Rheology and Microscopic Heterogeneity of Poly(ethylene oxide) Solid Polymer Electrolytes

Abstract

Lack of precise thermal control in poly(ethylene oxide) (PEO)‐based solid polymer electrolytes (SPEs) with molar masses well above M > 104 g mol−1 during preparatory stage often demonstrates molar mass dependence on thermal properties and ionic conductivities. In the earlier study, PEO‐based SPEs were heated under inert atmosphere above the melting temperature of PEO and then cooled down for subsequent isothermal crystallization. The system demonstrates insignificant variation with respect to molar mass of PEO at constant salt concentration for thermal properties, ionic conductivity and intermolecular interaction. Here, we report the subsequent results of rheology and microscopic heterogeneity as a function of PEO molar mass (Mɳ = 3 × 105 and 4 × 106 g mol−1) and lithium salt concentration (0–13 wt.%). Above the solubility limit of PEO, the glass transition studied using differential scanning calorimetry shows the presence of microscopic heterogeneity of the systems as indicated by the change in enthalpy of endothermic overshoot near the endset of glass transition. Rheological parameters were measured over a wide range of frequency (0.01 to 100 Hz) at different temperatures (30, 60 and 80 °C) using parallel plate geometry. Melt rheology system reveals that neat PEO at 80 °C exhibits restriction in the long‐range motion of the chains. When incorporated with salt, it exhibits further deviation from the terminal viscoelastic relaxation behaviour. This study agrees with our previous findings that influence of molar mass of PEO in this range is insignificant on the melt rheology and microscopic heterogeneity at constant salt concentration.

Correlation of thermal, morphological and melt rheological properties of miscible poly(ethylene oxide)/poly(methyl acrylate) and immiscible poly(ethylene oxide)/poly(n‐butyl methacrylate) blends

“…This observation is in agreement with the deviation in the power law for G′ . The observation for PEO in this study is in agreement with reported work (PEO, M η = 300 000 g mol −1 , T g = −58 °C, at 80 °C; 86 PEO, M η = 300 000 g mol −1 , T g = −58 °C, at 140 °C; 54 and PEO, M w = 932 000 g mol −1 and 610 000 g mol −1 measured at T = 105 and 75 °C, respectively 87 ). Additionally, work on the light scattering technique has also reported on the heterogeneity of molten PEO on a microscopic scale due to the structured random network formed by extensive inter‐ and intra‐polymers 12,88 .…”

Melt Rheological Behavior and Morphology of Poly(ethylene oxide)/Natural Rubber-graft-Poly(methyl methacrylate) Blends

“…This observation is in agreement with light scattering studies reported by Walter et al [6] and Walkenhorst et al [41], where they observed the PEO melt was not uniform on the microscopic scale due to the structured random network formed by extensive inter-and intrapolymer connections. A rheological study on PEO (M w = 300,000 g•mol −1 ; T g = −57 • C) measured at T = 80 • C also reported deviations in both G and G from terminal viscoelastic relaxation, which indicated the restrictions of the long-range motion of PEO (data are listed in Table 2) [42]. Furthermore, the heterogeneities of PEO can also be observed using impedance spectroscopy at 25 • C by adding very low salt concentrations (e.g., 0.05 wt %) due to the formation of a percolation network of conductive (polymer-poor) and dielectric (polymer-rich) domains [10].…”

Rheology of Concentrated Polymer/Ionic Liquid Solutions: An Anomalous Plasticizing Effect and a Universality in Nonlinear Shear Rheology

“…Rheological behavior of PEO is accordingly tuned by the content of salts. Harun et al [71] studied the calorimetry and rheology of PEO-lithium salt mixtures. They found T g increases with salt content, and the terminal relaxation is extended and broadened.…”