Properties of Graphene/Waterborne Polyurethane Nanocomposites Cast from Colloidal Dispersion Mixtures

Nanocomposites of waterborne polyurethane (WPU) reinforced with functionalized graphene sheets (FGSs) were effectively prepared by casting from a colloidal dispersion of FGS and WPU, and the morphology and physical properties were examined. The finer aqueous FGS dispersions or WPU with smaller particles yielded nanocomposites with enhanced electrical conductivity and thermal resistance due to finely dispersed FGS. The FGS nucleated the crystallization of the polycaprolactone (PCL) segments in WPU and improved its modulus. However, FGS inhibited crystal growth and deteriorated the tensile properties at high deformation, i.e., tensile strength and elongation at break, because the interaction between FGS and WPU hindered the chain rearrangement of WPU in the nanocomposite.     

Poly(ethylene oxide)-lithium difluoro(oxalato)borate new solid polymer electrolytes: ion–polymer interaction,structural, thermal,and ionic conductivity studies

Solid polymer electrolytes based on high molecular weight poly(ethylene oxide) (PEO) complexed with lithium difluoro(oxalato)borate (LiDFOB) salt in various EO:Li molar ratios from 30:1 to 8:1 were prepared by using solution casting technique. Ion–polymer interaction, structural, thermal, and ionic conductivity studies have been reported by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarized optical microscopy (POM), differential scanning calorimeter (DSC), and impedance analysis. FTIR spectral studies suggested that the interaction of Li⁺ cations with the ether oxygen of PEO, where a triple peak broad band centered at 1105 cm^?1, corresponds to C–O–C stretching and extreme deformation occurs. XRD, POM, and DSC indicated that the inclusion of LiDFOB salt could reduce the crystallinity of PEO. The melting temperature of PEO shifted to lower temperature side by the addition of LiDFOB. The glass transition temperature obtained for the system 10:1 was ?38.2 °C. An increase in the ionic conductivity from 3.95?×?10^?9 to 3.18?×?10^?5 S/cm at room temperature (23 °C) was obtained through the addition of LiDFOB to a high molecular weight PEO. In addition, the ionic conductivity of the polymer electrolyte films followed an Arrhenius relation, and the activation energy decreased with increasing LiDFOB concentration.     

Dielectric relaxation in PEO-based polymer electrolytes

Dielectric properties of cross-linked poly(ethylene oxide) (PEO) with different mesh sizes, doped with lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), have been studied in frequency region between 0.1 and 10⁷ Hz and in broad temperature range. Results were compared with linear PEO of 1000 g/mol. Dielectric responses of the systems are dependent on frequency and thermally activated. Systems exhibit different responses in semi-crystalline and molten state. Increase of temperature promotes polarization; whereas, increase of frequency lessens it. In other words, polarization is thermally activated and local conductivity reduced. Generally, one observes enhanced dc conductivity in linear PEO as compared to cross-linked PEO at high temperature and the opposite at low temperature. Resonance responses are observed in low-molecular cross-linked PEO and in linear PEO at low temperature. These responses lead to splitting of polarization relaxation at frequencies beyond low-frequency range. Salt-comprising systems display only relaxation-type dielectric response. Imaginary parts of response spectra show distribution of relaxation times. It turns out that this distribution is independent of temperature in the low-frequency range, but depends on concentration of salt in the cross-linked polymer. In both systems, neat cross-linked and linear polymer of low-molecular mass, one observes coexistence of non-local and local motions of charged entities even at very low temperature.     

Conductivity studies on PEO:NaClO3 electrolyte system with different plasticizers

A new ion conducting solid polymer electrolyte thin film based on Polyethylene oxide (PEO) with NaClO₃ salt is prepared by solution-casting method. The solvation of salt with PEO has been confirmed by X-ray diffraction and IR spectral studies. Plasticizer effects were studied in PEO:NaClO₃ system by using low molecular weight polyethylene glycol (PEG), dimethyl formamide (DMF) and propylene carbonate(PC). AC conductivity in the temperature range (308–378 K) was measured to evaluate the conductivity of the polymer electrolytes. From the conductivity data, it was found that the conductivity value of pure PEO increases 10²–10⁴ order of magnitude with the addition of salts as well as plasticizers. From the transference number experiments, it was confirmed that the charge transport in these electrolyte is mainly due to the ions (t_ion≈0.94). Finally, the conductivity value of all PEO: NaClO₃ systems were compared.     

Modeling and simulation of Li-ion conduction in poly(ethylene oxide)

Polyethylene oxide (PEO) containing a lithium salt (e.g., LiI) serves as a solid polymer electrolyte (SPE) in thin-film batteries and its ionic conductivity is a key parameter of their performance. We model and simulate Li⁺ ion conduction in a single PEO molecule. Our simplified stochastic model of ionic motion is based on an analogy between protein channels of biological membranes that conduct Na⁺, K⁺, and other ions, and the PEO helical chain that conducts Li⁺ ions. In contrast with protein channels and salt solutions, the PEO is both the channel and the solvent for the lithium salt (e.g., LiI). The mobile ions are treated as charged spherical Brownian particles. We simulate Smoluchowski dynamics in channels with a radius of ca. 0.1 nm and study the effect of stretching and temperature on ion conductivity. We assume that each helix (molecule) forms a random angle with the axis between these electrodes and the polymeric film is composed of many uniformly distributed oriented boxes that include molecules with the same direction. We further assume that mechanical stretching aligns the molecular structures in each box along the axis of stretching (intra-box alignment). Our model thus predicts the PEO conductivity as a function of the stretching, the salt concentration and the temperature. The computed enhancement of the ionic conductivity in the stretch direction is in good agreement with experimental results. The simulation results are also in qualitative agreement with recent theoretical and experimental results.     

Modeling and simulation of Li-ion conduction in poly(ethylene oxide)

Polyethylene oxide (PEO) containing a lithium salt (e.g., LiI) serves as a solid polymer electrolyte (SPE) in thin-film batteries and its ionic conductivity is a key parameter of their performance. We model and simulate Li⁺ ion conduction in a single PEO molecule. Our simplified stochastic model of ionic motion is based on an analogy between protein channels of biological membranes that conduct Na⁺, K⁺, and other ions, and the PEO helical chain that conducts Li⁺ ions. In contrast with protein channels and salt solutions, the PEO is both the channel and the solvent for the lithium salt (e.g., LiI). The mobile ions are treated as charged spherical Brownian particles. We simulate Smoluchowski dynamics in channels with a radius of ca. 0.1 nm and study the effect of stretching and temperature on ion conductivity. We assume that each helix (molecule) forms a random angle with the axis between these electrodes and the polymeric film is composed of many uniformly distributed oriented boxes that include molecules with the same direction. We further assume that mechanical stretching aligns the molecular structures in each box along the axis of stretching (intra-box alignment). Our model thus predicts the PEO conductivity as a function of the stretching, the salt concentration and the temperature. The computed enhancement of the ionic conductivity in the stretch direction is in good agreement with experimental results. The simulation results are also in qualitative agreement with recent theoretical and experimental results.     

A novel PEO-based blends solid polymer electrolytes doping liquid crystalline ionomers

A novel PEO-based blends solid polymer electrolytes doping liquid crystalline ionomers (LCI), PEO/PMMA/LiClO₄/LCI, and PEO/LiClO₄/LCI were prepared by solution casting technology. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) analysis proved that LCI uniformly dispersed into the solid electrolytes and restrained phase separation of PEO and PMMA. Differential scanning calorimetry (DSC) results showed that LCI decreases the crystallinity of blends solid polymer electrolytes. Thermogravimetric analysis (TGA) proved LCI not only improved thermal stability of PEO/PMMA/LiClO₄ blends but also prevent PEO/PMMA from phase separation. Infrared spectra results illustrated that there exists interaction among Li⁺ and O, and LCI that promotes the synergistic effects between PEO and PMMA. The EIS result revealed that the conductivity of the electrolytes increases with LiClO₄ concentration in PEO/PMMA blends, but it increases at first and reaches maximum value of 2.53?×?10^?4 S/cm at 1.0 % of LCI. The addition of 1.0 % LCI increases the conductivity of the electrolytes due to that LCl promoting compatibility and interaction of PEO and PMMA. Under the combined action of rigidity induced crystal unit, soft segment and the terminal ionic groups in LCI, PEO/PMMA interfacial interaction are improved, the reduction of crystallinity degree of PEO leads Li⁺ migration more freely.     

Effect of liquid crystal ionomer intercalated montmorillonite nanocomposites on PEO/PLA solid polymer electrolytes

A series of solid polymer electrolytes (SPEs) based on poly (ethylene oxide)/polylactic acid (PEO/PLA) with liquid crystal ionomer (LCI) intercalated montmorillonite (MMT) nanocomposites (LCI-MMT) has been prepared by solution blending method. The effects of LCI-MMT on the structural, crystallization, thermal, and ionic conductivity properties of solid polymer electrolytes have been analyzed. It is demonstrated that the incorporation of LCI-MMT into the blend suppressed the crystallinity of PEO and increased the crystallinity of PLA. The maximum ionic conductivity is found to be in the range of 1.05?×?10^?5 S/cm for 0.5 wt% LCI-MMT, which is higher than that of the LCI-MMT-free polymer electrolyte (5.36?×?10^?6 S/cm) at room temperature.     

Dielectric spectroscopy and viscosity studies of aqueous poly(ethylene oxide) and poly(vinyl pyrrolidone) blend

The complex dielectric function, electric modulus, impedance and ac electrical conductivity behaviour of aqueous solutions of 5 wt% poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) (PVP) and their different volume percent blends were investigated in the frequency range 20 Hz to 1 MHz at 15, 30 and 45 °C. It is found that the real part of dielectric function of these blends at 1 MHz decreases with the increase of PEO concentration and their dc electrical conductivity has strong correlation with the electrode polarization relaxation time. The static permittivity, ionic conductivity, electrode polarization relaxation time and apparent viscosity have linear behaviour with temperature variation at fixed volume concentration of the aqueous polymers blend. The viscosity of these aqueous polymeric blends increases with the increase of PEO concentration. The behaviour of hydrogen bond interactions between the polar segments of PEO and PVP were explored from the comparative change in dielectric parameters and viscosity of the two phase aqueous polymeric systems.     

Effect of nanofillers on thermal and transport properties of potassium iodide–polyethylene oxide solid polymer electrolyte

In order to enhance the ionic conductivity of polyethylene oxide (PEO)–KI(80:20) based alkaline polymer electrolytes, nanosized inorganic filler ZnS has been incorporated into PEO–KI matrix and the corresponding nanocomposite polymer electrolytes are synthesized by the usual solution casting procedure. Atomic force microscope image of composite polymer electrolyte exhibits that the introduction of ZnS nanoparticles changes the surface morphology and aggregates them to form an arborization pattern. The prepared nanocomposite polymer electrolyte reveals an ionic conductivity of about 10^?4 S cm^?1 for 5 wt% ZnS at room temperature.     

Effect of thermal history and characterization of plasticized,composite polymer electrolyte based on PEO and tetrapropylammonium iodide salt (Pr4N+I-)

The search for anionic conductors based on solid polymer electrolytes is important for the development of photo-electrochemical (PEC) solar cells due to their many favourable chemical and physical properties. Although solid polymer electrolytes have been extensively studied as cation, mainly lithium ion, conductors for applications in secondary batteries, their use as anionic conductors have not been studied in greater detail. In a previous paper we reported the application of a PEO based iodide ion conducting electrolyte in a PEC solar cell. This electrolyte had the composition PEO: Pr₄N⁺I^? = 9:1 with 50 wt.% ethylene carbonate (EC). In this work we have studied the effect of incorporating alumina filler on the properties of this electrolyte. The investigation was extended to electrical and dielectric measurements including high frequency impedance spectroscopy and thermal analysis.In the DSC themograms two endothermic peaks have been observed on heating, one of these peaks is attributed with the melting of the PEO crystallites, while the other peak with a melting temperature ~ 30 °C is attributed to the melting of the EC rich phase. The melting temperature of both these peaks shows a marked variation with alumina content in the electrolyte. The temperature dependence of the conductivity shows that there is an abrupt conductivity increase in the first heating run evidently due to the melting of the EC rich phase. High conductivity values are retained at lower temperatures in the second heating. Conductivity isotherms show the existence of two maxima, one at ~ 5% Al₂O₃ content and the other at ~ 15%. The occurrence of these two maxima has been explained in terms of the interactions caused by alumina grains, the crystallinity and melting of the PEO rich phase. As seen from latent heat of melting, the crystallinity of the electrolyte has reduced considerably during the first heating run. In contrast to the conductivity enhancement caused by ceramic fillers in PEO-based cation containing electrolytes, no conductivity enhancement has been observed in the present PEO based anionic conducting materials by adding alumina except at low temperatures.     

A novel PEO-based composite polymer electrolyte with NaAlOSiO molecular sieves powders

Ion-conducting thin film polymer electrolytes based on poly(ethylene oxide) (PEO) complexes with NaAlOSiO molecular sieves powders has been prepared by solution casting technique. X-ray diffraction, scanning electron microscopy, differential scanning calorimeter, and alternating current impedance techniques are employed to investigate the effect of NaAlOSiO molecular sieves on the crystallization mechanism of PEO in composite polymer electrolyte. The experimental results show that NaAlOSiO powders have great influence on the growth stage of PEO spherulites. PEO crystallization decrease and the amorphous region that the lithium-ion transport is expanded by adding appropriate NaAlOSiO, which leads to drastic enhancement in the ionic conductivity of the (PEO)₁₆LiClO₄ electrolyte. The ionic conductivity of (PEO)₁₆LiClO₄-12 wt.% NaAlOSiO achieves (2.370 ± 0.082) × 10⁻⁴ S · cm⁻¹ at room temperature (18 °C). Without NaAlOSiO, the ionic conductivity has only (8.382 ± 0.927) × 10⁻⁶ S · cm⁻¹, enhancing 2 orders of magnitude. Compared with inorganic oxide as filler, the addition of NaAlOSiO molecular sieves powders can disperse homogeneously in the electrolyte matrix without forming any crystal phase and the growth stage of PEO spherulites can be hindered more effectively.     

Enhanced electrical properties of polyethylene oxide (PEO) + polyvinylpyrrolidone (PVP):Li<Superscript>+</Superscript> blended polymer electrolyte films with addition of Ag nanofiller

Polymer blended films of polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):lithium perchlorate (LiClO₄) embedded with silver (Ag) nanofiller in different concentrations have been synthesized by a solution casting method. The semi-crystalline nature of these polymer films has been confirmed from their X-ray diffraction (XRD) profiles. Fourier transform infrared spectroscopy (FTIR) and Raman analysis confirmed the complex formation of the polymer with dopant ions. Dispersed Ag nanofiller size evaluation study has been done using transmission electron microscopy (TEM) analysis. It was observed that the conductivity increases when increasing the Ag nanofiller concentration. On the addition of Ag nanofiller to the polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):Li⁺ electrolyte system, it was found to result in the enhancement of ionic conductivity. The maximum ionic conductivity has been set up to be 1.14?×?10^?5 S cm^?1 at the optimized concentration of 4 wt% Ag nanofiller-embedded (45 wt%) polyethylene oxide (PEO)?+?(45 wt%) polyvinyl pyrrolidone (PVP):(10 wt%) Li⁺ polymer electrolyte nanocomposite at room temperature. Polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):Li⁺ +Ag nanofiller (4 wt%) cell exhibited better performance in terms of cell parameters. This is ascribed to the presence of flexible matrix and high ionic conductivity. The applicability of the present 4 wt% Ag nanofiller-dispersed polyethylene oxide (PEO)?+?polyvinyl pyrrolidone (PVP):Li⁺ polymer electrolyte system could be suggested as a potential candidate for solid-state battery applications. Dielectric constants and dielectric loss behaviours have been studied.     

Experimental investigations on poly(ethylene oxide) based sodium ion conducting composite polymer electrolytes dispersed with SnO2

New Na⁺ ion conducting composite polymer electrolytes comprising of polyethylene oxide (PEO)-NaClO₄ and PEO-NaI complexes dispersed with SnO₂ are reported. The results of the studies based on optical microscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infra-red (FTIR) spectroscopy, impedance analysis and mechanical testing are presented and discussed. The electrical conductivity of ≈5·10⁻⁵ S·cm⁻¹ at 40 °C was achieved for the dispersion of ≈10 wt.% of SnO₂ in both systems. The composition dependence of the conductivity has been well correlated with the variation in glass transition temperature and degree of crystallinity. A substantial enhancement in the mechanical properties of the composite films was observed at the cost of slight decrease in the conductivity at higher concentration of SnO₂. The temperature dependence of the conductivity follows apparently the Arrhenius type thermally activated process below and above the melting temperature of PEO. The conductivity of the materials has been found to be strongly humidity dependent. The materials are shown to be ionic with t_ion>0.9. The electrochemical stability of the materials has been observed to be up to ≈3.2 V for (PEO)₂₅NaClO₄+x% SnO₂ and is limited to ≈1.9 V for (PEO)₂₅NaI+x% SnO₂.     

On dielectrics of polymer electrolytes studied by impedance spectroscopy

We present a phenomenological view on dielectric relaxation in polymer electrolytes in the frequency range where conductivity is independent of frequency. Polymer electrolytes are seen as molecular mixtures of an organic polymer and an inorganic salt. The discussion applies also to ionic liquids. The following is based on systems with poly(ethylene oxide) (PEO) comprising the lithium perchlorate salt (LiClO₄) and also pure low-molecular PEO. In those systems, dipole-dipole interactions form an association/dissociation equilibrium which rules properties of the system in the low-frequency region. It turns out that effective concentration, c _S, of relaxing species provides a suitable variable for discussing electrochemical behavior of the electrolytes. Quantity c _S is proportional to the ratio of DC conductivity and mobility. Polymer salt mixtures form weak electrolytes. However, diffusion coefficient and corresponding molar conductivity display the typical (c _S)^1/2 dependence as well known from strong electrolytes, due to the low effective concentration c _S.     

Exploring low temperature Li+ ion conducting plastic battery electrolyte

We report blend-based plastic polymer electrolyte (i.e., polyethylene oxide (PEO)–polydimethyl siloxane (PDMS)–lithium hexafluorophosphate (LiPF₆)) with substantial improvement in DC conductivity at ambient and subambient temperatures when compared with literature reports. Conductivity variation with salt concentration, investigated within ±30 °C range, indicates an optimum conductivity of 5.6?×?10^?5 S cm^?1 at 30 °C for Ö/Li ~10 with a further lowering by one order at 0 °C and it remains unaltered at ?10 °C. Enhanced conductivity in this blend electrolyte, though lower than two copolymer counterparts, is attributed to very low glass transition temperatures of the host polymers. X-ray diffraction (XRD) and scanning electron microscopy (SEM) suggest an effective blending between the two polymers with an effective interaction between the Li salt and the blend polymer matrix. Raman spectroscopy results indicated that cation (Li⁺) coordination occurs at the C=Ö site in PEO out of the two electron-rich sites (i.e., CÖ and Si–Ö–Si) in the PEO–PDMS blend. The blend electrolytes are predominantly ionic (t _ion ~97 %).     

Conductance study of poly(ethylene oxide)- and poly(propylene oxide)-based polyelectrolytes

The ionic conductivity of poly(ethylene oxide) and poly(propylene oxide) in pure solution form, individually complexed with salts of Na⁺ and Li⁺, with and without plasticizer (propylene carbonate) and in blended form with individual salt with and without plasticizer, was studied. The conductance measurements were made at various concentrations of salt polymer complexes and at different temperatures. The effects of temperature and plasticizer concentration were measured from Arrhenius conductance plots. It is shown that the addition of salts in pure PEO increases conductance many times. The plasticizer has also same effect. The blending of PEO with PPO gives enhanced conductivity as compared to pure PEO. The activation energies were determined for all the systems which gave higher values for pure PEO and the value decreases with the addition of Li and Na salts and further decreases with the addition of plasticizer. The blending has also lowered the activation energy values which mean that incorporation of PPO in PEO has decreased crystallinity and the amorphous region has increased the local mobility of polymer chains resulting in lower activation energies.     

Investigations on the effect of complexation of NaF salt with polymer blend (PEO/PVP) electrolytes on ionic conductivity and optical energy band gaps

Sodium ion conducting polymer blend electrolyte films, based on polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) complexed with NaF salt, were prepared using solution casting technique. The complexation of the salt with the polymer blend was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-vis spectroscopy. Electrical conductivity of the films was measured with impedance analyzer in the frequency range of 1 Hz to 1 MHz and in the temperature range of 303-348 K. It was observed that the magnitude of conductivity increased with the increase in the salt concentration as well as the temperature. UV-vis absorption spectra in wavelength region of 200-800 nm were used to evaluate the optical properties like direct and indirect optical energy band gaps, optical absorption edge. The optical band gaps decreased with the increase in Na⁺ ion concentration. This suggests that NaF, as a dopant, is a good choice to improve the electrical properties of PEO/PVP polymer blend electrolytes.     

Lithium-doped PEO—a prospective solid electrolyte with high ionic conductivity,developed using <Emphasis Type="Italic">n</Emphasis>-Butyllithium in hexane as dopant

The present work is an effort to study the effects of Li doping on the structural and transport properties of the solid polymer electrolyte, poly-ethelene oxide (PEO) (molecular weight, 200,000). Li-doped PEO was synthesized by treating PEO with n-Butyllithium in hexane for different doping concentrations. It is seen that the crystallinity of the doped PEO decreases on increasing the Li doping concentration and XRD and FTIR studies support this observation. FESEM images give better details of surface morphology of doped PEO samples. The TGA curves of PEO and Li-doped PEO samples reveal the weight loss region, and it is observed that the weight loss process of the solid polymer electrolyte is gradual rather than abrupt, contrary to the case of liquid electrolytes. The purity and the electrochemical stability of the samples were established by cyclic voltammetry studies. Impedance measurements were carried out to estimate the ionic conductivity of Li-doped PEO samples. The present value of ionic conductivity observed at room temperature in Li-doped PEO is about five orders higher than that of pure PEO and is quite close to that of liquid electrolytes. It is inferred that, ionic conductivity of the sample is increasing on increasing the Li doping concentration due to enhanced charge carrier density and flexibility of the doped sample structure. The ionic mobility and ionic transport are significantly improved by the less crystallinity and higher flexibility of the Li-doped PEO samples which in turn are responsible for the enhanced ionic conductivity observed.     

Preparation and characterization of a new PEO-PPG blend polymer electrolyte system

This paper reports on preparation and characterization of thin films of a new zinc ion conducting blended polymer electrolyte system containing polyethylene oxide [PEO] and polypropylene glycol [PPG] complexed with zinc triflate [Zn(CF₃SO₃)₂] salt. The room temperature ionic conductivity (σ _298K) data of such PEO-PPG polymer blends prepared by solution casting technique were found to be of the order of 10^?5 S cm^?1, whereas the optimized composition containing 90:10 wt% ratio of PEO and PPG possessed an appreciably high ionic conductivity of 7.5?×?10^?5 S cm^?1. Subsequently, six different weight percentages of zinc triflate viz., 2.5, 5, 7.5, 10, 12.5 and 15, respectively, were added into the above polymer blend and resulting polymer-salt complexes were characterized by means of various analytical tools. Interestingly, the best conducting specimen namely 87.5 wt% (PEO:PPG)-12.5 wt% Zn(CF₃SO₃)₂ exhibited an enhanced room temperature ionic conductivity of 6.9?×?10^?4 S cm^?1 with an activation energy of 0.6 eV for ionic conduction. The present XRD results have indicated the occurrence of characteristic PEO peaks and effects of salt concentration on the observed intensity of these diffraction peaks. Appropriate values of degree of crystallinity for different samples were derived from both XRD and DSC analyses, while an examination of surface morphology of the blended polymer electrolyte system has revealed the formation of homogenous spherulites involving a rough surface and relevant zinc ionic transport number was found to be 0.59 at room temperature for the best conducting polymer electrolyte system thus developed.