Electrochemical characterization of a composite polymer electrolyte with improved lithium metal electrode interfacial properties

In the development of rechargeable lithium polymer batteries it is of paramount importance to control the passivation phenomena occurring at the lithium electrode interface. It is well estabilished that the type and the growth of the lithium passivation layer is unpredictably influenced by the presence of liquid components and/or impurities in the electrolyte. Therefore, one approach to improve the stability of the lithium interface is the use of liquid-free, highly pure electrolytes. The electrochemical properties of a composite polymer electrolyte obtained by hot pressing a mixture of polyethylene oxide (PEO), a lithium salt (lithium tetrafluoroborate, LiBF₄) and a powdered ceramic additive (γ-LiAlO₂), will be presented and discussed. The electrochemical characterization included the determination of the ionic conductivity, the anodic break-down voltage and, most importantly, the stability of the lithium metal electrode interface and the lithium stripping-plating process efficiency. The main feature of this dry, true solid-state electrolyte is a very good compatibility with the lithium metal electrode, demonstrated by a very high lithium cycling efficiency, which approaches a value of 99%. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

A new decomposition approach for the single machine total tardiness scheduling problem

This paper deals with the single machine total tardiness problem. From Emmons’ basic dominance conditions a new partition theorem is derived which generalises Lawler’s decomposition rule and leads to a new double decomposition procedure. This procedure is embedded into a branch and bound method which applies a new lower bound based on due dates reassignment. The branch and bound method is tested on problems with size up to 150 jobs.     

Wormlike micelles mediated by polyelectrolyte

Aqueous solutions of the anionic surfactant potassium oleate (K-oleate) were studied using small-angle neutron scattering (SANS), steady-state rheology, and cryogenic transmission electron microscopy (cryo-TEM). The micellar structural changes induced by the addition of potassium chloride (KCl) and sodium polystyrenesulfonate (PSS) of different molecular weights were investigated. Upon addition of KCl, a transition from spherical to wormlike micelles was detected from the SANS data and confirmed by the cryo-TEM pictures. The rheological measurements revealed a strong dependence of the low-shear viscosity on the concentration of salt: a broad maximum in the viscosity curve was observed upon addition of KCl, characteristic of the growth of micelles into long worms, followed by branching. The addition of PSS to salt-free solutions of K-oleate had a significant effect on the scattering patterns, revealing partial growth of the spherical micelles into rodlike micelles. In contrast, in the presence of high salt concentrations, addition of PSS to solutions of wormlike micelles did not bring any noticeable modifications in the scattering. However, in the same salt conditions, a clear effect was observed on the low shear viscosity upon addition of PSS, which was found to depend significantly on molecular weight. This suggests a novel way of impacting the viscosity of solutions of wormlike micelles.     

QUANTITATIVE ANALYSIS OF INTRACELLULAR BEHAVIOUR OF PORPHYRINS

Abstract Fluorometric analysis performed on L 1210 cells after treatment with Photofrin indicated that the interactions with cellular structures induce a significant modification of the equilibria among the different porphyrin species. This modification turned out to be dependent on the uptake and release processes. Thus, a comparative analysis of the dynamic aspects of the drug accumulation process was performed on cells treated with hematoporphyrin, Photofrin and Photofrin II. The results obtained were interpreted taking into account the different chemical composition of the drugs employed. The porphyrin species mainly released seem to be the monomeric ones and 'unfolded oligomers'. The release process results in further modifications of the aggregation and/or configu-rational state of intracellular porphyrins due to altered internal equilibrium.     

Numerical simulation of bubble and droplet deformation by a level set approach with surface tension in three dimensions

In this paper we present a three‐dimensional Navier–Stokes solver for incompressible two‐phase flow problems with surface tension and apply the proposed scheme to the simulation of bubble and droplet deformation. One of the main concerns of this study is the impact of surface tension and its discretization on the overall convergence behavior and conservation properties. Our approach employs a standard finite difference/finite volume discretization on uniform Cartesian staggered grids and uses Chorin's projection approach. The free surface between the two fluid phases is tracked with a level set (LS) technique. Here, the interface conditions are implicitly incorporated into the momentum equations by the continuum surface force method. Surface tension is evaluated using a smoothed delta function and a third‐order interpolation. The problem of mass conservation for the two phases is treated by a reinitialization of the LS function employing a regularized signum function and a global fixed point iteration. All convective terms are discretized by a WENO scheme of fifth order. Altogether, our approach exhibits a second‐order convergence away from the free surface. The discretization of surface tension requires a smoothing scheme near the free surface, which leads to a first‐order convergence in the smoothing region. We discuss the details of the proposed numerical scheme and present the results of several numerical experiments concerning mass conservation, convergence of curvature, and the application of our solver to the simulation of two rising bubble problems, one with small and one with large jumps in material parameters, and the simulation of a droplet deformation due to a shear flow in three space dimensions. Furthermore, we compare our three‐dimensional results with those of quasi‐two‐dimensional and two‐dimensional simulations. This comparison clearly shows the need for full three‐dimensional simulations of droplet and bubble deformation to capture the correct physical behavior. Copyright © 2009 John Wiley & Sons, Ltd.     

The analytical resolution of parallel first‐ and second‐order reaction mechanisms

Given the species A₁ and A₂, the competition among the three different elementary processes (1) (2) (3) is frequently found in thermal and photochemical reaction systems. In the present paper, an analytical resolution of the system (1)–(3), performed under plausible contour conditions, namely, finite initial molar concentrations for both reactants, [A₂]₀ and [A₁]₀, and nonzero reaction rate coefficients k₁, k₂, and k₃, leads to the equation [A₁] = ((δ[A₂]^γ ? [A₂])/β) ? α, where α = k₁/2k₃, γ = β + 1 = 2k₃/k₂, and δ = ([A₂]₀ + β[A₁]₀ + β α))/[A₂]₀^γ. The comparison with a numerical integration employing the fourth‐order Runge–Kutta algorithm for the well‐known case of the oxidation of organic compounds by ferrate ion is performed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 562–566, 2010     

Conductivities and transport properties of gelled electrolytes with and without an ionic liquid for Li and Li-ion batteries

Conductivity and transport properties have been determined for gelled polymer electrolytes of three compositions: a base PVdF-polymer gel with organic carbonate solvents as plasticizers and LiN(SO(2)C(2)F(5))(2) electrolyte, a second polymer electrolyte with 5 mass % 1-ethyl-3-methylimidazolium bisperfluoroethylsulfonyl imide (EMI-BETI) added to the base polymer electrolyte, and a third PVdF polymer electrolyte using only EMI-BETI as the plasticizer. Conductivities were studied over the temperature range +25 to -40 degrees C, and for all three gels, the temperature dependence of the conductivities was found to follow the VTF equation, which is consistent with the free volume model for ion transport. For the gel containing 5 mass % EMI-BETI, transport numbers were determined from +50 to -20 degrees C and were found to decrease as the temperature decreased. Although there are no theoretical models to treat and interpret the temperature dependence of transport numbers, we found that a modified VTF equation resulted in an excellent fit to the temperature dependence of the transport number, which is another confirmation of a free volume model for transport in these gelled polymer electrolytes.     

1,3-Dipolar cycloaddition of nitrones with α,β-unsaturated sulfones

C,N-Diphenyl nitrones react with substituted α,β-unsaturated phenylsulfones yielding isoxazolidinic cycloadducts whose structure and stereochemistry were assigned on the basis of ¹H and ¹³C nmr data. The ycloaddition regioselectivity is discussed in accordance with frontier orbital considerations.     

Excimer laser-induced temperature jump-measurements on the recombination kinetics of the gas-phase FSO3 + FSO3 ⇔ F2S2O6 equilibrium between 415 and 525 K

The kinetics of the recombination reaction corresponding to the FSO₃ + FSO₃ ? F₂S₂O₆ equilibrium system has been studied. A time-resolved absorption spectroscopy technique was employed to monitor the appearance of thermally generated FSO₃ radicals at 450 nm following a small temperature jump induced after partial laser photodissociation of F₂S₂O₆ at 193 rim. The recombination rate constants have been determined over the temperature range 415–525 K and a N₂ pressure range 10–600 torr. The reaction was found to be in its first order regime. The resulting limiting high pressure rate constants were combined with previous values measured in this laboratory at lower temperatures yielding the expression ??_{rec, x} = (4.5 ± 0.2) × 10^?14 (T/300)^{(1.0 ± 0.1)} cm³ molecule^?1 s^?1 between 293 and 525 K. The temperature coefficient of ??_{rec, x} is smaller than the one derived from steady-state experiments of the thermal dissociation of F₂S₂O₆ and the equilibrium constant of the system. A recently formulated version of the canonical statistical adiabatic channel model was used to interprete the rate constants.     

J(23)cis and J(23)trans of 2-carbonyl substituted 2,3-dihydrobenzofurans

The J(23)cis and J(23)trans values in several 2-carbonyl substituted 2,3-dihydrobenzofurans were measured. Although J(cis)>J(trans), the values found disagree with the Karplus rule.