The interplay between molecular structure and dielectric propertiesin ionic liquids: A comparative study

Abstract In this work, C2-Methylated [C3DMIM+][I−] versus C2-Protonated [C3MIM+][I−] Imidazolium-Based Ionic Liquids containing iodide anion, have been synthesized and characterized using 1H and 13C NMR spectroscopy methods. In order to investigate the methylation effect on thermal properties, we rely to three additional thermal analysis techniques. The thermal behavior confirmed that the methylated [C3DMIM+][I−] IL is more stable than the protonated one [C3MIM+][I−].The conductivity and dielectric relaxation properties of both ILs have been investigated in the frequency range [10−2, 107 Hz] and the temperature ranging between −30 °C and 60 °C. Dielectric permittivity studies show that the substitution of the hydrogen atom by a methyl group has a significant impact in both the reale′ and imaginary e′′ parts. In addition, the analysis of the observed relaxation times showed Arrhenius-type temperature dependence for the temperatures ranging between 20 °C and 60 °C for the protonated IL [C3MIM+][I−], and VFT temperature dependence for the temperatures ranging between −20 °C and 20 °C for the protonated IL [C3MIM+][I−], while, the methylated IL [C3DMIM +][I−] showed Vogel-Fulcher-Tamman-type temperature dependence in the entire investigated temperature range − 30 °C to 60 °C. The representation of σ″ (ν, T) shows the buildup of the electrochemical double layer and interfacial effect. However the real part of complex conductivity follows the empirical Jonscher equation. The determined dc-conductivity of both investigated Ionic liquids present a new behavior regarding the thermal activation an anomalous thermal activation behavior. It follows an Arrhenius relation at lower temperatures and then reach a steady state values at higher temperatures.