bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochromic Characteristics of Mixed WO3 – MoO3 Thin Films in Alcohol Vapors
Authors: Yao J. N. , Loo B. H. , Hashimoto K. , Fujishima A.
Published: July 2012

The photochromic responses of mixed WO3 – MoO3 thin films subjecting to UV irradiation were investigated in reducing environments, and they were compared with those of WO3 and MoO3 thin films. It was found that the photochromism of mixed 92% WO8% MoO3 thin film in ethanol vapor was significantly enhanced than that of WO3 or MoO3. The associated change in the absorbance (ΔABS) of the mixed‐oxide film was about 1.5 times that of the WO3 film, and about 2.7 times that of the MoO3 film.
Electromagnetic Response of an Electrically Small Bianisotropic Ellipsoid Immersed in a Chiral Fluid
Authors: Lakhtakia Akhlesh
Published: July 2012

The electromagnetic response of a homogeneous, electrically small ellipsoid made of a general linear bianisotropic material immersed in a chiral fluid has been obtained.
Dynamics of 18‐Crown‐6 Ether in Aqueous Solution Studied by Quasielastic Neutron Scattering
Authors: Pelc H. W. , Hempelmann R. , Prager M. , Zeidler M. D.
Published: July 2012

The dynamical behaviour of crown ether 18‐crown‐6 in water has been investigated over the whole concentration range by incoherent quasielastic neutron scattering using the high resolution backscattering spectrometer BSS1 and the time‐of‐flight instrument SV22 at the research reactor FRJ2 in Jülich. In addition we have determined the dynamic viscosities and the mass densities of this binary system. Evaluation of the neutron scattering data by use of appropriate diffusion models gives information about the temporal and spatial development of translational, rotational and conformational motion of 18‐crown‐6. The decrease of the measured dynamical quantities on addition of water up to a concentration of 50 mole‐% suggests the formation of a 1:1 crown ether‐water adduct. Addition of more water yields a rapid increase of the translational diffusion coefficient and a decrease of the viscosity.
Thermodynamic Studies on Beta‐Silver Sulfide
Authors: Mostafa S. N.
Published: July 2012

From the measurement of the emf of the solid‐state galvanic cell:

Pt/Ag/AgI/β‐Ag2+δS/Pt,

and its temperature dependence the following results for different Ag/S ratios in the temperature range between 200 and 350°C are obtained: the partial molar thermodynamic quantities of dissolution of one mole of silver into the compound, point defect concentrations and the width of band gap were determined as a function of the metal/sulfur ratio. The change of the thermodynamic quantities with the change of the stoichiometric composition can be explained by varying contributions of electrons and electron‐holes depending on the fact whether the electrons, which are brought into the compound by the dissolution of silver, go into the conduction band (excess of metal) or, by annihilation of electron‐holes into the valence band (deficit of metal). From the electrochemical measurements besides of other quantities – the band gap energy can be calculated and is of about 0.38 eV.
Zusammensetzung, Eigenschaften und Anwendungen mesomorpher Tensidphasen
Authors: Heusch Rudolf
Published: July 2012

Phasendiagramme, polarisations‐ und elektronenmikroskopische Untersuchungen sowie rheologische Messungen liefern eine Erklärung für in wäßrigen Tensidsystemen auftretende Phänomene. Es wird herausgestellt, daß Wasser bei dem Zustandekommen unterschiedlicher Phasen, bei ihren Übergängen, dem Auftreten von Mischungslücken und einer ablaufenden Phasenumkehr eine entscheidende Rolle spielt. Es wird die Konkurrenz zwischen Wasserstoffbrückenbindungen und hydrophoben Wechselwirkungen untersucht, sowie auf den Zusammenhang zwischen der Bildung einer mesomorphen Phase und der Oberflachenaktivität des beteiligten Tensids hingewiesen. Flüssigkristallbildung und Oberflächenaktivität sind dann eine Funktion der Löslichkeit eines Tensids.
Thermodynamics of Solution of Hydrogen in Pd  Cu and Pd  Cu  Au Solid Solution Alloys
Authors: Sakamoto Y. , Ishimaru N. , Mukai Y.
Published: July 2012

Thermodynamic quantities for absorption of hydrogen by Pd  Cu alloys with up to atom fraction of XCu = 0.2, and by Pd  Cu  Au ternary alloys with up to (XCu + XAu) = 0.2, where XCu = XAu, have been determined at temperatures between 273 K and 423 K and hydrogen pressures up to 1000 Torr by measurements of the pressure‐composition isotherms. The hydrogen absorption characteristics of these alloys have been compared with that of the previously reported Pd – Au binary alloys. The room temperature lattice parameters of hydrogen‐free Pd – Cu – Au alloys increases with the solute content, albeit by a small amount. The relative partial molar enthalpy, ΔHH0, at infinite dilution in Pd – Cu – Au alloys increases in exothermicity with increasing (Cu + Au) content, and the alloy composition dependence of the ΔHH0 value falls near the mid‐points between those of each Pd – Cu and Pd – Au binary alloy. The relative partial molar entropy, ΔSH0, at infinite dilution in Pd – Cu – Au alloys decreases with the solute content, and the ΔSH0 values at the same alloying content are larger than that of Pd – Au alloys, but are smaller than that of Pd – Cu alloys. The [H – Cu + H – Au] pair interaction energies between the dissolved hydrogen and the substitutional solute atoms in the ternary alloys have been evaluated according to a quasi‐chemical model with zeroth order approximation by taking into account the “constant pressure” to “constant volume” correction. The hydrogen solubility behaviour at low hydrogen concentration in Pd – Cu – Au ternary alloys can be described as due to the counteraction of the repulsive H – Cu pair interaction and the attractive H – Au pair one in the Pd host lattice. The stability of the β‐phase hydride at a given temperature in Pd – Cu – Au alloys decreases with the solute content, and the alloy composition dependence of the stability is also placed near the mid‐points between those for each Pd – Cu and Pd – Au binary alloy.
Representation of the Viscosity of Alkanes as a Function of Temperature and Pressure Using a Vogel Type Equation
Authors: Kanti M. , Alliez J. , Lagourette B. , Saint‐Guirons H. , Xans P. , Barnaud G.
Published: July 2012

Prior evaluation of the viscosity of oil field fluids according to pressure‐temperature conditions is a fundamental factor in exploitation. The aim of this article is to propose a representative form of the viscosity as a function only of pressure‐temperature variables and a parameter characteristic of the fluid, namely the molecular weight. This analytical expression applies to all the members of the same chemical family. It is based on known parameters and is consequently available without any additional experimental work. – This Vogel type analytical expression: lg η = A + B/(T – T∞) has been developed from experimental results concerning the viscosity of pure linear alkanes (n – C10 to n – C18) at different temperatures (20 – 100°C) and pressures (1 – 1000 bar) corresponding to the liquid state. The isobaric set [η = f(T)] of the different alkanes considered has been reduced to a single master curve, by double translation, a technique used for polymer study. This procedure allows the dependence of parameters A,B and T∞ to be specified with respect to pressure and molar mass. Numerical verification of the proposed representation shows that the experimental values for pure substances have on average an accuracy of 3%. The method yields results which remain acceptable for binary and quaternary mixtures of these alkanes.
A Cluster Model for Tetrahedrally Coordinated Chalcogenide Phases
Authors: Leute Volkmar
Published: July 2012

A model is described, which allows to calculate the energy dependent cluster probabilities for quasiternary systems of type AX/BX/CX, based on a concept of reactions between tetrahedral clusters. It is shown. that for the quasibinary section A3X3/B2CX3 with C standing for structural vacancies, the cluster model allows predictions concerning the occurence of ordered compounds.
Graphical Representation of Solid‐Solute Phase Equilibria in Aqueous Solution
Authors: Königsberger Erich , Gamsjäger Heinz
Published: July 2012

Solid‐solute phase diagrams are useful tools for the depiction of stable and metastable equilibria between binary mixed crystals with common ions and aqueous solutions. Generalized Gibbs‐Duhem equations provide the common basis and suggest natural co‐ordinates for the graphical representation of thermodynamic variables. Diagrams applicable even to highly soluble electrolytes can be constructed by plotting the osmotic coefficient of the solvent times the total molality πΣmvs. the mole fractionsxof the dissolved and solid components, respectively. According to Schmalzried and Pelton's topological classification the resulting phase diagrams are of Type II. They can be used for practical purposes, e.g., to predict the separability of the components by fractional crystallization.
Kinetic and Thermodynamic Parameters of the Ferro‐Ferricyanoferrate Redox System in Glycerol‐Water Mixed Solvent
Authors: Badawy W. A. , Hilal N. H. , El‐Shazly Sh. A.
Published: July 2012

The electrochemical behaviour of the Au‐rotating disc electrode (rde) in the Fe(CN)3‐/4‐6 redox system in pure water and water‐glycerol mixed solvents was studied. Using standard potentiostatic technique, the kinetic parameters controlling the anodic and cathodic processes were derived. The effect of the speed of rotation of the rde, the temperature, and the scan rate on the current‐potential characteristics of the system was investigated. The thermodynamic parameters of the Fe(CN)3‐/4‐6 in glycerol‐water mixed solvent were calculated. It turns out that the electrode processes are mass transport controlled. The presence of glycerol retards the charge transfer process and enhances the mass transport effects. The calculated thermodynamic data revealed that the rate of the anodic reaction is enthalpy controlled whereas that of the cathodic one is entropy controlled.
Phase Equilibria and Transport Properties in the Systems Water/n‐Butanol/Transition Metal Perchlorates
Authors: Mahr Michael , Weil Konrad G.
Published: July 2012

The miscibility gap between n‐butanol and water can be closed by the addition of transition metal perchlorates. As transition metal ions we used Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+. All phase diagrams are of the same shape when the salt contains a divalent cation, while the equilibrium curve in the Fe3+ system encloses a one third smaller region of the phase triangle. UV/VIS‐spectra of Ni(ClO4)2 in butanol/water show that nickel ions are preferentially hydrated. These facts lead to the conclusion that the closing of the miscibility gap is only due to butanol/perchlorate interactions. The finding that the change of the transition metal does not affect the behaviour of the system is corroborated by measurements of the density and the transport properties electrical conductivity and kinematic viscosity. All three properties depend on the concentration, but not on the nature of the salt. Investigations of the phase diagrams at lower temperatures show a second region with two coexisting liquid phases at higher salt concentrations. This region becomes smaller with increasing temperature while the miscibility gap in the region with lower salt contents grows with increasing temperature.
Small Angle Neutron Scattering Measurements on Iridescent Surfactant Solutions
Authors: Baumann J. , Kalus J. , Hoffmann H. , Thunig C. , Lindner P.
Published: July 2012

Quaternary solutions of the surfactant Tetradecyldimethylaminoxid (C14H29N(CH3)2O, TDMAO) in D2O, equimolar concentrations of Decane and some cosurfactant Hexanol show at low concentration the phenomenon of iridescence. The colour of the backscattered light changes from red to blue with increasing surfactant concentration. Small‐angle neutron diffraction (SANS) patterns were recorded for different concentrations between 27 and 584 mM TDMAO. It is shown that the iridescent colours are due to Bragg reflections of visible light from lamellar layers. By simulation based on a one‐dimensional crystal model the thickness of the bilayers and the lattice parameter of the liquid crystalline structure could be determined. At higher concentrations the samples showed a pronounced anisotropic SANS‐pattern, the origin of which is related to the procedure of filling the solution into the flat, disklike quartz cells of path length 1 mm.
Chaos and Interior Crisis in an Electrochemical Reaction
Authors: Krischer K. , Lübke M. , Wolf W. , Eiswirth M. , Ertl G.
Published: July 2012

The electrochemical oxidation of hydrogen on a platinum anode in the presence of copper ions exhibits under galvanostatic conditions kinetic oscillations due to periodic poisoning and activation transitions of the electrode by underpotential deposition and dissolution of a passivating Cu monolayer In the presence of chloride ions a transition to chaos from a stationary state via a Hopf bifurcation and a sequence of period doublings (Feigenbaum scenario) was observed upon increase of the current density. Further change of this control parameter caused a transition to another qualitatively different chaotic state through an interior crisis. Near the other end of the oscillatory region, this state evolved into periodic mixed‐mode behaviour.
Temperature and Pressure Dependence of Self Diffusion in Long Liquid n‐Alkanes
Authors: Vardag T. , Karger N. , Lüdemann H.‐D.
Published: July 2012

A titanium autoclave for the determination of self diffusion coefficients by the pulsed field gradient spin‐echo method is described, that has been used in the temperature range between 200 and 500 K at pressures up to 600 MPa.—In a first series of experiments, melts of n‐alkanes with chain lengths between 16 and 154 carbon atoms were studied. The data are analyzed with modifications of the hard sphere model and tested against the Rouse‐ and reptation model.
Critical Micelle Concentration in the AOT‐Water‐Benzene System as Determined by Small‐Angle Neutron Scattering
Authors: Gorski N. , Ostanevich Yu. M.
Published: July 2012

We describe an approach to the experimental determination of the critical micelle concentration (CMC) in solutions of uncharged micelles by the analysis of small‐angle neutron scattering data. It is shown that, in dilute solutions, the dependence of the product of forward scattering intensity and apparent squared radius of gyration is a linear function of the total surfactant concentration. The ratio of the two parameters of this function gives the concentration of surfactant in a monomeric state, which can be used as a reliable estimate of CMC. In the case under investigation (AOT + X · H2O + C6D6) at X = 0 we found CMC = 0.80 ± 0.04 mM, which is in reasonable agreement with the values reported by the other authors. Our first experiments at X = 4.3 and X = 8.6 show CMC = 2.2 ± 1.0 mM and 1.5 ± 0.6 mM, respectively. It seems plausible that the addition of water does not cause any serious diminution of the CMC in this system.
Dielectric Relaxation of N‐Cyano Substituted Morpholine, Piperidine and Pyrrolidine
Authors: Stockhausen M. , Wilke G.
Published: July 2012

The dynamic dielectric properties of the title substances are measured at 20 °C at frequencies up to 72 GHz in the pure liquid state and in mixtures (x = 0.4–1) with benzene and tetrachloromethane. Rotational tumbling motion of single (non‐associated) molecules is likely to be the main relaxation process. Peculiarities are found with two out of the six systems, namely mixtures of cyanopiperidine and cyanopyrrolidine with tetrachloromethane. These are discussed as possibly due to a concentration dependent conformational equilibrium.
S1‐Lifetime of Azulene in Solution
Authors: Schwarzer D. , Troe J. , Schroeder J.
Published: July 2012

Femtosecond two‐photon fluorescence was used to redetermine the S1‐lifetime of azulene and perdeutero‐azulene in solution. A value of 1.0 (±0.l) ps was obtained in both cases, which is a factor of two smaller than the lifetime measured previously with lower time resolution.
Theory. Relaxation Dynamics in Disordered Ionic Conductors
Authors: Dieterich W. , Knödler D. , Petersen J.
Published: July 2012

A microscopic mechanism for understanding fractional power‐laws in the ac‐response of ionic conductors is discussed in terms of hopping of charged particles in disordered lattices. We review recent Monte‐Carlo simulations for lattices with Gaussian disorder in the local site energies, which show that “anomalous diffusion” occurs at intermediate time‐scales as a result of the interplay of Coulomb‐interactions and structural disorder. A new model pertaining to ionic transport in oxid glasses is proposed, which emphasises the role of long‐range Coulomb‐potentials due to counter‐ions. Implications with respect to other dynamic probes e.g. inelastic neutron scattering and ultrasonic attenuation are also briefly discussed.
The Tricomi Time Correlation Function
Authors: Zeidler M. D.
Published: July 2012

A time correlation function based on the Tricomi function with two shape parameters is proposed For special values of these parameters the Debye and Cole‐Davidson functions are recovered. The Tricomi function can be Fourier transformed analytically and an equation for the spectral density is derived.
Anomalous a.c. Response due to Jump Diffusion in Disordered Materials
Authors: Wagener Michael , Schirmacher Walter
Published: July 2012

The a.c. response due to jump diffusion in systems with fluctuating energy barriers is calculated in effective medium approximation. The crossover from a frequency independent to a frequency dependent a.c. conductivity is shown to be related to a transition from normal to anomalous diffusion. To extract the non‐analytical frequency dependence of the dynamic conductivity for ω → 0 we study the loss function which – depending on the use of the proper local Green's function in the EMA equation – reveals a √ω dependence in the region of normal diffusion as it should. The loss function looks like ω−α with 0 < α < 1 in the region of anomalous diffusion, but the details of the frequency dependence are different for different models, i.e. the curves are non‐universal.
A Target Diffusion Theory for Nuclear Spin Relaxation in Ionically‐Conducting Glasses
Authors: Elliott S. R. , Owens A. P.
Published: July 2012

A theoretical mechanism is presented for nuclear spin relaxation in ionically‐conducting glasses (or disordered crystals) caused by ionic motion. This is based on the diffusion‐controlled relaxation model previously used to account for electrical relaxation in such materials: relaxation is assumed to occur at particular (interstitialcy) sites, triggered by the arrival of other diffusing ions. The experimental dependence of the spin‐lattice relaxation rate on temperature and ionic concentration can be understood on the basis of this model.
Transport Coefficients of Liquid Benzene by Molecular Dynamics Calculations
Authors: Luo H. , Hoheisel C.
Published: July 2012

With a 6‐centre Lennard‐Jones potential, we have studied thermal collective transport coefficients of the benzene model liquid by molecular dynamics (MD) calculations. Shear and bulk viscosity as well as thermal conductivity were determined for 8 different states of liquid benzene. Agreement between experimental values and MD results is surprisingly good for the shear viscosity and thermal conductivity. Unfortunately there are no experimental data available for the bulk viscosity. In the wider neighbourhood of the triple point of benzene, the time correlation functions for the shear and the bulk viscosity were found to have an extreme form, namely an initial short‐time decay within 0.5 ps followed by a long positive branch of very small amplitude up to about 4–6 ps. A comparable long time behaviour was also found in the reorientational correlation functions.
Molecular Dynamics Simulations of the Depolarized Rayleigh Spectra of CS2/CCI4 Liquid Mixtures
Authors: Stassen H. , Dorfmüller Th.
Published: July 2012

Molecular dynamics simulations were used to calculate the depolarized Rayleigh light scattering spectra of CS2/CCI4 liquid mixtures at 298 K modelling the intermolecular interactions by atom‐atom Lennard‐Jones potentials. Approximating each molecule as a point scatterer these spectra were obtained using the dipole‐induced dipole mechanism for the interaction‐induced polarizability. Intensities and lineshapes of the first‐order perturbation theory for the system polarizability of this model are compared to the exact all‐order results. The agreement of both models with experimental spectra is in some respects satisfactory, but also displays characteristic deviations.
Fractal Aspects of Superionic Conductors
Authors: Den Hartog H. W. , Ebens W. O. , Dorenbos P.
Published: July 2012

In this paper we will discuss the properties of a group of fluorite type superionic materials, which has been studied in detail in our laboratory. Some of these materials, which are denoted by A1‐xRxF2+x, can be considered as model materials for the description of extrinsic superionic conductors. We will concentrate mainly at the series of cubic solid solutions consisting of strontium and cerium fluoride. For small and moderate Ce concentrations the dominant defects in these materials are dipolar systems and consequently these defects are expected to play an important role in the conduction processes. – We have found strong evidence for percolation conduction if the concentration of the trivalent impurities is about 4 mol%. In the vicinity of this concentration the ionic conductivity increases sharply as a function of the concentration, while the dielectric constant reveals a maximum. The experimental results can be explained by assuming that the conductivity at concentrations close to and above the percolation threshold is governed by the easy jumps of interstitial fluoride ions in the vicinity of trivalent ions. We know from dielectric spectroscopy experiments, that these jumps occur with a rather small activation energy. At first sight the above mentioned concentration might be far to low, but one should realize, that the easy jumps take place in a relatively large area surrounding the trivalent impurity. Considering the geometry of the dipolar defects, however, one expects a percolation threshold of a few mol%.
Frequency‐Dependent Conductivities of RbAg4I5 and Na‐β″‐Alumina from Radio to FIR Frequencies
Authors: Hoppe R. , Kloidt T. , Funke K.
Published: July 2012

The electric conductivities of the two fast ionic conductors RbAg4I5 and Na‐β″‐alumina have been determined at various temperatures and frequencies from 4 MHz to 105 GHz. – The conductivity of RbAg4I5 is found to display a dispersion as expected by the so‐called “universal dynamic” response, a high‐frequency plateau in the range of 100 GHz and an Arrhenius behaviour at both low and high frequencies. – The spectra of Na‐β″‐alumima show a different behaviour. In addition to the “universal dynamic” response dispersion, a faster and thermally less activated relaxation process is observed at high frequencies and low temperatures. Up to 60 GHz, a high‐frequency plateau has not been encountered.
Impedance and 2H‐NMR Studies of Stoichiometric Alkaline Hydroxide Hydrates
Authors: Borkowska Z. , Frese U. , Kriegsmann E. , Stimming U. , Gavish M. , Adamic K. J. , Greenbaum S. G.
Published: July 2012

Hydrates of the alkaline hydroxides LiOH, NaOH, KOH and CsOH in their liquid and solid states were investigated using impedance spectroscopy. KOH · 4H2O was studied using deuteron NMR. From the impedance measurements the electrical conductivity of the hydrate was evaluated. It is an important result of these measurements that the lithium and sodium hydroxide hydrates exhibit a poor conductivity in the solid state; the activation energies of conductivity exceed 3 eV. The potassium and cesium hydroxide hydrates, however, are considerably more conductive in the solid state, especially at low temperatures with activation energies around 0.7 eV. Linewidths and T1 and T2 relaxation times were determined as a function of temperature in the liquid and solid hydrate. The NMR measurements indicate that the protons (deuterons) are the mobile species. The differences in conductivity may be due to a size effect of the cation in that large cations with a single charge favor an extended water network which maybe of clathrate‐like structure.
The Double α‐Peak Phenomenon in Polymers
Authors: Hofacker I. , Fuchs M. , Latz A.
Published: July 2012

We discuss the structure of the α‐peak in some high molecular weight polymers. A double α‐peak phenomenon appears as a generic feature of the mode coupling theory related to the self crossing of transition hypersurfaces. A schematic three component model is solved to fit quantitatively dielectric loss spectra of poly propylene glycol.
Investigation of Complex Intramolecular Motion in Supercooled Liquids
Authors: Pösch M. , Althoff G. , Killie S. , Wenning E. , Hertz H. G.
Published: July 2012

After a brief résumé of the Woessner theory which treats nuclear magnetic relaxation effects caused by internal and anisotropic motion of molecules in liquids we present proton magnetic relaxation rates of specifically deuterated molecules possessing an interacting group (–OH or –COOH) and a hydrocarbon chain of increasing length, namely methanol and acetic acid, ethanol and propionic acid, n‐propanol. Measurements were done in the range from room temperature to ∼ 15 K. Various interacting substances were added to slow down the movement of the interacting group relative to the internal molecular motions, yielding respective experimental manifestations. Some brief hints are given to show the shortcomings of the Woessner theory.
Diffusion of Positive Muons in Niobium Doped with Titanium
Authors: Fell H.‐J. , Hempelmann R. , Hartmann O. , Harris S. , Wäppling R.
Published: July 2012

The diffusional behaviour of positive muons in bcc NbTi with three different titanium dopings (0.1, 0.5, and 1.0 at%) was studied using muon spin relaxation both in transverse magnetic field and in zero field. The temperature range 2 to 200 K was covered in these experiments. The temperature dependence of the muon spin depolarization rate indicates the existence of different motional states: i) below 15 K the muons are localized somewhere in the lattice at Nb4 tetrahedral sites due to random strain fields; ii) between 20 and 50 K some of the muons are trapped at substitutional Ti atoms where they perform a rapid localized motion over four or six adjacent Nb3Ti sites; iii) in the same temperature range other muons are trapped at residual interstitial oxygen and nitrogen impurities (185 ppm); iv) between 80 and 150 K the muons appear to extend their localized motion to 24 adjacent Nb3Ti sites; v) eventually, above 200 K, we observe long range muon diffusion. The distinction between a diffusing muon and a muon performing a rapid localized motion over several sites is possible by examining the long time behaviour of the muon polarization function in zero field.
Light and Neutron Scattering Complex Relaxation Behaviour in Glass Forming Liquids from Brillouin Scattering
Authors: Quitmann D. , Soltwisch M. , Loheider S.
Published: July 2012

Propagation and damping of thermal longitudinal acoustic sound waves can be studied in detail by inelastic light scattering. We concentrate here on inorganic network glassformers. Relaxation leads to shifts of the Brillouin lines, and to deviations from Lorentzian shapes which may become very large (ZnCl2). From the shift and broadening, the relaxation and its time dependence or the relaxation time distribution, can be determined. The analysis is based on viscoelastic theory for density fluctuations. The method of analysis and the underlying assumptions are discussed. While the experimental precision is good, the largest drawback of Brillouin scattering is its restricted dynamical range. The difficulty of deciding unambiguously between single‐τ or complex relaxation from Brillouin spectra is discussed. An example (GeSBr2) where reasonably large ranges of frequency and temperature have been covered in a recent experiment, is used to demonstrate the combined effect of α‐ and β‐relaxation processes on LA Brillouin lines.
The Dynamic Structure Factor of Expanded Liquid Rubidium
Authors: Pilgrim C. , Winter R. , Hensel F. , Morkel C. , Gläser W.
Published: July 2012

By inelastic neutron scattering, the coherent dynamic structure factor S(Q, ω) of expanded liquid rubidium has been measured up to about 1700 K using the IN6 spectrometer at the Institut Laue‐Langevin, Grenoble. The scattering law S(Q,ω) has been determined for energy transfers from −3.5 to 20 meV in the momentum transfer region from 0.55 Å−1 to 2.6 Å−1. The existence of collective density excitations at short wavelength and high frequency for the expanded liquid metal is discussed and the Enskog self‐diffusion coefficient is evaluated from the experimental data.
Quasielastic Neutron Scattering from RbAg4I5 Single Crystal Gives Evidence of Jump Relaxation
Authors: Wilmer D. , Funke K. , Kloidt T. , Carlile C. J.
Published: July 2012

A quasielastic neutron scattering experiment has been performed on a single crystalline sample of the fast ionic conductor rubidium silver iodide (RbAg4I5) in order to study the dynamics of the mobile silver ions in this material. The corrected spectra show broad quasielastic components whose weight increases with increasing momentum transfer in the elastic Q‐range from 1.0 to 1.8 Å−1. The quasielastic broadening is explained by the frequent occurrence of so‐called forward‐backward hopping sequences of the silver ions which are key steps of jump relaxation. A calculation based on the jump relaxation model yields a normalized frequency spectrum of the silver hopping motion that simultaneously fits the dynamic structure factor and the dynamic conductivity spectra of this material.
Search for Quasielastic Neutron Scattering Components Due to Jump Relaxation in Glass
Authors: Cramer C. , Funke K. , Vortkamp C. , Dianoux A. J. , Grüne R.
Published: July 2012

A lithium bromide doped lithium borate glass has been studied by neutron scattering experiments and by measurement of the dynamic conductivity. Whereas the dispersion of the dynamic conductivity at lower frequencies can be interpreted in terms of a non‐Debye jump relaxation model, a quasielastic neutron scattering component, as predicted by the model, could not be resolved. However, in some other glassy systems there is evidence of quasielastic components due to jump relaxation processes. This is shown for two examples: the glass forming melt 3KNO3 · 2Ca(NO3)2 and an AgI · AgPO3 glass.
Dynamic Anomalies and their Relation to the Glass Transition: A Neutron Scattering Study of the Glass Forming Van der Waals Liquid Ortho‐terphenyl
Authors: Bartsch E. , Debus O. , Fujara F. , Kiebel M. , Sillescu H. , Petry W.
Published: July 2012

Neutron scattering experiments on the molecular glass former ortho‐terphenyl reveal a dynamic anomaly at a temperature Tc ≈ 290 K well above the calorimetric glass temperature Tg = 243 K. Close above Tc the density autocorrelation function ΦQ(t) shows a two step decay over 4–5 decades in time. The slower component obeys the time‐temperature superposition principle. Its line shape can be well parametrized by a Kohlrausch law and is strongly temperature dependent as its relaxation time scales with the shear viscosity. Thus this component is identified with the structural relaxation (α‐process). The faster component (β‐process) is much less temperature dependent. Its line shape factorizes in a purely Q‐dependent and a purely time‐dependent part and its time scale follows a power law with a critical exponent a. The crossover region between the α‐and ß‐process follows a power law (von Schweidler law) with a critical exponent b. Approaching Tc from below the plateau value separating the α and the β process (= Debye‐Waller factor) shows a critical decrease and bends over to a weak temperature dependence at Tc. These findings support several predictions made by the mode coupling theory of the glass transition which relates these dynamic anomalies to remnants of an ideal glass transition.
An Investigation of the Reaction of CH3 Radicals with O2 at High Temperatures
Authors: Klatt M. , Röhrig M. , Gg. Wagner H.
Published: July 2012

The reaction of CH3 radicals with O2 was investigated behind incident shock waves at temperatures between 1400 and 2300 K and total densities between 2 · 10−6 and 8 · 10−6 mol/cm3. The formation of O and H atoms was followed by atomic resonance absorption spectroscopy (ARAS) at 130.5 nm and 121.6 nm. A rate constant of 2.3 · 1013 exp(–15400 K/T) cm3/mol s for the reaction CH3 O2 + CH3O + O was determined.
An Investigation of the Reactions of NO3 Radicals with Cl and ClO
Authors: Becker E. , Wille U. , Rahman M. M. , Schindler R. N.
Published: July 2012

The reaction (1) Cl + NO3 → ClO + NO2 was studied at 298 K by observing the kinetic behaviour of NO3, Cl and ClO using discharge‐flow mass‐spectrometric technique. A rate constant k(1) = (2.26 ± 0.17) · 10–11 cm3 molecule−1 s−1 was obtained. The secondary processes between NO3 and ClO were also investigated and OClO was detected as a reaction product. For the rate constant of the reaction (2a) ClO + NO3 → ClOO + NO2 an upper limit of k(2a) = 1 · 10−13 cm3 molecule−1 s−1 was found. In contrast to previous findings it is shown that reaction (2b) ClO + NO3 → OClO + NO2 is the predominant channel with k(2b) = (4.3 ± 1.0) · 10−13 cm3 molecule−1 s−1.
Untersuchungen zur Adsorptionskinetik von Phenolen, Diphenolen und cyclischen aliphatischen Alkoholen mit der Methode des schnellen Elektrolytaustausches
Authors: Janoske Gido , Hamann Carl Heinz
Published: July 2012

The determination of thermodynamic and kinetic data of reactive chemisorption of organic molecules with an improved technique is described. It substitutes a rapid electrolyte exchange with potential control of the working electrode for an electrode transfer. The degree of coverage, rate of adsorption and interaction between adsorbate molecules from cyclic voltamograms recorded after adsorption and electrolyte exchange was determinated. The adsorption of Phenols, Diphenols and cyclic aliphatic alcohols on a platinum electrode in contact with an acidic electrolyte solution is studied. The adsorption rate of the phenolic compounds is very fast in reference to the corresponding cyclic alcohols. This effect can be explained by the strong chemisorption of aromatic π‐bonded species to the platinum surface. With the exception of Pentafluorphenol the interaction between the adsorbate molecules for all substances is similar and can be described as low repulsion.
Phasenzusammensetzung und Sauerstoffaktivität oxidischer Katalysatoren im Betriebszustand
Authors: Hildenbrand H.‐H. , Lintz H.‐G.
Published: July 2012

Solid electrolyte potentiometry (SEP) has been used to measure the oxygen activity in the catalyst during the oxidation of propene on copper oxides. The combined kinetic and potentiometric measurements have shown that SEP can be extended to oxidic catalysts prepared in an adequate fashion. The strong correlation between the phase composition of copper oxide and the formation of acrolein proves the applicability of the potentiometric method to monitor phase transitions of catalysts under working conditions.
Homogenization of Water/Chloroform and Water/n‐Butanol Mixtures with Tetraalkylammonium Halides. Phase Diagrams and Properties of the Homogeneous Phases
Authors: Geyer Claus , Mahr Michael , Paulus Helmut , Weil Konrad G.
Published: July 2012

We report on two ternary systems with a ternary miscibility gap. They consist of two immiscible solvents (water and chloroform or water and n‐butanol) and salts which can close the miscibility gap. These salts are unsymmetrical tetraalkylammoniumhalides R3R'N+X− (X− = Cl−, Br−, I−). We determined the binodal curves in the ternary phase diagrams. In the homogeneous region, we measured densities, kinematic viscosities, and electrical conductivities. At constant mole fractions of salt, the viscosities increase and reach constant values while the conductivities decrease monotonously with increasing mole fractions of the organic solvent. Addition of salt to a given mixture of the solvents leads to a monotonous increase of the viscosities while the conductivities first increase, then go through maxima and decrease again. By X‐ray analysis we determined the crystal structure of methyl‐tri‐n‐propylammonium iodide. The lattice is triclinic, space group P1. A ternary compound, containing the salt together with chloroform and water could also be prepared. The crystal is disordered at room temperature, a skeleton of tetraalkylammonium ions is present which contains channels. In these channels, chloroform and water molecules seem to be mobile. The X‐ray analysis shows no special positions for these solvent molecules. The structure of this compound does not indicate heteroselective solvation. This concept therefore should not be used in the discussion of the homogenization by these salts.
Vapor‐Liquid Equilibria of Mixtures of Methyl Butanoate + Propan‐2‐ol at 74.66, 101.32, and 127.99 kPa
Authors: Ortega J. , Susial P.
Published: July 2012

Vapor‐Liquid equilibrium data for binary system methyl butanoate + propan‐2‐ol were measured by a dynamic phase equilibrium apparatus at three different pressures of 74.66, 101.32 and 127.99 kPa. An azeotrope was found at low ester concentration, which decrease with the increase of the working pressure. In all cases studied, p‐T‐x‐y data exhibit a positive consistency being correlated through a suitable equation. Good predictions are obtained by ASOG [1] and UNIFAC [2, 3] methods and employing parameters corresponding to different alkanol/ester interactions. The mean overall errors for activity coefficients were smaller than 8% as expected.
SAXS Studies on Structure Formation in Microemulsion‐Triblock Copolymer Systems
Authors: Hilfiker Rolf
Published: July 2012

Small angle X‐ray scattering (SAXS) measurements were performed on water/AOT (sodium di‐2‐ethyl‐hexylsulfosuccinate)/i‐octane(2,2,4‐trimethylpentane) w/o‐microemulsions with various amounts of block‐copoly(oxyethylene/isoprene/oxyethylene). Addition of copolymer causes an aggregation of the microemulsion droplets. The first aggregation step is the formation of dimers (two droplets connected by a copolymer molecule). From the experimental form factors, structure and size of the dimers could be calculated. In particular, we could show that the radius of the droplets increases by about 10% after absorbing a copolymer block. The distance between two droplets and the width of the distance distribution were determined as well. From the decrease of the number of free nanodroplets as a function of the amount of copolymer it could be concluded that roughly one in four copolymer molecules acts as a bridge between two droplets.
Behaviour of Helical Pitch in Cholesteric and Chiral Smectic C* Phases
Authors: Bahr Ch. , Escher C. , Fliegner D. , Heppke G. , Molsen H.
Published: July 2012

Several nonchiral liquid crystals exhibiting nematic and smectic C phases have been doped with different chiral compounds. The handedness and the pitch of the induced helical structures were determined in both phases. Whereas some chiral dopants induce helical structures which, as to be expected, possess the same handedness in all matrices and phases, we found that in some cases the same dopant induces helical structures of opposing handedness in different nematic matrices. Moreover, it was observed that the helical sense in the chiral smectic C* phase can be opposite to the helical sense in the chiral nematic phase of the same liquid crystal system. The dependence of the helical structures on the composition was studied in several quasi‐binary diagrams.
HCN: Hydrogen‐Bonded Versus Conjugated Polymer
Authors: Springborg Michael
Published: July 2012

Results of a density‐functional study of linear HCN and CNH monomers, the corresponding hydrogen‐bonded polymers, and a conjugated polymer (CHN)x with C and N atoms alternating along a zigzag chain are reported. Minimizing the total energy as a function of structure results in realistic structures for the monomers and the conjugated polymer; but the local‐density approximation may be responsible for the too short hydrogen bonds found for the hydrogen‐bonded polymers. For the optimized structures we present electronic energies, densities of states, photoelectron spectra, momentum densities, and reciprocal form factors. Comparing these clearly demonstrates both similarities and differences for the various systems. It is further demonstrated that the conjugated polymer can lower the total energy upon a C–N bond‐length alternation. A model is then constructed with which solitons and polarons in the conjugated polymer are examined. Both types of structural defects are stable for the charged chains and induce two gap‐states. Finally, polarons in the hydrogen‐bonded chains are discussed.
Solid Phases from the Liquid System H2N(CH2)2NH2  CdBr2  HBr  H2O. An X‐ray and 79,81Br — NQR Study of (H3N(CH2)2NH3)CdBr4, (H3N(CH2)2NH3) (CdBr3)2 · H2O, and (H3N(CH2)2NH3)2CdBr6
Authors: Krishnan V. G. , Dou Shi‐Qi , Paulus Helmut , Weiss Alarich
Published: July 2012

From the aqueous system ethylenediamine, (en),  CdBr2  HBr  H2O of varying component concentrations, at room temperature the compounds (enH2)CdBr4, (enH2)(CdBr3)2 · H2O, and (enH2)2CdBr6 were crystallized. 79,81Br NQR spectroscopy shows that the three solid phases, crystallized at room temperature, are the stable ones in the temperature range 77 ≤ T/K ≤ 300. (enH2)CdBr4 shows a three line 81Br NQR spectrum, the frequencies lying in the range 53 ≤ v (81Br)/MHz < 68 and having negative temperature coefficients dv/dt over the whole temperature range covered. A phase transition with hysteresis is observed at 340 K. In the high temperature phase I only one 81Br NQR line is observed, with negative temperature coefficient, too.

(enH2)(CdBr3)2 · H2O shows also a three line 81Br NQR spectrum, the frequencies lying in the range 38 MHz to 72 MHz at room temperature with positive as well as negative temperature coefficients.

(enH2)2CdBr6 reveals a four line 81Br NQR spectrum, three of the lines lying in the range 40 MHz to 70 MHz; the fourth line was observed at frequencies as low as 10 MHz. (enH2)(CdBr3)2 · H2O crystallizes at room temperature monoclinic, space group C2h6‐C2/c with Z = 4 (formula units per unit cell) a = 818 pm, b = 2413 pm, c = 801 pm, β = 107.8°. The structure is characterized by chains of units [Cd4Br12]4. The chains are built up by edge connected octahedra CdBr6 and the corners of two neighbouring octahedra are part of a bridging tetrahedron CdBr4, located alternating cis and trans on the chain. (enH2)2CdBr6 crystallizes also monoclinic, space group C2h2‐P21/m, a = 669 pm, b = 2050 pm, c = 637 pm, β = 93.4°; Z = 4. The structure corresponds to a formulation ((enH2))2(CdBr4)2⊖ · 2Br⊖. In both compounds hydrogen bonding is observed. The NQR results are in full agreement with the crystal structures; structure and bond scheme are discussed.
First Evidence of the Preformation of an Inorganic Network in Sol‐Gel Processing of Lead Zirconate Titanate, obtained by EXAFS Spectroscopy
Authors: Ahlfänger R. , Bertagnolli H. , Ertel T. , Kolb U. , Peter D. , Naß R. , Schmidt H.
Published: July 2012

We report the results of EXAFS spectroscopical investigations on lead zirconium titanium precursors in the sol and gel state. Analysis of the second coordination shell for both the sol and the gel yields the contribution of titanium backscatterers at a mean distance of 3.48 Å (sol) and 3.44 Å (gel). We draw the conclusion that a uniform composition on a microscopic scale exists in the sol as well as the gel state. In other words, heterocondensation is favoured against homocondensation. This provides a good explanation of the low calcination and sintering temperatures in the sol‐gel processing of lead zirconate titanate compared with other preparation techniques.
Temporal and Spatial Averaging Effects in Local Tropospheric Hydroxyl Determination
Authors: Armerding W. , Herbert A. , Comes F. J.
Published: July 2012

Though the theory of the fast tropospheric photochemistry is well established its verification by experimental measurements e.g. of OH in the troposphere – including the simultaneous determination of all input parameters controlling the local chemistry – has not yet been achieved. The main reasons for this deficit are severe problems in realizing proper experimental procedures. The only accepted results in the past evolved from long path absorption measurements. But this method contains severe temporal and spatial averaging. In this paper we will discuss how to design a suitable experiment (based on model calculations) considering the temporal and spatial fluctuations of tropospheric trace gases and the resulting averaging problems.
Silicon Film Formation by Reaction of Active Hydrogen with Silane
Authors: Roth A. , Comes F. J.
Published: July 2012

Silane is reacted with active hydrogen in a flow reactor. Thin silicon films are produced which are amorphous or μ‐cristalline, depending only on flow conditions. Growth rates of the films are between 3 and 6 Å/s. The transition from μ‐cristalline to amorphous behaviour is continuous. Treating the material with atomic hydrogen results in a substantial change of the film properties. Etching of the material is also observed and found different for μc‐Si: H compared to a‐Si:H.
Growth, Structure and Properties of Thin Films and Superlattice Structures
Authors: Sundgren Jan‐Eric
Published: July 2012

This paper addresses growth mechanisms, characterization and properties of thin films grown from the vapor phase. The emphasis is placed on artificial structures such as metastable alloys and layered materials, including superlattices. For metastable alloy formation it is demonstrated that a bombardment of the growing film surface by low‐energy ions can be used to promote growth of metastable alloys even at temperatures high enough for epitaxial films to form. In the case of layered materials it is shown using a combination of X‐ray diffraction and high resolution transmission electron microscopy, that superlattices with atomically sharp interfaces can be grown not only in the case of materials with covalent bonds (e.g., semiconductors) but also in the case of materials with metallic bonds. Finally, some properties of metallic superlattices are also discussed.
Ultrathin Films of Polymers Plenary Lecture
Authors: Wegner Gerhard
Published: July 2012

The Langmuir‐Blodgett technique provides for the possibility to prepare ultrathin layers of macromolecules on solid, planar substrates. In this context a series of novel polymers was synthesized and tested with the aim to develop the materials science background and the methodology to fabricate devices based on such ultrathin layers. This made it necessary to develop or adapt a number of methods to characterize these ultrathin layers at surfaces with regard to homogeneity, orientation phenomena, optical properties and transport behavior. The design of macromolecules described as “hairy‐rods” proved to be particularly successful and novel types of supramolecular architectures could be realized best described as “molecularly reinforced liquids”. First attempts to build prototype devices based on layered assemblies of these nonconventional polymers are mentioned.