bluuebunny/crossref_metadata_2025 huggingface dataset:
Wide Range Control of Microstructure and Mechanical Properties of Carbon Nanotube Forests: A Comparison Between Fixed and Floating Catalyst CVD Techniques
Authors: Yaglioglu Onnik , Cao Anyuan , Hart A. John , Martens Rod , Slocum A. H.
Published: July 2012

Vertically aligned carbon nanotube (CNT) forests may be used as miniature springs, compliant thermal interfaces, and shock absorbers, and for these and other applications it is vital to understand how to engineer their mechanical properties. Herein is investigated how the diameter and packing density within CNT forests govern their deformation behavior, structural stiffness, and elastic energy absorption properties. The mechanical behavior of low‐density CNT forests grown by fixed catalyst CVD methods and high‐density CNT forests grown by a floating catalyst CVD method are studied by in situ SEM compression testing and tribometer measurements of force‐displacement relationships. Low‐density and small‐diameter CNT columns (fixed catalyst) exhibit large plastic deformation and can be pre‐deformed to act as springs within a specified elastic range, whereas high‐density and large‐diameter CNT columns (floating catalyst) exhibit significant elastic recovery after deformation. In this work the energy absorption capacity of CNT forests is tuned over three orders of magnitude and it is shown that CNT forest density can be tuned over a range of conventional foam materials, but corresponding stiffness is ∼10× higher. It is proposed that the elastic behavior of CNT forests is analogous to open‐cell foams and a simple model is presented. It is also shown that this model can be useful as a first‐order design tool to establish design guidelines for the mechanical properties of CNT forests and selection of the appropriate synthesis method.
Phase Equilibria of Multicomponent Fluid Systems to High Pressures and Temperatures
Authors: Heilig M. , Franck E. U.
Published: July 2012

An equation of state, suggested previously, has been extended and applied to calculate phase equilibria and critical phenomena of ternary and quaternary fluid systems to high temperatures and pressures. The equation consists of a modified hard sphere repulsion term and an additive perturbation term based on a square well potential to account for molecular attraction. The procedure of calculation is described. It uses exclusively binary interaction parameters, derived from properties of the binary sub‐systems. — In order to compare the calculated results, phase diagrams have been experimentally determined for the system H2O—N2‐hexane to 679 K and 270 MPa. The experimental procedure is described. The comparison is made with isothermal and isobaric prismatic diagrams. The agreement is satisfactory above 500 K. Results of calculations are also shown for the ternary systems H2O—N2—CO2and H2O—CO2‐hexane as well as for the quaternary system H2O—N2—CO2‐hexane.
The Reaction of OH Radicals with 1,1‐di‐, tri‐ and tetrachloroethylene
Authors: Kirchner K. , Helf D. , Ott P. , Vogt S.
Published: July 2012

The kinetics and product formation of the homogeneous gas‐phase reactions of the OH radical with 1,1‐di‐, tri‐ and tetrachloroethylene were investigated at temperatures between 298–459 K, in the pressure range of 0.5–5.6 mbar. Measurements were made in a discharge‐flow apparatus, using helium as the carrier gas. The OH radical and the reaction products were detected by mass spectrometry. The rate constants were observed to be pressure independent in the case of 1,1‐di‐ and tetrachloroethylene but slightly pressure dependent in the case of trichloroethylene. The temperature dependencies can be expressed by the Arrhenius equation (in units of 1012 cm3 mol−1 s−1).

k(T) = (0.136 ± 0.016) exp[(9.5 ± 0.4) kJ mol−1/RT] for 1,1‐dichloroethylene,

k(T) = (0.470 ± 0.051) exp[(2.0 ± 0.5) kJ mol−1/RT] for trichloroethylene, and

k(T) = (3.33 ± 0.19) exp[−(8.6 ± 0.1) kJ mol−1/RT] for tetrachloroethylene.

The major products are: CH2OH — CCl2 for 1,1‐dichloroethylene; 2,2‐dichloroethenol and Cl for trichloroethylene; trichloroethenol, dichloroacetyl chloride, Cl, CHCl2 and phosgene for tetrachloroethylene.
Self‐Diffusion and Conductance Studies of Acetonitrile — Water Solutions of Tetraethylammonium Iodide
Authors: Hawlicka E. , Grabowski R. , Reimschüssel W.
Published: July 2012

The self‐diffusion coefficients of acetonitrile, water and iodide ion and the conductance of Et4NI have been measured at 25.0°C in acetonitrile water mixtures for the whole composition range of the binary solvent, for the salt molarity ranging from 3 · 10−5 to 1 · 10−2. The limiting self‐diffusion coefficient of iodide ions is in the range between 1.6 · 10−5 and 2.8 · 10−5 cm2 s−1 with a minimum at about 10 mole% CH3CN, whereas the limiting self‐diffusion coefficient of tetraethylammonium ions increases monotonously form 0.8 · 10−5 in aqueous solution up to 2.2 · 10−5 in acetonitrile solution. Basing on the composition dependences of ionic radii an influence of the mixed solvent composition on the solvation of ions is discussed. Tetraethylammonium ion has been found to be unsolvated and to lose its hydrophobic properties in the presence of acetonitrile. The association constant, calculated from the conductivity measurements, increases monotonously with decreasing static dielectric constant of the acetonitrile‐water mixtures. The decrease of the self‐diffusion coefficients of water and of acetonitrile in the presence of Et4NJ results from the increase of the solution viscosity. The lack of the effect of Et4NI on the microphase separation of the acetonitrile‐water mixtures has been observed.
Dielectric Properties of Morpholine and Some of Its Derivatives in the Pure Liquid State and in Mixtures with Benzene or Water
Authors: Beine A. H. , Lux A. , Stockhausen M. , Jadyn J. , Czechowski G. , Zywucki B.
Published: July 2012

The following substances are regarded as pure liquids and in benzene mixtures: morpholine, 2,6‐dimethylmorpholine, N‐methyl‐(MeMo), N‐ethyl‐, N‐cyano‐(CyMo) and N‐formylmorpholine (FoMo). Their dielectric constant and complex permittivity over the whole dispersion range (up to 72 GHz) are determined at 20°C. By comparing dipole moments in dilute benzene solution and in the pure state and by considering the relaxation times, probable molecular conformations and the association behaviour are discussed. Chair forms are most likely, but some parameters point to enhanced planarity of CyMo and FoMo. Self‐association (probably dimerization) occurs if there is no N‐substituent. Additional relaxation measurements on aqueous mixtures of MeMo and FoMo reveal a considerable tendency towards hetero‐association.
A Thermodynamic Study of Pd — Ce Alloys Using CeF3 as Electrolyte
Authors: Bretschneider Th. , Schaller H.‐J.
Published: July 2012

The activity of Ce in Pd — Ce alloys was determined between 1000 and 1100 K by emf measurements on fluorine concentration cells with CeF3 as a solid electrolyte. The method of coulometric titration was used to deposit Ce on a thin Pd film and to control the composition of the alloys produced in situ. The system is characterized by pronounced negative deviations from ideal behavior which are attributed to the levelling of the Fermi energies upon the transfer of cerium valence electrons to the bands of the alloy. Including the lattice distortion as an additional effect, the thermodynamic behavior of Ce and other electropositive metals dissolved in Pd can be correlated and well described.
Thermodynamic Behavior of Hydrogen in Palladium‐Gadolinium Solid Solution Alloys
Authors: Sakamoto Y. , Chen F. L. , Furukawa M. , Flanagan Ted B.
Published: July 2012

The thermodynamic quantities for absorption of hydrogen by disordered Pd — Gd solid solution alloys containing up to 8.0 at.% Gd have been determined at temperatures between 273 and 473 K and hydrogen pressures up to 100 Torr by measuring the pressure‐composition isotherms. The standard relative partial molar enthalpy of solution of hydrogen, ΔH0H, at infinite dilution becomes more exothermic with increasing Gd content. Whereas the standard relative partial entropy, ΔS0H, at infinite dilution decreases with Gd content; this implies that the octahedral interstices are excluded for hydrogen occupation by Gd neighbors. Substitution of Gd in the Pd lattice decreases the apparent H‐H attractive interaction and for the Pd‐4.5 and 6.0 at.% Gd alloys the H‐H interaction becomes repulsive over a certain range of H contents. The results are discussed in terms of the quasi‐chemical model by taking into the constant volume correction. The stability of P‐hydride phase increases with Gd content, and the extent of the phase boundary, i.e., the hydrogen solvus composition at a given temperature, is more favourable by Pd alloying with Gd.
Nonlinear Response Theory and Rheology
Authors: Evans Denis J.
Published: July 2012

We give a brief outline of the theory and algorithms used in performing nonequilibrium molecular dynamics simulations of the properties of liquids undergoing planar Couette flow. We then give a very brief account of some of the results that can be performed using this type of calculation.
Generalized Stokes‐Einstein Relation
Authors: Balucani U. , Vallauri R. , Gaskell T.
Published: July 2012

A means of deriving a generalization of the Stokes‐Einstein relation, when the “Brownian” particle has a size comparable with that of the atoms of the surrounding medium, is discussed. Through the introduction of a velocity field concept, a physical meaning can be inferred for the “effective” particle radius. As a result of such a generalization, we discuss the relevance of the coupling with collective variables for the description of single particle motion. Computer simulation results for the involved quantities are also presented.
Dynamics and Orientation of Molecules Adsorbed on Graphite Studied by Deuteron NMR Spectroscopy
Authors: Boddenberg B. , Grundke V. , Auer G.
Published: July 2012

Deuteron magnetic resonance spectra and spin‐lattice relaxation times of deuterated molecules (fluorobenzene (C6D5F) and neopentane (C5D12)) adsorbed on the graphitized carbon black Graphon were measured as function of temperature (75 — 288 K) and resonance frequency (13.68 and 52.72 MHz). These data reveal a strong influence of the extramolecular magnetic shielding coupling on the spectra and relaxation times. Information is obtained about the orientation and the anisotropic rotational dynamics of the adsorbed molecules as well as about the translational dynamics across the surface of the microcrystalline graphite particles. Surface diffusion coefficients are evaluated which indicate a very high translational mobility of adsorbed molecules on graphite.
Vibrational Dephasing of Simple Liquids Investigated by Picosecond and Femtosecond CARS
Authors: Aechtner P. , Fickenscher M. , Laubereau A.
Published: July 2012

Using picosecond CARS the dephasing rate of the ν1‐mode of CS2 is investigated in several solvents and in the neat liquid. A large pressure effect (factor of ≤3) is reported for the range 0 to 4 kbar similar to spontaneous Raman results. For an extended interval of 160 to 450 K, a non‐monotonic temperature dependence is reported for the first time and compared with theoretical models. — A novel non‐degenerate CARS spectrometer is described with 80 fs time resolution and improved measuring accuracy. A dephasing time of T2 = 608 ± 6 fs is reported for the ν1 mode of neat acetone of 293 K; negligible inhomogeneous broadening (< 1%) is indicated by the scattering data for this vibration.
OH Radicals Generated by NO Photolysis in Aqueous Solution: Competition Kinetics and a Study of the Reaction OH + CH2(OH)SO
Authors: Deister Ursula , Warneck Peter , Wurzinger Christa
Published: July 2012

Nitrate ion photodecomposition is explored as a source of OH radicals for the determination of rate coefficients associated with OH reactions in aerated aqueous solutions. The oxidation of benzene to phenol serves as a standard reaction phenol provides an indicator for the extent of competition by other reactants. Rate coefficients for ten organic compounds, determined relative to that for benzene, are in good agreement with literature values over a range of 3 orders of magnitude. By comparison with the yield of acetone from the reaction of OH with 2‐propanol the yield of phenol from the reaction with benzene is found to be ∼0.95. The reaction of OH with hydroxymethane sulfonate generates sulfate as a major product. It was not possible to determine the associated rate coefficient with the competition technique because the data for sulfate and phenol show the reaction to be a chain process in which SO−4 radicals appear to be the main chain carrier. Steady state calculations based on a postulated reaction mechanism indicate for the reaction OH + HMS a rate coefficient exceeding 1 · 109 M−1 s−1.
Remarks on the Electrochemical Potential of Small Silver Clusters in Aqueous Solution
Authors: Henglein Arnim
Published: July 2012

Silver clusters in aqueous solutions containing excess Ag+ ions may be regarded as tiny metal‐electrodes. The electrochemical standard potentials of metal electrode equilibria Agn⇆Agn‐1 + Ag+ + e− are much more negative than that of the compact silver‐metal electrode. The potential generally strives toward the value of the compact electrode with increasing agglomeration n of the particles, although a strong oscillation occurs in the n = 1 to 3 range. The trend is opposite to the size dependence of the ionization potential in vacuo. The main factor determining the redox potential in solution is not the hydration of the clusters {as one may suppose at first sight} but the binding energy of a silver atom in a cluster. — The electrochemical potentials of equilibria of the type Agn⇆Agn + e− and Agn−⇆Agn + e− are also discussed. — It is pointed out that results from photoionization experiments on clusters in vacuo would importantly improve our present knowledge of the electrochemistry of clusters.
The Atmospheric Corrosion of Iron — A Discussion of the Physico‐Chemical Fundamentals of this Omnipresent Corrosion Process Invited Review
Authors: Stratmann M.
Published: July 2012

In this review the physico‐chemical fundamentals of the atmospheric corrosion of iron are discussed, as they result from a number of electrochemical and spectroscopic techniques, which have been applied in order to analyze the corrosion mechanism of the atmospheric corrosion during wet‐dry‐wet transitions. — After wetting a dry corroded metal surface the cathodic partial reaction of the corrosion process is given by the reduction of Fe3+‐ to Fe2+‐states within the lattice of γ‐FeOOH. If the corrosion potential is rather negative, then also magnetite is formed. As a consequence of the formation of Fe2+ states the electronic conductivity of oxide crystals close to the metal/oxide interface is increased. This results in an acceleration of the kinetics of the oxygen reduction. It could be shown, that oxygen is reduced predominantly at the oxide/electrolyte and not at the metal/electrolyte interface and therefore the rate of the oxygen reduction is determined by the electronic properties of the oxide crystals, the kinetics of the electron‐transfer reaction being very fast at oxides, which are highly doped with Fe2+ states. If the metal surface is covered with a thick electrolyte layer, then the charge transfer reaction is so fast within the reduced oxide scale, that the overall rate of the oxygen reduction is given by the diffusion of oxygen through the water filled pore system of the scale and by the surface area of the highly doped oxide scale, which allows an electron transfer to occur at the oxide/electrolyte interface. The size of this effective surface area is determined by the amount of the reduction of the oxide scale immediately after wetting the dry metal surface. During drying, oxygen diffuses rapidely into the pore system of the oxide scale by gas diffusion. Then the corrosion rate is increased dramatically due to the fast oxygen reduction at the electron‐conducting large surface area oxide cathode. Due to the fast corrosion a dense oxide layer is formed on top of the metal surface and the surface is passivated. The corrosion stage of drying is terminated by a reoxidation of the oxide scale by oxygen, which causes the rate of the oxygen reduction to decrease as the electronic conductivity of the oxide scale is reduced.
A New Process for Optical Data Recording by Photoelectrochemical Etching
Authors: Ryan M. A. , Levy‐Clement C. , Mahalu D. , Tenne R.
Published: July 2012

Photoetching of holographic gratings was performed on materials belonging to two families of compounds, exhibiting bidimensional and tridimensional structures. Fringes of poor quality only could be obtained on the Van der Waals face of quasi‐two dimensional (layered) semiconductors due to their high resistance to photocorrosion (WSe2), or large diffusion length of minority carriers along this face (InSe), while good morphological and optical contrasts were obtained on the surface of II — VI semiconductors. — Using a laser scanning setup, the photoresponse of Schottky diodes which were made from these semiconductors was used to convert optical information into electrical signal. The photoetched part exhibits an improved photoresponse, which produces electrical contrast between the two parts. This observation is used to transform optical information into an electrical signal. The diffusion length of minority carriers was determined from this photocurrent profile. Some applications for this method for holography and for optical data recording and its retrieval are discussed. Guidelines for materials' selection for this kind of application are proposed.
Untersuchungen zur Kinetik der Anatas‐Rutil‐Umwandlung an DeNOx‐Katalysatoren für V2O5—WO3—TiO2 (Anatas) und V2O5—MoO3—TiO2 (Anatas)
Authors: Hums Erich , Range Klaus‐Jürgen
Published: July 2012

The effect of preparation — specific parameters such as energy input, thermal treatment, V2O5‐content — on the kinetics of the anatase‐rutile transformation, were investigated and their relative contributions analysed. The various degrees of transformation were determined by quantitative X‐ray diffraction measurements and checked for various rate laws. The rate constants evaluated according to Avrami for the V2O5—WO3—TiO2 (anatase)‐system were extrapolated from Arrhenius plots for temperature values corresponding to conditions in power plants. The experimental results yield information on the stabilities (exposition periods) of the anatase‐modification which react sensitively towards changes in phase composition at the anatase phase boundary, thus reflecting activation and deactivation processes which have an effect on the kinetics of the anatase‐rutile phase transformation. The kinetic behaviour determined according to Avrami for the V2O5—WO3—TiO2 (anatase)‐system has not been found for the V2O5—MoO3—TiO2 (anatase)‐system. A unique feature of MoO3‐systems consists in the following: after passing through a kinetically controlled region they form stable phases which can no longer be influenced kinetically. The anatase content of such phases can be adjusted by maintaining specific preparation parameters.
Transition from Oscillatory to Chaotic Behaviour in the Belousov‐Zhabotinskii Reaction of Oxaloacetic Acid
Authors: Koo J.‐B. , Krüger A. , Richter P. , Steiger A. , Becker F.
Published: July 2012

The Belousov‐Zhabotinskii (BZ) reaction of oxaloacetic acid (OAA) = oxobutanedioic acid is investigated spectrophotometrically both in the closed system and in the continuous‐flow stirred tank reactor (CSTR). Using ferroin as catalyst, the reaction in the closed system exhibits a very complicated oscillatory pattern with three different types of oscillations being separated by induction periods. “Chemical chaos” = deterministic aperiodicity of the type 2 oscillations is observed in a very small range of the ferroin concentrations in the closed system. In the CSTR, change from sustained limit‐cycle oscillations to aperiodicity is produced by small variations of the temperature, or of the ferroin concentration. A qualitative discussion of these results is given in terms of coupled oscillators resulting from the simultaneous BZ reactions of the three equilibrium species of OAA in aqueous solution: the hydrate, the keto and the enol forms. The influence of the stirring rate on the oscillatory pattern in the CSTR is discussed.
The Advancement of Fuel Cell Systems and Spin‐off Battery Technology
Authors: Kordesch Karl
Published: July 2012

The possibly large influence of fuel cell technology on several energy conversion and environmental aspects of the future is discussed. Solar energy and other renewable energy sources must have electrochemical storage facilities. Nuclear power can be used efficiently to electrolize water. The replacement of combustion engines in vehicles by fuel cell systems operating on hydrogen is the only way of reducing the increase of CO2 in the atmosphere if the greenhouse effect is becoming a threat. The fuel cell projects related to the manned space vehicles can provide many important spin‐off's for accumulator designs and battery technology.
Impedance Measurements on Oxygen Reduction Reaction in Molten Carbonate
Authors: Makkus R. C. , Hemmes K. , De Witt J. H. W.
Published: July 2012

To elucidate the oxygen reduction in molten carbonate the process is studied by means of impedance measurements. On the basis of the super oxide mechanism a theoretical impedance model has been developed. It consists of a charge transfer resistance, a Warburg impedance and a Gerischer or homogeneous reaction impedance. The latter is due to the recombination reaction of oxide with carbon dioxide forming carbonate. This model also holds for the peroxide mechanism apart from a different dependency on the oxygen and carbon dioxide partial pressure. The impedance data measured on a flat electrode in a half cell for several gas mixtures were fitted according to this model under the assumption that only one mechanism, the peroxide or super oxide mechanism, dominates the reaction. The measured dependency of the various elements in the model on oxygen and carbon dioxide partial pressure do not fully agree with the theoretical expected dependency. This might be due to the fact that neither one of the mechanism predominates in the melt, but both occur simultaneously.
Wetting Behaviour of Candidate Molten Carbonate Fuel Cell Anode Materials and Electrolytes
Authors: Weewer R. , Vente J. F. , Hemmes K. , De Wit J. H. W. , Fisher J. M.
Published: July 2012

Contact angles of various electrolyte compositions were determined on some candidate molten carbonate fuel cell anode materials in a typical anode gas atmosphere using the sessile drop method. The contact angles showed to increase with the nobility of the substrate composition in the order: Cr—Ni/Al—Ni/Cr—Ni/Cu—Cu—Ni and to decrease with carbonate composition in the order: Li/Na—Li K—Li/K/Ba.
Electrode Kinetics and Interface Analysis of Solid Electrolytes for Fuel Cells and Sensors
Authors: Göpel Wolfgang , Wiemhöfer Hans‐Dieter
Published: July 2012

Typical experimental techniques and results are presented to characterize properties of solid electrolytes with particular emphasis on their different surfaces and interfaces which determine electrode processes in sensor and fuel cell applications. Experimental results are discussed of electronic structures and chemical compositions at reversible electrode/electrolyte interfaces of the “prototype material” yttria‐stabilized zirconia.
Bioelectrochemical Fuel Cells
Authors: Kreysa G. , Sell D. , Krämer P.
Published: July 2012

In a biochemical fuel cell different microorganisms were employed as biocatalysts and 2‐hydroxy‐1,4‐naphthoquinone as a redox mediator. An oxygen gas diffusion electrode was used successfully; by means of a packed bed electrode as an anode the electricity output of the fuel cell could be raised considerably. Even a mixed population from a plant for the biological treatment of industrial waste gas was successfully utilized as a biocatalyst.—Experiments were carried out using the biofuel cell for bioanalytical and biosensor purposes.—Microbial mediator reduction, which is the key reaction of such a fuel cell, was examined separately for different microorganisms.
Theoretical Study of the Pressure Dependence of the Knight Shift in Alkali Metals
Authors: Leiberich R. , Philipp S. , Schmidt P. C.
Published: July 2012

For Li and Na metals we investigated theoretically the pressure dependence of the atomic spin susceptibility χA, the probability density PF and the Knight shift Ks = (8π/3)χAPF by the spin polarized version of the scalar relativistic augmented plane wave method. The calculations were performed within the volume range V0 ≥ V ≥ 0.5 V0, where V0 is the volume at 1 bar. Recently it was found experimentally by Bertani et al. that a) the slopes of the curves Ks = Ks(V) have different signs for lithium and sodium metals and b) for high pressures Ks(V) goes through a minimum for Na metal. We found in the present investigation that this behavior can be understood in terms of a competition between the pressure dependence of χA and PF for these metals.
Ternary Systems Water‐Alkane‐Sodium Chloride and Methanol‐Methane‐Sodium Bromide to High Pressures and Temperatures
Authors: Michelberger Th. , Franck E. U.
Published: July 2012

Experimental results are reported for the fluid phase equilibria of the ternary system H2O—C2H6—NaCl, H2O—n‐hexane—NaCl and CH3OH—CH4—NaBr. Measurements were extended to 800 K and 250 MPa and to 450 K and 200 MPa with the methanol system. A “synthetic” method, described earlier, was used with a high pressure autoclave with improved sapphire window arrangement. Pressure‐temperature curves on the three‐dimensional pTx‐phase boundary surfaces at constant compositions, x, were obtained (“isopleths”). Temperatures, pressures and molar densities along 14, 5 and 7 isopleths for the systems with ethane, n‐hexane and methanol‐methane, respectively, are reported. Salt concentrations between 0.1 and 8 weight percent, relative to water or methanol, are applied. The addition of salt shifts the fluid‐fluid two‐phase region to higher temperatures and pressures in all three systems. The isobaric and isothermal shifts in certain regions can reach 100 K and more and 500 bar and more with 8 weight percent of salt. Even with only 0.1 weight percent 15 K shifts are observed near the respective critical curves. For the H2O—C2H6—NaCl and the H2O‐hexane‐NaCl systems computational descriptions of the isopleths, based on a “quasi‐binary” approach and a recently derived rational equation of state are given.
Effect of the Adsorption of Monovalent Intermediate on the Kinetics of Two‐Step Charge Transfer of Metal/Metal Ion Electrode
Authors: Plonski I. H.
Published: July 2012

Theoretical relationships for the kinetics of two‐step charge transfer of bivalent metal were derived taking into account the adsorption of the intermediate according to the Langmuir isotherm. The polarization transients can exhibit inductive behaviour in two anodic and two cathodic particular cases. Inductive transients in the range of low Tafel slope are excluded.
Cation‐Cation Association of Tetramethylammonium Ions in Aqueous Mixed Electrolyte Solutions
Authors: Holz M. , Patil K. J.
Published: July 2012

We have measured the1H nuclear magnetic relaxation rates and the self‐diffusion coefficients of (CH3)4N+ions in aqueous solution of (CH3)4NBr as a function of salt concentration and in aqueous mixed electrolyte solution ofx4m (CH3)4NBr + (1 ‐x) 4mMBr, (M = Li, K, Cs) as a function of the mole fractionxof (CH3)4N+. By measuring also the2H relaxation rate of the solvent D2O, we could separate the (CH3)4N+proton relaxation rates into the intra‐ and intermolecular contribution. This allowed the determination of the so‐called association parameterA, which is connected with the integral over the pair correlation function. The results for the cation‐cationA‐parameter show that in the pure (CH3)4NBr solution no or only weak (CH3)4N+‐(CH3)4N+attraction is present, whereas in the mixed electrolyte solutions containing KBr or CsBr a strong association of the hydrophobic cations occurs. With M = Li, this attractive interaction is also present, however less pronounced. The sequence of the effectiveness of the alkali ions is the same as in the so‐called Hofmeister series for salting‐out effects on biological macromolecules.
Determination of Lennard‐Jones Potential Parameters of Liquid Ethyliodide by Analysis of the X‐ray Scattering Intensity using Structure Modelling and RISM Calculations
Authors: Bertagnolli H. , Schulz G.
Published: July 2012

Liquid ethyliodide was studied by means of X‐ray diffraction experiments in order to investigate which type of intermolecular interaction determines the structure of the liquid state. The X‐ray diffraction studies of liquid ethyliodide were carried out at a wavelength of 1.54 Å. The data were corrected for polarization, absorption. Compton scattering and multiple scattering. The structure of the molecule was determined from the coherent distinct differential cross section. After subtraction of the intramolecular contribution a structure modelling technique was used to generate a model system which reproduces the Intermolecular cross section. The computed pair correlation functions of the model system were simulated by RISM calculations based on Lennard‐Jones interactions. The parameter values obtained by comparing the simulated atom pair correlation function with the model functions suggest the existence of strongly attractive interactions between the highly polarizable iodine atoms.
Steric Considerations in the Plastic Phase of Cyclohexane
Authors: Würflinger Albert
Published: July 2012

Possible orientations of the molecules in the plastic phase of cyclohexane are discussed by using different models, which are characterized by a certain coincidence of the symmetry elements of the molecular point group and of the fcc‐lattice site. For each model all possible combinations of orientations for nearest‐neighbour pairs are considered with respect to the occurrence of overlaps. For each combination also different rotational states about the molecular triad axis as well as varying intermolecular distances are accounted for. The least number of overlaps was found for model A, when the molecular triad axis is aligned parallel to [111] or equivalent directions of the lattice. This model represents the maximum number of common symmetry elements. In this case the four distinguishable orientations for the C3‐axis: [111], [&1macr;11], [1&1macr;1], [11&1macr;] can be equally distributed over the lattice sites such that all interactions between nearest neighbours are of the same kind. There are 8 solutions for such a distribution of orientations. Orientational disorder can be explained by switching from one solution to another, although this requires temporary closer contacts and more unfavourable overlaps of neighbouring molecules.
First Passage Times and Transport in Systems with Disorder
Authors: van Den Broeck C. , Balakrishnan V.
Published: July 2012

We illustrate how first passage times can be calculated in systems with disorder. We use a renormalization approach to discuss first passage times in one‐dimensional continuous time random walks and on deterministic fractals. We discuss the phenomenon of field‐induced trapping on a random comb. Finally, we calculate mean first‐passage times for one‐dimensional random random walks, and discuss, in particular, the case of Sinai disorder. In a short Appendix, we show how mean first‐passage times can be calculated for an arbitrary inhomogeneous continuous time random walk in one dimension, using a recursion relation similar in spirit to the renormalization approach.
Quantum Coherence in Rate Processes
Authors: Weiss Ulrich , Sassetti Maura
Published: July 2012

The quantum dissipative dynamics of a particle which tunnels through the barrier of a double well potential and is coupled to an Ohmic heat bath is studied. Exact formal expressions for correlation functions are presented and examined. Attention is focused on the region in which coherence effects are important, and on the algebraic long‐time tails at zero temperature. Coherence effects in the dissipative quantum transport of a particle in a tight‐binding lattice are also investigated.
In‐Situ Observation of the Ortho‐Para‐Hydrogen Conversion in Chabazite by Neutron Scattering
Authors: Stockmeyer Rolf
Published: July 2012

The ortho‐para conversion of hydrogen adsorbed in chabazite has been observed by recording the neutron transmission of the sample after gradual adsorption of hydrogen in steps of one molecule per unit cell at temperatures between 40 and 70 K. The neutron data were fitted by a model assuming that the o‐H2 (s = 1) state decays exponentially with a time constant K = 0.5% per minute at a porefilling of n = 1 (molecule/unitcell). With increasing adsorption the value found for the o‐p‐H2 conversion rate is smaller: K = 0.2% per minute at n = 9.
Water Dissociation Effects in Ion Transport Through Anion Exchange Membranes with Thin Cation Exchange Surface Films
Authors: Ramírez P. , Manzanares J. A. , Mafé S.
Published: July 2012

Water dissociation effects in ion transport through anion exchange membranes with adhered cation exchange surface films are studied on the basis of a theory previously proposed for bipolar membranes. The effects that the adhered surface film exerts on the limiting current and on the electric current carried by the ions coming from water dissociation are found to be of particular relevance for the fouling phenomena observed in ion exchange membranes. Finally, some limitations of the theory concerning the use of the Onsager's theory of the second Wien effect to describe the electric‐field‐enhanced water dissociation are discussed.
Gas‐Liquid Critical Temperatures of Binary Mixtures of Polar Compounds + Hydrocarbons or + other Polar Compounds
Authors: Christou G. , Young C. L. , Svejda P.
Published: July 2012

Gas‐liquid critical temperatures have been measured for binary mixtures of the polar compounds acetonitrile, 2‐butanone and monochlorobenzene + 2,2,4‐trimethylpentane or + n‐alkanes as well as + some other polar compounds. The data were analysed in terms of a parameter of interaction between unlike molecules using conformal solution theory. It was shown that the shape of the molecules did not play an important role at the critical state. The strength of intermolecular interaction could be quantified and corresponded to the excess properties of the same mixtures in the liquid state.
The Dissociation Constant of Pyruvic Acid: Determination by Spectrophotometric Measurements
Authors: Fischer Michael , Warneck Peter
Published: July 2012

Aqueous solutions of sodium pyruvate/hydrochloric acid mixtures were studied with regard to changes in the intensity of optical absorption at 317 nm wavelength, caused by varying pH and temperature. The data were evaluated to determine the pyruvic acid apparent dissociation constant at infinite dilution. Its temperature dependence followed the relation ln Kod = −(0.55 ± 0.47) − (1538 ± 135)/T or, if previous results of Pedersen at two temperatures are included, In Kod = −(0.97 ± 0.35) − (1418 ± 102)T. The effective absorption coefficient for pyruvic acid and its anion differ because the former species is largely hydrated, whereas the latter is not. The known hydration constant and its temperature dependence were used to derive the dissociation constant K1b for unhydrated pyruvic acid at infinite dilution. Its pK is 1.88 at 25°C with In K1d = −(8.67 ± 0.35) + (1296 ± 102)/T. The absorption coefficients for unhydrated pyruvic acid and its anion are essentially the same.
A Remark on the GIBBS‐Paradox of the Entropy of Mixing of Ideal Gases
Authors: Wantke Klaus‐Dieter
Published: July 2012

The GIBBS‐Paradox of the entropy of mixing of ideal gases is interpreted as the consequence of permuting two limiting values. Hence, no hint on the atomism of the matter can be derived from it.
Site Specific Surface Interaction of Electron Donors and Acceptors on FeS2(100) Cleavage Planes
Authors: Pettenkofer C. , Jaegermann W. , Bronold M.
Published: July 2012

The interaction of UHV cleaved FeS2(100) surfaces with adsorbed H2O as an electron donor and adsorbed Br2 as an electron acceptor has been studied with LEED, LEISS, UPS, and XPS to simulate semiconductor/electrolyte interfaces in UHV. The (100) cleavage plane is characterized by a c(2 × 2) or p(√2 × 2)R 45° LEED pattern which is interpreted in terms of the unreconstructed FeS2 surface. H2O is molecularly adsorbed at low temperatures (100 K) and desorbs completely at room temperature (RT). LEIS‐spectra taken at low coverages (<0.5 ML) suggest a preferential interaction with the Fe sites. Br2 is ionosorbed at low coverages (<0.5 ML) as well interacting specifically with Fe‐sites. It is molecularly adsorbed at higher coverages. The ionosorbed part does not desorb at RT. The behavior of specific adsorption is related to the electronic nature of the band edges which are derived from Fe d‐states.
Electrostatic Interactions of Bodies Bearing Thin Double‐Layers III. Dissimilar Double‐Layers
Authors: Adamczyk Z. , Belouschek P. , Lorenz D.
Published: July 2012

A new numerical algorythm was used to calculate the electrostatic interaction forces between regularly shaped particles bearing thin double‐layers immersed in an arbitrary electrolyte. Our numerical procedure enabled the solution of the nonlinear one‐dimensional Poisson‐Boltzmann (PB) equation in which the excluded volume effect is quantitatively considered for an arbitrary surface charge. Using these onedimensional solutions (parallel‐plate system) the electrostatic force of interaction between regularly shaped particles was calculated according to the modified Derjaguin summation method. Calculations were performed for plates and particles bearing dissimilar surface charge (heterointeractions) for simple electrolytes and electrolyte mixtures with constant charge and constant potential boundary conditions. From these solutions the range of validity of previously derived limiting analytical expressions was estimated. A significant role of trace amounts of higher valency electrolytes decreasing considerably the interaction force was confirmed.
Integration of Stiff Differential Equations Including Sensitivity Analysis by Laplace‐Transformation
Authors: Berndt T. , Picht R. , Scherzer K.
Published: July 2012

A new method has been developed to calculate analytical functions for the time‐dependence of concentration and sensitivity coefficients based on a system of ODE by LAPLACE‐transforms. The procedure is suitable for a special class of models containing first and second order steps. The usefulness of the method is demonstrated for the case of zinc dimethyl decomposition in toluene. Comparison with a conventional integration routine is made.
An in situ FTIR Study of the behavior of Phosphate Species at Platinum. Bulk Effects and their Influence on the Spectra for Adsorbed Ions
Authors: Iwasita T. , Nart F. C. , Polligkeit H.
Published: July 2012

Potential dependent pH changes in the microcavity of the thin layer cause the appearance of absorption bands for phosphate ions in the solution. This disturbs the measurement of spectra for adsorbed phosphate species, and has to be accounted for in the analysis of spectral data. Literature data are analyzed in the light of the results presented here.
The Mutual Influence of Ligands in Sb(III) Complex Salts. An X‐Ray Diffraction and NQR Study
Authors: Ishihara Hideta , Dou Shi‐Qi , Weiss Alarich
Published: July 2012

The crystal structure of 2,2'‐bipyridinium pentabromoantimonate (III), (2,2'‐C10H8N2H2)SbBr5, was determined (T = 297 K): C2h5‐P21/c, Z = 8, a = 1457.5 pm, b = 1472.6 pm, c = 1677.5 pm, β = 110.34°, Rw(F) = 0.057. Characteristic for the structure is the tetrameric anion {[SbBr5]2⊖}4. No 79,81Br NQR could be observed in this compound. The crystal structure of 4,4'‐bipyridinium pentabromoantimonate (III), (4,4'‐C10H8N2H2)SbBr5, was also studied (T = 300 K): Ci1‐P1, Z = 2, a = 1128.7 pm, b = 1012.1 pm, c = 854.8 pm, α = 98.94°, β = 101.06°, γ = 113.57°, Rw(F) = 0.052. Characteristic for the structure of this compound is the dimeric anion {[SbBr5]2⊖}2. The 81Br NQR spectrum of 4,4'‐bipyridinium pentabromoantimonate (III) was studied in the temperature range 77 ≤ T/K ≤ 300. A five line spectrum is present over the whole temperature range covered. The 81Br NQR frequencies are spread out over a wide range; at 77 K: 34 ≤ v(81Br)/MHz ≤ 113. 81Br NQR spectrum and crystal structure of 4,4'‐bipyridinium pentabromoantimonate (III) are discussed and a model for both, the temperature dependence of the NQR frequencies and of their spread is given as is an assignment: Position of the Br atom in the complex anion ↔ 81Br NQR frequency.
Etching of CdS in Aqueous Halogen Solutions
Authors: De Wit A. R. , Kelly J. J.
Published: July 2012

Dissolution of CdS in aqueous solutions of Br2 and I2 has been studied by ring‐disc voltammetry and flow‐cell measurements. The semiconductor is etched chemically at a considerable rate by Br2. CdS is dissolved in I2 solutions only when a high concentration of chloride ions is present. It is suggested that inter‐halogen species play a role. A novel chemical etching reaction was observed in the iodine case: cathodic reduction of iodine produces an intermediate capable of oxidizing the semiconductor.
Cobalt(II) — Cyanometallates as New Inorganic Polymeric Materials for Surface‐Modification of Some Conducting Substrates
Authors: Jiang Mian , Zhou Xingyao , Zhao Zaofan
Published: July 2012

Cobalt cyanometallate thin film modified electrodes have been prepared and also electrochemically and spectroscopically characterized. Results showed that these films can be considered as novel Prussian Blue analogues. The selective cation transport into or out of these films has been explained in terms of the effective ionic radii and the channel size in the film lattice whereas other factors can not be negligible. On the other hand, the high redox‐reversibility and high stability of the modified electrodes make them potentially attractive in application of catalysis and electrochromism.
Behaviour of the Electroclinic Effect in a Homologous Series of Ferroelectric Liquid Crystals
Authors: Bahr Ch. , Heppke G. , Klemke U.
Published: July 2012

The electroclinic effect, a kind of inverse piezoelectric effect, is studied in the smectic A phase of several homologous liquid crystal compounds. The induced tilt/applied field ratio θ/E is found to increase with increasing length of the alkyl chain whereas the coupling constant k = Pθ/θ between induced tilt and induced polarization decreases with increasing chain length. The measurements allow the determination of the tilt controlling susceptibility coefficient of the smectic A phase, which is found to decrease considerably with increasing alkyl chain length.
Towards a Theoretical Description of UV‐VIS Absorption Bands of Organic Molecules
Authors: Menzel Ralf , Naumann Karl‐Heinz
Published: July 2012

The UV‐Vis absorption spectra of organic molecules are calculated with a new ansatz based on the simultaneous coupling of several vibrations during the electronic transition. Even with the simplest assumption of a Boltzmann weighted statistical mixing of the vibrational modes it is possible to reproduce the experimental absorption spectra, e.g. of naphthalene, surprisingly well. Using this method the homogeneous line width can be determined with an error of less than 30% from the common absorption spectra.
Determination of the Bending Modulus in Microemulsions by Using the Dynamic Kerr Effect
Authors: Linden E. V. D. , Bedeaux D. , Hilfiker R. , Eicke H.‐F.
Published: July 2012

We have determined the value of the bending modulus k in w/o (decaline)‐microemulsions using the dynamic Kerr effect. The relaxation of the electrically induced birefringence in a dilute w/o‐microemulsion corresponds to the relaxation of the individual nanodroplets towards their spherical form. The experimental results were described by using a theory for the dynamics of a microemulsion droplet; two cases are discussed: (i) a model in which a constant mean excess surface area during relaxation has been assumed and (ii) where a variable surface area has been considered. For a polydispersity in droplet size of 30%, we find k = 0.4 kBT (± 20%). This is in accordance with findings using the static Kerr effect.
Studies on the Interactions of Co2+ and Zn2+ with the Polynucleotides Poly(A) and Poly(C)
Authors: Dhathathreyan K. S. , Diebler H.
Published: July 2012

UV‐Spectrophotometric techniques have been used to study the binding of Co2+ and Zn2+ to the single‐stranded polynucleotides poly(A) and poly(C). The spectrophotometric data can be described by a simple binding equilibrium, i.e. by a 2‐state model. The apparent binding constants which have been evaluated with poly(A), KCo‐poly(A) = 4.5 · 103 M−1 and KZn‐poly(A) = 2.9 · 103 M−1 (25°C, ionic strength I = 0.1 M, pH 6.5–7.0), are compared to those for Ni2+ and Mg2+ with poly(A), determined earlier. It is concluded that Co2+, Zn2+ and Ni2+ form inner‐sphere complexes with poly(A), in contrast to Mg2+. Kinetic studies confirmed the inner‐sphere binding mode for Co2+ (and Ni2+). In the case of Zn2+, however, the inner‐sphere substitution reactions are apparently too fast to be distinguished from the helix‐coil transitions of the poly‐nucleotide. A second method for equilibrium measurements, based on using murexide as an indicator of the concentration of free Co2+, gave for KCo‐poly(A) a value of 5.5 · 103 M−1 at I = 0.1 M. At I = 0.01 M, the binding constants KNi‐poly(A) and KCo‐poly(A) are about 30‐fold higher than at 0.1 M, according to the uv‐data. With poly(C), the stability constants of all 4 metal ions are nearly the same, about 650 (±100) M−1 at I = 0.1 M. The available evidence suggests that these metal ions are bound to poly(C) mainly by electrostatic interactions, with little or no inner‐sphere coordination.
Decay Dynamics of H2O(Ã 1B1): Excitation by two Photon Absorption at 354.6 nm
Authors: Mikulecky K. , Gericke K.‐H. , Comes F. J.
Published: July 2012

Water was photolyzed at 177.3 nm via a two‐photon excitation by a frequency‐tripled Nd:YAG laser (354.6 nm). The complete product state distribution of the ejected OH product was determined by LIF. The OH is produced in the vibrational ground state exclusively. OH shows a Boltzmann‐type rotational distribution with a temperature parameter of about 350 K. No preferred population of Λ‐ or spin‐orbit states was observed.
Ionic Transport in Oxide Glasses and Frequency Dependence of Conductivity
Authors: Kahnt H.
Published: July 2012

Current models attribute the power law frequency dependence of ionic conductivity in oxide glasses alternatively to structural disorder or to interactions between moving ions. To distinguish between the influence of disorder and of interaction the frequency dependence of conductivity was investigated for three different series of glasses that have been selected according to special considerations on network structure and bonding of alkali ions. It was shown that the frequency response is independent of alkali concentration and structure. This result is discussed in terms of Coulomb interactions between mobile charged point defects and favours the jump relaxation model of Funke.
Segmental Dynamics in a Glassy Polyelectrolyte: Solid‐State 2H‐NMR
Authors: Schaefer D. , Rietz R. R. , Meyer W. H. , Spiess H. W.
Published: July 2012

The segmental dynamics of a special “ionene” polyelectrolyte, poly[(dimethylimino)decamethylene‐tetra‐fluoroborate]‐[–(CH2)10–N+(CH3)2–]n*BF4−, has been investigated by applying one‐and two‐dimensional deuteron NMR techniques. Selective deuteration in the methyl groups and in the α‐, β‐ and γ‐positions of the methylene chain allow for investigation of the molecular mobility of each site. Below the glass transition the ammonium groups are essentially static, due to strong Coulombic interactions between the cationic centres, whereas the methylene chains undergo trans‐gauche isomerizations. At Tg the ammonium groups become mobile, and we discuss the coupling of this glass transition process to the local methylene dynamics.