bluuebunny/crossref_metadata_2025 huggingface dataset:
Columnare und nematische Phasen neuer makrodiscotischer Materialien [1]
Authors: Praefcke K. , Singer D. , Gündogan B. , Gutbier K. , Langner M.
Published: July 2012

The first radially multi(biphenylethinyl) substituted arenes possessing benzene or naphthalene cycles as molecular centers as well as Palladium atoms containing macrocyclic complexes derived from hexaalkoxy substituted aldobisimines by cyclopalladation have been synthesized and investigated by physical methods. Most of these flat compounds with molecular core diameters ≧24 Å and molecular weights up to 4000 are novel thermotropic liquid crystals, in part highly unsaturated or metallomesogens in structure, respectively, exhibiting columnar and/or nematic phases. Sterical influences on the mesophase formation of these spacious molecules are discussed as well as interesting changes of their properties by variation of their self‐organization occurring in binary systems. Thus, addition of an electron acceptor, for example 2,4,7‐trinitrofluorenone, leads to the formation of charge transfer complexes, mesophase stabilizations or even to inductions of other mesophases including nematic ones of the ND or NC type. Dissolving such thermotropic columnar mesogens in various organic solvents gives rise to lyomesomorphism; in case of at least one of the palladomesogens a transition between two different lyotropic nematic phases (N1 and N2) has been observed.
Conformational Order of Amphiphilic Chain Molecules in Lyotropic Liquid‐Crystalline Phases
Authors: Schnepp WErner , Schmidt Claudia
Published: July 2012

The nonionic surfactant hexa(ethyleneglycol) n‐dodecyl methylether in aqueous liquid‐crystalline phases is studied by deuterium NMR spectroscopy. From the quadrupole splittings of the surfactant, which is deuterated either in the hydrophobic alkyl chain or in the hydrophilic oxyethylene chain, order profiles of both the alkyl and oxyethylene moiety are obtained. Characteristic features of the order profiles are related to the conformations of the surfactant molecules. The observed temperature dependence of the quadrupole splittings is explained by changes of the conformational equilibrium.
On the Identification of Oxiranes Formed in the Reactions of NO3 Radicals with Alkenes
Authors: Wille U. , Schindler R. N.
Published: July 2012

Products of the reaction of the NO3 radical with monoalkenes, i.e. 2,3‐dimethyl‐2‐butene, 2‐methyl‐2‐butene, cis‐2‐butene, isobutene and propene were identified using a fast flow system with mass spectrometric detection. The reaction mixtures were analyzed in situ without applying enrichment procedures. Oxiranes were found to be the predominant hydrocarbon compound produced at low pressures with yields of (90±10)% for 2,3‐dimethyl‐2‐butene and (80±10)% for cis‐2‐butene. For the unsubstituted butenes and for propene formation of products containing a carbonyl group was also suggested.
Ultrasensitive Chemical Analysis. Ultrasensitive Laser Spectroscopy of Trace Elements
Authors: Letokhov V. S.
Published: July 2012

The application of the ultrasensitive method of laser spectroscopy – resonance ionization spectroscopy (RIS) – is briefly reviewed. It is used for trace analysis of elements in different samples: high‐purity materials, sea water, ores, etc.
Planar Liquid and Gas Visualization
Authors: Melton Lynn A.
Published: July 2012

Planar Laser Induced Fluorescence (PLIF) diagnostics based on the fluorescent intensity, lifetime, and/or quenching properties of organic molecules have been developed for a variety of applications: (1) Exciplex‐Based Vapor/Liquid Visualization systems provide spectrally‐separated emissions from the vapor and liquid phases and thus allow the separate visualization of the vapor and liquid phases of an evaporating fuel spray; (2) Exciplex Fluorescence Thermometry systems allow the measurement of liquid phase temperatures over the range 20–400 °C. Such systems have been used to measure the temperature of hydrocarbon droplets falling through heated nitrogen; (3) Streamlines by Oxygen Quenching, in combination with droplet‐slicing‐imaging, has allowed the visualization of internal circulation patterns within sub‐millimeter droplets hydrocarbon droplets; and (4) Fluorescence Lifetime Imaging, a technique which uses two PLIF images, one obtained a few nanoseconds after the other, has been applied to the imaging of the fuel/oxygen equivalence ratio in isothermal methane jets and to the imaging of temperature in oxygen‐free jets. This paper reviews the photophysical and diagnostic principles upon which the current systems are based and addresses their applications and limitations.
Optical Characterization of Soot
Authors: D'Alessio A. , Minutolo P. , Gambi G. , D'Anna A.
Published: July 2012

The chemistry of fuel‐rich hydrocarbon flames is extremely complex because different types of high molecular mass structures are produced. In fact, Polycyclic Aromatic Hydrocarbons (PAH) and submicronic turbostratic graphitic‐like particles (soot) are not the only products present but also partially aromatic polymers, gums, fullerenes and diamond‐like particles may be formed during pyrolysis and rich combustion. In addition, the heavy fractions of liquid fuels like the asphaltenes or the large polar‐aromatic compounds pyrolyze to specific forms of solid carbon. The tight requirement of a high space‐time resolution of the measurements during the high temperature combustion privileges the optical and spectroscopic diagnostics. This contribution will shortly review the main optical effects employed in this field namely absorption and fluorescence spectroscopy and elastic light scattering.
Fiber‐Optic Quasielastic Light Scattering in Concentrated Dispersions: The On‐Line Process Control of Carotenoid Micronization
Authors: Wiese H. , Horn D.
Published: July 2012

The article reviews the application of fiber‐optic quasielastic light scattering (FOQELS) for the on‐line and in‐situ characterization of concentrated dispersions. In the typical configuration a single optical fiber is directly immersed in the system and is used both for illuminating the particles by laser light and recollecting part of the scattered light. Specifically, when a single‐mode telecommunication fiber is used, only singly scattered light is intercepted even from highly turbid dispersions. In this case the autocorrelation function of the scattered light can be analyzed directly in terms of the diffusion coefficient of the particles which is strongly related to their size. The application range of the single‐fiber approach in terms of concentration, particle size and dispersant viscosity is complemented by two‐fiber techniques, which, e.g., can be used to measure the light multiply scattered from the dispersions (fiber‐optic diffusing‐wave spectroscopy, FODWS). As an example for the application of the FOQELS method, the on‐line control of the carotenoid micronization process is described.
Tomographic Measurements of Carbon Monoxide Temperature and Concentration in a Bunsen Flame Using Diode Laser Absorption
Authors: Nguyen Q. V. , W. Dibble R. , Hofmann D. , Kampmann S.
Published: July 2012

The temperature and concentration profiles of carbon monoxide (CO) in a laminar, axisymmetric, premixed methane‐air Bunsen flame are measured using line‐of‐sight diode laser absorption spectroscopy in conjunction with computer tomographic (CT) reconstruction. The absorption spectra for the P(20) (v = 2 ← 1) and P(27) (v = 1 ← 0) vibrotational transitions of CO were measured at 21 evenly spaced positions over a 1.33 cm span for a 1.3 cm radius flame. The CT reconstruction algorithm was based on the Fourier convolution technique. The tomographically reconstructed normalized transmission profiles derived from the absorption spectra, in conjunction with a quantum mechanical model for the vibrotational behavior of CO, yielded both the temperature and concentration profiles. The Bunsen flame investigated had 3 distinct zones: (1) an inner rich‐premixed flame zone, (2) an outer non‐premixed flame zone and (3) an unburnt core region. The reconstructed temperature profile showed that the core region temperature was close to ambient and rapidly increased to the adiabatic flame temperature at the inner flame zone. The temperature was observed to reach a local minima of approximately 200 K less than the adiabatic flame temperature. At the outer flame zone, the temperature increased to the adiabatic flame temperature at the outer flame zone. The reconstructed concentration profile was reasonable, low in the core region, with a maximum at the approximate location of the inner fuel‐rich flame zone and subsequently decreased to a low level towards the outer flame zone where the CO concentration goes towards zero as expected for a non‐premixed flame zone. An advantage of the tomographic technique is that the knowledge of the laser pathlength across the actual flame is not required for quantitative measurements of the concentration.

In an attempt to measure the low concentrations of CO as it occurs at the edge of a Bunsen flame, we switched from direct absorption to the second harmonic technique. With this improved sensitivity, we have discovered a large spectral shift of the CO P(38) (v = 1 ← 0) transition depending on whether the post flame combustion products are fuel‐lean (blue shift +0.009 cm−1) or fuel‐rich (no shift).
Poster Contributions. Double Pulse 2D LIF as a Means for Following Flow and Chemistry Development in Turbulent Combustion
Authors: Atakan B. , Jörres V. , Kohse‐Höinghaus K.
Published: July 2012

A new approach for the measurement of turbulence time scales was developed based on double‐pulse two‐dimensional laser‐induced fluorescence in combination with a correlation analysis. In a first application, the reaction zone of a turbulent H2/air diffusion flame was studied with this method. For this, OH molecules were excited using two laser pulses which were delayed with respect to each other, but which pumped the same transition in the OH A‐X (1,0) band. The laser‐induced fluorescence of the same spatial region was detected using two gated CCD cameras. By varying the time delay between the laser pulses from 5 μs to 1 ms, the temporal changes of the OH‐ containing structures were determined. Spatial structures were also examined. Correlation analysis was used for a quantitative evaluation of the experimentally observed time and length scales for the regions where OH was present. The double‐pulse 2D LIF method appears to be a promising tool for the investigation of turbulent flows. Its applicability is not limited to the example presented here. With the possibility to detect stable as well as radical species, it may provide a wealth of data on the temporal and spatial changes of a variety of scalars in both non‐reacting and reacting turbulent flows which can be compared to mathematical turbulence models.
Monte Carlo simulation studies of binary mixtures: A measure of the mixing
Authors: Karaaslan Hasan , Yurtsever Ersin
Published: July 2012

A Monte Carlo algorithm tailored to fast equilibration of binary mixtures is applied to Lennard‐Jones fluids and solids. In order to study phase transitions as functions of interaction parameters as well as of the temperature, a measure of the mixing is defined which is based on the normalized differences of radial distribution functions. At all temperatures sharp transitions are observed when the ratio of the interaction strengths of like and unlike particles reaches a threshold value.
Kinetics and mechanisms of the formation of iron(III) complexes with Nα‐pyridoxyl‐L‐phenylalanine, Nα‐pyridoxyl‐L‐alanine, and Nα‐pyridoxyl‐L‐aspartic acid
Authors: Ozawa Tomohiro , Jitsukawa Koichiro , Masuda Hideki , Einaga Hisahiko
Published: July 2012

The coordination reaction characteristics and mechanisms of the title new ligands (1(H2plpa), 2(H2plal), and 3(H3plas) stated in the order) to iron(III) have been investigated in an aqueous 0.10mol dm−3 sodium perchlorate solution at 25°C by means of electronic absorption spectral and stopped‐flow spectrophotometric methods. They equally form the corresponding bis(ligand)iron(III) complexes with slower coordination of the first one through the same two parallel pathways of Fe3+ +H3+L + (or 0) and FeOH2+ +H4L2+(or +) and also another pathway of FeOH2+ +H3L+(or0) (L is fully deprotonated species of 1, 2, and 3); the mechanistic rate‐determining step is the coordination of phenolato oxygen of the first ligand. The thermodynamic stability constant (log β12/mol−2dm6. 0.10mol dm−3 (NaClO4), 25°C) of iron(III)‐3 complex (48.33±0.21) is very large in comparison with the constants of the iron(III) complexes of 1(39.06 ±0.26) and 2(39.81 ± 0.20). A possibility is concluded for the formation of more stable iron(III) complexes without changing the complex formation reaction mechanism by designing the ligand structure of the amino acid moiety of pyridoxal‐L‐amino acid derivatives as a siderophore.
On further treatment of oxidic‐hydroxidic compounds in partly discharged electrodes on the basis of structural investigations of manganese dioxide
Authors: Axmann P. , Glemser O.
Published: July 2012

The effects of further treatment of aquoxide electrodes, e.g. storage in the electrolyte, washing and drying are studied by means of X‐ray investigations. These methods of treatment lead to the disappearance of the reflections of β‐Mn(OH)2 which is formed initially in a partly discharged electrode. Simultaneously new reflections arise, showing the formation of β‐MnOOH.
Surface chemistry of colloidal gold: Deposition and reoxidation of Pb, Cd, and Tl
Authors: Henglein Frank , Henglein Arnim , Mulvaney Paul
Published: July 2012

Lead, cadmium and thallium are deposited on colloidal gold particles in aqueous solution. The deposition occurs through the reduction of the metal ions by excess electrons which are donated to the gold particles by free organic radicals generated radiolytically. The absorption spectra of the composite particles are measured and compared to calculated ones (using Mie theory and the optical constants of the pure metals). — Au‐Pb particles are stable and well separated, and there is reasonable agreement between experimental and calculated spectra. Reoxidation of the lead mantle by Ag+ ions leads to a silver mantle, although about 5% of the deposited lead is not oxidized; this is attributed to the strong binding of Pb adatoms to the gold surface. The reoxidation of Pb adatoms by Ag+ occurs much more slowly than the oxidation of individual Pbn particles, which is attributed to the more electropositive nature of the deposited metal. — Au‐Cd particles tend to agglomerate, especially when the Cd mantle is reoxidized by Ag+ ions. The resulting Au‐Ag particles contain a large percentage of non‐oxidized cadmium; alloy formation seems to be a possible explanation. — The spectra of Au‐Tl particles are not in good agreement with the calculated ones; it seems that the reduced Tl does not form an even mantle around the Aun particles.
Ultrasonic absorption of aniline/cyclohexane mixtures of critical and non‐critical composition
Authors: Bittmann E. , Alig I. , Woermann D.
Published: July 2012

Results of measurements of the temperature and frequency dependence of ultrasonic absorption (a/f2) of aniline/cyclohexane mixtures of critical and non‐critical composition are reported. The data obtained with the mixture of critical composition are analysed in terms of the Ferrell‐Bhattacharjee theory (Phys. Rev. A31, 1788 (1985)). The value of the critical amplitude ω0 of the relaxation rate used for calculation of the scaling variable Ω is obtained from static and dynamic light scattering data taken from the literature (ω0 = (42±3)GHz). This value of ω0 agrees with that obtained from a fit of the dynamic scaling function F(Ω) to the experimental ultrasonic absorption data (ω0 = (42±5) GHz).
On‐line multi‐photon ionization mass spectrometry applied to PAH and fullerenes in flames
Authors: Ahrens J. , Kovacs R. , Shafranovskii E. A. , Homann K. H.
Published: July 2012

A new approach is presented, that enables on‐line detection of large polycyclic aromatic hydrocarbons (PAH) and fullerenes in premixed flat low‐pressure flames by molecular beam resonance‐enhanced multiphoton ionization mass spectrometry (REMPI‐MS). A multi‐pass mirror system for the laser beam was developed to increase the amount of ions formed. In benzene/oxygen flames, PAH with molecular masses up to more than 103 u were observed. For the first time, this method has also provided on‐line mass spectra of electrically neutral flame‐generated fullerenes (C32 to about C300) after the investigation of fullerene flame ions. The fragmentation induced by laser irradiation is discussed.
Fiber‐optic diffusing‐wave spectroscopy on concentrated dispersions of large polymer latex spheres
Authors: van Keuren E. R. , Wiese H. , Horn D.
Published: July 2012

Fiber‐optic diffusing‐wave spectroscopy (FODWS) measurements were carried out on polymer latex dispersions (10 wt%) with large particle diameters (1.07, 3.2 and 5.6 μm). Autocorrelation functions (ACFs) were measured from light multiply scattered between two single‐mode optical fibers immersed in the dispersion. As expected from a photon diffusion approximation the logarithms of the ACFs were linear functions of the fiber separation and the square root of the correlation delay time. A small downward curvature of the curves at short delay times could be attributed to a slight absorption by the samples. From the ACFs a parameter κ was derived which strongly depended on particle size. Reasonable agreement was found between the experimental κ‐values and predictions by a hard‐sphere model. Potential applications of FODWS are the on‐line process control of emulsions, viscous pigment or ceramic dispersions.
Oscillatory behaviour of density profiles: Relevance for fluid interfacial phenomena
Authors: Evans R.
Published: July 2012

For a given short‐ranged interatomic potential the density profile of an inhomogeneous fluid decays into bulk in the same fashion as the bulk radial distribution function g(r). General statistical mechanical arguments predict damped oscillatory decay of the liquid‐vapour density profile into the saturated liquid for temperatures T removed from the critical value Tc. Explicit density functional calculations for a square‐well model fluid near its triple point yield an oscillatory profile whose amplitude is about 2% of the bulk liquid density. The amplitude decreases for higher T and for T≥0.9 Tc only pure exponential decay is found. Capillary‐wave fluctuations reduce the amplitude of the oscillations but do not change their period and decay length. The existence of density oscillations gives rise to an oscillatory binding potential for an adsorbed liquid film. This has significant repercussions for wetting transitions and allows the possibility of a sequence of layering transitions between adsorbed liquid layers. The same length scales which determine the decay of g(r) determine the asymptotic decay of the solvation force for a fluid confined between two planar walls. In the case of long‐ranged interatomic potentials, density profiles exhibit power‐law decay at longest range but, for liquid densities, their intermediate range damped oscillatory decay is governed by the same leading‐order pole structure that describes short‐ranged forces. Recent work on the decay of correlations in liquid mixtures is also described.
Nematic and smectic surface order in the isotropic phase of low molar mass and polymeric liquid crystals
Authors: Immerschitt S. , Elben H. , Holthoff H. , Strobl G.
Published: July 2012

Pretransitional surface ordering phenomena, as they occur in the isotropic phase of liquid crystals upon approaching the clearing point, were studied by variable angle ellipsometry and X‐ray reflectivity measurements. Ellipsometric data obtained for two phenylcyclohexanes indicate a logarithmic divergence of the thickness of a nematic boundary layer with homeotropic orientation, which corresponds to a complete wetting behaviour. Data can be represented by a model based on a Landau‐de Gennes approach. An investigation of a LC‐side group polyacrylate showed a boundary layer with planar orientation. The thickness, which increases on approaching the clearing point, is clearly larger than in the case of the low molar mass samples. In X‐ray reflectivity studies on a film of a LC‐side group polymer boundary layers with smectic order were detected. They possess a remarkable stability and exist also at larger distances from the clearing point. A stepwise procedure in the data analysis enables a detailed, complete characterization.
Continuous Wetting Transitions in Systems with Van der Waals Interaction
Authors: Fenzl Willi
Published: July 2012

Wetting transitions in systems with long‐ranged interactions are now well understood theoretically. Although the existence of continuous transitions is predicted, an experimental example has not been found to date. The search for an appropriate system is supported by a calculation of the free energy of interfacial interaction for liquid films on solid substrates within the framework of the Dzyaloshinskii, Lifshitz and Pitaevskii theory of Van der Waals interaction. It is shown that a minimum in the interfacial interaction energy can be obtained by the competition of the nonretarded zero‐frequency and the retarded dispersion term, if they have comparable magnitude and different sign. In certain systems the zero frequency term changes its sign on varying the static dielectric constant of the substrate or the liquid. Then, in combination with a repulsive dispersion interaction, the necessary conditions for a continuous wetting transition are fulfilled. The possibility of realizing this transition experimentally is discussed.
Line tension at continuous wetting
Authors: Backx G. , Indekeu J. O.
Published: July 2012

The interface displacement model has proven very useful for calculating the line tension τ near first‐order and continuous (critical or multicritical) wetting transitions. Since the upper critical dimension, du, for contact line phenomena has been argued to be the same as for surface phenomena at wetting, it follows that du < 3 for intermolecular forces with algebraic decay. Consequently, the mean‐field exponents for τ should be exact in d = 3, for most experimentally relevant systems. Here we review the mean‐field results for continuous wetting.
Transport phenomena in physisorbed films: Investigations with optically excited surface plasmons
Authors: Herminghaus S. , Sigel U. , Paatzsch T. , Musil H. , Leiderer P.
Published: July 2012

Experiments were performed on the lateral transport kinetics of wetting layers. Optically excited surface plasmons were used to study both the spreading behaviour of silicon oil and the equilibration dynamics of ethanol. The precursor film profiles of silicon oil were found to agree well with the theory of viscous flow of nonvolatile liquids. For ethanol, evaporation effects and viscous transport could be observed separately. Apparently, the viscous transport is suppressed by almost two orders of magnitude. Possible explanations are discussed.
Dynamical formation of metastable phases at interfaces
Authors: Löwen Hartmut
Published: July 2012

A Ginzburg‐Landau model of non‐conserved order parameter dynamics is analyzed. The model involves three different phases: a stable high‐temperature phase, a stable low‐temperature phase and a metastable phase. It is shown that a macroscopic portion of metastable phase can be formed by a dynamic instability which splits the front separating the stable high‐ and low‐temperature phases. The presence of an external field blocks this metastable phase formation and leads to a non‐monotonic behaviour of the metastable phase portion as a function of time.
Critical adsorption of SF6 on a finely divided graphite substrate
Authors: Thommes M. , Findenegg G. H. , Lewandowski H.
Published: July 2012

The adsorption behavior of a near‐critical fluid (SF6) on a finely dispersed graphitic adsorbent (graphitized carbon black; Vulcan 3‐G) has been studied. The surface excess concentration γ was measured by approaching the critical point along near‐critical isochores using a volumetric technique. From the scaling theory of critical adsorption by Fisher and de Gennes it is expected that γ diverges at the critical point. At temperatures well above criticality of the fluid (T–Tc≥ 3 K) we find the expected increase of Γ with decreasing T; however, closer to Tc the adsorption does not increase further but decreases sharply for T → Tc. This unexpected behavior was also found when the experiment was repeated under microgravity conditions on the space platform EURECA I. A similar maximum in Γ(T) was also observed for SF6 adsorbed in a mesoporous controlled‐pore glass (CPG‐10) with 31 nm mean pore diameter.
Cross over towards the reflectivity discontinuity at total reflection edge. A test for the observation of critical adsorption profiles
Authors: Sans A. , Jannink G.
Published: July 2012

We propose to use the discontinuity at total reflection as an experimental test of the universal critical adsorption profile. Neutron optical properties corresponding to the cross over state are derived from the wave equation, and exact results are displayed. They indicate that the critical index can be derived from experimental data, at a reasonable vicinity of the critical temperature.
Liquid monolayers. Dynamical lateral order in binary lipid alloys and its coupling to membrane functions
Authors: Knoll Wolfgang
Published: July 2012

This contribution deals with the relation between the dynamical lateral order in model membranes composed of lipid mixtures, and its influence on the function of an integral model protein, the ion‐channel gramicidin. Firstly, densitometric and small angle neutron scattering experiments are described for binary alloys organized as liposomal dispersions. These results establish some basic concepts for the understanding of the phase behavior, mixing properties and critical lateral compositional fluctuations in these quasi two‐dimensional fluid systems. Next it is shown how the current fluctuations across a bimolecular lipid layer observed when two monomeric gramicidin molecules dimerize within the membrane thus forming an ion‐conducting channel can be analyzed to give information about the lateral organization of the lipid matrix. It is shown that phase separation and critical fluctuation, indeed, control the performance parameters of a membrane‐integral functional unit.
Mixed polymer‐surfactant layers at the air‐water interface
Authors: Mann E. K. , Langevin D. , Hénon S. , Meunier J. , Lee L. T.
Published: July 2012

We have studied mixed molecular layers of polydimethylsiloxane (PDMS) and surfactants, using different techniques: surface tension, ellipsometry, neutron reflectivity and Brewster angle microscopy. On pure water, the polymer layer is generally inhomogeneous, showing surface domains of different discrete thicknesses. The penetration of the polymer into the surfactant monolayer found on the surface of aqueous surfactant solutions depends on the surfactant. On a surfactant layer with little penetration by the polymer, the polymer layer remained inhomogeneous. With other surfactants, the polymer penetrated appreciably into the surfactant layer, and the polymer layer was homogeneous. These differences between surfactants correlate with the wetting behavior of PDMS on the aqueous surfactant solutions.
High pressure heat capacity of benzene derivatives from pVT measurements
Authors: Cáceres Mercedes , Baonza Valentín G. , Rubio José E. F. , Arsuaga Jesús M. , Núñez Javier
Published: July 2012

Accurate thermal expansion coefficient αp, speed‐of‐sound and density measurements found in the literature have been used to characterize the general behavior with pressure of the constant pressure heat capacity Cp of benzene and toluene. The results agree well with direct measurements of Cp found in the literature. Indirect methods for estimating Cp at high pressures are discussed. αp results obtained with an expansion technique using a differential method have been used to characterize the high‐pressure behavior of Cp for mesitylene.
Polymerization‐pressure dependencies of properties of perfluorosulfonate cation‐exchanger thin films by plasma polymerization
Authors: Yasuda Kazuaki , Uchimoto Yoshiharu , Ogumi Zempachi , Takehara Zen‐Ichiro
Published: July 2012

Perfluorinated thin cation‐exchanger films fixed with sulfonic acid group were prepared by plasma polymerization of trifluoromethanesulfonic acid and hexafluoropropylene. The influence of polymerization pressure on their structural changes was focused. FT‐IR and ESCA measurements indicated that the decomposition of sulfonic acid group was remarkable under low polymerization pressure conditions. The higher the pressure, the more the decomposition was suppressed and the more the sulfonic acid group was introduced. The plasma polymer formed at polymerization pressure as high as 0.5 Torr was about 1 μm thick and free from pinhole, and gave an ionic conductivity of 1.8×10−4 S cm−1 and a K+ transference number was as big as 0.99 in an aqueous KCl solution showing a high cation perm‐selectivity.
Description of alkali‐arsenic (antimony) clusters using one‐electron extended Hückel energies with two‐body repulsions and geometry optimization
Authors: Lies Hartmut , Böhm Michael C. , Weil Konrad G.
Published: July 2012

Geometries of clusters formed by the group‐V‐atoms As, Sb and alkali metals M = Na, K, Cs are studied by extended Hückel (EH) calculations supplemented by a repulsive two‐body interaction and a geometry optimization of the Fletcher‐Powell‐type. The computational results are compared with available ab initio and pseudopotential data as well as experimental findings. The improved EH formalism allows a straightforward analysis of geometric preferences of clusters as a function of the alkali coordination. These findings are then interpreted in terms of qualitative orbital pictures. For clusters containing four group‐V‐atoms, e.g. As4, Sb4, M2As4, M2Sb4, M4As4, M4Sb4, M6As4, M6Sb4, it is shown that the geometry of the central As4 (Sb4) unit depends on the number of valence electrons. The bare As4 and Sb4 clusters have a tetrahedral Td minimum, while the metal‐to‐group‐V‐atom electron transfer in the alkali coordinated systems stabilizes a square‐planar As4 (Sb4) arrangement of D4h symmetry.
Pressure induced lattice distortion in some Co(III)‐Ammine complexes, [Co(NH3)5NO2]XY (XY = Cl2, Br2, ClNO3))
Authors: Boldyreva Elena , Ahsbahs Hans , Uchtmann Hermann
Published: July 2012

Lattice parameters were measured at pressures up to 4GPa (40kbar) for [Co(NH3)5NO2]XY (XY=Cl2, Br2, Cl(NO3)) by X‐ray powder diffraction using a Diamond Anvil Cell (DAC) technique. Continuous anisotropic lattice distortion with increasing pressure was observed. Strain tensors were calculated at different pressures, and the orientation of strain ellipsoids with respect to the crystallographic axes and the directions of various bonds in the structures was considered. Pressure induced lattice distortion was compared with lattice distortion in the course of homogeneous nitro‐nitrito linkage isomerization in the crystals. The data on the orientation of Co‐NO2 bonds with respect to the directions of main compression in the crystals correlate with previously obtained data on pressure induced frequency shifts in the solid state IR‐absorption spectra in the same series.
The structure of cold condensed lead chloride (PbCl2)
Authors: Zuber Ralf , Weil Konrad G.
Published: July 2012

When lead chloride is deposited onto substrates at temperatures below 150 K, a non‐crystalline film is formed. This material crystallizes at temperatures above 260 K, as could be demonstrated by UV‐VIS‐spectroscopy. In order to determine whether or not the deposited material consists of extremely small crystals with a high degree of disorder or of a genuine amorphous phase, it was investigated by electron diffraction. We describe the procedure which we applied for the determination of the elastically scattered intensity as a function of the scattering vector. From this function, the reduced radial distribution function was determined. The results were compared with those reported about crystalline and molten lead chloride. The short range order in the cold condensed material is different from that in the crystal and that in the melt. Hence, cold condensation of lead chloride leads to the formation of an ionic glass.
Thermodynamic parameters of liquid cobalt‐palladium alloys by computer‐aided Knudsen cell mass spectrometry
Authors: Tomiska J. , Belegratis M. S. , Wang H.
Published: July 2012

The computer‐aided Knudsen cell mass spectrometry has been applied for the determination of the molar thermodynamic excess properties of liquid binary Co‐Pd alloys. Thermodynamic evaluation followed the “Digital Intensity‐Ratio” (D.I.R.)‐method. Two‐parameter thermodynamically adapted power (TAP) series are used for the algebraic representation of the molar excess properties. Liquid Co‐Pd alloys are characterized by exothermic molar heats of mixing HE, slight negative molar excess entropies, and negative molar excess Gibbs energies GE. At 1850 K the minimum HE value is −13000 J/mol (55.1 at.% Pd), the minimum SE value is −4 J/(mol K) (52.7 at.% Pd), and the minimum GE value is −5700 J/mol (57.9 at.% Pd). At 1850 K the thermodynamic activities of both components, Pd and Co, show slight negative deviations from Raoult's law over the entire range of composition. The Co activities of the Co‐richest alloys (xPd<0.14) are nearly ideal.
Spatial and functional organization. Coupled models for spatial organization in development
Authors: Maini P. K.
Published: July 2012

Several simple models have been proposed to account for spatial organization in early development. Recently, a number of models have been proposed in which such patterning mechanisms are coupled. Here, we present a review of some of the latest theoretical results on such systems. In particular, we consider two cases: in one, the coupling of two mechanisms greatly enhances the robustness of the patterns produced; in the other, a hierarchical model exhibits spatially asymmetric patterns that are consistent with certain experimental observations.
Synthetische Polymere: Von der Empirie zum Design von Makromolekülen
Authors: Cherdron Harald
Published: July 2012

Intensive studies at both, academic and industrial, laboratories have led to a much better understanding of the relationships between structure/morphology and properties of synthetic polymers. Hence, it became possible in many cases to predict what structures and/or morphologies macromolecules should have in order to meet certain property requirements. This will be demonstrated with four examples: Temperature resistant polymers, alternating copolymers, polymers with liquid crystalline main chains, and highly ordered polymers with nonlinear optical properties.
Properties of liquids at the boiling point: Equation of state, internal pressure and vaporization entropy
Authors: Matyushov Dmitry V. , Schmid Roland
Published: July 2012

Liquids at their respective boiling points are considered in the framework of factorization of density and temperature dependencies in the attraction term of the liquid equation of state. The factorization functions Ψ(η) and a(T) are expressed through the vaporization enthalpy and the liquid packing density η. The latter is computed from the compressibility of the liquid with correcting for dipole‐dipole interactions in the framework of the mean‐spherical approximation. On the basis of the functional dependencies of Ψ(η) and a(T), derived from experimental data for a number of liquids, the applicability of equations of state to dense liquids at the boiling point can be analyzed. The function of η determined in this way relates the internal pressure to the cohesive energy. Upon decomposing the entropy of vaporization into the contributions from repulsions and attractions, the famous Trouton constant is shown to be largely determined by the unpacking of molecular hard spheres.
Thermodynamics of iron‐chromium alloys: Mass spectrometric determination of the excess properties in the bbc phase and calculation of the phase diagram
Authors: Vrestal J. , Broz P. , Tomiska J.
Published: July 2012

Thermodynamic excess properties of iron‐chromium alloys in the bcc phase have been investigated by Knudsen cell mass spectrometry in the temperature range 1470–1750K. The molar excess Gibbs energies, entropies and heats of mixing as well as the thermodynamic activities were determined from the ion intensities as a function of composition by fitting to a sub‐regular solution model (2 parameter T.A.P.‐series; C in J/mol: C = 16800, C = 4490; C in J/(mol·K): C = 4.155, C = 2.065). Solid Fe‐Cr alloys in the bcc phase are characterized by positive molar excess Gibbs energy GE, positive molar excess entropies SE and endothermic molar heat of mixing HE. The following maximum excess properties result at 1725K: HE = 4780 J/mol (53.1 at.‐% Cr), SE = 1.31 J/mol·K (54.7 at.‐% Cr), and GE = 2525 J/mol (51 at.‐% Cr). The phase diagram has been recalculated by using these data. The optimized new sets of T.A.P.‐parameter resulted as: C = −7800, C = 3500 (C in J/mol), C = −6.8, C = 3.8 (C in J/mol·K) for the liquid phase; as well as C = 7800, C = 4500 (C in J/mol), C = 3.1, C = 3.5 (C in J/mol·K) for the fcc phase.
Investigation of Charge Transport Across the Ag | AgI‐interface: (I) Occurrence of Periodic Phenomena During Anodic Dissolution of Silver
Authors: Janek J. , Majoni S.
Published: July 2012

By drawing a constant electric current through a symmetric electrochemical cell of the type Ag|a‐AgI|Ag we observed, under certain experimental conditions, strong periodic oscillations of the voltage across the cell. Depending on current density and applied mechanical force, these oscillations show either periodic or irregular behaviour.

Further experiments show that these strong voltage oscillations are caused by the anodic interface at which Ag‐metal is dissolved electrochemically into the solid electrolyte. The phenomenon itself is reproducible, but the appearance of the oscillations is very sensitive to the experimental conditions. We present experimental results for different experimental conditions and cell types and discuss a possible mechanism for the observed phenomenon. An important element of the attempt to find a microscopic explanation is the basic process of forming lattice vacancies in the metal at the anodic interface. The behaviour of these vacancies is crucial for the kinetic properties of the metal‐solid electrolyte interface under non‐equilibrium conditions.
Viscosity of the System KF–K2MoO4–B2O3
Authors: Silný A. , Danêk V. , Chrenkovå M.
Published: July 2012

The viscosity of the melts of the system KF–K2MoO4–B2O3 has been measured by means of the computerised torsional pendulum method.

The viscosity of the melts increases both with the increased content of K2MoO4 and B2O3. In the binary system KF–K2MoO4 the simple additivity of the viscosity has been found. In the ternary system strong deviation from the additive behaviour was found which is possible to ascribe to the chemical reactions between the components.

From the obtained results it follows, that the binary interaction in the KF‐B203 system corresponds to the chemical reaction

8KF+7B2O3 = 3K2B4O7 + 2KBF4, while the interaction in the K2MoO4–B2O3 system corresponds most probably to the formation of the heteropolyanion of the type [BMo6O24]9‐ according to the chemical reaction: 6K2MoO4 + B2O3 = K9[BMo6O24] + 3 KBO2.

Statistically significant ternary interaction may be explained as the entrance of the fluorine atoms into the coordination sphere of the molybdenum in the heteropolyanions.
A Modification of the Knudsen Method for Determining the Molecular Weight of Vapors
Authors: Schönherr E. , Freiberg M.
Published: July 2012

Two Knudsen cells, which evaporate condensed material in opposite vertical directions, are hung to the arms of a vacuum beam microbalance. The molecular weight of the effused vapor is computed from the recoil force and individual evaporation rates of the two cells. The recoil force of the cells is determined from the mass change which appears when the evaporation under high vacuum conditions is abruptly suppressed by the inlet of an inert vapor. The method is presented with water as an example.
Solvent and Temperature Effects on the Intramolecular Fluorescence Quenching in Dipeptide Model Compounds [1]
Authors: Sakurai Tadamitsu , Miyoshi Kenichiro , Obitsu Mitsuhiro , Inoue Hiroyasu
Published: July 2012

The mechanism of fluorescence quenching through intramolecular electron transfer (ET) was investigated in the dipeptide model compounds DL‐N‐[4‐(diethylamino)alkyl]‐2‐acetylamino‐3‐(1‐naphthyl)propionamides (1) by stationary and time‐resolved fluorescence spectroscopy in non‐polar and polar solvents. An analysis of the observed singlet‐exciplex fluorescence and the biexponential decay of monomer fluorescence established that emission quenching in non‐polar solvents proceeds through the singlet‐exciplex intermediate with a strong charge‐transfer character, and that the quenching rate constant increases with a decrease in free‐energy change for ET (ΔGet) but it is not very sensitive to the variation of methylene chain length in 1. The observations of biexponential emission decay and very weak exciplex emission in polar solvents suggest that a singlet exciplex and/or a solvent‐separated radical ion pair become a key intermediate in the quenching process. The finding that the magnitude of ΔGet, being regarded as a measure of the stability of an intermediate formed, linearly correlates with the logarithm of solvent viscosity is explained in terms of a short‐lived singlet exciplex that serves as a precursor of the radical ion pair intermediate. Thus, solvent viscosity effects on the biexponential emission decay processes of 1 with small ΔGet in protic polar solvents provide a good criterion for the exclusive operation of a singlet‐exciplex mechanism in the case that a short‐lived exciplex and a long‐lived radical ion pair are produced. It was also found that any of activation parameters for ET fluorescence quenching process in acetonitrile is comparable to the corresponding parameter obtained in methylcyclohexane. This finding may present kinetic evidence for the participation of a singlet‐exciplex mechanism in the aprotic polar solvent, acetonitrile.
Nanocrystalline Palladium by Pulsed Electrodeposition
Authors: Natter H. , Hempelmann R. , Krajewski T.
Published: July 2012

A pulsed electrochemical deposition technique is developed which allows to produce large amounts of nanocrystalline palladium with very low porosity. By an appropriate choice of the deposition parameters the shape and the size of the crystallites can be varied.
Solution of Hydrogen in Cold‐Worked Pd‐Ni, Pd‐Pt, and Pd‐Ni‐Ag Alloys
Authors: Kishimoto S. , Yoshida N. , Masui T. , Ibaragi T. , Nakano A. , Hiratsuka T.
Published: July 2012

The effect of cold‐working on hydrogen solubilities in the dilute region (α phase) has been investigated for Pd1‐xNix(x≤0.2), Pd1‐xPtx(x≤0.19), and Pd1‐xNi(1/2)xAg(1/2)x(x≤0.2) alloys by measuring pressure‐composition isotherms between 273 and 348 K. The enhancement of hydrogen solubility in Pd‐Ni alloys resulting from dislocation‐hydrogen interaction tends to increase with increasing Ni content, in contrast to the case of Pd‐Ag and Pd‐Au alloys. On the other hand, the solubility enhancements in Pd‐Pt and Pd‐Ni‐Ag alloys did not change significantly with alloying metal contents. These results can be qualitatively explained by the interactions between the alloying elements with different sizes and the stress fields of dislocations. The hydrogen trapping at defects such as vacancies was also predicted from the observation of the initial region of the isotherms for cold‐worked alloys. It was found that the extent of pressure hysteresis in the isotherm for Pd0.9Ni0.1 alloy which has been initially cold‐worked is less than for the well‐annealed alloy and in the case of Pd0.85Ni0.075Ag0.075 alloy the hysteresis disappears completely.
Measurements of Interaction Second Virial Coefficients of Binary Mixtures of Inert Gases and Gases
Authors: Vatter K. , Schmidt H. J. , Elias E. , Schramm B.
Published: July 2012

The interaction second virial coefficients of the mixtures Ar/CO, Ar/N2, Ar/O2, Ne/CO, Ne/N2, and Ne/O2were measured from 296 K to 463 K, utilizing the expansion method and the temperature changing method. Improvements in the previously described apparatuses reduced systematical errors and provided more accurate measurements of the coefficients. The experimental data were compared to calculations of interaction second virial coefficients based on modern potential energy surfaces. None of the previously reported potential energy surfaces was sufficient to account for the measured interaction second virial coefficients over our experimental temperature range from 296 K to 463 K.
Electronic Structure of Molten Salts: A Numerical Approach
Authors: Koslowski Thorsten
Published: July 2012

We present a numerical study of the electronic structure of a simple model of molten salts, with application to alkali halides. The geometry of the model is simulated using the primitive model of charged hard spheres, the electronic structure is described by a tight‐binding Hamiltonian. We study the influence of the topological and Madelung potential disorder on the evolution of the density of states upon melting and the optical absorption, the latter directly comparable to experiments. A population analysis of the cationic conduction band is performed, the results are discussed with respect to the possible formation of dipolar atoms in the corresponding metal‐molten salt solutions.
Curvature Elasticity Models of Microemulsions
Authors: Safran S. A. , Tlusty T.
Published: July 2012

We review the theory of curvature elasticity of thin, fluid films starting with a phenomenological formalism motivated by microscopic, physical examples. The effects of finite compressibility of the layer, exchange of molecules between the film and the solution, and the intrinsic bending stiffness of the film are taken into account; these degrees of freedom account for all the important molecular modes of the system. The effects of fluctuations of the number of molecules in the film (which is in equilibrium with surfactant molecules or micelles in solution) and in the area per molecule about its equilibrium value is shown to soften the curvature elastic moduli. The relationship of the bending moduli to the pressure distribution in the film is discussed and it is demonstrated that isotropic liquid films have no bending modulus, in the continuum limit. The bending moduli for charged membranes and for block copolymers and estimated. Finally, some recent experimental measure of curvature elasticity are discussed and compared with the theory.
FTIR‐Spectroscopic Study of Reactions of FCO and FC(O)OO Radicals in the Presence of O2 and NO2
Authors: Bednarek G. , Argüello G. A. , Zellner R.
Published: July 2012

Steady‐state photolysis of oxalylfluoride (FC(O)C(O)F) together with FTIR‐spectroscopy has been used to investigate the reactions of FCO and FC(O)OO radicals in the presence of O2 and NO2. Formation of FCO radicals has been identified as the main photodissociation process of oxalylfluoride at λ = 254 nm. However, a quantum yield of ø = 0.11±0.02 was attributed to the direct formation of CF2O and CO in this process. In the presence of O2, the products of reactions of FC(O)Ox(x = 0, 1, 2) radicals were bis‐fluoroformylperoxide (FC(O)OOC(O)F) and bis‐fluoroformyltrioxide (FC(O)OOOC(O)F), as well as CF2O, CO and CO2. Addition of NO2 to the reaction system led to the formation of fluoroformylperoxynitrate (FC(O)OONO2). The rate constant for the thermal decomposition of fluoroformylperoxynitrate in the temperature range 275–307 K was measured to be k(T) = 3.5 × 1016 exp (‐13 900+1700−2600/T) s−1. For bis‐fluoroformyltrioxide, a rate constant for thermal decomposition of 6.0×10−4 s−1 was measured at temperatures around 250 K. The thermal stability of bisfluoroformyltrioxide and fluoroformylperoxynitrate is discussed in terms of a comparison with the stability of similar molecules.