bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of the rotator phase of cyclohexane at higher pressures
Authors: Würflinger A.
Published: July 2012

The reorientational behaviour of cyclohexane molecules in the rotator phase has been investigated with a Monte Carlo simulation in a cubic box with periodic boundary conditions. A previous simulation for state points at normal pressure is extended to higher pressure. This enables us also to perform simulations along isochors and isotherms, thus to distinguish between isothermal density changes and isochoric temperature changes. Reorientational correlation functions for various molecular axes are calculated in order to analyse the orientational disorder. It was found that in the immediate neighbourhood to the low‐temperature phase transition the orientational freedom is limited. At larger distances to the solid‐solid transition line no preferred orientations can be detected. The reorientational behaviour changes significantly when a displacement of the molecular centers is allowed, in particular the otherwise retarded decay of the correlation function for the C3‐axis is accelerated near the low‐temperature phase boundary of solid I.
I. Electronic structure and thermodynamics of alloys: Alloy Metastability During Nucleation‐Controlled Reactions
Authors: Perepezko J.H. , Wilde G.
Published: July 2012

The initial stage of a first order transformation reactions is controlled by a nucleation process. In fact, the kinetic constraints provided by nucleation and growth difficulties of the new phase provide the necessary condition to expose metastable reaction pathways. The resulting hierarchy of metastability is viewed in terms of the severity of the imposed kinetic constraints. The identification of nucleation control has been extended to cover solid state reactions such as those involved in solid state amorphization reactions (SSAR) of so‐called driven systems. Some of the fundamental characteristics of alloy metastability under kinetic constraints are illustrated by experimental observations and model analyses that highlight the current understanding.
The Bragg‐Williams‐Gorsky (BWG) ordering treatment in the compound energy formalism (CEF)
Authors: Fries Suzana G. , Lukas Hans Leo , Ansara Ibrahim , Sundman Bo
Published: July 2012

The BWG type of approximation describing chemical ordering has been available in thermodynamic calculation‐optimisation software. Developments were done for special cases of symmetry, e.g. the γ‐γ′ ordering, based on the fcc lattice, in Ni‐based superalloys or the β‐β′ ordering in the Cu‐Zn system, based on the bcc lattice.

The technological importance of materials presenting order‐disorder transformations, demands a versatile Gibbs energy modelling, able to describe the changes taking place during ordering as functions of composition and temperature. Recently practical use of Gibbs energy descriptions of ordered phases are becoming a daily procedure.

In this communication we present a general method for deriving the constraints in the compound energy formalism (CEF) for the model parameters describing an order‐disorder transformation. The cases discussed include, for example, the oxygen ordering in its interstitial solution in α‐Zr (hep).
Sound velocity in the molten As‐Te system
Authors: Tsuchiya Y.
Published: July 2012

The velocity of sound in the molten As‐Te has been measured as a function of temperature, which shows up to 60 at.% As a pronounced minimum like in pure liquid Te. In an As‐ rich alloy, only a high temperature branch of the whole vs‐T curve that the sound velocity decreases rapidly with lowering temperature was obtained, because solidification took place before a minimum could be observed. The results suggest that rapid structural changes occur with varying temperature over the whole composition and confirm the recent experiments indicating that liquid As undergoes rapid structural changes with raising temperature like in supercooled Te. An extrapolation predicts a minimum in the sound velocity in As to occur at 736±6°C. The Peierls distortion mechanism and stability of structure of the liquid sp‐bonded elements are discussed.
EMF‐Study of the thermodynamics of liquid Kx(KI)1‐x and Csx(CsI)1‐x melts
Authors: von Blanckenhagen B. , Nattland D. , Freyland W.
Published: July 2012

We report EMF measurements of the metal activity aK and aCs in Kx(KI)1‐x(xK≤0.0136) and Csx(CsI)1‐x (xCs≤0.25) at T=800°C. The data have been obtained simultaneously with optical absorption spectra. The composition has been controlled in situ via coulometric titration. The data of Kx(KI)1‐x are discussed in terms of a thermodynamic defect model, taking into account different electronic defect species in the melt: mobile electrons, monomer F‐center like and bipolaronic states. The results of the analysis of the thermodynamic data are in good agreement with the results of the quantitative analysis of the optical absorption spectra. For Csx(CsI)1‐x we report data for the partial molar excess‐free enthalpies and the integral‐free enthalpy. As expected the Csx(CsI)1‐x system shows only little deviation from ideal mixing behaviour in comparison to other Mx(MX)1‐x melts, a fact which is also established in the phase diagram by the absence of a miscibility gap in the caesium‐caesium halide mixtures.
II. Surface and interfacial phenomena: Surface phases in binary liquid metal alloys: An X‐ray study
Authors: Tostmann H. , Dimasi E. , Shpyrko O. G. , Pershan P. S. , Ocko B. M. , Deutsch M.
Published: July 2012

Surface‐sensitive x‐ray scattering techniques with atomic scale resolution are employed to investigate the microscopic structure of the surface of three classes of liquid binary alloys: (i) Surface segregation in partly miscible binary alloys as predicted by the Gibbs adsorption rule is investigated for Ga‐In. The first layer consists of a supercooled In monolayer and the bulk composition is reached after about two atomic diameters. (ii) The Ga‐Bi system displays a wetting transition at a characteristic temperature Tw ≈︁ 220°C. The transition from a Bi monolayer on Ga below Tw to a thick Bi‐rich wetting film above Tw is studied. (iii) The effect of attractive interactions between the two components of a binary alloy on the surface structure is investigated for two Hg‐Au alloys.
Wetting and prewetting transitions in Ga‐Pb alloys
Authors: Wynblatt Paul , Chatain Dominique
Published: July 2012

This paper summarizes previous work on wetting and adsorption transitions in the Ga‐Pb system. It describes a model of these transitions which is based on the regular solution approximation in conjunction with nearest neighbor interactions. It also reviews several recent novel experimental results obtained in Ga‐Pb, including: (a) evidence that complete wetting prevails in Ga‐Pb alloys within the domain of liquid‐liquid coexistence; (b) a demonstration that the thickness of Pb at the surface of Ga diverges logarithmically as liquid‐liquid coexistence is approached, as expected for metallic systems characterized by short‐range interactions, and (c) studies of adsorption transitions by two complementary experimental approaches which map out the extension of the prewetting line and provide estimates of the prewetting critical point and the wetting temperature.
Surface and bulk properties of strongly non‐ideal liquid binary metallic systems
Authors: Rösner‐Kuhn M. , Kuppermann G. , Thiedemann U. , Drewes K. , Schmidt‐Lehmann T. , Frohberg M. G.
Published: July 2012

Based on activity data for the components in the bulk phase and the surface tension of the constituent metals, the Butler equation is applied to liquid Fe‐Ti alloys to calculate the surface composition, the activities of the components in the surface, and the surface tension of the entire concentration range of the system. Using thermodynamic modeling the bulk activities of the components are derived from mixing enthalpy data. A comparison between the calculated temperature dependence of the surface tension and experimental values obtained by oscillating drop technique measurements is given for the liquid Fe2Ti intermetallic alloy, where a sufficient agreement can be stated.
Study of the effect of zirconium addition to the Al‐rich alloys of the Al‐Cu and Al‐Cu‐Mg systems
Authors: Soares Delfim F. , De Castro Portela Fernando
Published: July 2012

The effect of zirconium addition on the eutectic reactions, on the Al‐rich part of the Al‐Cu and Al‐Cu‐Mg systems, were studied by differential thermal analysis (DTA). The temperature of the reactions and, for Al‐Cu alloys, the heat of the reactions were determined. After the DTA experiments the alloys were studied by scanning electron microscopy (SEM) and the chemical analysis of the phases have been determined by energy‐dispersive spectroscopy (EDS).

The temperature of the eutectic reactions does not change significantly by the presence of zirconium in the system. The phase distribution on the ternary and quaternary systems shows that the zirconium present is essentially in the Al3Zr and “X” phases. The Al3Zr phase has a low solubility range for copper, ∼ 0.5 at.%, and no solubility for magnesium. The X‐ray pattern of the ternary phase “X” is presented, for alloys belonging to the Al‐rich part of the Al‐Cu‐Zr system
Thermodynamic assessment of the Al‐Nb‐Ti system
Authors: Servant C. , Ansara I.
Published: July 2012

The Gibbs energy of formation of the solution and compound phases in the Al‐Nb‐Ti system were derived from an optimisation procedure using all the available experimental thermodynamic and phase diagram data. The thermodynamic description of the ordered compounds was made using a multi‐sublattice model, while a Redlich‐Kister polynomial was used for the solution phases.
Phase equilibria and stability of the bcc aluminide in the Co‐Cr‐Al system
Authors: Ishikawa K. , Ise M. , Ohnuma I. , Kainuma R. , Ishida K.
Published: July 2012

Phase equilibria and ordering reactions in the bcc aluminides of the Co‐Cr‐Al systems over a temperature range of 1000‐1350°C have been investigated mainly by the diffusion couple method. The compositions of the γ (Al: fcc‐Co), β (B2: CoAl), α (A2: bcc‐Cr) and σ (sigma phase: D8b) phases in equilibrium, and the critical boundaries of the A2/B2 continuous ordering transition in the bcc phase region have been determined. It is shown that both continuous and discontinuous A2 to B2 phase ordering transitions and elliptically shaped A2+B2 miscibility gap islands with wide composition ranges exist in these systems in isothermal sections. The phase equilibria involving the γ, β, α and σ phases are presented and stability of the ordered bcc aluminides is discussed.
IV. Progress in experimental methods: Thermodynamic investigations in the Si‐Ge‐rich part of the ruthenium‐silicon‐germanium system
Authors: Perring L. , Bussy F. , Kuntz J. J. , Gachon J. C.
Published: July 2012

This paper reports molar heat capacities of Ru50SixGe(50‐x) and Ru40SiyGe(60‐y) ternary solid solutions determined by differential scanning calorimetry. A second order transition has been characterised for alloys ranging from Ru40Ge60 to Ru40Si10Ge50 at temperatures ranging from 850 to 1040 K, respectively. Tie lines have been established at 1000‐900‐800‐700‐600°C by electron microprobe measurements on annealed alloys of the two phase domains: Ru50SixGe(50‐x)‐Ru40SiyGe(60‐y) and Ru40SiyGe(60‐y)‐Si zGe(100‐z).
Vapor pressure methods: A source of experimental thermodynamic data
Authors: Ipser Herbert
Published: July 2012

An overview is given of the vapor pressure methods which are used for the determination of partial thermodynamic quantities. The methods are divided into four groups: static methods (pressure gauges, atomic absorption, and others); dynamic methods (boiling point method, transpiration method); effusion methods (Langmuir method, different variants of the Knudsen method); equilibration methods (equilibration with gas mixtures, isopiestic method, dew point method). The characteristics of each group are discussed shortly, and some examples of application are given from the recent literature.
Heat capacity of liquid eutectic tellurium alloys
Authors: Schmid J. , Sommer F.
Published: July 2012

Using an adiabatic calorimeter direct measurements of the heat capacity of the liquid Si15Te85, Ge15Te85, Sn15Te85, Pb11Te89, Pb11Te89 and Bi10Te90 alloys and of liquid tellurium have been performed. The heat capacity has been measured as a function of temperature up to about 100 K above the eutectic temperature. The heat capacity decreases with increasing temperature. The excess heat capacity ΔCp of Sn15Te85, Pb11Te89 and Bi10Te90 is pnearly constant within the examined temperature range and is smaller than 5 J mol−1 K−1. ΔCp of Sb11Te89 slightly depends on temperature, while ΔCp of Si15Te85 and Ge15Te85 exhibit large values and temperature dependences. ΔCp reflects the chemical short range order (CSRO) in the liquid state due to the strong compound forming tendency in these alloys. The influence of CSRO is discussed in the light of the measured ΔCp and other structure sensitive properties given in literature.
V. Practical applications: PGM‐Alloys as corrosion‐resistant high‐temperature materials
Authors: Kock W. , Lupton D. , Merker J. , Meinhardt J.
Published: July 2012

The available thermodynamic data on the platinum group metals (PGMs) are summarized with reference to the use of these metals and their alloys at high temperatures. The significance of these data with regard to reactions with various environments and resulting corrosion effects are discussed. The influence of solubility limits in platinum solid solutions on achievable strength properties and the importance of oxide dispersion hardening for further improving strength and corrosion resistance are illustrated.
Glass formation in metallic systems
Authors: Clavaguera‐Mora M. T.
Published: July 2012

The aim of the present paper is to analyse the formation and stability of metallic glasses. Attention is focused to the history of the progress on new glassy alloys with specific applications: from soft magnetic Fe‐based ribbons obtained by melt spinning or planar flow casting, through metallic glasses acting as precursors of nanocrystalline precipitates embedded in an amorphous matrix, towards the finding of new multicomponent metallic alloys with large glass‐forming ability that open a new area of development and applications of bulk metallic glasses. The glass formation process is discussed in terms of the structure of the resultant material and in terms of the thermodynamics and kinetics of the process. The development of structural criteria for glass formation is based upon the notion that the free energy of particularly stable glassy structures will be low enough to make the driving force for crystallization negligible. Both structural and energetic criteria point to an enhanced glass‐forming ability in multicomponent alloys. Kinetic criteria allow to differentiate between the ease of glass formation from an undercooled melt (or from a mixture of crystalline grains, as in solid state amorphization) and the stability of the glassy state versus devitrification or crystallization. Key kinetic parameters are viscosity and, more specifically in multicomponent systems, diffusivities of the different elements in the crystalline, glassy and metastable liquid state, respectively. The formation of nanostructured materials from controlled thermal treatment and their temperature stability is discussed in terms of the concentration gradients developing at the interface between the nanocrystals and the amorphous matrix. The qualitative influence of several parameters in the glass‐forming ability and glass‐stability as well as their link to the empirical criteria that have been successfully employed to predict the glass‐forming ability are presented.
Experimental applications of sodium‐containing alloys in molten alkali halides
Authors: Haarberg G.M. , Egan J.J.
Published: July 2012

Sodium‐bismuth alloys were used as reference electrodes in contact with molten alkali halides to establish sodium activities. Electronic conductivity versus sodium activity was obtained for molten sodium halides using such alloys (ã5 mol% Na) in polarization experiments. Results are presented for molten NaI. Also concentration versus activity data for Na in Na‐Bi alloys were determined as a function of composition (xNa: 0.01–0.15) and temperature (700–900°C) by using a simple coulometric titration technique. Sodium‐lead alloys (ã 8 mol% Na) were used to study the kinetics of the sodium electrode in molten NaCl using ac impedance spectroscopy combined with galvanostatic perturbation. Results from potential measurements between aluminium and a sodium alloy electrode performed in cryolite‐alumina melts to study the effects of electrolyte composition are also presented.
Distribution of elements between liquid alloy and slag phases in extractive metallurgy
Authors: Itagaki Kimio , Hino Mitsuhisa , Pagador Romeo U. , Surapunt Supachai
Published: July 2012

The distribution ratio of the component elements between the liquid Cu‐Zn‐Fe or Cu‐Ni‐Fe alloy and the FeOx‐SiO2‐CaO or MgO‐saturated FeOx‐SiO2‐CaO slag was evaluated thermodynamically based on the activity coefficients of the alloy components determined using a transpiration method and a double Knudsen cell‐mass spectrometer.
Phase relations in the Sn‐Ag‐Sb system at 220°C
Authors: Oberndorff P. J. T. L. , Kodentsov A.A. , Vuorinen V. , Kivilahti J.K. , van Loo F.J.J.
Published: July 2012

The isothermal cross‐section through the ternary phase diagram Sn‐Ag‐Sb at 220°C was constructed by means of diffusion couples and equilibrated alloys.

It is proposed that only two phases, Sn4Sb3 and Sn3Sb4, exist in the binary Sn‐Sb system, and no equi‐atomic compound SnSb is present as an equilibrium phase at this temperature.

No ternary phases were found in the Sn‐Ag‐Sb system at 220°C; the topology of the isotherm is largely determined by the presence of the extended region of solid solution between the ζ‐Ag4Sn and ζ‐Ag4Sb intermetallic phases.
Thermodynamics and kinetics of internal reactions: Nitridation of Ni‐Cr alloys
Authors: Kodentsov A.A. , van Dal M.J.H. , Kivilahti J.K. , van Loo F.J.J
Published: July 2012

The implementation of Wagner's theory of internal precipitation for evaluating nitriding kinetics has been discussed. Nitriding experiments on Ni‐Cr alloys were carried out in the range of 1‐6000 bar of hydrostatic N2‐pressure and under a flowing NH3+H2 gas mixture at 873‐1398 K. When a moderately stable phase is precipitated out during an internal reaction, the behaviour of the penetrating atoms within the diffusion zone can be interpreted based on thermodynamic considerations. The thermodynamic assessment of the Ni‐Cr‐N system was performed using the Thermo‐Calc databank and the results were verified experimentally. However, “uphill” diffusion of the penetrating species through the matrix towards the precipitation front can be predicted in certain cases and then Wagner's treatment cannot be utilised. It was demonstrated that under suitable experimental conditions of solute content, temperature and external activity of the penetrating element, Wagner's analysis can be applied to internal precipitation process in any material system.
Reversible and irreversible biopolymer gels — Structure and mechanical properties
Authors: Ross‐Murphy Simon B.
Published: July 2012

The majority of synthetic polymer gels are formed by the covalent cross‐linking of linear or branched macro‐molecules using multi‐functional cross‐linking agents. Such gels are networks, or true macromolecules with (nominally) infinite molecular weight and consequently they swell rather than dissolve if immersed in a good solvent. However, there are also a whole class of materials called physical gels where non‐covalent crosslinks occur. These show similarities to covalent networks, but because the cross‐links are not permanent, they will show creep behaviour at very long times. Some of these form on cooling a heated solution, such as gelatin gels, while others form only on heating. Also, some gels are thermoreversible, while others are not.

Physical gels can be formed from synthetic or biopolymers. In the latter case non‐covalent cross‐links often comprise more specific and complex mechanisms involving, rather than point‐like cross‐links, “junction zones” of known, ordered secondary structure such as multiple helices. Typically there is a specific, and often intricate, hierarchy of arrangements, which are more familiar to molecular biologists than to polymer physical chemists. In this paper we introduce viscoelastic techniques for characteristing physical gels, and then relate the properties to the underlying structure at the macromolecular and junction zone level. The parallels between synthetic and biopolymer gels will also be illustrated. Finally we describe recent work on the heat‐set gelation of globular proteins, and an attempt to relate the important parameter of the gelation time, tc, to both polymer concentration and temperature.
Luminescent inorganic networks
Authors: Bredol M. , Kynast U. , Boldhaus M. , Lau C.
Published: July 2012

Silica‐based inorganic networks combined with organic rare earth complexes should lead to a new class of luminescent materials, adding the chemical stability of silica to the strong UV absorption of organic ligands and the emissive properties of rare earth ions. This concept is demonstrated by the preparation of silica xerogels containing benzoic acid in its network and subsequent reaction (ion exchange) of these gels with terbium chloride solution. The product yields green luminescence similar to the one of solid terbium benzoate. Alternatively, complete rare earth complexes (example: europium thenoyltrifluoracetonate) may be immobilized in silica xerogels, yielding luminescent hybrid materials.
Investigations on the organic crosslinking in ORMOCERs by means of Raman spectroscopy
Authors: Riegel B. , Kiefer W. , Hofacker S. , Schottner G.
Published: July 2012

FT‐Raman spectroscopy was used together with supplementary 13C‐NMR measurements to analyze the reaction of the epoxy moieties of 3‐glycidoxypropyltrimethoxysilane and 5,6‐epoxyhexyltrimethoxysilane during sol‐gel processing. The corresponding reactions of the model compounds epoxypropane and epoxyhexane were analyzed to obtain the necessary Raman assignments of the resulting products. Based on these results the formation of the β‐hydroxy methyl ethers could be derived for the silanes. An additional polyaddition of the epoxy rings yielding a mixture of oligo ethers is also consistent with the Raman measurements.
Effect of synthesis conditions on properties of covalently cross‐linked thermosensitive hydrophilic gels
Authors: Groß Hans‐Jürgen , Wack Holger , Althaus Wilhelm
Published: July 2012

Gel synthesis conditions have a considerable influence on the characteristic properties of the polymerized gel system. Under variation of total amount of monomer, cross‐linker concentration and synthesis temperature, different covalently cross‐linked hydrophilic gels based on N‐isopropylacrylamide were synthesized.

The shear modulus, the phase transition temperature and ‐enthalpy and the swelling degree of the hydrophilic gels were measured. Synthesis conditions had a significant influence on the shear modulus and the swelling degree. An influence on the phase transition temperature and ‐enthalpy could only be found in some special cases.
Effect of connectivity and charge density on the swelling and local structural and dynamic properties of colloidal PNIPAM microgels
Authors: Kratz Karl , Hellweg Thomas , Eimer Wolfgang
Published: July 2012

The structural and dynamic properties of thermosensitive neutral and partially charged colloidal microgels of poly(N‐isopropylacrylamide‐co‐acrylic acid) (PNIPAM/AAc) have been investigated by neutron and light scattering techniques. Introduction of cross‐linker induces topological constraints into the polymer network, and hence reduces the swelling capability of the particles as expressed in the variation of their hydrodynamic radii. Small‐angle neutron scattering experiments reveal that below the transition temperature the inhomogeneous structure of the microgel consists of local solid‐like frozen regions and solution‐like regions where the polymer chain behaves as in semidilute polymer solution. The temperature‐induced collapse leads to a strongly segregated micro‐phase separated particle. The swelling of charged microgels is determined by their charge density, controlled through the amount of acrylic acid comonomer, the pH, and the salt concentration.
Praktische Anwendungen von quervernetztem Polyvinylpyrrolidon
Authors: Feifel Klaus , Zeiler Martin , Oechsle Dietmar
Published: July 2012

Quervernetztes Polyvinylpyrrolidon (PVPP) ist ein inertes, toxisch unbedenkliches Popkornpolymerisat auf der Basis von N‐Vinylpyrrolidon. PVPP bildet mit Gerbstoffen reversibel Komplexe und kann aufgrund dieser Eigenschaft zur Stabilisierung von Bier und anderen Getränken eingesetzt werden. Ein Komplex von PVPP mit Iod, PVPP‐Iod, kann in einem neu entwickelten Verfahren, der „Bioziden Filtration”︁, zur Inaktivierung von Mikroorganismen in empfindlichen Flüssigkeiten genutzt werden. Der Einsatz des Polymers zur Getränkestabilisierung und in der “Bioziden Filtration” wird in der folgenden Publikation beschrieben.
Fibers and wires in organogels from low‐mass compounds: Typical structural and rheological properties
Authors: Terech P.
Published: July 2012

An overview is given of the special class of thermoreversible organogels and jellies formed with low‐mass compounds. Two distinct rheological behaviors can characterize these binary systems: (1) viscoelastic liquids which develop an elasticity over short times, (2) viscoelastic solids which are constituted on long‐lived 3‐d networks at a temperature T in the gel domain of the phase diagram. Entangled, breakable giant micelles (molecular wires) are opposed to fibers interconnected through crystalline‐like microdomains. Certain thermal and rheological properties are presented as well as the detailed structural context at different scales of the fibrillar networks. A brief review of the different chemical classes of organogelators illustrates the growing development in the field. The class of viscoelastic liquids (jellies) is illustrated with the special category of monomolecular organometallic wires.
Gels of semifluorinated alkanes: Structural investigations by small angle X‐ray scattering
Authors: Lang P. , Marczuk P. , Lermann E. , Möller M.
Published: July 2012

The gels of perfluorododecylalkanes F12Hn in dodecane were investigated with small angle x‐ray scattering (SAXS). These gels can be categorised into three groups according to their stability and optical appearance. The short chain samples with n≤6 form highly turbid gels which eventually undergo a phase separation, the samples with 8≤n≤12 form opaque stable gels and the long chain homologues form stable gels which are transparent. This categorisation is also reflected in the SAXS patterns which show that the F12H6 gel has a monolayered lamellar structure, while the SAXS data from the gels with 8≤n≤12 have to be interpreted in terms of double layered undulating stacks. The structure of the gels formed by the long chain members could not be clarified yet.
Network formation in water‐in‐oil microemulsions stabilised by the amphiphilic triblock‐copolymer PEO13PPO30PEO13 in p‐xylene
Authors: Mays Holger , Almgren Mats , Brown Wyn
Published: July 2012

The properties of pseudo‐ternary mixtures of p‐Xylene, PEO13PPO30PEO13 (Pluronic L64) and aqueous phase in water‐in‐oil microemulsions (L2‐phase) have been studied by electric conductivity and viscosity measurements, and by the methods time‐resolved luminescence quenching and dynamic light scattering. Varied system parameters were the content of aqueous phase in the mixture and the temperature. An increase of the water content leads to a swelling of the spherical reversed micelles. An aggregate shrinkage is observed upon temperature decrease. The microemulsion with the largest water amount exhibits a percolative transition of the electric conductivity upon decreasing temperature, which is accompanied by a strong viscosity increase and a fast inter‐droplet exchange. The time‐resolved decay curves from luminescence quenching experiments prove that the droplet‐structure is maintained in the highly conducting state. Viscosity and dynamic light scattering data suggest a gradual network build‐up of physically connected reversed micelles when the temperature is lowered. The observations are interpreted in a self‐consistent picture by temperature induced changes in the solvent quality with regard to the amphiphile.
Molecular simulation: Understanding polymer gels at the molecular level
Authors: Müller‐Plathe Florian
Published: July 2012

It is shown how insight into fundamental atomistic processes in water‐swollen poly(vinyl alcohol) can be obtained from molecular simulation. Molecular dynamics is used both to calculate quantitatively diffusion coefficients and to examine the qualitative concepts of different states of water in such systems. While concentration‐dependent diffusion coefficients are useful quantities in their own right, here they are also being used to validate the simulations. With confidence in the simulated dynamics established, the distribution of re‐orientational correlation times of water molecules is calculated. It shows that, above the freezing point of water, there is only a single, albeit broad, distribution of correlation times, whereas at 250 K the distribution becomes bimodal. The concept of different dynamical states of water in this hydrogel, therefore, makes sense at low temperatures but not at room temperature or above. Moreover, contrary to the purported picture of “free” and “bound” water in hydrogels, at all temperatures the re‐orientation of a water molecule is faster if it is surrounded by other water molecules than if it is close to the polymer.
Determination of hydrodynamic properties in colloidal systems by static and dynamic light scattering
Authors: Härtl W. , Beck Ch. , Hempelmann R.
Published: July 2012

The structure and dynamics of silica hard spheres and charged colloidal systems has been investigated at high concentrations by means of light scattering. The index of refraction at these high volume fractions was matched using a mixture of water/isopropanol for the Yukawa particles and toluene/ethanol for the hard spheres. By simultaneously measuring the dynamic and static properties of the colloidal systems we were able to extract the hydrodynamic function H(Q) at different concentrations. Our results are in good agreement with theoretical calculations over a large concentration range.
Properties of differently charged poly(N‐isopropylacrylamide) Latex dispersions in alcohol‐water mixtures
Authors: Mielke Mark , Zimehl Ralf
Published: July 2012

Results of size control experiments, TEM and viscosity measurements on both negatively and positively charged poly(N‐isopropylacrylamide) (PNIPAAM) latex dispersions are reported. In alcohol‐water mixtures containing low weight fractions of alcohols higher than methanol, negatively and positively charged PNIPAAM particles exhibit both opposite swelling behaviour and flow characteristics at 20°C. Negatively charged particles shrink due to cononsolvency. Shrinking leads to a decreased viscosity. Conversely, positively charged particles swell dramatically and exhibit an increased viscosity. At 40°C, the negatively charged particles collapse and show a similar behaviour to those with positive charge. We observed with TEM that positively charged particles form random flocks after drying on the grid whereas negatively charged ones form arrays of separated particles. This underlines our general concept that the positively charged particles are in general more hydrophobic.
On electric field induced processes in ionic compounds
Authors: Schmalzried H. , Smolin S.
Published: July 2012

With the help of the solid solution (Mg,Fe)O, where Fe‐ions are the dilute species, we investigate the behaviour of a ternary ionic crystal under a d.c. electric current load. The transport equations of the ions and the electronic defects predict that even with reversible electrodes demixing, and in particular decomposition of the compound will occur if the applied d.c. current density is sufficiently high. These predictions are illustrated by appropriate experiments. In this context several additional phenomena are discussed: The internal oxidation of AgBr and the internal reduction of yttria stabilized zirconia. All the compounds mentioned were placed in a galvanic cell, and the internal reactions which then could be observed were driven by the electric field in this cell.
High temperature point defect equilibria in iron‐doped MgO: An in situ Fe‐K XAFS study on the valence and site distribution of iron in (Mg1‐xFex)O
Authors: Hilbrandt N. , Martin M.
Published: July 2012

The point defect structure of a doped (oxide) system was quantitatively studied by applying in situ X‐ray absorption spectroscopy in the vicinity of the absorption edge of the dopant at high temperature (T>270 K) and under defined oxygen activity. Based on refined phase diagrams of second kind (oxygen activity vs. composition x, at constant T), the nearest neighbour dopant‐oxygen bond distances, the corresponding coordination numbers and intensity changes in the near K‐edge structure of iron in (Mg1‐xFex)1‐δO were analysed in terms of the iron oxidation degree at various compositions, x = 0.011–0.106, varying the oxygen activity within the stability field of the mixed oxide (T = 1273–1468 K). At low oxygen activities, near the metal 1 mixed oxide phase boundary (a10−12), iron was found to be divalent and octahedrally coordinated by oxygen. Over a wide range of higher oxygen activities, however, the EXAFS is predominated by two iron species. Identified via the bond length and confirmed by XANES analysis of the pre‐edge region, one species is attributed to Fe2+ (FeO bond distance R = 215.8 pm), the other to Fe3+ (R = 205.0 pm) (averaged over T and x), both occupying magnesium lattice sites. The obtained dependencies of the oxidation degree of iron can be described consistently within a point defect model in which divalent iron ions are randomly distributed within the cation sublattice and trivalent iron ions form defect associates involving two Fe3+ and a cation vacancy. Near the phase boundary to MgFe2O4, indications for trivalent iron ions dissolved in the interstitial sublattice of the NaCl type structure were found.
The density of toluene at high pressures to 673 K and 300 MPa
Authors: Franck E. U. , Kerschbaum S. , Wiegand G.
Published: July 2012

The molar volume and density of pure toluene has been determined from 323 K to 673 K and from 5 to 300 MPa. An autoclave is described which has a variable internal sample volume. 16 different constant volumes have been used and with stepwise increasing temperatures, pairs of temperature and pressure values have been taken along isochors. For the pressure range of 5 to 300 MPa and for 8 isotherms a Tait equation of state is adapted and the calculated data are given. The Tait parameters are presented. The average deviation between experimental and calculated data is below 0.15%. Up to 100 MPa, comparison with recent NIST calculations and other literature data is made. The data are in good agreement.
Photoelectron spectra of toluene rare gas and toluene diethylether 1:1 complexes
Authors: Eisenhardt C. G. , Baumgärtel H.
Published: July 2012

The photoelectron spectra of van der Waals dimers of toluene with rare gases or diethylether have been measured using resonant two‐photon laser ionization and a magnetic bottle spectrometer.
Kinetics of the Birch reduction
Authors: Greenfield A. , Schindewolf U.
Published: July 2012

Because of contradictions in the literature, we reinvestigated the kinetics of the Birch reduction, i.e. the hydrogenation of benzene and its derivatives in metal ammonia solutions (MAS: containing solvated electrons e− and metal cations M+) with alcohols to yield the corresponding cyclohexa‐1,4‐dien compounds (e.g. 2 Li+2CH3OH+C6H6⟹2CH3OLi+C6H8). The kinetics of this reaction are obscured since the hydrogen reaction proceeds parallel to it (2Li+2CH3OH⟹2CH3OLi+H2). The two reactions differ in their activation energies (6.5 and 22.5 kJ/Mol resp.); and in the series of the alkali metals Li, Na and K the rate of the Birch reduction decreases, whereas that of the hydrogen reaction increases. However, in the metal concentration range around 0.01 M. both reactions have within the experimental error the same reaction order with respect to the metal (≈︁0.8). Both are accelerated by addition of alkali cations common to the dissolved alkali metal, and both are decelerated by addition of alkali cation complexing cryptands. Thus we conclude that the cations are involved in the kinetics of both reactions, probably by forming intermediate ion pairs or shifting pre‐equilibria in which solvated electrons are involved. The experimental data of both reactions can be described very well with the rate laws v(B) = kBf2[e−][Li+)[CH3OH][C6H6]and v(H)=kHf2[e−][Li+](CH3OH]resp. (f activity coefficients after Debye‐Hückel) inserting the concentrations of e− and Li+ as calculated from the known thermodynamics of LiAS. The experimental rate constants kB and kH are the products of the rate constants of the rate determining steps and the equilibrium constants of the pre‐equilibria.
Large molecules, radicals, ions, and small soot particles in fuel‐rich hydrocarbon flames: Part III: REMPI mass spectrometry of large flame PAHs and fullerenes and their quantitative calibration through sublimation
Authors: Ahrens J. , Keller A. , Kovacs R. , Homann K.‐H.
Published: July 2012

Large polycyclic aromatic hydrocarbons (PAHs) and fullerenes have been studied using nozzle/molecular beam sampling from flames and from a sublimator with subsequent resonance enhanced multi‐photon ionization (REMPI) mass spectrometry. The mass spectrometer was of the time‐of‐flight type with an ion reflector. The sublimator for large molecules generated a definite gas phase concentration of the respective PAHs or fullerene which was controlled by determining the mass loss of the substance in a stream of heated nitrogen. The purpose of these calibrations is the quantitative analysis of these large molecules when sampling fuel‐rich flames. Twenty‐three PAHs with masses up to 596 u (dicoronylene), some oxygen‐containing PAHs, C60, C70, and C84 were used. Sublimation energies of low‐volatility PAHs and of fullerenes were determined.

Multi‐photon ionization of PAHs and fullerenes was investigated as function of the effective laser power density in the ion source and the wavelength. Furthermore, ion fragmentation of large PAHs and fullerenes was studied for different power densities and wavelengths. For PAHs with up to about 20 C atoms a wavelength of 265 nm with laser power densities of 0.5 to 1 MW/cm2 are suitable. For larger PAHs, C60. and C70 a wavelength of 208 nm is more favorable. At the shorter wavelength PAHs have considerably higher ionization efficiencies and the fullerenes do not show delayed ionization and fragmentation. Quantitative relationships between the ion signal and the absolute number density for a large number of PAHs and fullerenes in the source were determined for standardized inflow and ionization conditions.
CF3CFHO• radical: Decomposition vs. reaction with O2
Authors: Schneider W. F. , Wallington T. J. , Barker J.R. , Stahlberg E. A.
Published: July 2012

Two puzzles are associated with reactions of the CF3CFHO alkoxy radical: first, the ratio of A‐factors for the reaction with O2 and that for decomposition is about 500 times greater than expected; second, decomposition is more favored when the alkoxy radicals are produced by the reaction of peroxy radicals (RO2) with NO, compared to when they are produced by RO2 radical disproportionation. Recent experimental evidence suggests that a major fraction of the exothermicity of the reaction RO2+NO is deposited into vibrational excitation of the alkoxy radical product. A combined electronic structure and kinetic modeling study has been conducted to examine these issues. The results reported here implicate the reaction with O2 as responsible for the surprisingly large A‐factor ratio. They also support the notion that significant numbers of vibrationally excited CF3CFHO alkoxy radicals are produced in the reaction of peroxy radicals with NO and that the radicals subsequently decompose promptly on a nanosecond time scale.
γ‐Ray polymerization of cationic surfactant methacrylates in lyotropic mesophases
Authors: Pawlowski Dirk , Haibel Astrid , Ticke Bernd
Published: July 2012

The γ‐ray polymerization of (2‐methacryloylethyl)dodecyldimethylammonium bromide 1 and (11‐methacryloylundecyl)trimethylammonium bromide 2 in lyotropic mesophase is described. 1 forms hexagonal (Hα), cubic (Qα) and lamellar phases as indicated by polarizing microscopy and small angle X‐ray scattering (SAXS). Dose versus conversion curves indicate a complete polymerization of 1 in organized aqueous phases, the reaction rate being highest in the Hα phase. 2 is less reactive and polymerization in the Hα phase ceases at about 60% conversion to polymer. Both surfactants polymerize under retention of the macroscopic order of the mesophase. Nanostructured gel‐like materials with hydrophilic and hydrophobic compartments are obtained, which after removal of water can be swollen in polar and nonpolar solvents.
Differential thermal analysis under high pressure on liquid‐crystalline compounds with lateral aromatic branches
Authors: Ernst C. R. , Schneider G. M. , Würflinger A. , Weißflog W.
Published: July 2012

The high pressure phase behaviour of four liquid crystals, belonging to the class of laterally aryl‐substituted mesogens has been studied with differential thermal analysis. The pressure dependence of the phase transitions has been determined up to 300 MPa. Transition enthalpies have been determined with the aid of differential scanning calorimetry. Volume changes accompanying the phase transitions have been calculated using the Clausius‐Clapeyron equation. Several metastable phase transitions have been discovered.
Influence of thermodynamic and thermochemical data errors on calculated equilibrium composition
Authors: Belov Gleb V. , Trusov Boris G.
Published: July 2012

Influence of thermodynamic data errors upon the results of calculation of equilibrium composition of complex chemically reacting systems is examined. Two possible approaches (sensitivity analysis and statistical approach) are described. The examples showing significance of the error influence are presented.
Influences of nuclear mass, size, shape and spin on chemical isotope effect of titanium
Authors: Fujii Toshiyuki , Inagawa Jun , Nishizawa Kazushige
Published: July 2012

Titanium isotopes of Ti (III) or Ti (IV) were fractionated by liquid‐liquid extraction system using dicyclohexano‐18‐crown‐6. The nuclear size and shape effect and the nuclear spin effect resulted in the breakdowns of the linear dependency of the enrichment factors to the mass difference. The nuclear mass effect, the nuclear size and shape effect and the nuclear spin effect were calculated by the isotope pair evaluation method. The nuclear mass effects were 0.000634 for 48Ti‐46Ti (III) and 0.000559 for 48Ti‐46Ti (IV), where the total enrichment factor were 0.000989 and −0.000166, respectively. The nuclear size and shape effects were 0.000356 for 48Ti‐46Ti (III) and −0.000725 for 48Ti‐46Ti (IV). The nuclear spin effects were 0.000180 for 47Ti (III), 0.000369 for 49Ti (III), −0.000303 for 47Ti (IV) and −0.000526 for 49Ti (IV). The ratio of chemical effect given by the field shift of 3d‐orbital to that of 4s‐orbital was −1.54, which had same direction and quantity with the field shift ratio of 3d‐orbital to 4s‐orbital in Ti I in atomic spectra. This showed that the nuclear size and shape effect on the chemical isotope effect directly reflected the field shifts of Ti I. The nuclear spin effect was the function of the number of the hyperfine splitting vibrational energy levels and the coordination number. This effect was found when the coordination numbers differ nonstoichiometrically between the aqueous phase and the organic phase.
Comparison of two methods for designing calorimeters using stirred tank reactors
Authors: Regestein Lars , Giese Heiner , Zavrel Michael , Büchs Jochen
Published: July 2012

Calorimetry is a robust method for online monitoring and controlling bioprocesses in stirred tank reactors. Up to now, reactor calorimeters have not been optimally constructed for pilot scale applications. Thus, the objective of this paper is to compare two different ways for designing reactor calorimeters and validate them. The “heat capacity” method based on the mass flow of the cooling liquid in the jacket was compared with the “heat transfer” method based on the heat transfer coefficient continuously measured in the cultivation of Escherichia coli VH33 in a 50 L stirred tank reactor. It was found that the values of the “heat transfer” method agreed very well with the calculated values from the oxygen consumption. By contrast, the curve of the “heat capacity” method deviated from that of the oxygen consumption calculated with the oxycaloric equivalent. In conclusion, the “heat transfer” method has been proven to have a higher degree of validity than the “heat capacity” method. Thus, it is a better and more robust means to measure heat generation of fermentations in stirred tank bioreactors on a pilot scale. Biotechnol. Bioeng. 2013; 110: 180–190. © 2012 Wiley Periodicals, Inc.
From Crime Scene Actions in Stranger Rape to Prediction of Rapist Type: Single‐Victim or Serial Rapist?
Authors: Corovic Jelena , Christianson Sven Å. , Bergman Lars R.
Published: July 2012

The differences in crime scene actions in cases of stranger rape committed by convicted offenders were examined between 31 single‐victim rapists and 35 serial rapists. Data were collected from police files, court verdicts, psychiatric evaluations, and criminal records. Findings indicate that the serial rapists were more criminally sophisticated than the single‐victim rapists, during their first and second rapes. The single‐victim rapists were significantly more likely to engage in the interpersonal involvement behavior of kissing the victim, and to engage in pre‐assault alcohol use, than the serial rapists. There was, however, no significant difference in physically violent or sexual behaviors. To investigate the possibility of predicting rapist type, logistic regression analyses were performed. Results indicate that three behaviors in conjunction, kissed victim, controlled victim, and offender drank alcohol before the offense, predicted whether an unknown offender is a single‐victim or serial rapist with a classification accuracy of 80.4%. The findings have implications for the classification of stranger rapists in offender profiling. Copyright © 2012 John Wiley & Sons, Ltd.
Reactivity Control of CH Bond Activation over Vanadium–Silver Bimetallic Oxide Cluster Cations
Authors: Li Xiao‐Na , Wu Xiao‐Nan , Ding Xun‐Lei , Xu Bo , He Sheng‐Gui
Published: July 2012

Vanadium–silver bimetallic oxide cluster ions (VxAgyOz+; x=1–4, y=1–4, z=3–11) are produced by laser ablation and reacted with ethane in a fast‐flow reactor. A reflectron time of flight (Re‐TOF) mass spectrometer is used to detect the cluster distribution before and after the reactions. Hydrogen atom abstraction (HAA) reactions are identified over VAgO3+, V2Ag2O6+, V2Ag4O7+, V3AgO8+, V3Ag3O9+, and V4Ag2O11+ ions, in which the oxygen‐centered radicals terminally bonded on V atoms are active sites for the facile HAA reactions. DFT calculations are performed to study the structures, bonding, and reactivity. The reaction mechanisms of V2Ag2O6++C2H6 are also given. The doped Ag atoms with a valence state of +1 are highly dispersed at the periphery of the VxAgyOz+ cluster ions. The reactivity can be well‐tuned gradually by controlling the number of Ag atoms. The steric protection due to the peripherally bonded Ag atoms greatly enhances the selectivity of the V–Ag bimetallic oxide clusters with respect to the corresponding pure vanadium oxide systems.