bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of Hydrogen Dissolved in Palladium‐rich PdErAg(Au,Cu) Ternary Solid Solution Alloys
Authors: El‐Sanabary Fatma , Ramaprabhu Sundara , Weiss Alarich
Published: July 2012

Using a volumetric method, pressure‐composition hydrogen absorption isotherms have been determined for the ternary face centered cubic solid solution alloys (Pd1‐xMx)1‐yEry (M = Ag, Au, Cu; xAg = xAu = 0.079; xCu = 0.08; yEr = 0.00‐0.08) within 10 ≤ PH2/mbar ≤ 1000 and 473 ≤ T/K ≤ 873. The lattice constants a0 of the ternary alloys increase with increasing yEr and the increase in a0 with a given erbium and noble metal content is in the order ao[(Pd1‐xAux)1‐yEry] > ao[(Pd1‐xAgx)1‐yEry] > a0[(Pd1‐xCux)1‐yEry], as in the erbium free binary Pd1‐xMx (M = Au, Ag, Cu) solid solution alloys. The hydrogen solubility r increases with increasing yEr in the (Pd1‐xMx)1‐yEry ternary solid solution alloys; the increase in r with a given erbium and noble metal content is in the order r[(Pd1‐xAgx)1‐yEry] > r[(Pd1‐xAux)1‐yEry] > r[(Pd1‐xCux)1‐yEry], a trend noted in the erbium free binary alloys Pd1‐xMx (M = Ag, Au, Cu). The partial molar enthalpy of hydrogen solution at infinite dilution (ΔH0H) becomes more exothermic with yEr and the increase of exothermicity of hydrogen absorption at given yEr and xM is in the order (ΔH0H[(Pd1‐xAgx)1‐yEry] > (ΔH0H[Pd1‐xAux)1‐yEry] > (ΔH0H[Pd1‐xCux)1‐yEry]. The partial molar excess entropy of hydrogen solution at infinite dilution (ΔSE,0H) and the chemical potential of dissolved hydrogen at infinite dilution (Δ0H), both, decrease with yEr. The hydrogen solubility and the exothermicity of hydrogen absorption in Pd0.903Cu0.078Er0.019 alloy are higher than those in pure palladium, even though a0 of Pd0.903Cu0.078Er0.019 alloy is less that of pure palladium, due to the larger metal‐hydrogen attractive interaction in Pd0.903Cu0.078Er0.019 alloy than in pure Pd. As in Pd1‐yREy‐H (RE = Er, Y, Dy, Gd, and Sm) and Pd1‐xMx‐H systems, a correlation between ΔH0H and ΔSE,0H exists in (Pd1‐xMx)1‐yErx‐H systems.
Links Between Bulk and Surface Activity in Micellar Solutions
Authors: Mesa Camillo La , Ranieri Giuseppe A.
Published: July 2012

The surface tension of aqueous surfactant systems and its dependence on the concentration of surfactant in micellar form, Xm ≅ X‐CMC, have been investigated. A modification of the adsorption equation, based on the introduction of activity coefficients, allows to get information on micelle aggregation numbers, 〈N〉, from the slope of surface tension versus ln Xm. The resulting equation, tested on data relative to non ionic surfactants, gives aggregation values in fair good agreement with those inferred from other methods. The limits of the model are discussed in some detail.
Highly Monodisperse Quantum Sized CdS Particles by Size Selective Precipitation
Authors: Chemseddine A. , Weller H.
Published: July 2012

Nanometer sized cadmium sulfide particles were prepared in N,N‐dimethylformamide, using thiourea as the sulfurizing agent and thioglycerine as stabilizer. For particles with diameters of less than 40 Å the size dependent solubility was utilized to separate the particles according to their size. The absorption spectra of the size separated samples exhibit well pronounced excitonic absorption bands indicating a very narrow size distribution.
Prediction of the Thermodynamic Properties of Hydrogen‐Oxygen Mixtures from 80 to 373 K and to 100 MPa
Authors: Deiters Ulrich K. , Neichel Monika , Franck Ernst U.
Published: July 2012

The equations of state of Deiters and of Christoforakos and Franck, together with appropriate mixing rules, have been used to predict fluid phase equilibria, the critical curve, molar volumes and excess enthalpies of the binary hydrogen‐oxygen system between 80 and 373 K and to pressures of 100 MPa. The applicability of the equations of state has been tested with experimental data which exist for the hydrogen‐nitrogen system and, to some extent, for the systems neon‐nitrogen and neon‐oxygen. Binary interaction parameters for the hydrogen‐oxygen system have been derived from these systems. Results from both equations of state have been compared. Numerical values for the thermodynamic properties of the hydrogen‐oxygen system are given. The calculated critical line is of the interrupted type; the upper branch begins at the critical point of oxygen (154.6 K) and tends to approximately 83–99 K at 100 MPa, depending on the calculation method. Hydrogen appears to be considerably less miscible with oxygen than with nitrogen at high pressures. Predicted pressures for oxygen‐hydrogen solid‐gas equilibria at 49.8 K agree well with experimental data to 12 MPa.
Kinetic and Primary Product Studies of the Reaction of O (3P) with Styrene in the Gas Phase
Authors: Buchta Chr. , Frerichs H. , Stucken D.‐V. , Tappe M. , Wagner H. G. G.
Published: July 2012

The rates of the reaction of styrene with atomic oxygen have been measured in a discharge flow system with mass spectrometric detection. The measurements were carried out under oxygen atom excess in the temperature range 298 K < T < 873 K. The main reaction channel at room temperature is O atom addition to the vinyl side chain, yielding as main product (identified by mass spectrometric product analysis) styrene oxide. Towards higher temperatures O atom addition to the aromatic ring as a second reaction channel becomes more important. Using Hammett plots the following Arrhenius expressions for the addition to the aromatic ring (kar) and to the alkene double bond (kdb) of the side chain can be derived: magnified image First experiments with indene give similar results, showing a somewhat higher reactivity for this molecule compared to styrene.
Nitrogen Quadrupole Coupling Constants of Nitrobenzene and o‐Nitrophenol
Authors: Heineking N. , Dreizler H.
Published: July 2012

The microwave spectra of nitrobenzene, C6H5NO2, and o‐nitrophenol, C6H4 (OH)NO2, have been observed with high resolution using a waveguide microwave Fourier transform spectrometer. Nuclear quadrupole hyperfine structures have been resolved and analysed to obtain the following nitrogen quadrupole coupling constants: χaa = ‐1.1589 (24) MHz, χbb = 0.3195 (36) MHz, χcc = 0.8394 (36) MHz for nitrobenzene; χaa = ‐1.234 (4) MHz, χbb = 0.348 (3) MHz, χcc = 0.886 (3) MHz for o‐nitrophenol. For nitrobenzene, the variation of the coupling constants with torsional state has also been studied.
Solution and Solid State Properties of 1,4‐Diketo‐3,6‐bis‐(4'‐pyridyl)‐pyrrolo‐[3,4‐c]‐pyrrole on Protonation and Deprotonation
Authors: Mizuguchi Jin
Published: July 2012

Solution and solid state properties of 1,4‐diketo‐3,6‐bis‐(4'‐pyridyl)‐pyrrolo‐[3,4‐c]‐pyrrole (DPPP: red pigment) have been investigated with respect to protonation and deprotonation. DPPP undergoes both protonation and deprotonation, because it behaves not only as a base due to electron lone pairs of the nitrogen in the pyridyl ring but also as an acid due to the NH group in the heterocyclic chromophore. Protonation at the pyridyl nitrogen and deprotonation at the NH group induce large bathochromic shifts in solution. These are interpreted in terms of Pariser‐Parr‐Pople calculations, using the variable β, γ‐approximation. Protonation in the solid state due to acid vapor brings about significant changes in photoelectrical properties, such as a reduction in electrical resistivity from about 1010 to 105 Ωcm and strong photoconduction enhancement. The protonated solid state has been characterized systematically through spectroscopy, crystallography and thermo‐analysis with particular attention to its potential applications, e.g., to proton sensors and optical information storage systems.
Temperature Dependence of the Permittivity of o‐Nitroanisole‐Benzene and o‐Nitroanisole‐Carbon Tetrachloride Mixtures in the Vicinity of its Melting Point
Authors: Szurkowski B. , Hilczer T. , Saliwińska‐Bartkowiak M.
Published: July 2012

An investigation of the permittivity of o‐nitroanisole mixtures with benzene and carbon tetrachloride was performed in the vicinity of the liquid‐solid state phase transition. In the concentration range considered, the phase diagrams (T, x2)p of these mixtures were proved to be similar in character to those of the ideal eutectic systems, where molecular interactions are a simple function of the mixture composition.
In situ FTIR Study on the Adsorption of Phosphate Species on Well Ordered Platinum (111) Single Crystal Surfaces
Authors: Nart F. C. , Iwasita T. , Weber M.
Published: July 2012

The adsorption of ions on single crystal electrodes is followed via in situ Fourier transform infrared spectroscopy. The results for the adsorption of phosphate species on Pt(111) indicate a strong influence of the substrate structure on the adsorption geometry. A change in the nature of the adsorbed species is observed as the potential is shifted in the anodic direction.
The Mechanism of the Anodic Oxidation of Silicon in Acidic Fluoride Solutions Revisited
Authors: Gerischer H. , Allongue P. , Costa Kieling V.
Published: July 2012

The present experience of the electrochemical dissolution of silicon and previous assumptions upon the mechanism are briefly reviewed. A new model is developed which explains how the coverage of the surface by hydrogen can be maintained in spite of the continuous anodic dissolution.
Characterization of Vanadia/Silica Mixed Gel Catalysts by 51V and 29Si CP/MAS Solid State NMR Spectroscopy
Authors: Walther K. L. , Kümmerlen J. , Wokaun A. , Baiker A.
Published: July 2012

The structure of V2O5/SiO2 mixed oxides prepared by sol‐gel techniques is investigated by solid state NMR experiments. For low V2O5 contents ( < 10 mol%), 51V wideline spectra reveal a predominance of tetrahedrally coordinated vanadia, as found in oligomeric vanadate species. With higher vanadia concentrations (15–25 mol%), an increasing fraction of vanadium centers in an octahedral environment is observed. This transition indicates an increasing degree of cross‐linking of the vanadia, to form two‐ and three‐dimensional aggregates. The influence of the vanadia component on the compactness of the network is reflected in the 29Si MAS spectra, where the fraction of completely cross‐linked Q4 sites is observed to increase with the vanadia contents. The 1H → 29Si cross polarization dynamics is characterized by a bi‐exponential time dependence. Evidence for the existence of Si—O—V bridges at vanadia contents of 1 wt.% is derived from an analysis of the relevant cross polarization time constants.
p,T‐Dependence of Self‐diffusion in Liquid Ethanol and the Propanols
Authors: Shaker‐Gaafar N. , Karger N. , Wappmann S. , Lüdemann H.‐D.
Published: July 2012

The p,T‐dependence of the self diffusion coefficients D for ethanol‐OD, 1‐ and 2‐propanol‐OH and ‐OD have been studied in a wide temperature range at pressures up to 200 MPa. The experiments were performed in strengthened high pressure glass cells by the pulsed field gradient NMR‐technique. The isobaric temperature dependence of D is given by the VTF‐equation. The isotherms can be fitted to the rough hard sphere model with an A‐parameter that decreases strongly with falling temperature.
Calculation of High Pressure Counterflow Diffusion Flames up to 3000 bar
Authors: Saur A. M. , Behrendt F. , Franck E. U.
Published: July 2012

The combustion of methane, hydrogen and carbon monoxide at atmospheric pressure in one‐dimensional diffusion flames was quantitatively described with computer simulations by Warnatz et al. and others. The present paper extends the one‐dimensional flame description from dilute gas regions to pressures of 3000 bar, where particles are mostly in contact with each other. A realistic equation of state with repulsion and attraction terms is used. Transport phenomena are modelled with a modified Enskog equation. A special problem arises from the stiffness of the systems of differential equations. Integration uses methods developed by Deuflhard et al.

Flames of methane and hydrogen burning in mixtures with argon or supercritical water with injected oxygen are simulated and discussed. Profiles of temperature and other functions at high pressures through the reaction coordinate are shown. The width of the reaction zone is narrowed to less than 5% if pressure is increased from 1 to 1000 bar. Maximum temperatures of 3500 K are attained with CH4/Ar‐O2‐flames. Maximum flame temperatures decrease with pressure above about 500 bar. Several concentration profiles including those of H‐ and O‐radicals and H2O2 are presented. Comparison with recently measured high pressure flame temperatures is made.
Solid State Reactions in the Quasiternary System (ZnkCd1−k)(SelTe1−l
Authors: Leute Volkmar , Wulff Birgit
Published: July 2012

In this study solid state reactions between the binary components of the quasiternary system (ZnkCd1‐k)(SelTe1‐l) are investigated for chalcogen saturated and for metal saturated samples at different temperatures. The X‐ray intensity profiles, taken with an electron microprobe, are transformed to reaction paths, which are projected onto isothermal sections of the phase diagram. From these representations and from diffusion data of the quasibinary subsystems conclusions can be drawn concerning the defect mechanism of the diffusion processes of the solid state reaction.
On the Composition of Higher Solid Nickel Oxocompounds
Authors: Balej Jan , Divisek Jiri
Published: July 2012

Critically selected equilibrium or rest potentials of solid nickel oxocompounds with 2<zNi≦3.6 measured at ambient temperatures by various authors were reevaluated. Comparing the measured data converted to uniform conditions (25 °C, aKOH = aH2O = 1.0 Evr vs. RHE) with the theoretical course of Er vs. zNi, derived for the case that the NiOx system can be formed either by Ni(II)+Ni(III)+Ni(IV) or by Ni(II)+Ni(IV) components, it was found that the so called “βNi(OH)2/β‐NiOOH” systems with zNi<3.0 can be regarded as thermodynamically unstable or metastable, as they exhibit an unusual decrease of EvT with increasing zNi in the range of 2.6<zNi<3.0. Experimental results corresponding to a sequence of stable valence stages Ni(II) → Ni(III) → Ni(IV) were not observed. In contrary, the so called “α‐Ni(OH)2/γ‐NiOOH” systems exhibit a monotonous S‐shaped course of Evr vs. zNi in the whole investigated range of 2.0<zNi≦3.6, with the lowest Evr values at the given zNi, so that they can be regarded as thermodynamically stable systems representing solid solutions of Ni(II)+Ni(IV) components only.
On the Photoionization Mechanism of Liquid Water
Authors: Sander Martin U. , Luther Klaus , Troe JüRgen
Published: July 2012

Experimental data on the photoionization of liquid water are reviewed and reanalyzed. It is suggested that, near to the ionization threshold at 6.5 eV and up to about 8 eV, an optical Charge Transfer (CT) mechanism leads to the formation of hydrated electrons with a low quantum yield. The absorption band of liquid water at the longest UV wavelengths is assigned to this CT transition superimposed on an intramolecular transition into the R3s state. At excitation energies where the R3p states become attainable, i.e. somewhere between 6.5 and 8 eV, a photo‐induced electron transfer mechanism sets in which is characterized by high quantum yields of hydrated electrons and by average electron‐ion separations below those expected for intermediately “quasi‐free” electrons. This mechanism is dominant up to at least 10 eV, i.e. up to the highest excitation energies for which subpicosecond studies are currently available. In this energy range, autoionization generates only a minor part of all hydrated electrons produced. Only at excitation energies approaching the gas‐phase ionization potential, autoionization and direct photoionization are supposed to become dominant. If any autoionization channels are open below excitation energies of 10 eV, then the band gap energy of water, which is currently believed to be about 8.9 eV, has to be located as high as 10–12 eV.
The Effect of Short‐Range Hydrogen‐Bonded Interactions on the Nature of the Critical Point of Ionic Fluids. Part II: Static and Dynamic Light Scattering on Solutions of Ethylammonium Nitrate in n‐Octanol
Authors: Schröer W. , Wiegand S. , Weingärtner H.
Published: July 2012

We report on static and dynamic light scattering measurements of near‐critical fluctuations of an ionic liquid. The system is ethylammonium nitrate (EAN) dissolved in n‐octanol which exhibits a liquid‐liquid phase transition in the salt rich regime with an upper critical point near 315 K at a mole fraction of the salt x1 = 0.773. The correlation lengths and scattering intensities scale with temperature corresponding to an Ising‐like critical point. This contrasts with previous observations of mean‐field behaviour in electrolyte systems with liquid‐liquid phase transitions driven by long‐range Coulombic interactions. Rationalizations of this discrepancy are offered taking into account a) the competition of intermolecular interactions with long‐range and short‐range character and b) the possibility of crossover from mean‐field to Ising behaviour as predicted by the Landau‐Ginzburg theory.
Modelling the H3O+‐Ion: A Simulation Study of an Aqueous HCl Solution
Authors: Laurs Norbert , Bopp Philippe
Published: July 2012

A molecular dynamics (MD) simulation study of structural and dynamical properties of a dilute solution of HCl in water is presented. We assume that the acid is completely dissociated at the low concentration which is investigated, and that H3O+ and Cl− are the ionic species. A new model interaction potential is constructed on the basis of available experimental and theoretical information for this cation. In keeping with the flexible model employed for the water, it is also modelled as a flexible entity. The intermolecular H3O+‐water potential is constructed on the basis of an ab‐initio charge distribution and the short‐range parts from the water‐water potential. The other potentials are taken from the literature. Simulations of 1.1 m HCl solutions are performed at several temperatures. The structure of the liquid, and specially the hydration of H3O+, are discussed in terms of radial and many‐body distribution functions. Dynamical properties are calculated from velocity‐ and other autocorrelation functions. A stabilization of the pyramidal structure of H3O+ is observed in the solutions.
A Study of the Equitransference Level of Concentrated Aqueous RbBr, RbI and NH4I, and their Characterization as Ultra‐Concentrated Salt Bridges for the Minimization of Liquid Junction Potentials
Authors: Mussini P. R. , Rondinini S. , Cipolii A. , Manenti R. , Mauretti M.
Published: July 2012

Ion and solvent transference numbers for aqueous RbBr, RbI and NH4I solutions have been determined at molalities up to 5.5, 6.5 and 7.5mol·kg−1, respectively, from e.m,f. measurements on appropriate transference cells. The results demonstrate that, for the minimization of liquid junction potentials, all the three salts above are better “salt bridges” than the popular saturated‐KCl one, both because they are more nearly equitransferent (over the whole molality range) and because they can reach saturation molalities (7.01, 7.38 and 12.69 mol·kg−1, respectively, at 25°C) much higher than that of KCl (4.804 mol·kg−1). Therefore, concentrated RbBr, RbI and NH4I solutions can be recommended as advantageous salt bridges for replacement of the KCl one.
Planar Membrane‐Cable: Voltage‐Profile Recorded by Fluorescent Dye
Authors: Fromherz Peter , Müller Jörg Uwe
Published: July 2012

A black lipid membrane of glycerolmonooleate was spanned over a shallow groove in silica. Gramicidin was incorporated into the bilayer. The electrical properties of the cable were characterized by admittance measurements. The membrane was stained with the voltage‐sensitive dye di4ANEPPS. A voltage was applied to one end of the cable. The change of fluorescence was recorded along the cable. The profile of the relative change of fluorescence corresponds closely to the profile of voltage for a linear core‐coat conductor computed from the Kelvin‐equation.
Oxidation and Hydrothermolysis of Hydrocarbons in Supercritical Water at High Pressures
Authors: Hirth Th. , Franck E. U.
Published: July 2012

Oxidation, pyrolysis and hydrolysis of methane, ethane, methanol and to some extent heptane and toluene, in supercritical water or nitrogen, at temperatures to 600°C and pressures to 1000 bar were studied. Temperatures of the reactive mixtures were always above the respective critical curves. Oxidation was performed with oxygen or air injection, flameless or with diffusion flames. High pressure, non‐corrosive reaction vessels of different types and the complementary apparatus for high pressure injection and analysis are described.

Flameless oxidation of methane in homogeneous supercritical aqueous mixtures produces CO, CO2, H2and CH3OH. Methanol formation can reach 30% of reacted methane, “selectivity”, at 600 bar. High pressure increases the methanol selectivity, flame reaction decreases it. Overall rate constants are given. Similar studies were made with supercritical aqueous ethane mixtures. Hydrothermal pyrolysis, “hydrothermolysis”, was investigated. Even at 600°C and 600 bar less than 3% methane decomposed after 120 minutes. Pyrolysis of methanol at 500°C and 600 bar is much slower in an aqueous environment than in nitrogen. Hydrothermal soot formation was studied with several hydrocarbons in supercritical fluids. Water, as compared with argon, as a mixture component appears to suppress soot formation. CO conversion with supercritical water was also quantitatively pursued.
Ab initio Monte Carlo‐Studies of Concentrated Aqueous Cesium Hydroxide‐Solutions
Authors: Bertagnolli H. , Zweier H. , David A.
Published: July 2012

Ab initio Monte Carlo simulations of concentrated aqueous cesium hydroxide solutions are reported. This method of structure modelling that requires no intermolecular interaction potential as input was applied to ionic solutions for the first time. The comparison of the resulting atom pair correlation functions with those of pure liquid water indicated a disordered arrangement of the water molecules. The influence of the structure breaking cesium ions seems to prevent an orientation of the water molecules according to the pure water structure even in the dilutest solution.
Structure Modelling of Fluid Carbon Dioxide Using ab initio Monte Carlo‐Simulation
Authors: Bertagnolli H. , Glania C. , Zweier H. , David A.
Published: July 2012

Ab initio Monte Carlo simulations of fluid carbon dioxide are reported. The technique, which does not require intermolecular potential as input, was used to investigate the effects of density variation on the short range order. Experimental data could be reproduced to perfection; the resulting atom‐atom pair correlation functions and angular distribution functions revealed no preferred conformation at lower densities, whereas parallel conformations were more likely at higher densities.
2H, 14N, and 35Cl Nuclear Magnetic Resonance in Crystalline Deuterated Guanidinium Perchlorate [C(ND2)3]ClO4
Authors: Furukawa Yoshihiro , Ikeda Ryuichi
Published: July 2012

The temperature dependences of 2H, 14N, and 35Cl NMR spin‐lattice relaxation times (T1) were measured for deuterated guanidinium perchlorate [C(ND2)3]ClO4. The 2H T1 (41.6 MHz) minimum of 2.2 ms observed in the room‐temperature phase obtainable below 451 K was assigned to the three‐fold reorientation of the planar cation. The ionic‐plastic phase obtained above 452 K forms a cubic CsCl‐type crystal with a = 5.56 Å and Z = 1 as determined for the protonated sample at 360 K. In this phase, 2H and 14N T1 values are mainly governed by the overall reorientation of the cations although slow self‐diffusion also takes place. The quadrupole coupling constant (e2Qq/h) and asymmetry parameter η were determined as a function of temperature for 2H and 35Cl nuclei.
Effects of Bismuth(III)‐Oxide on the Structural and Electrochemical Properties of Pyrolusite (β‐MnO2)
Authors: Axmann P. , Glemser O.
Published: July 2012

Cycle‐life and charge/discharge curves of pure and physically Bi2O3‐doped pyrolusite (β‐MnO2) were studied. Crystalline intermediate products of the first three semi‐cycles give information about the effects of Bi2O3. A mechanism is postulated. In the first two semi cycles pyrolusite (β‐MnO2) is converted to the layered δ‐MnO2 with β‐Mn(OH)2 in the fully discharged state. In the course of the following discharge hausmannite Mn3O4, which is electrochemically inert, is formed. No hausmannite is found in presence of Bi2O3.

Pieces of information on mechanistical aspects can be gathered from the initial discharge process. During the initial discharge of β‐MnO2, δ‐MnO2 is formed as an intermediate product. In the undoped case this species can be found around MnO1.75. In presence of Bi2O3, however, δ‐MnO2 is existent nearly down to MnO1.25 over the whole discharge region.

The reaction path diverges at the [MnIII(OH)4(H2O)2]− ion, dissoluted during the cycling process: in presence of Bi2O3 the reaction is controlled kinetically by a quick disproportionation of the [MnIII(OH)4(H2O)2]− ions resulting in δ‐MnO2 and β‐Mn(OH)2. In absence of Bi2O3, thermodynamical control occurs, and [MnIII(OH)4(H2O)2]− reacts with [MnII(OH)4(H2O)2]2‐ forming the electrochemical non‐reactive hausmannite Mn3O4.
Orientational Order in Liquid Crystals: Experiment and Theory
Authors: Luckhurst G. R.
Published: July 2012

The long range orientational order of a liquid crystal is one of its prime characteristics. Before the extent of this order can be measured, however, it is necessary to define what is meant by the orientational order. This can be achieved in a variety of ways the most pragmatic of which is via the order parameters; these vanish in the isotropic phase and are one for systems with complete order. The techniques available for the determination of the order parameters are described, with particular attention paid to deuterium NMR spectroscopy. The results obtained for rod‐like mesogenic molecules are considered and the use of model systems, as studied by computer simulation, to understand them is discussed. Of particular significance is the relative role of anisotropic attractive and repulsive forces in determining liquid crystal behaviour. In recent years chemists have developed a new generation of liquid‐crystalline materials in which the fundamental building blocks of rods, discs and chains are linked together in many ways. As an example the transitional behaviour of liquid crystal dimers is considered in detail. The orientational order for dimers with both odd and even spacers has been studied using NMR. The results of such investigations have prompted the development of a novel model for the molecular organisation in the nematic phase. Finally, the synergy of order and conformation for mesogens composed of the simplest flexible liquid crystal dimers is explored using computer simulation techniques.
Molecular Dynamics Simulation Study of Isotropic and Nematic PCH‐5
Authors: Krümer G. , Paschek D. , Geiger A.
Published: July 2012

4‐(trans‐4‐Pentyl‐cyclohexyl)‐benzonitril (PCH‐5) has been studied by molecular dynamics simulations of the isotropic liquid as well as the nematic mesophase. The intra‐ and intermolecular interaction are described in pseudoatom approach. Besides the nematic order parameters S we calculate various distributions functions to characterize and compare the microscopic structure. In both phases we find a distinct antiparallel arrangement of neighbouring molecules, in accord with the known crystal structure of homologous substances. The molecular dynamics shows strong anisotropic behaviour in both phases. The corresponding diffusion coefficients are determined and compared with an experimental value.
Druckabhängigkeit der optischen Aktivität in der isotropen Phase eines chiralen Flüssigkristalls
Authors: Voß E. , Pollmann P. , Hollmann J.
Published: July 2012

Optical activity measurements in the isotropic liquid phase of cholesteryl oleyl carbonate just above the liquid‐crystal transition pressure were performed for various temperatures up to 200 MPa. The observed optical activity exceeds the molecular activity and can be explained as a pretransitional phenomenon.

The maximum value, which the optical activity reaches as the transition to the liquid‐crystal phase is approached, first decreases then increases when clearing temperature and pressure are raised. A theoretical relationship between the pretransitional optical activity and two structural modes is used to interpret this unusual behaviour.
An Extended Microscopic Model of the Spontaneous Polarization in Ferroelectric Liquid Crystals
Authors: Meister R. , Stegemeyer H.
Published: July 2012

The well‐known microscopic model from Žekš et al. for the spontaneous polarization of smectic C* phases has been extended by taking into account different orientations of the considered molecular transverse axes. A stronger temperature dependence of the tilt angle reduced polarization P0 = PS/θ results. The extended model explains differences between the quadrupolar order parameters calculated from P0(T) and from 14N‐NQR measurements. Additionally, temperature induced sign inversions of PS, described in the literature, can be explained by considering a possible competition between polar and quadrupolar ordering.
The Domain Mode in a Single Component Ferroelectric Liquid Crystal — Dielectrical and Electrooptical Investigations
Authors: Hiller S. , Beresnev L. A. , Wrobel S. , Haase W.
Published: July 2012

In this paper we present the dielectric and electrooptic investigations on the single component ferroelectric liquid crystal 3‐Octyloxy‐6‐[2‐fluoro‐4‐(2‐fluoro‐octyloxy)phenyl]‐pyridine (FFP), synthesized by E. Merck Company. The investigations were performed in an ITO‐cell with the thickness of 900 nm. The sample was aligned planarly.

Under the polarization microscope a Domain structure was observed. The threshold voltage for the helix unwinding in the SmC* phase was determined.

The complex dielectric permittivity component ε* was measured in the frequency range from 10 Hz up to 10 MHz. Beside the Goldstone mode, a Domain mode relaxation was found in the dielectric spectra of this substance. Due to the small cell thickness only one Domain process, namely the surface Domain mode could be detected. BIAS field and temperature dependent measurements of this Domain mode process were performed. In order to obtain the characteristic relaxation strengths and dispersion frequencies of the observed processes the Havriliak‐Negami equation was fitted to the data obtained.
Optische Eigenschaften von Flüssigkristall‐Mikrolinsen und Adaptierungslinsen, Vergleich von numerischen Simulationen und Messungen
Authors: Schwabe F. , Knoll P. M. , Nerding R. , Dickmann S. , Eschler J. , Miyuski D. A.
Published: July 2012

Liquid Crystal (LC) cells with a suitable electrode structure can be used as electrically controlled lenses. Two types of LC‐lenses are known: LC‐adaptive lenses [1] (LCAL) and LC‐microlenses [2, 3] (LCML). LC‐microlenses have a simple electrode structure, but offer only slow response times up to several seconds and apertures up to 1 mm.

A LCML works as follows: The front electrode is divided by a gap, which can be up to 10 times larger than the cell gap. The inhomogeneous electrical field within the gap produces an inhomogeneous director distribution. This distribution allows to focus monochrome light from the infinity down to about 1 mm.

With a 2‐D numerical simulation [4–6] it is possible to describe the behaviour of the director in an inhomogeneous electrical field. It can be seen, that there are some configurations, which cause distortions between the electrodes. These make the optical properties worse. From the director configuration the optical properties of the LC‐lens can be calculated.

The influence of inhomogenities can be improved with LC‐adaptive lenses. Here we use several parallel electrodes to produce directly the director distribution to focus monochrome light. The advantages of adaptive lenses are: the switching times are shorter. There are less inhomogenities. But the minimum focal distance is about some cm.
Photoinduced Reorientation of Cholesteric Liquid Crystalline Polysiloxanes and Applications in Optical Information Storage and Second Harmonic Generation
Authors: Petri A. , Kummer S. , Anneser H. , Feiner F. , Bräuchles Ch.
Published: July 2012

When liquid crystalline polymers, which contain an azo dye as a side chain, are irradiated with light which is absorbed by the azo dye, both the index of refraction and the absorbance are changed. It was proven that the modulation of the optical properties mainly rests upon a reorientation of the long molecular axis of the chromophores and of the mesogenic units. This change of the alignment of the side chains occurs after numerous trans‐cis‐isomerization cycles of the azo dye. Spectroscopic investigations show that by irradiating the samples completely new and well ordered textures appear. The characteristic features of the new textures depend on the structure of the liquid‐crystalline polymer before irradiation and on the polarization state of the actinic light.

We investigated cholesteric polysiloxanes which were either irradiated with linearly or with circularly polarized light (unpolarized light respectively). The characterization of the new textures was done with different spectroscopic methods. The photochemically induced changes of the texture are usable in applications like optical information storage, e.g. for the generation of holograms or for the production of displays. We further investigated samples with dipolar azo dyes which were reoriented with light under the influence of an electrical field. The cooperative effect of light and field results in a polar alignment of the azo dye which was proven by second harmonic generation (SHG). We compare material properties like longterm stability and efficiency of the SHG in samples which were prepared by this new procedure, by contact poling and by corona poling.
Structure and Dynamics of Liquid‐Crystalline Polymers with Different Molecular Architectures from Multidimensional NMR Plenary Lecture
Authors: Spiess H. W.
Published: July 2012

A survey is given on the structure and dynamics of liquid‐crystalline polymers with different molecular architectures as revealed by multidimensional NMR. Specific examples discussed include semiflexible systems, rigid‐rod systems, calamitic, and discotic liquid crystals. Structural aspects include the determination of high rank order parameters, the micro‐order in frozen liquid crystals and the packing of flexible side chains. Dynamic processes discussed are local dynamics in the glassy state, conformational dynamics and collective phenomena such as the development of convective director structures and dynamic density modulations along columnar structures. It is demonstrated that advanced NMR spectroscopy yields highly specific information not available from conventional scattering, microscopic and relaxation techniques.
Molecular Dynamics in Side‐Group Polymers with and without Liquid Crystalline Phases from 2H NMR
Authors: Leisen J. , Ohlemacher A. , Boeffel C. , Spiess H. W.
Published: July 2012

Side‐group liquid crystalline polymers were investigated by 1D and 2D solid state 2H NMR methods in the glassy state. The side‐group dynamics of liquid crystalline systems were compared to those of amorphous systems of the same molecular architecture. The onset of fast rotational motion of the phenylene rings additionally to phenylene flips was detected at considerably lower absolute and reduced temperature in the liquid crystalline systems indicating the influence of the ordered state on local dynamics. In 2D exchange spectra, the lineshapes are particularly sensitive towards possible slow motion of the flip axis itself which could be envisaged to fluctuate within the orientational distribution of the mesogen. However, the experimental spectra for the investigated side‐group liquid crystalline polymers show no indication of the characteristic features, thereby proving that the flip axis is rigid within ±3° even after a large number of flips.
Organization and Desorganization of Short Range Structures in Swallow‐Tailed Liquid Crystals
Authors: Kresse Horst , Heinemann Susanne , Paschke Reinhard , Weissflog Wolfgang
Published: July 2012

Swallow‐tailed liquid crystals are antiparallel oriented in the short range‐order. The organization and destruction of this order was studied by addition of other swallow‐tailed molecules, molecules with lateral substitution, a double swallow‐tailed and a rod‐like component. Induction and destruction of liquid crystalline phases was investigated by phase diagrams and dielectric methods. This survey contains new experimental data as well as for comparison already published results. It is a good example for the importance of geometrical relations for the formation of the liquid crystalline state.
Monodisperse Liquid Crystalline Oligomer Systems with Controlled Dipolar Structure
Authors: Festag R. , Wendorff J. H. , Birkel S. , Eisenbach C. D.
Published: July 2012

Monodisperse oligomer systems characterized by a well defined dipolar structure were synthesized: the longitudinal dipole components were either parallel or antiparallel to each other. Such systems were obtained employing a step‐by‐step reaction using protective groups which are selectively cleavable. We investigated the influence of the dipole structure of the molecule on the phase and the dielectric behavior, combining computer simulations and experimental investigations. In addition we analyzed networks formed by such oligomers.
Stabilization and Destabilization of Thermotropic Liquid Crystalline Phases by Hydrogen Bondings
Authors: Kresse Horst , Dorscheid Claudia , Szulzewski Ilka , Frank Robert , Paschke Reinhard
Published: July 2012

Six phase diagrams of liquid crystalline acids E and a phenole F mixed with derivatives of pyridine P, nicotinic acid Ni and pyrrolidine Py were investigated. Congruent melting compounds of the type PE and NiE were detected. Stabilization of the nematic and induction of a smectic A phase was observed in the P/E and P/F systems whereas in Py/E mixture an extremely strong destabilization of the nematic phase takes place. In the Ni/E diagrams a weak destabilization of the nematic phase was found. The results are explained by associates formed by hydrogen bridges which show a more or less strong deviation from the rod‐like molecular shape.
Liquid Crystalline Perylene Derivatives: Orientation and Phase Variation of Discotic Dyes
Authors: Pressner D. , Gültner Chr. , Spieß H. W. , Müllen K.
Published: July 2012

Discotic liquid‐crystalline perylene derivatives can be oriented in the magnetic field far below their clearing temperatures as shown by 2H solid‐state n.m.r. spectroscopy. A mechanical orientation of these materials was achieved by drawing fibers, which were investigated by X‐ray diffraction. In addition, it is shown that not only the melting and clearing temperatures, but also the structure of the mesophases depend sensitively on the substitution pattern. The type of liquid crystalline phase can be varied from discotic to smectic.
Discotic Liquid Crystals — A New Class of Fast Photoconductors
Authors: Adam D. , Haarer D. , Closs F. , Frey T. , Funhoff D. , Siemensmeyer K. , Schuhmacher P. , Ringsdorf H.
Published: July 2012

We showed for the first time that discotic liquid crystals are well suited for a new class of fast photoconducting materials. Due to their spontaneous orientation and their dynamical fluctuations in the mesophase, they show exceptionally high mobilities of 1·10−3 cm2/Vs, about two to three orders of magnitude higher than those obtained for conventional amorphous polymers. Further on, the Gaussian transport (for holes in the mesophase) is remarkable, which is characterized by the existence of a conduction band and the absence of trapping states. In contrast, the charge carrier transport in amorphous photoconductors is generally trap‐dominated which limits technical properties, leading to low carrier mobilities and undesirable memory effects. Measurements of the transient photocurrents, using the time‐of‐flight technique, have been carried out in the discotic liquid crystalline photoconductor hexapentyloxytriphenylene. The carrier mobilities and the underlying transport mechanisms both in the crystalline phase and in the mesophase are discussed in the framework of ideal intrinsic (Gaussian) transport, multiple shallow trapping, and deep trapping transport, respectively.
Surface Ordering and Finite‐size Effects at the First Order Phase Transition SmA‐SmC in Liquid‐crystalline Free‐standing Films
Authors: Kraus I. , Pieranski P. , Demikhov E. , Stegemeyer H. , Goodby J. , Slaney A. , Osipov M.
Published: July 2012

High precision optical reflectivity measurements and optical image analyses are applied to investigate the first order SmA‐SmC* phase transition in free‐standing films. By decreasing the thickness of the films the critical point is observed, where the first order phase transition disappears. A mean‐field theory describing the process of surface ordering in smectic membranes is presented.
Separation of Enantiomers in a Monolayer of Racemic 3‐Hexadecyl‐oxy‐propane‐1,2‐diol
Authors: Rietz Roland , Brezesinski Gerald , Möhwald Helmuth
Published: July 2012

Monolayers of a racemic mixture and of the pure S enantiomer of 3‐hexadecyloxy‐propane‐1,2‐diol have been characterized by thermodynamic measurements at the air/water interface as well as by fluorescence microscopy. The critical temperature Tc, the limiting molecular area at high pressure and the pressure πc corresponding to the observed main phase transition, derived from the isotherms, slightly depend on chiral purity. Above πc domains with a polygonal shape appear. However, if the domains are compressed shape instabilities occur. While the spirals of the enantiomer turn only in one direction, the spirals arising from one domain of the racemate exhibit opposite handedness. This behavior is explained by a separation of enantiomers on the molecular level in the condensed state of the racemate. A phase diagram is suggested.
Complex Salts of TCNQ with Substituted Phenyl Pyridines and Their Characterization by Scanning Tunneling Microscopy
Authors: Magonov S. N. , Bar G. , Cantow H.‐J. , Kabbeck‐Kupijai D. , Koßmehl G.
Published: July 2012

New conductive complex salts of tetracyanoquinodimethane (TCNQ) with substituted phenylpyridines have been prepared and characterized by optical microscopy, conductivity measurements, X‐ray powder diagrams and scanning tunneling microscopy (STM). The molecular stacking, which is responsible for the one‐dimensional conductivity, was revealed from the diffraction data and STM images. The analysis of the STM images was based on the results obtained on a model compound, the complex salt of TCNQ and quinolinium. Although in STM the surface partial electron density is measured, several crystallographic parameters of the molecular arrangement have been determined from these images.
Detection of Toxic Emissions from Incinerators
Authors: Tanada Tony N. , Velazquez Jon , Hemmi Naoki , Cool Terrill A.
Published: July 2012

Continuous monitoring techniques are needed for assurance that the stack gases of hazardous and municipal waste incinerators do not emit unacceptable levels of dangerous compounds. The development of suitable on‐line “real‐time” monitors may help answer current public concerns regarding the safety of thermal processing methods and may simplify the permitting process for new facilities. Recent research is reviewed which suggests that resonance ionization mass spectrometry is capable of real‐time monitoring of wide classes of toxic molecules at the part‐per‐billion level against complex backgrounds of interferant species. Recent advances in laser technology promise to make on‐line repetitive multispecies monitoring of hazardous emissions a practical reality.
Application of Single Molecule Detection to DNA Sequencing and Sizing
Authors: Ambrose W. Patrick , Goodwin Peter M. , Jett James H. , Johnson Mitchell E. , Martin John C , Marrone Babetta L. , Schecker Jay A. , Wilkerson Charles W. , Keller Richard A. , Haces Alberto , Shih Po Jen , Harding John D.
Published: July 2012

We are developing a laser‐based technique for the rapid sequencing of 40‐kb or larger fragments of DNA at a rate of 100 to 1000 bases per second. Our approach relies on fluorescent labeling of the bases in a single fragment of DNA, attachment of this labeled DNA fragment to a support, movement of the supported DNA into a flowing sample stream, and detection of the individual, fluorescently labeled bases by laser‐induced fluorescence as they are cleaved from the DNA fragment by an exonuclease. The ability to sequence large fragments of DNA will reduce significantly the amount of subcloning and the number of overlapping sequences required to assemble megabase segments of sequence information.

We are also applying our sensitive fluorescence detection to sizing of DNA fragments. Large, fluorescently stained restriction fragments of lambda phage DNA are sized by passing individual fragments through a focused, continuous‐wave laser beam in an ultrasensitive flow cytometer at a rate of ∼60 fragments per second. The size of the fluorescence burst emitted by each stained fragment as it passes through the laser beam is measured in one millisecond. We have demonstrated flow cytometric sizing of DNA fragments in a ∼0.1‐pg sample of a restriction digest of lambda DNA in 164 seconds with sizing accuracy better than 98%.
Flow and Particle Diagnostics. Multi‐Parameter and Multi‐Point Measurements
Authors: Hanson R. K. , Baer D. S. , Mcmillin B. K. , Arroyo P.
Published: July 2012

Laser‐based diagnostic techniques, developed primarily within the combustion community, offer considerable promise for nonintrusive measurements in gaseous flows relevant to industry. In this paper, we review two diagnostic methods under development in our laboratory. The first technique allows simultaneous measurement of multiple parameters through analysis of the shape and shift of fully resolved absorption lineshapes. The light source is a tunable, narrow‐linewidth semiconductor diode laser, applied in the present case to either water vapor (1.39 microns) at combustion gas temperatures (to 1700 K) or to argon (800 nm) in an atmospheric pressure plasma (at temperatures to 8000 K). Parameters inferred include, for water: temperature, pressure, velocity and species density; for argon, the parameters are electron density, kinetic temperature and the population temperature for the 4 s levels of argon. The second diagnostic technique is planar laser‐induced fluorescence (PL1F), which allows instantaneous measurements of a single parameter at multiple points in the flowfield. The example application to be discussed is single‐shot temperature imaging in a model scramjet flowfield using a two laser‐two camera imaging scheme.
Flow Field Diagnostics in Industrial Devices
Authors: Köhler J. , Lawrenz W. , Meier F. , Meinhardt P. , Stolz W. , Bloss W. H.
Published: July 2012

A new 2‐dimensional time resolved (200 frames/s) flow field measuring technique (PIV‐Movie) has been developed and applied to quantitative cycle resolved measurements of the instationary flow field within the combustion chamber of a transparent square piston engine. A conventional Particle Image Velocimetry (PIV) setup was modified using a double pulsed copper vapor laser (200 Hz, pulse separation 33 microseconds) and a rotating drum camera, which was used to record the Mie‐scattered signals from seeding particles. The circumferential velocity of the drum of the camera causes an image shifting of the two exposures taken with a double pulse. Because the copper vapor laser can be run continuously in the double pulse mode a series of up to 70 double pulsed images per individual engine cycle could be recorded on photographic film. These film data were evaluated with respect to both magnitude and direction of individual flow vectors in the flow field.