Melting Point Of PEO Research Articles

High Conductivity in a Fluorine-Free K-Ion Polymer Electrolyte

Solid polymer electrolytes (SPEs) could play a major role in the transition to safer and high-energy-density potassium-based batteries. However, most polymeric K-ion electrolytes are based on fluorine-containing anions and flammable organic solvents, whose safety is nowadays in question. Herein, we report a facile solvent-free synthesis of a series of several poly(ethylene oxide) (PEO)-based SPE solid solutions with KBPh4 salt as potassium-ion source, including the formation of two crystalline (PEO)n/KBPh4 complexes. The ionic conductivity of these novel K-ion SPEs above and below the melting point of PEO is rationalized in light of their glass-transition temperature and chemical composition. We highlight that below the melting point of PEO, the crystalline complexes may not be intrinsically ionically conducting, but they act as ion sinks preventing the polymer cross-linking and the formation of contact ion pairs and lower the glass-transition temperature leading to a conductivity of 1.1 × 10–4 S cm–1 at 55 °C. A high ionic conductivity of 1.8 × 10–3 S cm–1 is achieved at 80 °C for the optimum (PEO)30/KBPh4 composition (3.2 mol % KBPh4). Besides, the SPE compositions were found to be stable up to 4 V vs K0 metal electrode at 60 °C. The (PEO)30/KBPh4 composite electrolyte employed in an all-solid-state symmetric cell with Prussian Blue electrodes showed reversible K+-ion (de)intercalation, where a reversible capacity of 20 mAh g–1 and low voltage hysteresis were achieved for 20 cycles. Considering the material availability, ease of synthesis, and promising electrochemical properties, this work may encourage future research on fluorine-free polymer electrolytes for K-ion batteries.

Ionic Conductivity Enhancement of Polymer Electrolytes by Directed Crystallization

We report that hot stretching of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) can lead to a preferred orientation of PEO crystalline lamellae, thereby reducing the tortuosity of the ion-conduction pathway along the thickness direction of the SPE film, causing improved ionic conductivity. The hot stretching method is implemented by stretching SPE films above the melting point of PEO in an inert environment followed by crystallization at room temperature while maintaining the applied strain. The effect of hot stretching on the crystalline orientation, crystallinity, morphology, and ion transport in PEO with two types of salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium triflate (LiCF3SO3), is investigated in detail. Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) show that the orientation of PEO crystalline lamellae induces the formation of a short ion-conduction pathway along the through-plane direction of the SPE films, leading to 1.4- to 3.5-fold enhancement in the through-plane ionic conductivity.

Influence of poly(ethylene oxide) sample preparation on the results of thermogravimetric analysis

Aim: To investigate whether the sample preparation process of poly(ethylene oxide) (PEO) affects kinetic analysis of the thermal degradation process. Kinetic analysis was performed to describe the course of a chemical reaction regardless of the reaction conditions and the reaction system complexity. One differential method, the Friedman method, and one integral Kissinger-Akahira-Sunose method (KAS), were applied in this work. Methods: The PEO sample was prepared in 4 different ways. Thermogravimetric analysis was performed to determine the thermal degradation of prepared samples. Infrared spectroscopic analysis was performed during the preparation of the PEO film obtained by casting from the solution. Results: Dynamic thermal decomposition of PEO, regardless of the method of preparation, takes place through a single decomposition stage, which is manifested by the appearance of one peak on derivative thermogravimetric (DTG) curve. During the preparation of the PEO film, the procedure was carried out at a temperature higher than its melting temperature (Tm=65°C). After the cooling, the obtained sample didn’t solidify and it had an intense odor of acetic acid, which was confirmed by infrared spectroscopic analysis. Samples III and IV were re-prepared at a temperature lower than the melting point of PEO, obtaining samples of satisfactory quality. Conclusion: In order to prepare poly(ethylene oxide) films by solution casting technique, drying should be carried out at temperatures below the melting point of PEO. If TG analysis of pure PEO powder is compared with the results of hot pressed samples and solution cast samples, it can be concluded that the preparation of the sample doesn’t affect the thermal stability of the PEO. The dependence of activation energy calculated by the differential Friedman and integral KAS method on conversion is constant for all samples in a broad conversion range, regardless of how the samples were prepared. The hot pressed samples and solution cast samples have lower activation energy than the commercial PEO powder.

Polyrotaxane: New Generation of Sustainable, Ultra-Flexible and Form-Stable Phase Change Materials

The development of thermal energy storage materials is the most attractive strategy to harvest the solar energy and increase the energy utilization efficiency. Phase change materials (PCMs) have received much attention in this research field for several decades. Herein, we reported a new kind of PCM micro topological structure, design direction, and the ultra-flexible form-stable PCMs, polyrotaxane. The structure of polyrotaxane was fully confirmed by 1H Nuclear Magnetic Resonance, Attenuated Total Reflection-Fourier Transform Infrared and X-ray diffraction. Then the tensile properties, organic solvent resistance, thermal stability, fire safety and phase change energy storage properties of the films were systematically analyzed. The results showed that all the mechanical performance, organic solvent resistance, thermal stability and fire safety of PLRs were enhanced significantly compared to those of PEO. Nevertheless, the form stability at temperatures above the melting point of PEO significantly increased with the α-CD addition. Further with the high phase transition enthalpy and excellent cycle performance, the polyrotaxane films are therefore promising sustainable and advanced solid-solid phase-change materials for thermal energy storage.

Toward ambient temperature operation with all-solid-state lithium metal batteries with a sp3 boron-based solid single ion conducting polymer electrolyte

The ionic conductivity decay problem of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) when increase the lithium salt of the SPEs up to high concentration is here functionally overcome by the incorporation of a charge delocalized sp3 boron based single ion conducting polymer electrolyte (SIPE) with poly(ethylene oxide) to fabricate solid-state sp3 boron based SIPE membranes (S-BSMs). By characterizations, particularly differential scanning calorimeter (DSC) and ionic conductivity studies, the fabricated S-BSMs showed decreased melting points and increased ionic conductivity as steadily increase the content of sp3 boron based SIPE, which significantly improved the low temperature performance of the all-solid-state lithium batteries. The fabricated Li | S-BSMs | LiFePO4 cells exhibit highly electrochemical stability and excellent cycling at temperature below melting point of PEO, which has never been reported so far for SIPEs based all-solid-state lithium batteries.

Blending with Non‐responsive Polymers to Incorporate Nanoparticles into Shape‐Memory Materials and Enable Photothermal Heating: The Effects of Heterogeneous Temperature Distribution

Blending a shape‐memory polymer (SMP) (e.g., thermoplastic polyurethane) with an immiscible carrier polymer (e.g., poly(ethylene oxide) (PEO) or poly(vinyl alcohol) (PVA)) containing dispersed metal nanoparticles (AuNPs) is a simple approach to enable actuation via photothermal heating. For blends containing up to 90% carrier polymer, the shape‐memory capability can be thermally triggered either conventionally or utilizing internal heating via application of light that is resonant with the particle's surface plasmon resonance. When incorporating nanoparticles in this manner, neither chemical modification of the shape‐memory moiety nor solvation of the SMP is necessary. Actuation times are determined by the particular heterogeneous temperature distribution, which generally occurs under both conventional and photothermal heating methods, but with different spatial patterns. Blending an SMP with PEO containing AuNPs imposes a higher transition temperature (the melting point of PEO), enabling heat generated within the nanoparticle‐containing regions to equilibrate throughout the sample, resulting in performance under photothermal conditions comparable with that achieved in a conventional heating approach. SMP:PVA blends actuate at the SMP transition temperature and the response depends on the size of phase segregation between the PVA and SMP; when decreasing the characteristic size of the segregated regions, heat is efficiently transferred and optimal photothermal performance is observed. image

Extrusion Processed Polymer Electrolytes based on Poly(ethylene oxide) and Modified Sepiolite Nanofibers: Effect of Composition and Filler Nature on Rheology and Conductivity

A series of poly(ethylene oxide) (PEO)/lithium trifluoromethanesulfonate(LiTf)/ethylene carbonate(EC)/sepiolite composite electrolytes have been prepared by melt compounding. Neat sepiolite, sepiolite coated with polyethylene glycol and with D-α-tocopherol polyethylene glycol 1000 succinate have been used as fillers, and nanocomposites with different ratio of the components have been prepared. The concentration of EC and LiTf has been progressively increased from low to high values and in this way, electrolytes with conductivities from 2×10−6 to 3×10−4 S cm−1 at 30°C have been prepared. Together with conductivity, viscoelasticity has also been studied, evidencing a complex rheological behaviour which depends on the type of filler introduced in the blend. Some of the thermoplastic electrolytes are seen to display a liquid-like conductivity together with solid-like mechanical properties over the melting point of PEO. The solid-like performance is featured by shear moduli crossover G’=G” at 75°C at very low frequencies. This combination of properties makes them appealing starting points for the development of solid polymer electrolytes.

Effective Morphology Control in an Immiscible Crystalline/Crystalline Blend by Artificially Selected Viscoelastic Phase Separation Pathways

We investigated the interplay between viscoelastic phase separation (VPS) and crystallization in a dynamically asymmetric crystalline/crystalline polymer blend system of poly(butylene succinate) (PBS)/poly(ethylene oxide) (PEO). The dynamic asymmetry came from the large molecular weight difference between the slow relaxing PEO and the fast relaxing PBS molecules. The evolution of network-like structures, phase inversion, and volume shrinking processes were studied by a phase contrast microscope (PCOM). The crystallization kinetics of PBS was determined by a differential scanning calorimeter (DSC). It was found that both the crystal nucleation and growth of PBS were strongly influenced by the existence and relaxation of the entangled PEO network, even though PEO was the minor component. The nuclei of PBS were more inclined to form at the interface between phase domains due to the effect of interface-assisted crystallization. Thus, the nucleation density decreased with the decrease of interfacial area. Meanwhile, the corresponding crystal growth rate was also dependent on the VPS processes. After a second quench to a temperature below the melting point of PEO, the spatial distribution of both components and the final crystallization morphology were also significantly controlled by the initial phase structures. Compared to dynamically symmetric polymer systems, the VPS process provided more versatile pathways to control the phase and crystallization morphologies in such immiscible crystalline/crystalline polymer blends.

Relation between structural and conductivity relaxation in PEO and PEO based electrolytes

The effect of a lithium salt on the general polymer dynamics of poly( ethylene oxide) (PEO) and how these dynamical alterations affect the ionic conductivity and structural relaxations in (PEO)(4):LiClO4 have been investigated. The study was based on differential scanning calorimetry (DSC) and dielectric relaxation studies. The DSC studies indicated an increased glass transition temperature of (PEO)(4):LiClO4 as compared to that of PEO. The polymer-salt complex exhibited enhanced conductivity of sigma(D.C). = 3.2 x 10(-7) S . cm(-1) at room temperature (298 K) due to the presence of mobile Li+ ions. Impedance data have been scaled and analyzed under conductivity and modulus formalisms over wide ranges of frequency and temperature for both PEO and (PEO)(4):LiClO4. For PEO, the analysis of the scaled formalisms indicates that both the conductivity and the structural relaxation mechanisms are temperature-independent above the melting point of PEO. However, below the melting point, the nucleation and growth of spherulites and also the formation of 'interphase' regions in PEO result in a hindered long range D.C. conductivity, which, in turn, leads to a decoupling of the D.C. conductivity and the structural relaxation. However, for (PEO)(4):LiClO4, by comparing the conductivity relaxation data with the calorimetric glass transition and analysis of scaled formalisms, a direct coupling between Li+ ion motions and polymer segmental dynamics is observed for the polymer electrolyte.

Dynamics of Poly(ethylene oxide) around Its Melting Temperature

This study has focused on the ionic conductivity (of impurities) and the changes in relaxation behavior of semicrystalline poly(ethylene oxide) (PEO) around its melting temperature of the crystalline regions. Our main aim was to understand the implications of nucleation and growth of spherulitic structures on the general dynamical properties of the polymer chains and how these dynamical alterations affect the ionic conductivity. Impedance data have been scaled and analyzed under conductivity and modulus formalisms over wide ranges of frequency and temperature. The analysis of the scaled formalisms indicates that both the conductivity and the structural relaxation mechanisms are temperature independent above the melting point of PEO. However, below the melting, point, the slow crystallization of PEO leads to growth of spherulites and also to the formation of interphase regions. These morphological changes result in a hindered long-range dc conductivity, which, in turn, leads to a decoupling of the dc conductivity and the structural relaxation below the melting point of PEO.

Significantly Accelerated Spherulitic Growth Rates for Semicrystalline Polymers through the Layer-by-Layer Film Method

The influence of a molten liquid polymer layer on the crystallization of the beneath semicrystalline polymer has been seldom considered. In the study, the nucleation and growth of spherulites for the beneath polylactide (PLA) layer in poly(ethylene oxide)/polylactide (PEO/PLA) double-layer films during isothermal crystallization at various temperatures above the melting point of PEO have been investigated by using polarized optical microscopy, with the particular results compared with that for neat PLA and PLA/PEO blend films. It is interesting to find that the top covering molten PEO layer can greatly accelerate the spherulitic growth rate (G) of the beneath PLA layer. Another significant result is that the temperature for the measurable nucleation and spherulitic growth of PLA in the double-layer films can be eventually pushed down close to the glass transition temperature of neat PLA. The changes of glass transition temperature, Tg, for PEO/PLA multilayer films have been measured by using modulated dif...

Effect of lower critical solution temperature phase separation on crystallization kinetics and morphology of poly(butylenes succinate)/poly(ethylene oxide) blend

The crystalline/crystalline polymer blend of poly(butylenes succinate)/poly(ethylene oxide) (PBS/PEO) exhibited lower critical solution temperature (LCST) phase separation behavior at temperatures above the melting point of PBS, which was measured by phase contrast optical microscopy (PCOM) technique. In this work, we determined the LCST phase diagram of PBS/PEO blends, and then investigated the effect of liquid–liquid phase separation (LLPS) on the crystallization kinetics and morphologies of PBS/PEO (40/60 wt/wt) blend. Based on polarized optical microscopy (POM), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC) results, we found that the spherulite morphology and crystallization kinetics of PBS were strongly influenced by the initial LLPS structure; because the kinetics of liquid–liquid phase dissolution was much slower than that of crystallization. The effect of LLPS on the primary nucleation density and crystal growth rate of PBS were strongly dependent on the crystallization temperature of PBS. After a second quench to a temperature below the melting point of PEO, the fractionated crystallization of PEO was observed. The competition between the kinetics of LLPS and the driving force of PBS crystallization controlled the spatial distribution of PEO in PBS spherulites, thus essentially determined the confined conditions of the PEO crystallization. The results indicated that the LLPS was an effective process to control the crystallization kinetics and morphology in crystalline/crystalline polymer blend systems.

Phase diagram of polymer electrolyte: (x)(PEO) – ( 1-x)CF3COOLi

Solid polymer electrolytes based on poly(ethylene oxide) (PEO) and lithium trifluoroacetate (CF3COOLi) were prepared by a solvent casting method by different concentrations of salt. The membranes resulting of slow evaporation were analyzed by differential scanning calorimetry (DSC) and its phase diagram was drawing for a second thermal scan. The DSC curves on the first thermal cycle show three anomalies at 303, 338 and 393 K, that are slightly shifted with the salt content. For high concentrations, the intensity of the endothermic peak associated with the melting point of PEO (338 K) decreases, that one for the third transition increases with the salt content, the second peak (melting point of PEO) disappear when the concentration reaches the value of X = 0,405 (given in fraction of mass: salt/(salt + polymer)). These results and the change of conductivity demonstrate the formation of a new complex between the PEO and the CF3COOLi.

Crystallization and Morphology in a 30/70 Poly(ethylene succinate-co-6 mol % butylene succinate)/Poly(ethylene oxide) Blend

Crystallization and morphology were studied in a 30/70 poly(ethylene succinate-co-6 mol % butylene succinate)/poly(ethylene oxide) (P(ES-co-6 mol % BS)/PEO) blend in this work. Depending on the crystallization conditions, including one-step and two-step crystallization, both components may crystallize separately or simultaneously. P(ES-co-6 mol % BS) and PEO crystallized separately via two-step crystallization. When the crystallization temperature was between the melting points of the two components, both the spherulitic growth rate and the overall crystallization rate of P(ES-co-6 mol % BS) decreased with increasing crystallization temperature; moreover, they were slower in the blend than in neat P(ES-co-6 mol % BS) at the same crystallization temperature. When the crystallization temperature was further lowered below the melting point of PEO, PEO crystallized only as tiny crystals within the P(ES-co-6 mol % BS) spherulites formed earlier, while its overall crystallization rate was increased significantl...

Effects of a Block Copolymer as Multifunctional Fillers on Ionic Conductivity, Mechanical Properties, and Dimensional Stability of Solid Polymer Electrolytes

Solid polymer electrolytes with high ionic conductivities, good mechanical properties, dimensional stability, and easy processability were obtained from poly(ethylene oxide)-block-polyethylene (PEO-b-PE)-loaded poly(ethylene oxide) (PEO)/lithium perchlorate (LiClO(4)). In this article, we reported that the ionic conductivity and mechanical properties were remarkably increased due to the addition of the PEO-b-PE compared to that of PEO/LiClO(4) electrolyte. Scanning electron microscope (SEM), optical micrograph, and X-ray diffraction (XRD) results indicate that the addition of the copolymer, PEO-b-PE, decreased the defects of the PEO electrolyte films. Good dimensional stability was observed by dynamic rheological techniques up to 100 °C (higher than the melting point of PEO, 65 °C). A bicontinuous phase structure, that is crystalline PE domains within a matrix of PEO/salt, was proposed as the mechanism for such comprehensive enhancements in the ionic conductivity, mechanical properties, and dimensional stability obtained simultaneously in this study through a facile approach based on incorporation of a copolymer.

Enhanced ionic conductivity in PEO/PMMA glassy miscible blends: Role of nano‐confinement of minority component chains

AbstractAC impedance spectroscopy was used to investigate the ionic conductivity of solution cast poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends doped with lithium perchlorate. At low PEO contents (below overlap weight fraction w*), ionic conductivities are almost low. This could be due to nearly distant PEO chains in blend, which means ion transportation cannot be performed adequately. However, at weight fractions well above w*, a significant increase in ionic conductivity was observed. This enhanced ionic conductivity mimics the PEO segmental relaxation in rigid PMMA matrix, which can be attributed to the accelerated motions of confined PEO chains in PMMA matrix. At PEO content higher than 20 wt % the conductivity measured at room temperature drops due to crystallization of PEO. However by increasing temperature to temperatures well above the melting point of PEO, a sudden increase of conductivity was observed which was attributed to phase transition from crystalline to amorphous state. The results indicate that some PEO/PMMA blends with well enough PEO content, which are structurally solid, can be considered as an interesting candidate for usage as solid‐state electrolytes in Lithium batteries. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2065–2071, 2010

Microphase-Separated Brushes on Square Platelets in PS-b -PEO Thin Films

In polystyrene-block-poly(ethylene oxide) thin films, microphase-separated brushes on the square platelets can be obtained via fast solvent evaporation by controlling the tethering density (0.08 < σ < 0.11). The tethering density of the brushes is proportional to the thickness of the PEO crystal and increases with increasing initial solution heating temperature (T(i) ). When T(i) < T(m) , where T(m) is the melting point of PEO, brushes with microphase-separated structures are observed. The formation of microphase-separated brushes depends on two factors: the strong incompatibility between PS and noncrystalline PEO chains (attached to the crystalline PEO) and the weak interaction between PS-PS brushes.

Crystallization-induced switching of the morphology of poly(ethylene oxide)-block-polybutadiene micelles

We studied the morphology of micelles formed by a well-defined poly(1,2-butadiene)-block-poly(ethylene oxide) diblock copolymer (PB-b-PEO). Dissolved in n-heptane at 70 °C, that is, above the melting point of PEO, spherical micelles are formed due to the selectivity of the solvent for the PB-block. If the solutions are cooled down to low temperatures, the liquid PEO-block crystallizes within the cores of the spherical micelles that remain stable. If, however, the solutions are quenched to 30 °C, the spherical micelles aggregate to a novel meander-like structure within several minutes. In its final state, the meander-like super-structure is crystalline, as revealed by time-resolved wide-angle X-ray scattering. The super-structure is shown to result from crystallization-induced aggregation of spherical micelles. Moreover, crystallization leads to well-defined angles between subsequent aggregating units. A quantitative Avrami-type analysis of the crystallization kinetics demonstrates that the formation of the meander-type structure resembles a 2D growth process combined with a breakout crystallization, showing an Avrami-exponent of 2.5. In contrast to this, crystallization at low temperatures resembles a confined crystallization with a low Avrami-exponent of 0.7. All data demonstrate that the morphology of block copolymers having a crystallizable block can be switched by the competition of aggregation and crystallization.

Spherulitic morphology and crystallization kinetics of melt-miscible blends of poly(3-hydroxybutyrate) with low molecular weight poly(ethylene oxide)

The spherulitic morphology and crystallization kinetics of the blends of poly(3-hydroxybutyrate) (PHB) with the low molecular weight poly(ethylene oxide) (PEO) prepared by the solution casting have been investigated by differential scanning calorimetry and polarized optical microscopy. The blend was a crystalline/amorphous system when temperatures lie between the melting point of PEO (T m PEO = ca. 60 ° C) and that of PHB (T m PHB = ca. 170 ° C), while it became a crystalline/crystalline system below T m PEO. With PHB crystallization at the crystallization temperature ( T c) of 70 °C, the blends showed PHB banded spherulitic texture, which could be perturbed by the subsequent PEO crystallization in PEO-rich compositions upon further cooling to room temperature. When PHB and PEO were allowed to crystallize upon quench from melt to room temperature, fairly competitive crystallization emerged where crystallization and segregation of PHB and PEO may occur simultaneously, leading to a complicated spherulitic morphology. As for the results of crystallization kinetics, the PHB crystallization exothermic temperature ( T f PHB ) on cooling, PHB spherulitic growth rate ( G PHB), and overall crystallization rate of PHB ( k n ) exhibited maxima in their dependences of PEO composition. This was attributed to the coupling between enhanced chain mobility and depression in equilibrium melting point ( T m 0), since the low molecular weight PEO has a very low glass transition temperature ( T g) over the T c range studied, G PHB increased with T c but k n was found to decrease. The drop of k n with increasing T c was therefore predominately governed by the large depression in nucleation rate at higher T c.

Electrochemical and solid state NMR characterization of composite PEO-based polymer electrolytes

A comprehensive matrix of composite poly(ethyleneoxide) (PEO)-based solid-state electrolytes was developed in order to systematically study a number of variables and their impact upon the electrochemical properties of the resulting materials. The different parameters studied in the fabrication of these materials include: (i) the lithium electrolyte salt type, (ii) the ether oxygen to lithium ratio, (iii) the molecular weight of PEO, (iv) the type of ceramic additive used, either aluminum oxide (Al 2O 3), silicon oxide (SiO 2), or titanium oxide (TiO 2), (v) the particle size of the additives used, and (vi) the concentration of additive (wt.%). The standard lithium salt used for the preparation of these electrolytes was lithium trifluoromethanesulfonate (lithium triflate or LiSO 3CF 3), which served as the baseline electrolyte salt. Other lithium salts investigated include: lithium perchlorate (LiClO 4) and lithium bis-trifluoromethanesulfonimide (LiN(SO 2CF 3) 2). Conductivity measurements were performed for each electrolyte membrane over a wide temperature range (23–100 °C). In addition, cyclic voltammetry measurements were performed on selected PEO membranes as a function of temperature to determine the impact of various parameters upon the electrochemical stability. It was observed that the parameter that displayed the most significant effect upon the PEO-base polymer conductivity was the lithium salt type employed. The lithium triflate salt-containing PEO polymers demonstrated the best mechanical properties before and after heat treatment. Ceramic fillers also appear to enhance the mechanical properties of PEO polymer electrolytes at temperatures above the melting point of PEO (60–70 °C). In addition to investigating the electrochemical characteristics of the composite membrane, solid state 7Li NMR characterization was performed to study ionic mobility by measuring spectral line widths and lithium self-diffusion coefficients. It was determined that ceramic nanoparticle additives can enhance the Li + diffusivity without a corresponding increase in polymer segmental mobility.