Conductivities and ion association of 1:1 electrolytes in mixed aprotic solvents

Molar conductivities of the 1:1 electrolytes LiClO₄, LiAsF₆, n-Bu₄NClO₄ and n-Bu₄NBPh₄ were measured in mixtures of propylene carbonate and dimethoxymethane over the concentration range 0.01?1 × 10^?4 mol dm^?3. In all cases a maximum in molar conductivity (and hence in electrolytic conductivity) is observed in a solvent mixture having a composition of around 40 mass % propylene carbonate. Molar conductivities at infinite dilution (Λ^∞) and thermodynamic ion association constants (K^∞_a) were evaluated from these data. Single ion molar conductivities (λ^∞_i) were evaluated using the assumption that λ^∞(n-BuN⁺₄) = λ^∞(BPh^?₄). In order to account for the observed conductivity behavior it is necessary to assume that lithium salts from solvent separated ion pairs in ethereal solvents. All other salts from contact ion pairs.     

Kinetic models for alloy and semiconductor electrodeposition

The residence time τ of an atom in a kink site position is a characteristic property of a growing phase. For alloys kink site positions and associated residence times must be defined for the different alloy components. For instance, for an alloy AB kink site positions A^* and B^* must be distinguished. Each kink site atom can react either with ions of type A or B to form new kink site positions AA^*, AB^*, BA^* or BB^*. The selectivity of the kink site positions for either A or B can be expressed by residence times τ_AA, τ_AB, τ_BA and τ_BB. Another characterization of the selectivity is possible by the application of the finite Markov chain theory. Then selectivity constants g_A and g_B can be defined. Assuming equilibrium between the atoms in kink site positions and the respective ions in the electrolyte, the selectivity constants represent the ratios of the respective equilibrium constants between kink site positions and electrolyte concentrations g_A = K_AA/K_AB and g_B = K_BB/K_BA. If the process is rate-controlled, the selectivity constants represent the ratios of the respective rate constants of deposition. The model is applied to CoNi and SnNi alloys and to bismuth telluride. A relation is derived between selectivity constants and residence times.     

The nature of phase transitions of symmetric diblock copolymer melts under confinement

The effects of confinement, both the structure frustration and the surface field, on phase transitions of symmetric diblock copolymer melts are investigated within several theoretical methods on the mean-field level. Confinements are applied by restricting polymer chains in the finite spaces of slabs. The surface can be neutral or preferential depending on the strength of the surface field. Within the one-dimensional self-consistent mean-field theory, for the neutral surface case, an oscillative behavior is observed for the size dependence of the order-disorder transition (ODT) point (χN)_t due to the structure frustration. The spinodal (χN)_s for this corresponding confined system is also calculated using the Gaussian fluctuation theory and the Landau-Brazovskii theory, and (χN)_s coincides exactly with (χN)_t. On the other hand, the surface effect plays the role to decrease (χN)_t due to the surface-induced spatial oscillation for the preferential surface case. In all confined systems considered, the ODT for symmetric diblock copolymer melts is a continuous second-order phase transition in the present mean-field calculation.     

Accuracy of approximations for CIELAB chroma and hue difference computation

The transformation in CIELAB from differences in the L^*, a^*, b^* coordinates to those in lightness, chroma, and hue, ΔL^*, ΔC_ab^*, ΔH_ab^*, can be approximated by a rotation in 3-space. Expressions for the error in the approximation of chroma and hue differences are developed. Significant errors are introduced if either the hue angle or chroma difference between reference and sample colors are large. A computed example illustrates the use of the analysis. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 61–64, 1997.     

Thermodynamic parameters of polyacrylamides in water

The heats of dilution of polyacrylamide and its N-methyl derivatives have been measured calorimetrically. Their apparent partial specific volumes have also been determined. For the unsubstituted polymer, χ_h was endothermic whereas for both the N-substituted polymers χ_h was exothermic. From a comparison with similar data on small amides it was thought likely that the endothermic heat of dilution arose from the energy required to separate the amide dipoles. The difference between the exothermic and endothermic heats of dilution may arise from the different mutual orientations of the substituted and unsubstituted amide groups. Osmotic pressure data indicates that water is a poor solvent for polyacrylamide.     

Study of morphology and phase diagram of the H-shaped (AC)B(CA) ternary block copolymers using self-consistent field theory

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymer systems, the micro-phase morphologies of the H-shaped (AC)B(CA) ternary block copolymer system are studied in three-dimensional (3D) space. By systematically varying the volume fractions of the components A, B, and C, six triangle phase diagrams of this H-shaped (AC)B(CA) ternary block copolymer system with equal interaction energies among the three components are constructed from the weaker segregation regime to the strong segregation regime. In this study, thirteen 3D micro-phase morphologies for this H-shaped ternary block copolymer system are identified to be stable and seven 3D micro-phase morphologies are found to be metastable. It is found that in the weaker segregation regime (χ_ABN = χ_ACN = χ_BCN = 45), the minority component can be mixed with other two majority components to form the mixed phase regions, while in the intermediate segregation regime (χ_ABN = χ_ACN = χ_BCN = 60 and 75), the mixed phase regions phase-separate into three distinct phase regions. In the strong segregation regime (χ_ABN = χ_ACN = χ_BCN = 90, 100, and 125), the distinct blocks tend to separate with each other and the phase behavior of this H-shaped (AC)B(CA) ternary block copolymer is similar to that of the three-arm star-like ABC ternary block copolymer. Moreover, the order-disorder transitions and the order-order transitions by varying the interaction parameters are discussed. These results may help in the design of the microstructures of complex block copolymers.     

Determination of transition points and thermodynamic interaction parameters of poly(2,6-dimethyl-1,4-phenylene oxide)

Abstract

The specific retention volumes V _g⁰ of n-butyl acetate, isobutyl acetate, isoamyl acetate, n-undecane, n-dodecane, n-tridecane, ethyl benzene, n-propyl benzene, isopropyl benzene and chloro benzene on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were obtained by inverse gas chromatography. Below glass transition temperature, two secondary transition points of PPO which occur at 90 and 130°C were observed from the retention diagrams of n-butyl acetate, isobutyl acetate and isoamyl acetate.

Weight fraction activity coefficient at infinite dilution Ω ₁^∞, Flory–Huggins polymer–solvent interaction parameter χ ₁₂^∞, hard core polymer–solvent interaction parameter χ ₁₂^* and effective exchange energy parameter X _eff were determined from the experimental V _g⁰ of studied solvents on PPO at temperatures above 220°C by inverse gas chromatography.     

SYNERGISTIC EXTRACTION OF CADMIUM AND ZINC WITH 1-PHENYL-3-METHYL-4-BENZOYLPYRAZOL-5-OL AND n-DODBCYLAMINE MIXTURES,EMULSION FORMATION.

The synergistic extraction of zinc and cadmium (M^2*) from sulphate, nitrate and perchlorate media with mixtures of 1-phenyl-3-methyl-4-benzoylpyra2ol-5-ol (HL) and n-dodecylammoniura salts (DDAH^*,X^?) in toluene has been studied. In sulphate medium, the lipophilic ammonium pyrazololate (DDAK^*L^?) is the predominating ammonium species : the synergy observed can be considered as the addition of (DDAH^*,L^?) on HL₂ perchlorate and nitrate media, the amphiphilic ammonium salts {DDAH^*, CIO₄?) and (DDAH⁺N0₃ ^?) predominate, leading to the formation of an aqueous emulsion in equilibrium with a clear organic phase. Metal distribution curves show that the formation of the lipophilic synergistic species (DDAH⁺ML₂ ^?) results from a X^?/ML₃ ^? exchange in the interfacial region between the aqueous and the organic phase. The addition of n-octanol or 4-nonylphenol in the organic phase turns the emulsion into a micro-emulsion whereas the substitution of toluene by chloroform largely decreases the emulsion stability.     

Novel role of polymer-solvent and clay-solvent interaction parameters on the thermal, mechanical and optical properties of polymer nanocomposites

Solvent-polymer and solvent-clay interactions are very important in determining the properties of polymer-clay nanocomposites. In the present work, hydrogenated nitrile rubber-sepiolite nanocomposites were prepared and the interaction parameters of various solvents with rubber (χ_AB) and clay (χ_CD) were studied. Nine different sets of solvent combination were chosen based on their solubility parameter. A correlation between thermal, mechanical and optical transmittance properties of polymer-clay nanocomposites and the difference in their interaction parameters with various solvents (χ_AB − χ_CD) was analyzed for the first time. This study helped to identify chloroform/methyl ethyl ketone as the best solvent combination, where temperature at which maximum degradation of the polymer took place was raised by 65 °C and tensile strength and modulus at 100% elongation were enhanced by almost 200% over the neat rubber. The results were correlated with the data of X-Ray Diffraction study, Atomic Force Microscopy and Transmission Electron Microscopy. Finally, thermodynamic interpretation was made to explain the results.     

The effects of dilution rate and glucose concentration on continuous acetone–butanol–ethanol fermentation by Clostridium acetobutylicum immobilized on bricks

BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of butanol through biological routes has attracted increasing attention. However, low butanol productivity severely impedes its potential industrial production. It is known that the immobilization of whole cells can enhance productivity in the acetone‐butanol‐ethanol (ABE) continuous fermentation process. Therefore, the objective of this study was to develop a low‐cost continuous operation for butanol production. RESULTS: Bricks were chosen as cell support because of their low cost and ease of use for immobilization. The solvent productivity for the bricks with immobilized cells was 0.7 g L^?1 h^?1, 1.89 times that of free cells (0.37 g L^?1 h^?1) at a dilution rate of 0.054 h^?1. The productivity improvement can contribute to greater retention of biomass inside the reactor due to immobilization. The increase in glucose feed concentration raised total solvent production. However, it resulted in a decrease in yield (grams of solvents produced per gram of glucose introduced). Continuous operation with immobilized cells at a dilution rate of 0.107 h^?1 resulted in a solvent productivity of 1.21 g L^?1 h^?1, 2.1 times that of the operation at 0.027 h^?1. However, the yield (butanol produced per glucose consumed) was decreased to 0.19 from 0.29 under the same glucose feeding condition of 60 g L^?1. CONCLUSION: The increase in dilution rate and feed glucose concentration enhanced productivity, but decreased the utilization of substrates and the final solvent concentration. Therefore, a balance between productivity and glucose utilization is required to ensure continuous process operation. Copyright © 2011 Society of Chemical Industry     

Uranyl ion-selective optical test strip

A novel, optical sensor, test strip has been developed for the spectrophotometric determination of trace amounts of uranyl ions, UO₂²⁺, based on immobilization of C.I. Mordant Blue 29 (Chromazurol S)/cetyl N,N,N-trimethyl ammonium bromide ion pair on a triacetyl cellulose membrane. Optimization of the sensor for the detection of low levels of uranyl ion is described. The test strip responded linearly to uranyl ions between 3.0 × 10^?7 and 6.0 × 10^?5 mol L^?1; the reproducibility of the sensor at a medium level of UO₂²⁺ activity was ±0.55%. The optical sensor can be regenerated using 0.01 mol L^?1 HCl or 0.01 mol L^?1 NaF solution after 10 min. The developed test strip was used in the determination of UO₂²⁺ in ground water samples.     

Transition behavior of PS-b-PMMA films on the balanced interfacial interactions

The thickness dependence of the order-to-disorder transition (ODT), measured by in situ grazing-incidence small-angle X-ray scattering (GISAXS), has been investigated in thin films of a symmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) on a random copolymer (P(S-r-MMA)) grafted to the substrate where the interfacial interactions are balanced. With decreasing film thickness less than 25L₀, the ODT significantly decreases to 193 °C for film of 10L₀ in thickness, because the interfacial interactions by a random copolymer grafted to the substrate provide a surface-induced compatibilization toward two block components. However, a plateau of the ODT at ∼213 °C for films thicker than 25L₀ was observed above the bulk value of 200 °C. The elevation of this ODT indicates a suppression of compositional fluctuations normal to the film surface, more than likely because the dominant orientation of the lamellar microdomains was found to be parallel to the film surface.     

Turbulence level significance of the coalescence-dispersion rate parameter

The random coalescence-and-dispersion (C–D) models for non-ideal mixing in reactors involve a rate parameter, I, which is the frequency of the coalescence and dispersion events divided by the available number of coalescence sites per unit residence time, where residence time is a measure of reactor size. An approximate relationship between I and hydrodynamic parameters has been found by carefully comparing C–D computations, where I varies with location, with actual measurements of the turbulent energy dissipation rate, ε, and the turbulence length scale, L_s, in a tubular reactor. At each location I was determined such that the calculated conversion of a second-order reaction matched the measured conversion. The relationship found was: I≈ 1333(ε/L_s²)^{$\text{1}\text{3}$}(^?τ/N) where L_s, is the length scale of segregation, ε has dimensions of velocity squared per unit time, and (^?τN) is the residence time divided by the number of coalescence sites.The relationship above was applied to the C–D modeling of a semi-batch reactor with a consecutive-competitive reaction. The resulting yields and selectivities under the various conditions of the experimental data were very close to experimental results.     

Synthesis,Surface Activities and Toluene Solubilization by Amine-oxide Gemini Surfactants

A series of amine-oxide gemini surfactants featuring amide groups [N, N’-dimethyl-N, N’-bis(2-alkylamideethyl)-ethylenediamine oxide (alkyl = C₁₁H₂₃, C₁₃H₂₇, C₁₅H₃₁, C₁₇H₃₅)] have been synthesized via a three-step synthetic route, and their chemical structures were confirmed by mass spectra, FTIR and ¹H-NMR spectra. The surface activities of these compounds have been measured. The results show that these synthesized amine-oxide gemini surfactants reduced the surface tension of water to a minimum value of approximately 26.91 mN m^?1 at a concentration of 2.92 × 10^?5mol L^?1. Furthermore, their critical micelle concentration (CMC) values and solubilization of toluene decrease with an increase of the hydrophobic chain length from 12 to 18. Isoelectric point measurements revealed that their pI values range from 4.0 to 10.5.     

Electrochemical parametrization of a series of penta- and tetradentate EDTA complexes of ruthenium

This paper reports on the electrochemical parametrization of a series of mono- and disubstituted ruthenium–EDTA complexes (EDTA = ethylenediamine-N,N,N^′,N^′-tetraacetate ligand) on the basis of Lever’s parameters (E_L). The electrochemical parameters for 45 ligands with unknown E_L have been compiled.     

Electrochemical impedance spectroscopy study during accelerated life test of conductive oxides: Ti/(Ru + Ti + Ce)O2-system

Ti-supported (Ru + Ti + Ce)O₂-electrodes were prepared at 450 °C and the service life, t_6V, determined recording chronopotentiometric curves at 0.75 A cm⁻² (25 ± 1 °C). The results revealed a strong influence of the nominal cerium concentration, [CeO₂]_N, on t_6V, showing substitution of Ti by Ce causes a major decrease in t_6V. The degree of electrode instability, Λ, calculated from the slope of the linear segment present in the chronopotentiometric profiles, showed [CeO₂]_N exerts a strong influence on Λ. Voltammetric curves recorded at several anodisation times, t, support final electrode deactivation is due to Ti-support passivation. The chronopotentiometric and voltammetric data permitted to present a model for the porous electrode/electrolyte interface. The electrochemical impedance spectroscopic, EIS, investigation as function of t supports the proposed model denouncing a fast growth a TiO₂ interlayer at the Ti^o/oxide interface for [CeO₂]_N ≥ 30 mol%. The studies also support substitution of Ti by Ce leads to an increase in the coating porosity, thus favouring electrode deactivation by passivation of the Ti-substrate. The model proposed for the porous electrode/electrolyte interface combined with the results of the EIS investigation permitted to propose an equivalent circuit to describe the modifications occurring in the electrode structure during anodisation. The true electrocatalytic activity for the oxygen evolution reaction, OER, depends on t and [CeO₂]_N. The dependency of the inductive behaviour on t was investigated according to the model proposed for the effective inductance, L_E, in the high frequency domain.     

Supersaturation of oxygen in acidic solution in the vicinity of an oxygen-evolving platinum anode

The concentration of O₂ in 1 M H₂SO₄ solution in the vicinity of the O₂-evolving smooth Pt anode was measured as a function of anodic cdi_a using the galvanostatic potential—transient method.The solution near the O₂-evolving anode was supersaturated with O₂. When the anodic current was interrupted, supersaturated concentration C^* decreased at a rate proportional to C^*  C₀, where C₀ is the solubility of O₂ in the electrolyte at 1 atm. The rate constant of the decay of the supersaturation under the open circuit condition was measured to be 0.069 sec^?1 at 25°C.At i_a < 40 mA/cm² there was a linear relation between log(C^*  C₀) and log i_a. At i_a > 200 mA/cm², however, the supersaturation exhibited a limiting value of 9.0 × 10^?2 mol/l.     

An efficient method for a numerical description of virgin olive oil color with only two absorbance measurements

Four polynomial expressions are obtained that provide a good approximation and an easy, rapid calculation of the chromatic coordinates and the chroma—L ^*, a ^*, b ^*, and C—for the illuminant C and the standard observer, for a virgin or extra virgin olive oil; absorbance is measured at only 480 and 670 nm. These are as follows: L ^*=0.556458(A₄₈₀)²−2.51145A₄₈₀+0.55504(A₆₇₀)²−8.53016A₆₇₀+98.4089; a ^*=0.177372(A₄₈₀)²+2.1363A₄₈₀+1.43254(A₆₇₀)²−0.789231A₆₇₀−13.9246; b ^*=−16.0277(A₄₈₀)²+79.8932A₄₈₀−5.06558(A₆₇₀)²+3.36169A₆₇₀+31.9405; C=−15.8439(A₄₈₀)²+78.9312A₄₈₀−5.26784(A₆₇₀)²+3.56917A₆₇₀+33.3927. These give acceptable results, making the method a practical alternative to the extremely laborious Commission Internationale d’Eclairage (CIE) L ^* a ^* b ^* system, by which 391 absorbance values must be measured individually, nanometer by nanometer, before applying more complex equations. The validity of the proposed method has been confirmed by comparison, using a set of 20 sample oils different from the set of 25 oils used to generate the order of the equations. The variations between the values provided by the proposed and standard methods, respectively, had a mean of 0.00 for each of the chromatic variables—L ^* , a ^* , b ^* , and C; SD were moderate (0.71, 0.52, 1.22, and 1.22, respectively); the root mean square and the R ²-terms also confirmed the validity of the method.     

Solvothermal in situ synthesis of (Schiff-base)-containing dinuclear cobalt compound

A new dinuclear cobalt compound, namely Co₂(L)(H₂O)Cl₂ (1, H₂L = N,N′-o-phenylenebis(salicylide-neimine) was obtained by one-pot solvothermal self-assembly of CoCl₂, 1,2-phenylenediamine, and salicylaldehyde in C₂H₅OH. The magnetic studies suggest weak antiferromagnetic behavior and the magnetic data were interpreted by means of a dinuclear cobalt model with the parameters of g = 2.12, J = ?1.25 cm^?1, θ = ?3.12 K.     

Decomposition of pyrite under coal liquefaction conditions: A kinetic study

The decomposition of FeS₂, both as a single phase and as it exists in coal, has been studied between 250 and 350 °C, in hydrogen and nitrogen atmospheres, and in the presence of a coal-derived solvent. The first-order rate constant for decomposition of FeS₂ at 350 °C with H₂ alone is 6.7 × 10^?1min^?1; with H₂ and coal-derived solvent, it is 5.5 × 10^?2min^?1; for FeS₂ contained within coal, solvent and H₂, it is 8.6 × 10^?3min^?1. Although the rate constant for decomposition is dependent upon temperature and the system, the activation energy in each case has been calculated to be 88 kJ mol^?1. A mechanism consistent with these data is the thermal decomposition of FeS₂ to produce Fe_1?xS and S, followed by reaction of the sulphur with available hydrogen (from H₂, solvent or coal) to form H₂S.