Anelastic relaxations and molecular motions in polymeric electrolytes

A study of the frequency (0.1-30 Hz) and temperature (120-373 K) behavior of the internal friction and of the dynamic modulus was carried out in polyethylene oxide (PEO)-Ba(SCN)2 polymeric electrolytes. The mechanical spectra reveal the presence of the following anelastic relaxations: (a) the ? process due to localized movements within the main chain, (b) a process due to relaxing particles introduced by salt, and (c) the ?a process associated to the glass-rubber like transition. Both the ?- and ?a -loss peaks are shifted to higher temperatures by the addition of salt. A careful analysis of the observed peculiarities permits us to gain an insight on the microscopic nature of the relaxation mechanisms and to associate the ? relaxation with localized segmental motion within the amorphous phase. In pure PEO and in the complex with the lowest salt content, the loss due to the melting transition of PEO crystals is also observed. The cited loss is lacking in the complexes with a salt molar fraction X>0.05, which show an enormous enhancement of the strength of the ?a relaxation. It is argued that the addition of a salt with a divalent cation to semicrystalline PEO gives rise to completely amorphous single phase structures.