Ionic transport and glass transition temperature of polyether–salt complexes: dependence on molecular mass of polymer

Abstract

Poly(ethylene oxide) (PEO) of different molecular masses (Mη = 6×105, 1×106 and 4×106 g mol−1) and lithium perchlorate complexes were prepared by solution casting method. The salt concentrations of the samples were varied between 2 and 23 wt-%. Room temperature (30°C) conductivity, glass transition temperature and Fourier transform infrared spectroscopy (FTIR) for the samples are reported. The conductivities acquired at 13 wt-% salt concentration for PEO with Mη = 6×105, 1×106 and 4×106 g mol−1 are 9×10−6, 1×10−4 and 7×10−4 S cm−1 respectively. This indicates that higher molecular mass PEO samples exhibit higher conductivity. An interesting trend is found for variation in glass transition temperature Tg with variation in concentration of complexing salt. It shows a linear variation until ∼13 wt-% and then slowly levels off. The slope of the linear region is found to be dependent on the polymer molecular masses. The rise in Tg for each salt concentration increases linearly with ascending molecular mass of PEO. This suggests that PEO with higher molecular mass exhibits greater extent of complexation with LiClO4 as supported by FTIR studies.