Influence of molar mass on the thermal properties, conductivity and intermolecular interaction of poly(ethylene oxide) solid polymer electrolytes

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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.

“…PEO 1 at Y S = 0.15) in reducing the melting temperature of PEO to around 60 °C or below (data after Ref. ), the sample moves towards liquid‐like behavior.…”

Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Harun

Chan

Guo

2017

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Thermal Properties and Morphology of Poly(ethylene oxide)/Poly(n‐butyl methacrylate) Blends

Ramli

Chan

Ali

2018

From the thermodynamic point of view, most of the high molar‐mass binary polymer blends are immiscible due to the entropic contribution to the free energy of mixing is relatively small. The miscibility of the systems on the molecular scale can be assessed by the thermal properties such as quantities of glass transition temperature (Tg) and change in heat capacity (ΔCp) of the polymers. For a semi‐crystalline polymer such as poly(ethylene oxide) (PEO), the crystallinity (X*) and the melting temperature (Tm) can also give some hints on the miscibility. Apart from the thermal properties, additional scientific findings such as morphology of the blends are needed as supplementary evidences to support the results. We focus on the PEO as the polymer host, blends with poly(n‐butyl methacrylate) (PnBMA) which were prepared using solution casting technique. Thermal properties of PEO/PnBMA polymer blends were investigated by modulated differential scanning calorimeter (MDSC) on the isothermal crystallized samples at 25 °C. Tg of PEO in the blends do not show significant variation with addition of PnBMA for entire composition range while for Tg of PnBMA in the blends, it is challenging to be estimated under the experimental condition due to the overlapping of the Tg of PnBMA and melting endotherm of PEO. Constancy of quantity Tg of PEO and ΔCp of PEO corresponding to the content of PEO in the blends suggest that PEO and PnBMA are immiscible for entire blend composition. X* and Tm of PEO in the blends show insignificant variation in PEO/PnBMA blends, when PEO as major component. This implies that these blends are immiscible under the experimental conditions as agreed with results of Tg and ΔCp. Spherulitic morphologies of PEO in the blends were studied by polarized optical microscopy (POM). PnBMA phase disperses randomly in PEO matrix when PEO in excess. The absence of significant change for the fibrillar spherulitic structures of PEO spherulites with addition of PnBMA (when PEO is the major component) suggests that immiscibility of PEO and PnBMA. Besides, the crystalline structure of PEO in PEO/PnBMA blends using X‐ray diffraction (XRD) reveals that the crystalline structure of PEO is not disturbed with the addition of PnBMA when PEO is in excess as the two distinct peaks of PEO do not shift as compared to neat PEO. Impedance spectroscopy (IS) studies show that the ionic conductivities (σDC) of the polymer blends at room temperature slightly increase with increasing of PEO with the order of magnitude of 10−11–10−10 S cm−1. This system serves as a potential polymer host as solid polymer electrolytes when added with inorganic salt.

Thermal Properties and Morphological Studies of Poly(ethylene oxide) with the Addition of Salt or Nanofiller

Yusoff

Halim

Tarmizi

et al. 2023

The increasing demand of the functional polymers in the global industry has led to extensive development of new polymeric materials with enhanced properties. This work focuses on the effect of addition of lithium perchlorate (LiClO 4 ) or titanium dioxide (TiO 2 ) on the thermal properties (i.e., glass transition temperature [T g ], change in heat capacity [𝚫C P ], crystallinity [X * ], melting temperature [T m ]) and morphology of poly(ethylene oxide) (PEO) investigated by using differential scanning calorimetry (DSC) and polarized optical microscope (POM). The T g and 𝚫C P of PEO at a mass fraction of salt, W S ≤ 0.0196, increase with the addition of salt. Whereas the values of crystallinity and T m of PEO at the same salt fraction decrease slightly with increasing salt fraction, suggesting the presence of an interaction between the salt molecules and PEO matrix. However, at W S ≥ 0.107, the T g , crystallinity, and T m of PEO decrease significantly with the addition of salt, suggesting the phase separation of the binary mixtures of PEO and salt into salt-rich and salt-poor phases are developed. This observation is supported by optical inspections where the salt precipitations can be seen. Meanwhile, the values of T g , 𝚫C P , crystallinity, and T m of PEO show insignificant changes with increasing nanofiller fraction indicating no interaction between PEO and the nanofiller. The two-phase of PEO and nanofiller in the PEO-TiO 2 can be observed clearly from the optical inspection for all PEO-nanofiller compositions. Hence, the addition of LiClO 4 at low content exhibits relatively prominence on the PEO matrix than the TiO 2 . LiClO 4 possesses better molecular interaction with PEO than TiO 2 with PEO.