Ionic transport on composite polymers containing covalently attached and absorbed ionic liquid fragments

Abstract

The ionic transport of five supported ionic liquid-like phases (SILLPs) based on 1-butyl imidazolium ion covalently attached to a polymeric matrix has been analysed by means of electrochemical impedance spectroscopy (EIS) using the electrode polarization analysis. The structure of three of the SILLPs contains variable amounts of 1-butyl-3-methyl imidazolium chloride (BMIM[Cl]) strongly absorbed on the functional polymeric surfaces. The impedance spectra of the SILLPs show different ionic conductivity processes at different regions of the spectra. At higher frequency, the high conductivity observed is associated to the bis-((trifluoromethyl) sulfonyl) imide) (NTf2) anion mobility. The ionic conductivity of SILLPs is increased up to 3 orders of magnitude in the presence of BMIM[Cl]. In this case, the highest ionic conductivity obtained was 2.56 x 10(-3) S/cm at 30 degrees C and 1.3 x 10(-2) S/cm at 80 degrees C. The experimental results show than the variation of ionic conductivity with the temperature is of VFT type. From the maximum loss tangent the inverse of Debye length has been obtained being 100 times higher when free bulk BMIM[Cl] is absorbed into the polymeric matrix. Finally the electrode polarization analysis overestimates the free ion diffusivity while underestimates the free ion number density.