FTIR studies of PEMA/PVdF-HFP blend polymer electrolyte system incorporated with LiCF 3SO 3 salt

Abstract

Poly(ethyl methacrylate), PEMA and poly(vinylidenefluoride-co-hexafluoropropylene), PVdF-HFP have been chosen as hosts for the development of a polymer blend electrolyte system. Lithium trifluoromethanesulfonate (triflate), LiCF 3SO 3 is the lithium ion, Li + provider. The ratio of PEMA:PVdF-HFP in the blend is fixed at 70:30 in order to obtain transparent films with good mechanical stability. The polymers and LiCF 3SO 3 salt have been refluxed for 2 h at temperatures between 55 and 65 °C. The concentration of LiCF 3SO 3 salt has been varied from 0 to 40 wt.%. Fourier transform infrared (FTIR) spectroscopy has shown that blending between PEMA and PVdF-HFP has occurred from the changes in the CH 2 scissoring [ δ(CH 2)], asymmetrical O–C 2H 5 bending [ γ(OC 2H 5)], CH 2 twisting [ τ(CH 2)], C–O stretching of –COO– group [ ν(CO)], asymmetrical C–O–C stretching [ ν a(COC)] and C–O stretching of –OC 2H 5 [ ν(C–O)] from PEMA as well as the symmetrical CF 2 stretching [ ν s(CF 2)], α-phase and the amorphous region of PVdF-HFP. Complexation occurs via the coordination of Li + ions with the oxygen atom in the carbonyl (C O) and ester (–COC–) groups of PEMA as well as with the fluorine atom in –CF 2 and –CF 3 groups in PVdF-HFP. Curve fitting of spectral bands in the symmetrical ν s(SO 3) stretching region in the polymer blend–salt complexes has shown that free ions (1031–1032 cm −1) and ion pairs (1040–1042 cm −1) are present in samples incorporated with 10 wt.% LiCF 3SO 3 and above, while ion aggregates at 1049 cm −1 are formed when 40 wt.% LiCF 3SO 3 is added into the polymer blend. The increase in the ionic conductivity at high salt contents could be explained by the greater amount of free ions as compared to ion pairs and ion aggregates.