Polymer Salt Complex Research Articles

Polymer‐salt intercalation complexes in layer silicates

Composite ionic conductors based on homoionic montmorillonites (2:1 charged layers silicates containing metal ions in their interlayer space) cinteracted with poly(ethylene oxide) exhibit enhanced condcutivity between silicate layers (see figure). The presence of tunnels in the intercalated polymer–salt complex is thought to facilitate intracrystalline ion mobility.magnified image

Influence of cryptands and crown ethers on ion transport and vibrational spectra of polymer-salt complexes

Influence of cryptands and crown ethers on ion transport and vibrational spectra of polymer-salt complexes

Crystallinity and thermomechanical properties of lead halide-PEO complexes

It is known that polymer-salt complexes can be formed between PEO and certain metal halides. In this work, the degree of crystallinity within the system PbX 2(PEO) 16, for X= Cl, Br and I, has been studied by X-ray diffraction methods in the temperature range RT-200°C. The results obtained are related to earlier dynamical mechanical analysis (DMA) studies of the same series. An intimate relationship between degree of crystallinity, stiffness and temperature can be identified.

MD Studies of Transport in Polymer-Salt Complexes: A Progress Report

AbstractMolecular dynamics simulations performed on highly concentrated Coulomb/solvent systems are used to help interpret the transport mechanism in polymer ionics. Using simple Coulomb and Lennard-Jones forces among the ions and a solvent model of a fixed dipole contained in a spherical solvent particle, we investigated the nature of ion pair formation and stability. For a model NaI system, we find that ion pairs decrease with increase in solvent dipole moment or temperature. The latter observation is at variance with experimental results on polymer electrolytes, probably because of entropy terms that do not occur with our simple solvent molecule.

Raman Study of Free Volume Effects on Ion Pairs in Polymer Electrolytes

AbstractIon associations are demonstrated from Raman spectra of the anion symmetric stretch in NaCF3SO3 and LiCF3SO3 containing salt polymer complexes based on PPO and siloxane modified PPO. The observation of increasing amount of ion pairs with increasing molecular weight and temperature can be explained by an entropically driven process. The entropy effect includes contributions from several factors related to transient cross-linking via the cations, conformational entropy of the polymer chains, and free volume dissimilarities between the solvated ions and the macromolecules.

Structural Dynamics of Polymer Electrolytes

AbstractThe structure of polyethylene oxide doped with lithium perchlorate was studied. The macroscopic structure of the polymer-salt complexes was studied by thermal analysis and xray diffraction. The microscopic structure and polymer dynamics were studied by infrared, Raman and nuclear magnetic resonance spectroscopy. Thermal analysis and x-ray diffraction studies clearly revealed the change of crystalline phase to an amorphous phase by the addition of salt. The vibrational analysis showed a conformational transformation of the polymer chain by the addition of salt. Vibrational analysis also showed clearly the formation of free ion, ion-pair and salt cluster in the polymer as the concentration of the salt increased.

Vibrational spectroscopic studies of low molecular weight poly(propylene oxide)-sodium thiocyanate complexes

This paper presents the results of room temperature Raman scattering and infra-red transmission studies of a poly(propylene oxide), PPO, of average molecular weight approximately 450, complexed with varying concentrations of sodium thiocyanate, NaSCN. Observed changes in the polarized Raman and infra-red spectra of the polymer and polymer-salt complexes permit some insight into the basic nature of the complexes which are formed and the effect of successive complexation on polymer dynamics. In addition, characteristic frequencies observed for the thiocyanate anion in these complexes indicate that the thiocyanate anion is involved in contact ion pairing with the sodium cations at the nitrogen end of the anion.

Near-edge x-ray-absorption fine-structure spectroscopy investigation of poly(ethylene oxide)-KI complexes.

We have measured the near-edge x-ray-absorption fine-structure spectra of the K edge of potassium in the polymer-salt complex poly(ethylene oxide)-KI. Changes are observed as a function of temperature due to modifications of the K-ion coordination. Comparison with model systems suggests that the lower activation energy of this ionic conducting polymer complex at elevated temperature (T>70 \ifmmode^\circ\else\textdegree\fi{}C) is partially due to reduced oxygen complexation of the K ions.

Solid polymer electrolytes: attempts to improve conductivity

To attempt to improve conductivity in solid polymer electrolytes, we have examined several approaches. These include the preparation of new polymer-salt complexes, the use of soluble additives that would provide conduction pathways and the use of certain insoluble additives that might also tend to improve electrical properties. In this paper we report on these attempts and the effect that such materials have on conductivities. Metal-ion complexes of poly(vinyl acetate), a polyphosphinate, and a crown ether containing polymer were prepared and evaluated. All exhibited significant conductivity but the best result was obtained when the polymeric crown ether was combined with poly(vinylene carbonate). Conductivity near 10 −3 Scm −1 close to room temperature was observed. Silver(I) and mercury (II) salts were also shown to form conducting complexes with poly(ethylene oxide) with the silver complexes having about 100 times better conductivities than the mercury complexes. Addition of high surface area materials, for example silica gel, microcrystalline cellulose and carbon black, to polymeric electrolytes did not improve conductivities.

Nature of the Chemical Bonds in Polymer-Salt Complexes: Raman and IR Studies

AbstractPolymer electrolytes are attracting interest because of potential use in ‘solid state’ batteries and electrochromic windows. In this work the nature of the chemical bonds and ion association in polymer-salt complexes were studied. The fundamental vibrational frequencies of LiClO4− were calculated using valence force constants which are obtained from the ClO4− anion. The calculated frequencies and the band assignments agree quite well with the observed frequencies. Raman and IR spectroscopy were used to investigate the interaction of Li+ and ClO4− with the PEO chains. Lithium ion interacted with the negatively charged oxygen of PEO and C104 interacted electro- statically with the positively charged hydrogens. The strong electrostatic interactions induced changes in the intensity of the Raman bands and IR absorption bands of the polymer. The Raman and IR spectra of the polymer-salt complexes clearly show the existence of ‘free’ ions, ionpairs and salt clusters at various concentrations of the lithium salt. The maximum concentration of “free” ions deduced from the spectroscopy is in excellent agreement with the salt concentration required to obtain maximum ionic conductivity.

Preparation and characterisation of PEOHg(ClO 4) 2 complexes and some thoughts on ion transport in polymer electrolytes

A new solid polymer electrolyte, PEOHg(ClO 4) 2 has been prepared and characterised over a composition range 100 ⩽ x⩽ 4, where x represents the molar ratio of EO units to salt. Films of this material are amorphous at high salt concentrations and there is no evidence for the formation of a crystalline polymer-salt complex over the entire composition range studied. Electrical measurements indicate that both cations and anions are mobile, with a cation transference number of 0.25±0.05 at 52°C for an EO/salt molar ratio of 20:1. The overall conductivity of PEOHg(ClO 4) 2 is significantly higher than that of other strictly anhydrous polymer electrolytes containing mobile divalent cations, previously reported. The variation of conductivity with temperature and composition is discussed, and cation mobility in general is considered in terms of hard and soft character, and in relation to the lability of the coordinated etheroxygens.

Synthesis, NMR characterization, and electrical properties of siloxane-based polymer electrolytes

Abstract : A crosslinked siloxane-based polymer has been prepared by the reaction of Poly(methylhudrosiloxane), monomethyl ether poly(ethylene glycol), and poly(ethylene glycol). The polymer, which has been structurally characterized by 29 Si NMR, forms complexes with LISO CF3 that exhibit good ionic conductivities (for a LiSO3CF3 15 wt% complex). The polymer and its salt complexes have been characterized by elemental analysis, 29 Si NMR powder diffraction X-ray powder diffraction, DSC, and AC complex impedance spectroscopy. The dependence of the ionic conductivity was investigated as a function of temperature, salt concentration (91 wt % to 25 wt %), and alkali metal cation (Li, Na, K, Rb, and Cs). Keywords: Polysiloxane, Polyethylene glycol, Copolymers, Polymer electrolytes, Polymer salt complexes, Ionic conductivity.

Ion Association in Polymer Electrolytes; A Raman Study of Poly (Propylene Oxide) Based Complexes

AbstractRaman spectra of a series of PPO-LiClO4 and PPO-NaCF3SO3 complexes have been obtained for different temperatures and salt concentrations to study the various ion associations of the dopant salt. It was found that ion-ion interactions dramatically influenced the internal symmetric stretching modes ν1 of the anions. Splitting of ν1 into a multicomponent band was observed. The intensity profile of the band was found to change rapidly with salt concentration and temperature. A three component band analysis led to the identification of dissociated ions, ion pairs and multiple ion aggregates, respectively. Increased ion association with increased temperature and/or salt concentration was observed for both LiCIO4- and NaCF3SO3- complexes. It is likely to initiate the phase separation and salt precipitation observed in many salt-polymer complexes at higher temperatures. Considerably stronger ion-ion interaction was observed in the NaCF3SO3-system than in the LiCIO4-complex, which may explain the lower conductivities reported for PPO-NaCF3SO3 electrolytes. The drastic conductivity drop observed in both systems at higher salt concentrations can however only partly be due to a decreased concentration of “free” ions, the major effect being attributed to decreased ion mobility.

Ionic conductivity in branched polyethylenimine-sodium trifluoromethanesulfonate complexes: comparisons to analogous complexes made with linear polyethylenimine

Abstract : Complexes between branched polyethyleneimine and Sodium trifluoromethane sulfonate were formed with a polymer repeat unit to salt ratio of 6:1, 12:1 and 20:1. All three complexes are amorphous in contrast to linear polyethyleneimine which forms partially crystalline complexes at ratios above 6;1 (lower salt concentrations). The 6:1 complex of branched polyethyleneimine has a higher glass transition temperature (12 C) and a lower conductivity than the corresponding complex of linear polyethyleneimine. The glass transition temperature of the polymer-salt complex decreases by 43 degrees upon decreasing the salt concentration from that of the 6:1 complex to that of the 20:1 complex. Correspondingly, the conductivity of the 20:1 complex at 40 C is two orders of magnitude higher than that of the 6:1 complex. N-H stretching frequencies of linear and branched polyethyleneimine and their polymer-salt complexes were studied by infrared spectroscopy. An increase in frequency of the N-H stretching mode of both polymers is seen upon complex formation. Keywords: Polymer electrolytes, Ionic conductivity.

Complex formation and ionic conductivity of polyphosphazene solid electrolytes

The linear poly[(alkoxy)phosphazene], [NP(OC 2H 4OC 2H 4OCH 3) 2] n (MEEP), has been synthesized and investigated as a polymeric electrolyte host material. Amorphous solvent free polymersalt complexes formed with a variety of mono-, di-, and trivalent salts and exhibit high ionic conductivity. The conductivity varies with changes in the identify of the cation, the anion and the salt concentration. It also exhibits a non-Arrhenius temperature dependence. For alkali-metal salt complexes the cations and anions both contribute to the ionic conductivity. The complex (LiSO 3CF 3) 0.25·MEEP exhibits a conductivity at room temperature which is 2.5 orders of magnitude greater that the corresponding poly(ethylene oxide) complex.

Criteria of choice of the helix type in crystalline dextran

A reduction in the water content in dextran samples crystallized from water-salt solution results in transformation of the crystal lattice of the polymer-salt complex due to stretching of the polysaccharide chains. A right helix of the 5 2 type has been selected as the most preferential for crystalline dextran on the basis of energy, thermodynamic and crystallographic criteria. It is concluded that maximally stretched helices with the lowest (for the theoretically possible isoenergic conformers) symmetry and a minimal diameter are realized in polysaccharide crystals.

Structure and ion transport in polymer-salt complexes

Polymer electrolytes based on alkali metal complexes of polyethers and cross-linked polyethers have significant cation mobility, which appears to arise from large-amplitude motions of the polymer. High chain flexibility not only promotes ion transport but it also is important for the initial formation of polymer-salt complexes. Several new polymer electrolyte systems are discussed which contain flexible polymer backbones and high concentrations of polar groups.

Vibrational spectroscopy and structure of polymer electrolytes, poly(ethylene oxide) complexes of alkali metal salts

Complexes of poly(ethylene oxide) (PEO), with various alkali metal salts are known to exhibit ionic conductivities which exceed 10 −5(Ωcm) −1 at moderate temperatures. We have employed IR and Raman spectroseopy to study well characterized samples of the following polymer-salt complexes: PEO·NaBr, PEO·NaI, PEO·NaSCN, PEO·NaBF 4, PEO·NaCF 3SO 3, PEO·KSCN, PEO·RbSCN and PEO·CsSCN. Cation-dependent vibrational bands observed in the far IR and M-O n symmetric stretching bands observed in the Raman support a cation-oxygen atom interaction, and indicate the polyether chain may wrap around the cations. In particular, NaX and KX complexes of PEO are believed to have a helical configuration for the polymer which differs from that of pure PEO. Some general rules are presented for polymer-salt complex formation.