Rheological, thermal and electrical properties of Poly(ethylene oxide) / MMT nanocomposites

Polyethylene oxide (PEO) has been used for several years as an electrolyte solvent in lithium polymer cells. One beneficial quality is its high viscosity, that remains high up to temperatures just short of its solid-state T_m, allowing the production of thin electrolyte layers. PEO batteries are sometimes preferred over lithium ion due to their greater power/weight ratio. PEO is a polar polymer and is water-soluble, which is beneficial for composite dispersion. Its solubility suggests that, with addition of a nanofiller during the solution phase, it could provide easily implemented high levels of dispersion. With the availability of many different average molecular weights it constitutes an ideal model system for studies. This paper details an investigation into the physical, thermal and electrical properties of PEO and PEO-MMT nanocomposites. Three different molecular weight PEO systems were used as the polymer matrix- 100,000 g mol^-1, 400,000 g mol^-1 and 1,000,000 g mol^-1. Properties investigated include-rheological behaviour of solutions; crystallisation and melting; the AC ramp breakdown strength and dielectric response. Dispersion was achieved during initial mixing and the solution stage in the rheometer. After previous investigations, this dispersion method has been seen to be acceptable.