex dielectric modulus as well as the calorimetric glass transition temperature (Tg), is strongly composition-dependent, with the fastest dynamics, lowest Tg, and highest fragility observed for the Lewis acidic 67 mol% AlCl3 + 1-ethyl-3-methylimidazolium chloride composition. The DC ionic conductivity scales directly by the ion dynamics for all compositions indicating the primary effect of ion speciation is an alteration of the underlying ion mobility. The fragility (m) of the 67 mol% AlCl3 + 1-ethyl-3-methylimidazolium chloride ionic liquid, m=148, is among the highest reported fragilities for a glass-forming liquid.