Molecular relaxation and ionic conductivity of ionic liquids confined in a poly(vinylidene fluoride) polymer matrix: Influence of anion and cation type

Abstract

Blends of poly(vinylidene fluoride) (PVDF) and ionic liquids (ILs) with different cations and anions have been prepared by solvent casting. The IL content was the same in all blends of the series. Molecular relaxation and ionic conductivity have been systematically studied by broadband dielectric relaxation spectroscopy (BDS) in wide frequency (0.1 Hz–1 MHz) and temperature ranges (−120 to 150 °C) and the results have been analysed in terms of dielectric modulus M*(ω) and conductivity σ*(ω) formalisms. The main relaxation process (β-relaxation) of the amorphous phase of the blend that integrates amorphous polymer chain segments and IL molecules was observed. Significant differences in the Vogel-Fulcher-Tammann (VFT) fitting parameters in the PVDF/IL blends with different anions were detected. The conductivity σ*(ω) formalism shows that it is strongly dependent on the miscibility of the IL with the amorphous PVDF chains and the type of anion. The Barton-Namikawa-Nakajima (BNN) relation σ0 ∼ ωc is fulfilled for all PVDF/IL blends except for that containing 1-ethyl-3- methylimidazolium hydrogen sulfate, [Emim][HSO4]. The activation energy of the ac conductivity, calculated according to the Dyre model, decreases for all PVDF/IL blends with respect to neat PVDF. The structure of the cation of the IL has been found to exert less influence on the dielectric and conductivity properties of the blends.