Grafted natural rubber-based polymer electrolytes: ATR-FTIR and conductivity studies

Attenuated total reflectance-Fourier transformed infrared spectroscopy measurement is employed to study the interactions between the components of 30% methyl-grafted natural rubber (MG30), lithium trifluromethanesulfonate (LiCF3SO3 or LiTF), and propylene carbonate (PC). Vibrational spectra data of LiTF reveals that the nu(s)(SO3) at 1,045 cm(-1), delta(s)(CF3) at 777 cm(-1), and C=O stretching mode at 1,728 cm(-1) for MG30 have shifted to lower wave numbers in MG30-LiTF complexes indicating that complexation has occurred between MG30 and LiTF. The solvation of lithium ion is manifested in Li+<- O=C interaction as shown by the downshifting and upshifting of C=O mode at 1,788 to 1,775 cm(-1) and nu(as)(SO3) at 1,250 to 1258 cm(-1), respectively, in LiTF-PC electrolytes. There is no experimental evidence of the interaction between MG30 and PC. Competition between MG30 and PC on associating with lithium ion is studied, and the studies show that the interaction between MG30-LiTF is stronger than that of the PC-LiTF in plasticized polymer-salt complexes. The effect of PC on the ionic conductivity of the MG30-LiTF system is explained in terms of the polymer, plasticizer, and salt interactions. The temperature dependence of conductivity of the polymer films obeys the Vogel-Tamman-Fulcher relation. Values of conductivity and activation energy of the MG30-based polymer electrolyte systems are presented and discussed.