Miscibility and Conductivities of PEO/PMMA-LiClO4 Solid Polymer Electrolyte

Abstract

Thin films of poly (ethylene oxide) (PEO), poly (methyl methacrylate) (PMMA) and selected blends of PEO/PMMA with and without the addition of LiClO4 were prepared using solution casting technique. The presence of a single Tg which corresponds closely to that of the Gordon Taylor equation confirms the miscibility of both the salt-free and salt-doped blends. The Tgs and the ion conductivity (σ) at room temperature of PEO, PMMA and the PEO/PMMA blends generally increase with ascending salt concentration (Y). Variations in the σ value as a function of Y for all the three systems correlate closely with their respective Tg results. PMMA-salt complex records the lowest σ value at all salt concentrations. PEO/PMMA/LiClO4 blend with 75 wt% PEO exhibits the highest σ value of 5 x 10-7 S cm-1 at Y = 0.10. The σ value of the blend-salt system is observed to be slightly lower than that of the PEO-salt system. This is due to reduced segmental motion cause by increased Tg of the blend and a decrease in free ions in the amorphous phase of PEO as a small amount of the salt is solvated by PMMA in the blend. Therefore, the percolation path lies in the amorphous PEO rich phase of the blend.