Ionic conductivity in polyethylene-b-poly(ethylene oxide)/lithium perchlorate solid polymer electrolytes

The ionic conductivity and phase arrangement of solid polymeric electrolytes based on the block copolymer polyethylene-b-poly(ethylene oxide) (PE-b-PEO) and LiClO₄ have been investigated. One set of electrolytes was prepared from copolymers with 75% of PEO units and another set was based on a blend of copolymer with 50% PEO units and homopolymers. The differential scanning calorimetry (DSC) results, for electrolytes based on the copolymer with 75% of PEO units, were dominated by the PEO phase. The PEO block crystallinity dropped and the glass transition increased with salt addition due to the coordination of the cation by PEO oxygen. The conductivity for copolymers 75% PEO-based electrolyte with 15 wt% of salt was higher than 10⁻⁵ S/cm at room temperature and reached to 10⁻³ S/cm at 100 °C on a heating measurement. The blend of PE-b-PEO (50% PEO)/PEO/PE showed a complex thermal behavior with decoupled melting of the blocks and the homopolymers. Upon salt addition the endotherms associated with PEO domains disappeared and the PE crystals remained untouched. The conductivity results were limited at 100 °C to values close to 10⁻⁴ S/cm and at room temperature values close to 3 × 10⁻⁶ S/cm were obtained for the 15 wt% salt electrolyte. Raman study showed that the ionic association of the highly concentrated blend electrolytes at room temperature is not significant. Therefore, the lower values of conductivity in the case of the blend with 50% PEO can be assigned to the higher content of PE domains leading to a morphology with lower connectivity for ionic conduction both in the crystalline and melted state of the PE domains.     

Temperature dependence of distortion in poly(ethylene oxide) crystals

X-ray studies of poly(ethylene oxide) crystals have been made on integrated intensities of 31 Bragg peaks and the diffraction profile of 120 reflection, which gives information about lateral molecular packing, over the temperature range from ?150° to 50°C. Both the integrated intensities of 25 Bragg peaks and the integral breadth of 120 reflection have maxima in their temperature changes. These unusual temperature changes can be attributed to static crystal distortion: static displacement of atoms from their average positions over all crystals. Thermal vibration actually takes place around the displaced positions. Many Bragg peaks were required to be investigated in order to study the effect of the static distortion on the integrated intensities, since temperature changes of the displaced positions lead to changes of both the average positions (crystal structure) and magnitude of the static displacement. A model for the static displacement is proposed:; intermolecular interaction is the origin of the static displacement, which is decreased with increasing temperature by a smearing-out effect on the intermolecular interaction due to thermal vibration. Fourier analysis of the profile of 120 reflection suggests that crystalline order is maintained at short range, 20 molecules or more in diameter.     

Ionic transport behavior in poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) and LiClO4 complex

The effect of LiClO₄ on the ionic transport behavior in poly(ethylene oxide)₂₀-poly(propylene oxide)₇₀-poly(ethylene oxide)₂₀ (P123) polymer electrolyte was studied. Its conductivity reaches maximum as molar ratio between ether O atoms and lithium ions [n(O)/n(Li)] equals 8. The results show that LiClO₄ could interact with P123 well and has impacts on polymer organization and chain dynamics. As LiClO₄ concentration decreases, the glass transition temperature (T_g) decreases and the free ion percentage increases. The tendency of conductivity with LiClO₄ concentration is the result of competing effects between polymer chain mobility and free charge carrier concentration.     

Lithium ion conductivity of molecularly compatibilized chitosan-poly(aminopropyltriethoxysilane)-poly(ethylene oxide) nanocomposites

Films of composites of chitosan/poly(aminopropyltriethoxysilane)/poly(ethylene oxide) (CHI/pAPS/PEO) containing a fixed amount of lithium salt are studied. The ternary composition diagram of the composites, reporting information on the mechanic stability, the transparence and the electrical conductivity of the films, shows there is a window in which the molecular compatibility of the components is optimal. In this window, defined by the components ratios CHI/PEO 3:2, pAPS/PEO 2:3 and CHI/PEO 1:2, there is a particular composition Li_x(CHI)₁(PEO)₂(pAPS)_1.2 for which the conductivity reaches a value of 1.7 × 10⁻⁵ S cm⁻¹ at near room temperature. Considering the balance between the Lewis acid and basic sites available in the component and the observed stoichiometry limits of formed polymer complexes, the conductivity values of these products may be understood by the formation of a layered structure in which the lithium ions, stabilized by the donors, poly(ethylene oxide) and/or poly(aminopropyltriethoxysilane), are intercalated in a chitosan matrix.     

Radiotracer self-diffusion measurements in poly(ethylene oxide) and poly(propylene oxide) electrolytes

Radiotracer measurements of the ²²Na⁺ and S¹⁴CN^? diffusion coefficients in PEO-NaSCN (x = 6, 8 and 12) and PPO-NaSCN (x = 8) are reported, where PEO = poly(ethylene oxide), PPO = poly(propylene oxide), and x = [EO units]/[NaSCN] or [PO units]/[NaSCN]. The results are compared with ionic conductivity measurements on the same samples. Measurements for the PEO samples were taken above the melting point of pure PEO and the results interpreted, particularly for the sample most dilute in salt, in terms of ‘free ions’ as the dominant charge carriers. For PPO the results are less clear, although there is good evidence for the onset of ion aggregation prior to separation of salt at higher temperatures.     

Syntheses of poly(ethylene oxide) polyurethane ionomers

Sulfonated dimethyl fumarate (SDMF) was prepared with dimethyl fumarate (DMF) and sodium hydrogensulfite (NaHSO₃). Sodium sulfonate side‐chain poly(ethylene oxide) (SPEO) was synthesized by grafting sodium sulfonate onto the chain of PEO with molecular weights of 400, 600, 800, and 1000. SPEO was used subsequently in step‐growth polymerization to give a polyurethane ionomer (SPU). Samples were characterized by element analysis, FTIR, ¹H‐NMR, EDX mapping, X‐ray, gel permeation chromatography, and impedance analysis. The SPUs exhibited an amorphous structure. The maximum conductivity of the SPU was 1.02 × 10⁻⁶ S cm⁻¹ at the room temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 184–188, 2000     

Structural studies of poly(butyl acrylate) - poly(ethylene oxide) miktoarm star polymers

Structural behavior of miktoarm star polymers comprising poly(butyl acrylate) (PBA) and poly(ethylene oxide) (PEO) arms was studied by means of Differential Scanning Calorimetry (DSC), Wide Angle X-Ray Scattering (WAXS), Polarized Optical Microscopy (POM) and Fourier Transform Infrared Spectroscopy (FTIR) methods. The aim of this study was to correlate changes in the composition of the arms of the PBA/PEO miktoarm star polymers with their structures. As a consequence of increasing PBA content, the decrease in crystallinity of the studied PBA/PEO heteroarm star copolymers was observed. Regardless of the copolymer composition, fraction of oxyethylene units in the crystalline PEO phase was similar in all investigated systems. The POM images showed spherulitic morphology of the materials having low PBA content, while an increase in PBA arms fraction leads to the formation of less ordered structures. The analysis of FTIR vibrational spectrum indicates helical conformation of PEO chains in the crystalline phase. Isothermal crystallization studies carried out using the FTIR technique suggest the existence of isolated domains in the nanoscopic scale of investigated materials.     

Composite polyether electrolytes with a poly(styrenesulfonate) lithium salt and Lewis acid type additive

A poly(styrenesulfonate) lithium salt was tested as a single-ion conductor in a poly(ethylene oxide)/poly(ethylene glycol) dimethyl ether matrix. Impedance spectroscopy and voltage step polarization were used to characterize the composite electrolytes. A specific conductivity of about 7×10⁻⁸ S cm⁻¹ was evaluated at 70 °C. The very low conductivity was attributed to the poor solubility of Li⁺ in the polymer matrix. AlCl₃ was added to the polymer electrolyte to increase the salt dissolution. The addition of the Lewis acid strongly increases the conductivity and a specific conductivity of about 4×10⁻⁶ S cm⁻¹ was measured at 20 °C. For temperature lower than 60 °C, the specific conductivity dependence with increasing temperature follows an Arrhenius-type behavior. An activation energy of about 55.6 kJ mol⁻¹ was calculated. A very similar activation energy (60.3 kJ mol⁻¹) was found for the charge transfer resistance. The transport properties of the polymer electrolyte were tested by applying a d.c. voltage step to a symmetrical lithium cell. The current at the applied voltage decreased with time. The decrease was related to an increase in the cell resistance due to the continuous growth of a passivation layer on the lithium surface.     

Structural and electrical studies on poly(ethylene oxide) complexed with inorganic salts

Summary Poly(ethylene oxide) (PEO) complexes were synthethized in methanol solution with five different alkali and earth alkali metal perchlorates. The intermolecular association was studied in solution with NMR and the structures of the formed solid complexes were analysed by IR-spectroscopy and X-ray-diffractometry. The conductivities of pure PEO and of the complexes were measured in vacuum and at room temperature. The variation in the properties of the samples is due to the association of PEO with charged ions.     

Study of poly(ethylene oxide) electrolyte with polyurethane/sulfonate side chains

Sulfonated dimethyl fumarate (SDMF) was prepared. Poly(ethylene oxide) (PEO) with sodium sulfonate side chains (SPEO) was synthesized by transesterification between SDMF and PEO with molecular weights of 200, 400, 600, 800, and 1000. The SPEO was subsequently mixed as a plasticizer with PEO polyurethane (PU). Samples were characterized by elemental analysis, FTIR, ¹H-NMR, gel permeation chromatography, and impedance analysis. The mixture exhibited a homogeneous domain. The maximum conductivity of the CPU1000/SPEO600 was 2.6 × 10⁻⁷ S cm⁻¹ at room temperature. The relation between the ionic conductivity and the temperature was in agreement with the Arrhenius equation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 541–545, 2001     

Ionic conductivity studies of poly(ethylene oxide)-lithium salt electrolytes in high-pressure carbon dioxide

We have measured ionic conductivity of PEO-LiX [anion X=N(CF₃SO₂)₂ (TFSI), ClO₄, CF₃SO₃, BF₄, NO₃, and CH₃SO₃] polymer electrolytes in CO₂ at pressures varied from 0.1 to 20 MPa. From the temperature dependence in supercritical CO₂, a large increase in the conductivity for PEO-LiBF₄ and LiCF₃SO₃ electrolytes has been observed. Permeation of the CO₂ molecules gave rise to the plasticization for crystal domains in the electrolytes, which is related to the reduction in transition point of the Arrhenius plot corresponding to the melting of crystal PEO. Relation between the conductivity and CO₂ reduced density revealed that the electrolytes containing fluorinated anions such as ‘CO₂-philic’ BF₄ and CF₃SO₃ increase in the conductivity with increasing the density. This indicates that the salt dissociation was promoted by the CO₂ permeation and the Lewis acid-base interactions between fluorinated anions and CO₂ molecules.     

Practical applications of modified poly(ethylene oxide) networks

Modified poly(ethylene oxide) (PEO) networks have been studied as phase transfer catalysts, flocculates and solvent-free polymer electrolytes. The activity of the hydrogels has been investigated with respect to the structure and crosslinking density of the networks, their degree of quaternization and amphiphilic properties (hydrophilicity coefficients). It has been found that the microenvironment of the active sites (EO segments and ammonium ions) affects the catalytic activity and sorption ability of the modified networks. Hydrophobic organic compounds such as sodium picrate and bromophenolblue are bound predominantly to the lipophilic quaternary ammonium ions. A stable level of electrical conductivity of 5.0×10⁻⁵ S cm⁻¹ was achieved without using of additives. A probable mechanism of ion transport within the networks has been proposed. Potential applications of PEO-based materials as solvent-free solid polymer electrolytes are also discussed.     

Structure and conductive properties of poly(ethylene oxide)/layered double hydroxide nanocomposite polymer electrolytes

The oligo(ethylene oxide) modified layered double hydroxide (LDH) prepared by template method was added as a nanoscale nucleating agent into poly(ethylene oxide) (PEO) to form PEO/OLDH nanocomposite electrolytes. The effects of OLDH addition on morphology and conductivities of nanocomposite electrolytes were studied using wide-angle X-ray diffractometer, polarized optical microscopy, differential scanning calorimetry and ionic conductivity measurement. The results show that the exfoliated morphology of nanocomposites is formed due to the surface modification of LDH layers with PEO matrix compatible oligo(ethylene oxide)s. The nanoscale dispersed OLDH layers inhibit the crystal growth of PEO crystallites and result in a plenty amount of intercrystalline grain boundary within PEO/OLDH nanocomposites. The ionic conductivities of nanocomposite electrolytes are enhanced by three orders of magnitude compared to the pure PEO polymer electrolytes at ambient temperature. It can be attributed to the ease transport of Li⁺ along intercrystalline amorphous phase. This novel nanocomposite electrolytes system with high conductivities will be benefited to fabricate the thin-film type of Li-polymer secondary battery.     

Electric double layer capacitors with gelled polymer electrolytes based on poly(ethylene oxide) cured with poly(propylene oxide) diamines

Using a gel electrolyte for electric double layer capacitors usually encountered a drawback of poor contact between the electrolyte and the electrode surface. A gel electrolyte consisting of poly(ethylene oxide) crosslinked with poly(propylene oxide) as a host, propylene carbonate (PC) as a plasticizer, and LiClO₄ as a electrolytic salt was synthesized for double layer capacitors. Diglycidyl ether of bisphenol-A was blended with the polymer precursors to enhance the mechanical properties and increase the internal free volume. This gel electrolyte showed an ionic conductivity as high as 2 × 10⁻³ S cm⁻¹ at 25 °C and was electrochemically stable over a wide potential range (ca. 5 V). By sandwiching this gel-electrolyte film with two activated carbon cloth electrodes (1100 m² g⁻¹ in surface area), we obtained a capacitor with a specific capacitance of 86 F g⁻¹ discharged at 0.5 mA cm⁻², while the capacitance was 82 F g⁻¹ for a capacitor equipped with a liquid electrolyte of 1 M LiClO₄/PC. The capacitance decrease with the current density was less significant for the gel-electrolyte capacitor. We found that the less restricted ion diffusion near the electrolyte/electrode interface led to the smaller overall resistance of the gel-electrolyte capacitor. The high performance of the gel-electrolyte capacitor has demonstrated that the developed polymer network not only facilitated ion motion in the electrolyte bulk phase but also gave an intimate contact with the carbon surface. The side chains of the polymer in the amorphous phase could stretch across the boundary layer at the electrolyte/electrode interface to come into contact with the carbon surface, thus improving transport of Li⁺ ions by the segmental mobility in polymer.     

Nanocomposite polymer electrolytes containing silica nanoparticles: Comparison between poly(ethylene glycol) and poly(ethylene oxide) dimethyl ether

Nanocomposite polymer electrolytes consisting of low molecular weight poly(ethylene oxide) (PEO), iodine salt MI (M = K⁺, imidazolium⁺), and fumed silica nanoparticles have been prepared and characterized. The effect of terminal group in PEO, i.e., hydroxyl (? OH) and methyl (CH₃) using poly(ethylene glycol) (PEG) and PEO dimethyl ether (PEODME), respectively, was investigated on the interactions, structures, and ionic conductivities of polymer electrolytes. Wide angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), and complex viscositymeasurements clearly showed that the gelation of PEG electrolytes occurred more effectively than that of PEODME electrolytes. It was attributed to the fact that the hydroxyl groups of PEG participated in the hydrogen‐bonding interaction between silica nanoparticles, and consequently helped to accelerate the gelation reaction, as confirmed by FTIR spectroscopy. Because of its interaction, the ionic conductivities of PEG electrolytes (maximum value ～ 6.9 × 10^?4 S/cm) were lower than that of PEODME electrolytes (2.3 × 10^?3 S/cm). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Electrical conductivity in ionic complexes of poly(ethylene oxide)

The temperature dependence of d.c. conductivity of poly(ethylene oxide) complexes with sodium iodide and the thiocyanates of sodium, potassium and ammonium has been investigated. In each case a transition to a lower activation energy at higher temperatures was observed. For the sodium complexes this transition occurs at ca 55°C which is well below the crystalline melting points at 200°C. For the potassium and ammonium complexes however, the transitions coincide with the melting points at ca 100 and 70°C respectively. It is proposed that at the transitions, thermal disintegration of complexes in the amorphous regions occurs. The complexes involve coordination of the cations to the ether oxygen atoms in the polymer backbone.     

Pressure-volume-temperature properties for binary and ternary polymer solutions of poly(ethylene glycol), poly(propylene glycol), and poly(ethylene glycol methyl ether) with anisole

Pressure-volume-temperature properties were measured for polymer solutions of poly(propylene glycol) (PPG)+anisole, polymer blends of PPG+poly(ethylene glycol methyl ether) (PEGME), and the blends of PPG+PEGME and poly(ethylene glycol) (PEG)+PPG with anisole at temperatures from 298.15 to 348.15 K and pressures up to 50 MPa. The Tait equation represents accurately the pressure effect on the liquid densities over the entire pressure range. The excess volumes change from positive to negative as increasing the mole fraction of PPG in the binary systems of PPG+anisole and PPG+PEGME. The volumetric data of the related binary systems were correlated with the Flory-Orwoll-Vrij and the Schotte equations of state to determine the binary parameters. By using these determined binary parameters, both equations predicted the specific volumes of the polymer blends with anisole to average absolute deviations of better than 0.13%.     

Miscibility of polystyrene with poly(ethylene oxide) and poly(ethylene glycol)

The intrinsic viscosity of polystyrene–poly(ethylene oxide) (PS–PEO) and PS–poly(ethylene glycol) (PEG) blends have been measured in benzene as a function of blend composition for various molecular weights of PEO and PEG at 303.15 K. The compatibility of polymer pairs in solution were determined on the basis of the interaction parameter term, Δb, and the difference between the experimental and theoretical weight-average intrinsic viscosities of the two polymers, Δ[η]. The theoretical weight-average intrinsic viscosities were calculated by interpolation of the individual intrinsic viscosities of the blend components. The compatibility data based on [η] determined by a single specific viscosity measurement, as a quick method for the determination of the intrinsic viscosity, were compared with that obtained from [η] determined via the Huggins equation. The effect of molecular weights of the blend components and the polymer structure on the extent of compatibility was studied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1471–1482, 1998     

Reduction of radiation-induced conductivity in poly(ethylene terephthalate): Effect of dopant structure

This paper focuses on developing radiation tolerant polymeric films by incorporating small molecule dopants into the material formulation. The radiation tolerance is imparted to the polymer by dopants capturing the mobile electrons generated upon radiation exposure. A wide range of conjugated small molecules was utilized for the reduction of radiation-induced conductivity (RIC) in semi-crystalline poly(ethylene terephthalate). Using these results, the process of electron and hole trapping by π-conjugated molecules may be generalized to many organic systems. All conjugated ring cores examined, when substituted with an appropriate electron-withdrawing species, led to excellent RIC reduction. The nitro group is the strongest electron-withdrawing substituent, and therefore leads to the lowest RIC, but other substituents also reduce RIC, and the interactions may be quantified by the Hammett parameter. It was also found that the dopant must be present in a certain range of concentrations, between 10 and 200 mol/m³ (6 × 10¹⁸ and 1 × 10²⁰ molecules/cm³), for proper trapping of the photo-induced electron-hole pairs. This understanding of the interactions between conjugated dopants, photons, and electrons will benefit other applications, such as controlled conductivity in coatings and organic electronics.     

Optical tweezers to measure the interaction between poly(acrylic acid) brushes

Optical tweezers are employed to measure the forces of interaction within single pairs of poly(acrylic acid) (PAA) grafted colloids with an extraordinary resolution of ±0.5 pN. Parameters varied are the concentration and valency of the counterions (KCl, CaCl₂) of the surrounding medium as well as its pH. The data are quantitatively described by a recently published model of Jusufi et al. [Colloid Polym Sci 2004; 282:910] for spherical polyelectrolyte brushes which takes into account the entropic effect of the counterions. For the scaling of the brush height a power law is found having an exponent of 0.25 ± 0.02 which ranges between the values expected for spherical and planar brushes. From the model the ionic concentration inside the brush is estimated in reasonable agreement with the literature.