Ternary blends of poly(ethylene oxide) and acrylate-based copolymers: Crystallinity, miscibility, interactions and proton conductivity

In the present work, blends of poly(ethylene oxide) (PEO), poly(acrylonitrile-co-methyl acrylate) (PANMA) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM) were studied by DSC, FTIR and electrochemical impedance spectroscopy (EIS). PEO/PANMA blends were found to be immiscible, while PEO/PVPh-HEM blends are miscible and PVPh-HEM/PANMA exhibits partial miscibility behaviour. The ternary PEO/PANMA/PVPh-HEM blends exhibited miscible compositions for PVPh-HEM and PEO-rich systems. The miscibility observed is a direct consequence of the hydrogen bond interactions among the polymer chains, in which the phenol groups in PVPh-HEM interact with both PEO and PANMA chains. The proton conductivity of a selected membrane based on the ternary blend containing 60% PEO and doped with H₃PO₄ aqueous solution reached 8 × 10⁻³ Ω⁻¹ cm⁻¹ at room temperature and 3 × 10⁻² Ω⁻¹ cm⁻¹ at 80 °C.     

Inorganic–organic hybrid polymers with pendent sulfonated cyclic phosphazene side groups as potential proton conductive materials for direct methanol fuel cells

A synthetic method is described to produce a proton conductive polymer membrane with a polynorbornane backbone and inorganic–organic cyclic phosphazene pendent groups that bear sulfonic acid units. This hybrid polymer combines the inherent hydrophobicity and flexibility of the organic polymer with the tuning advantages of the cyclic phosphazene to produce a membrane with high proton conductivity and low methanol crossover at room temperature. The ion exchange capacity (IEC), the water swelling behavior of the polymer, and the effect of gamma radiation crosslinking were studied, together with the proton conductivity and methanol permeability of these materials. A typical membrane had an IEC of 0.329 mmol g⁻¹ and had water swelling of 50 wt%. The maximum proton conductivity of 1.13 × 10⁻⁴ S cm⁻¹ at room temperature is less than values reported for some commercially available materials such as Nafion. However the average methanol permeability was around 10⁻⁹ cm s⁻¹, which is one hundred times smaller than the value for Nafion. Thus, the new polymers are candidates for low-temperature direct methanol fuel cell membranes.     

Electrochemical synthesis and study of polydiphenylamine

The electrochemical oxidation of diphenylamine in acetonitrile produces an adherent conducting polymer film at the electrode. Conductivity measurements on pressed pellets of this polymer give a room temperature conductivity of 10 S cm⁻¹. The polymer can be cycled between 25 and 200°C without deterioration in the conductivity. Preliminary SEM/EDS studies suggest that there is one BF⁻₄ counter ion for every four monomer units in the oxidised polymer film.     

Lipid barrier layers on surfaces of synthetic water permeable membranes

Barrier layers (area 0.79 cm²) from oxidized cholesterol or mixtures of oxidized cholesterol with phosphatidyl serine or phosphatidyl ethanol amine were formed on surfaces of different water-permeable synthetic membranes in 0.1 M NaCl as models of biological membranes. Ionic conductivity across the membranes decreased from 10⁻²-10⁻³ to 10⁻⁷-10⁻⁸ Ω⁻¹ cm⁻² when the barrier layers were formed on their surfaces. Average thicknesses of barrier layers 4.5–11 nm were estimated from electric capacitance. The layers were unstable with lifetimes ranging from several minutes to 50 hr according to the support membrane used. The interfacial tension between synthetic membrane surface and either water or lipid solution was calculated from contact angle measurement. The relation between barrier layer stability and hydrophobic and polar interaction of lipids with support surface was studied. The most stable barrier layers (lifetimes 30–50 hr) were formed on cellophane and gelatin membranes with surfaces hydrophobized by reaction with palmytoyl chloride.     

Effect of Dibenzo-18-crown-6 on the Polymer Electrolyte/Lithium Anode Interface

Photocured polymer electrolytes, applied onto a porous polypropylene separator, with conduction by lithium cations (1 × 10⁻⁴ S cm⁻¹ at 20°C) are designed. The polymer is formed from a 1 : 1 mixture of oligourethane dimethacrylate and polypropylene glycol monomethacrylate, which are capable of undergoing polymerization via double bonds in a liquid organic electrolyte (0.5 M LiClO₄) in a 1 : 1 mixture of propylene carbonate and dimethoxyethane. The polymer electrolyte comprises a polymer composition (20 wt %), a liquid electrolyte (78 wt %), and a photoinducer (2 wt %). Effect of insertion of dibenzo-18-crown-6 into the electrolyte on its electrochemical characteristics (on the electrolyte/Li interface) is investigated. Dependences of the bulk conductivity and exchange currents at the interface on the temperature and storage duration are studied at different crown ether contents.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 646–650.Original Russian Text Copyright © 2005 by Yarmolenko, Efimov.     

Etude des propriétés de conduction électrique des polyphosphates: Li3Ba2(PO3)7, LiPb2(PO3)5, LiCs(PO3)2, et αLiK(PO3)2

The electrical conductivity of the crystallized polyphosphates Li₃Ba₂(PO₃)₇, LiPb₂(PO₃)₅, LiCs(PO₃)₂, and αLiK(PO₃)₂ has been determined at different temperatures by impedance spectroscopy. The conductivity, σ, spreads within a range of 1.59 × 10⁻⁸ to 1.79 × 10⁻⁷ S cm⁻¹ at 573 K, and from 1.71 × 10⁻⁵ to 9.86 × 10⁻⁴ S cm⁻¹ at 773 K. The transport should be assumed in the majority by the lithium ions with regard to the structural characteristics of these polyphosphates. The results are discussed and compared to the conductivity properties of other lithium ion conductors.     

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ_p=3 × 10⁻¹³ s, f_p = 0.5 Hz, E_p = 1.1 × 10⁻³J cm⁻², I_av = 5.5 × 10⁻⁴ W cm⁻², I_p = 10⁹ W cm⁻²) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm⁻²). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10³ lower for pulsed radiation than for CW radiation (3.3 × 10⁻¹ and 7.8 × 10² J cm⁻² respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.     

Conductivity of Lanthanum-Strontium Cuprate LaSrCuO<Subscript>4−δ</Subscript> and Ionic Reversibility of Relevant Electrodes

A single-phase sample of the LaSrCuO_3.58 composition is prepared by solid-state synthesis at 1473 K in air. The conductivity of LaSrCuO_3.58 is measured by a four-probe method at direct current in the temperature range from 298 to 1173 K at oxygen partial pressures from 28 to 2.1 × 10⁴ Pa. Heating samples above ∼670 K is shown to result in a changeover of the conduction type from semiconducting (p-type) to metallic. Exchange currents at the LSCuO/YSZ interface are measured by impedance spectroscopy. The measurements are carried out in high-density symmetrical cells LSCuO|YSZ|LSCuO, fabricated by hot pressing of powders under a pressure of 3.5 × 10⁹ Pa at 773 K. Experimental exchange currents i ₀ (varying from 10⁻³ to 10⁻⁴ A/cm² in the temperature interval from 800 to 1173 K) are comparable with such of materials based of lanthanum-strontium manganite.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 516–522.Original Russian Text Copyright © 2005 by Mazo, Savvin, Mychka, Dobrovol’skii, Leonova.     

Electrostriction around colloid molecules and interfacial action of inhalation anesthetic: Volume function

Poly( -lysine) exists as a polyelectrolyte in an aqueous solution with charged -NH₃⁺ of the side-chain terminals at pH values below 10.5, while it loses the charges above this pH. Due to the electrostatic repulsion, the conformation of the charged form is random coil while that of the uncharged form is helix. The densities of each form were measured by an oscillation densimeter at several poly( -lysine · HBr) concentrations and the apparent molal volumes were estimated. By extrapolating the apparent molal volumes to infinite dilution, the partial molal volumes of each form at infinite dilution were obtained. When expressed by the partial molal volume per residue at infinite dilution, the values were 125.3 cm³ residue⁻¹ for the uncharged form and 112.8 cm³ residue⁻¹ for the charged form at 298.15°K. From the temperature dependence of the partial molal volume, the partial molal expansibilities were found to be 0.070 cm³ residue⁻¹ deg⁻¹ for the uncharged form and 0.106 cm³ residue⁻¹ deg⁻¹ for the charged form. The smaller partial molal expansibility of the uncharged form compared to the charged form is in agreement with the general pattern that hydrophobic macromolecules show smaller expansibility than hydrophilic macromolecules. An inhalation anesthetic, methoxyflurane, did not alter the volume of the uncharged form and expanded only the charged form. At the anesthetic concentration of 1.7 × 10⁻³ m, the partial molal volume of the charged poly( -lysine · HBr) was expanded by 0.27%. The partial molal volume of methoxyflurane in aqueous solution was 108.5 cm³ mole⁻¹ at 278.15°K while that of the pure liquid state was 113.1 cm³ mole⁻¹. The decrease of the partial molal volume of methoxyflurane in aqueous solution is attributable to the structuring of water molecules around the anesthetic. The partial molal volume of the anesthetic in the 1.0 × 10⁻⁴ m charged poly( -lysine · HBr) solution was 110.9 cm³ mole⁻¹. This increase of the partial molal volume of methoxyflurane in the peptide solution indicates that the anesthetic-water contact is partially destroyed by the binding.     

Is small particle size more important than carbon coating? An example study on LiFePO4 cathodes

Based on careful analysis of nine papers by different research groups, we show, for the first time, that in LiFePO₄-based cathode materials the electrode resistance depends solely on the mean particle size. The effect of carbon coating is marginal, it suffices that each LiFePO₄ particle is point-contacted with a reasonable number of carbon black particles usually added in the course of electrode preparation. We present a simple but general theoretical model that consistently explains this unexpected result. The main reason for the relatively small importance of carbon coatings is the fact that the ionic conductivity (ca. 10⁻¹¹–10⁻¹⁰ S cm⁻¹ at RT) is much smaller than the electronic (>10⁻⁹ S cm⁻¹ at RT). The present finding could be of significant importance not only for further optimization of LiFePO₄ cathodes, but also for preparation of other cathode materials in which the ionic conductivity is much lower than the electronic.     

Synthesis and spectroscopic properties of a new bipyridine-bipyrazoyl(pyridine)-thiocyanato-ruthenium(II) complex

The complex [Ru(II)(dcbpyH₂)(bdmpp)NCS](PF₆) (1) (where dcbpyH₂ is 2,2′-bipyridine-4,4′-dicarboxylic acid, bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine,) is synthesized and characterized extensively by ¹H NMR and ¹³C NMR 1D and 2D, mass spectroscopy, cyclic voltammetry, electronic absorption spectroscopy and IR. The half-wave potential of the Ru(II)/Ru(III) redox couple was measured at E_1/2=+0.795 V versus Ag/AgCl in CH₃CN. The complex presents three intense metal-to-ligand charge transfer (MLCT) (d_M→π_L*) absorption bands centered at 383 (=21 300 M⁻¹ cm⁻¹), 432 (=22 400 M⁻¹ cm⁻¹) and 475 nm (=23 400 M⁻¹ cm⁻¹), respectively. The absorbance is extremely strong between 400 and 500 nm and even at 620 nm, the extinction coefficient is still high (=3768 M⁻¹ cm⁻¹). The strong π-acceptor property of the trans-isothiocyanate ligand compared with the Cl⁻ ligand is probably the cause of the blue-shift observed in complex 1. These properties make the complex potentially promising for the photosensitization process. The incorporation of TiO₂ photoelectrodes derivatized with this complex into a solar cell using a composite polymer/inorganic oxide solid-state electrolyte confirmed its sensitizing ability. Incident monochromatic photon-to-current conversion efficiency (IPCE) values of about 30% and overall energy conversion efficiency (η) of 1.7% were obtained.     

Redox features of β-VOPO4 catalyst using tracer and laser Raman spectroscopy

The oxygen ions of the β-VOPO₄ catalyst were exchanged with an tracer by a reduction–oxidation method and by a catalytic oxidation of but-1-ene using ₂. The bands at 992 and 900 cm⁻¹ were more shifted to lower frequencies than those at 1076 and 1002 cm⁻¹. Applying the correlation between the Raman bands and stretching vibrations in the literature, the exchanged oxygen species were estimated. The results suggest that the P–O–V vacancies corresponding to 992 and 900 cm⁻¹ were responsible for reoxidation and the V=O oxygen corresponding to the 1002 cm⁻¹ band of β-VOPO₄ was not. The (VO)₂P₂O₇ was oxidized to β-VOPO₄ by O₂ above 823 K. The insertion position of oxygen was determined at the bands at 992 and 900 cm⁻¹ of β-VOPO₄ using ₂, which is the same as the exchanged position.     

Preparation and electrical properties of new oxide ion conductors Ce6−xDyxMoO15−δ (0.0 ≤ x ≤ 1.8)

Ce_6−xDy_xMoO_15−δ (0.0 ≤ x ≤ 1.8) were synthesized by modified sol–gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 °C and 800 °C indicated a sharp increase in conductivity for the system containing small amount of Dy₂O₃. The Ce_5.6Dy_0.4MoO_15−δ detected to be the best conducting phase with the highest conductivity (σ_t = 8.93 × 10⁻³ S cm⁻¹) is higher than that of Ce_5.6Sm_0.4MoO_15−δ (σ_t = 2.93 × 10⁻³ S cm⁻¹) at 800 °C, and the corresponding activation energy of Ce_5.6Dy_0.4MoO_15−δ (0.994 eV) is lower than that of Ce_5.6Sm_0.4MoO_15−δ (1.002 eV).     

Vibrational spectroscopic study of the arsenate mineral strashimirite Cu8(AsO4)4(OH)4·5H2O—Relationship to other basic copper arsenates

The basic copper arsenate mineral strashimirite Cu₈(AsO₄)₄(OH)₄·5H₂O from two different localities has been studied by Raman spectroscopy and complemented by infrared spectroscopy. Two strashimirite mineral samples were obtained from the Czech (sample A) and Slovak (sample B) Republics. Two Raman bands for sample A are identified at 839 and 856 cm⁻¹ and for sample B at 843 and 891 cm⁻¹ are assigned to the ν₁ (AsO₄³⁻) symmetric and the ν₃ (AsO₄³⁻) antisymmetric stretching modes, respectively. The broad band for sample A centred upon 500 cm⁻¹, resolved into component bands at 467, 497, 526 and 554 cm⁻¹ and for sample B at 507 and 560 cm⁻¹ include bands which are attributable to the ν₄ (AsO₄³⁻) bending mode. In the Raman spectra, two bands (sample A) at 337 and 393 cm⁻¹ and at 343 and 374 cm⁻¹ for sample B are attributed to the ν₂ (AsO₄³⁻) bending mode. The Raman spectrum of strashimirite sample A shows three resolved bands at 3450, 3488 and 3585 cm⁻¹. The first two bands are attributed to water stretching vibrations whereas the band at 3585 cm⁻¹ to OH stretching vibrations of the hydroxyl units. Two bands (3497 and 3444 cm⁻¹) are observed in the Raman spectrum of B. A comparison is made of the Raman spectrum of strashimirite with the Raman spectra of other selected basic copper arsenates including olivenite, cornwallite, cornubite and clinoclase.     

Direct electrosynthesis and characterization of a new soluble polyfluorene derivative containing carboxyl group in boron trifluoride diethyl etherate

High-quality poly(fluorene-9-acetic acid) (PFAA), a new soluble polyfluorene derivative, was synthesized electrochemically by direct anodic oxidation of fluorene-9-acetic acid (FAA) in boron trifluoride diethyl etherate (BFEE) containing a certain amount of trifluoroacetic acid (TFA). This electrolyte enables facile anodic oxidation of FAA monomer at lower potential (1.05 V vs. SCE). PFAA films with conductivity of 0.53 S cm⁻¹ obtained from this medium showed better redox activity and thermal stability in relation to unsoluble poly(fluorene-9-carboxylic acid). Fluorescent spectral studies indicate that PFAA film with high fluorescence quantum yields and photochemical stability is a good blue-light emitter. The structure and morphology of the polymer were studied by UV–vis, FT-IR, ¹H NMR spectra and scanning electron microscopy, respectively.     

Resonance Raman spectroscopy of mass selected Al2 in an argon matrix

In an excitation range of 620–760 nm, resonance Raman spectra of aluminum dimers (Al₂) in an argon matrix have been obtained for the first time. Temperature annealing experiments were performed to remove Raman lines attributed site effects caused by the Al₂/Ar matrix. We observe a single fundamental at 293.3 (5) cm⁻¹ along with a progression up to 1149 (1) cm⁻¹. Taking successive differences of band centers we obtain spectroscopic constants for the ground state fundamental, ω_e=297.5 (5) cm⁻¹, the anharmonicity, ω_ex_e=1.68 (8) cm⁻¹. Our results are in close agreement with previous experimental results for Al₂ which designate the ground state as a ³Π_u state, and may be considered as confirmation of this assignment.     

Thermodynamics of Binary and Ternary Copper-, Cadmium,and Indium-Containing Semiconducting Phases: An Electrochemical Study

Optimum compositions of ion-selective membranes in quasi-binary systems CuCl-CdCl₂, LiCl-CdCl₂, and In₂S₃-InCl₃ are selected by a method of coulometric titration in cells with solid electrolytes. Transport numbers for ions are close to unity for the optimum compositions; transport numbers for electrons are vanishingly small ( ≺10⁻³ to 10⁻⁴); the electroconductivity is equal to ≈ 10⁻³ S cm⁻¹ at 200°C; the diffusion coefficients for the current-producing component are on the order of 10⁻⁶ to 10⁻⁷ cm² s⁻¹. When using a solid electrolyte of the composition CuCl-CdCl₂, which contains 30 mol % CdCl₂, methods of emf and electroconduction reveal that the region of homogeneity of copper(I) selenide falls in the region of compositions Cu_1.33Se-Cu_2.67Se.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 721–727.Original Russian Text Copyright © 2005 by Leushina, Kolesnikova, Makhanova, Zlomanov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

UV–visible spectrum of the phenyl radical and kinetics of its reaction with NO in the gas phase

Pulse radiolysis transient UV–visible absorption spectroscopy was used to study the UV–visible absorption spectrum (225–575 nm) of the phenyl radical, C₆H₅(), and kinetics of its reaction with NO. Phenyl radicals have a strong broad featureless absorption in the region of 225–340 nm. In the presence of NO phenyl radicals are converted into nitrosobenzene. The phenyl radical spectrum was measured relative to that of nitrosobenzene. Based upon σ(C₆H₅NO)_{270 nm}=3.82×10⁻¹⁷ cm² molecule⁻¹ we derive an absorption cross-section for phenyl radicals at 250 nm, σ(C₆H₅())_{250 nm}=(2.75±0.58)×10⁻¹⁷ cm² molecule⁻¹. At 295 K in 200–1000 mbar of Ar diluent k(C₆H₅()+NO)=(2.09±0.15)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

Studies of the hydrogen evolution reaction on smooth Co and electrodeposited Ni–Co ultramicroelectrodes

The hydrogen evolution reaction (HER) was studied on smooth Co and on electrodeposited Ni–Co ultramicroelectrodes (UMEs) in alkaline solutions at several temperatures by steady-state polarisation curves. The real electrochemical area was previously estimated by cyclic voltammetry to account for the large difference in roughness factor of the two surfaces. The values obtained for the Tafel slopes were very close to 2.303RT/βnF while the ‘apparent’ energies of activation were 59 and 41 kJ mol⁻¹ for Co and Ni–Co, respectively. A common Volmer–Heyrovsky mechanism with Heyrovsky as the rate-determining step (RDS) was initially proposed. This was confirmed when the experimental results were mathematically treated by a non-linear fitting procedure using the kinetic equations derived for that mechanism. The calculations revealed that Ni–Co is a more efficient catalyst for the HER then pure Co, with a rate constant value of 0.16×10⁻¹⁰ mol s⁻¹ cm⁻² at 25°C for the slow step. Although this value is more than one order of magnitude smaller than that already reported for deposited Ni, it is considerably larger than the one measured here (0.02×10⁻¹⁰ mol s⁻¹ cm⁻²) for pure Co at 25°C.     

EPR and optical absorption studies of Cr ions in d-gluconic acid monohydrate

EPR studies are carried out on Cr³⁺ ions doped in d-gluconic acid monohydrate (C₆H₁₂O₇·H₂O) single crystals at 77 K. From the observed EPR spectra, the spin Hamiltonian parameters g, |D| and |E| are measured to be 1.9919, 349 (×10⁻⁴) cm⁻¹ and 113 (×10⁻⁴) cm⁻¹, respectively. The optical absorption of the crystal is also studied at room temperature. From the observed band positions, the cubic crystal field splitting parameter Dq (2052 cm⁻¹) and the Racah interelectronic repulsion parameter B (653 cm⁻¹) are evaluated. From the correlation of EPR and optical data the nature of bonding of Cr³⁺ ion with its ligands is discussed.