Structural and transport studies on polymeric membranes of PEO containing ionic liquid, EMIM-TY: Evidence of complexation

PEO:IL(1-ethyl-3-methylimidazolium tosylate, EMIM-TY) polymer electrolyte films are prepared by solvent free hot-pressing and characterized by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and Complex Impedance Spectroscopy. The FTIR/DSC/XRD studies confirm the complexation of the ionic liquid cation (EMIM+) with the ether oxygen, i.e. C–O–C group of PEO polymer backbone. The crystallinity of PEO+IL(EMIM-TY) electrolyte membranes has been found to decrease (plasticization effect) with ionic liquid EMIM-TY content in PEO up to a threshold weight ratio of ~ 20 wt.% and then the crystallinity tends to increase. The room temperature ionic conductivity is found to depend both on the ionic liquid, EMIM-TY content and degree of crystallinity. The temperature dependence of the ionic conductivity of pure ionic liquid EMIM-TY, and the same ionic liquid in PEO matrix is also studied and discussed in this paper.

Research Highlights
► Polymer + ionic liquid (EMIM-TY) electrolyte films have been prepared by novel hot-press technique.
► The incorporation of IL(EMIM-TY) produces plasticization effect by lowering the degree of crystallinity.
► FTIR, XRD, DSC and conductivity results suggest that IL-cation complexes with the ether oxygen of PEO.