bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and Intermolecular Interaction in Liquid Crystalline Mixed Phases. Progress Report
Authors: Diele S.
Published: July 2012

Examples of specific intermolecular interaction (dipole, EDA, steric interactions as well as hydrogen bonds) are discussed in binary mixtures of calamitic, columnar and polymeric systems. It is shown, that on the base of the complete miscibility in the liquid crystalline state a continuous change of the intermolecular interaction is achieved in dependence on the concentration. In this way the properties of the mixtures can be definitively influenced by admixing of a proper second component.
Bowl‐shaped Liquid Crystals — New Derivatives of Cyclotriveratrylene and Calix[4]arene
Authors: Budig H. , Paschke R. , Diele S. , Letko I. , Pelzl G.
Published: July 2012

Some new Calix[4]arenes and Cyclotriveratrylenes incorporating cyclohexane rings, phenyl rings or ether oxygen atoms in their lateral chains have been synthesised and investigated by calorimetry and X‐ray studies. Only some long chain calix[4]arenes exhibit mesomorphic behaviour. The mesomorphic ranges and clearing temperatures of the mesophases of hexasubstituted cyclotriveratrylenes are largely increased by the introduction of cyclohexane rings or oxygen atoms into the alkyl chains. X‐ray studies proved the columnar structure of the mesophases.
First Observation of Selective Reflection and Blue Phases in Chiral Discotic Liquid Crystals
Authors: Krüerke D. , Kitzerow H.‐S. , Heppke G. , Vill V.
Published: July 2012

We investigated the helical structure of discotic cholesteric liquid crystals using cellobiose derivatives as chiral dopants in a discotic nematic host. A characteristic property of the new mixtures is the occurrence of a glass‐like state. Due to extremely small pitches we observed for the first time selective reflection in a chiral discotic system. In addition, we report on the first observation of discotic blue phases. Microscopic studies, reflection spectra, and Kossel diagrams indicate the appearance of three discotic blue phases, BPDI, BPDII, and BPDIII, which behave similar to the known calamitic modifications.
The Smectic‐C‐Smectic‐A Transition in Free‐Standing Liquid‐Crystal Films: An Example for Critical Behaviour Induced by a Confined Geometry
Authors: Bahr Ch. , Fliegner D.
Published: July 2012

We report on an ellipsometric study of a phase transition in thin free‐standing films of a smectic liquid crystal. The smectic‐C‐smectic‐A transition, which is first‐order in bulk, becomes continuous in films thinner than about 15 molecular layers indicating the influence of a strong ordering field resulting from surface interactions. The experimental results are discussed within the framework of a simple Landau model consisting of the bulk parameters and extended by a linear coupling to a surface field which decays exponentially from the surface to the interior of the film.
Time Reversal and the Law of Reciprocity in Raman Scattering
Authors: Hecht Lutz , Barron Laurence D.
Published: July 2012

Employing exact energy operators for the construction of effective polarizability operators, the previously derived approximate relationship (ααβ)mn = (αβα)θnθm) between a complex transition polarizability and the corresponding transition polarizability with time‐reversed initial and final molecular states has been found to represent an exact identity for a single microscopic Raman scattering event. Based on this result and the associated time ordered diagrams, macroscopic pictorial arguments are used to generalize the law of reciprocity to cover Raman scattering, thereby eliminating the prejudice that it applies only to Rayleigh scattering. Our predictions accord with the results of recent Stokes and anti‐Stokes resonance Raman experiments.
Thermophysical Properties of Alkali Metal Vapours Part I.A — Prediction and Correlation of Transport Properties for Monatomic Systems
Authors: Fialho P. S. , Fareleira J. M. N. A. , Ramires M. L. V. , Nieto De Castro C. A.
Published: July 2012

New calculations of the collision integrals for the singlet potential functions involved in the determination of viscosity, thermal conductivity and self‐diffusion coefficients of the monatomic alkali metal vapours are presented. An interpolation procedure for the calculation of the monatomic systems transport coefficients in a large temperature range is provided. This is based on temperature correlations of the collision integrals for the singlet and triplet potential functions.

The calculations have been carried out using a new potential function for the ground singlet state of the alkali diatomics. This is a recent version of the Extended Hartree‐Fock Approximate Correlation Energy (EHFACE2U), proposed by Varandas et al., which is believed to give a correct description of the potential energy to vanishing internuclear distances.

The results which are compared with previous calculations, are intended to be utilized in Part II of this paper in order to assess available experimental data on the viscosity and thermal conductivity coefficients of the alkali metal vapours.
Biodiagnostics and Polymer Identification with Multiplex Dyes
Authors: Seeger S. , Bachteler G. , Drexhage K. H. , Arden‐Jacob J. , Deltau G. , Galla K. , Han K. T. , Müller R. , Köllner M. , Rumphorst A. , Sauer M. , Schulz A. , Wolfrum J.
Published: July 2012

A new analytical concept based on time‐resolved fluorescence spectroscopy is presented, which uses the characteristic fluorescence lifetimes as information to identify new fluorescent dyes, called multiplex dyes. Several dyes can be distinguished at nearly fixed excitation and emission wavelength by recognition of the lifetimes. A pattern recognition technique is used for data analysis. As light sources a pulsed laser diode is used. First experiments are shown in several application fields, like DNA sequencing, immunoassays and tagging of polymer material.
A Technique for Mixture Fraction Imaging in Turbulent Nonpremixed Flames
Authors: Long Marshall B. , Frank Jonathan H. , Lyons Kevin M. , Marran David F. , Stårner Sten H.
Published: July 2012

A technique is presented for making instantaneous, two‐dimensional measurements of the mixture fraction in turbulent nonpremixed flames. The technique uses acetaldehyde fluorescence imaging and Rayleigh imaging to determine the mixture fraction in an iterative manner. Preliminary experimental results for the mixture fraction and its gradient in a turbulent acetaldehyde flame are presented. To verify the degree to which the acetaldehyde fluorescence tracks the fuel concentration, simultaneous fluorescence and fuel Raman scattering measurements are performed. The strength of the signals from the Rayleigh scattering and the fuel fluorescence allows computations of the mixture fraction high in spatial resolution and low in noise, thus making determination of the scalar dissipation feasible.
High Precision Optical Surface Topometry
Authors: Tiziani H. J.
Published: July 2012

For contactless measurement of the surface topography optical techniques are promissing. A lot of progress was made by the development of laser supported methods. It is due to the development of new different lasers, the introduction of solid state detectors and powerful computers for the information processing. Time of flight, phase measurements, active and passive triangulation and projected fringes are very robust techniques for industrial applications.

A lot of progress was made in the application of interferometry to surface and vibration measurements. One or more wavelength together with diode lasers are used. Although interferometry requires polished surfaces, however, by using synthetic wavelengths, it can also be applied for optically rougher surfaces. In addition the unambiguity range will be extended when longer synthetic wavelengths are used.

Furthermore scanning and whole field confocal microscopy can be used for macro‐ and microstructure analysis. New techniques will be described to extend the field of view.

Some limits especially with respect to resolution and industrial application will be discussed for the methods presented together with some experimental results and future developments.
Determination of Alkali Traces in Coal Combustion by Excimer Laser Induced Fragmentation Fluorescence
Authors: Hartinger K. T. , Monkhouse P. B. , Wolfrum J.
Published: July 2012

Gas phase sodium concentrations were measured in situ in the flue gas of a fluidised bed reactor using the excimer laser induced fragmentation fluorescence (ELIF) technique. Several different coals were investigated for a fixed set of reactor conditions at ∼ 1 bar total pressure. Measured signals were converted to absolute concentrations using a calibration system that monitors alkali compounds under well‐defined conditions. Concentrations ranging from the sub‐ppb region to 25 ppb were obtained. Contrasting concentration histories were observed for the brown and hard coals studied.
Quantitative Determination of Fuel Air Mixture Distributions in an Internal Combustion Engine using PLIF of Acetone
Authors: Wolff D. , Schlüter H. , Beushausen V. , Andresen P.
Published: July 2012

Quantitative determination of planar fuel/air mixture distribution in an internal SI engine are obtained using planar laser induced fluorescence of acetone. In order to get quantitative information different fuel tracer substances have been investigated. Special requirements have to be fulfilled by the tracer molecule with regard to the application under the unstationary and hostile conditions of internal combustion. The most important is that the fluorescence intensity has to be directly proportional to the fuel density. It must be unaffected by surrounding gas composition, temperature‐ and pressure‐fluctuations. As it turned out during the experiments acetone meets this unusual requirements almost perfectly.

The experiments were carried out in one cylinder of a modified production line four cylinder SI engine from Volkswagen AG. Time resolved planar fuel distributions were obtained for the whole mixture formation process during the intake, the compression and at the beginning of the combustion stroke. Single shot and cyclic averaged measurements revealed a) cycle‐to‐cycle variations as well as recurring structures of the fuel distribution, b) mixture uniformity and c) flow field structures. The direct relationship between the acetone fluorescence intensity and the fuel density allows the quantitative determination of 2‐D fuel/air ratio maps for a multitude of different crankangles.
Microheterogeneity of monohydric alcohol/water mixtures. Extended view of ultrasonic relaxation
Authors: Kaatze U. , Brai M. , Menzel K.
Published: July 2012

Recently measured broadband ultrasonic spectra of binary mixtures of water with various monohydric alcohols are discussed with respect to precritical behaviour of the liquids. It is shown that the frequency‐dependent excess absorption can indeed be empirically represented by a very few parameters if a special relaxation function is used. Moreover, the coupling of the acoustic field to the heterogeneous structure can be alternatively considered. The interest is particularly focussed on visco‐inertial and thermal conductivity effects which have so far been taken into account in acoustically more heterogeneous systems like emulsions, suspensions, and biological tissues only. Though the shape of the spectra of the alcohol/water mixtures excellently agrees with that predicted by the theories of frequency‐dependent visco‐inertial and thermal conductivity losses some discrepancies in the parameter values result if these theoretical models are fitted to the measured data. It is, however, suggested that such effects, in addition to the previously considered fluctuations in concentration, contribute to the precritical ultrasonic spectra. This view involves not only fluctuations of mass but also special modes of impuls and energy transport to be important at internal interfaces of the micro‐heterogeneous liquids.
Generalized van der Waals Model Applied to Tetramethylsilane
Authors: Baonza V. Garcia , Alonso M. Cáceres , Delgado J. Núñez
Published: July 2012

The Generalized van der Waals model has been examined and discussed using high‐pressure experimental data previously reported for tetramethylsilane over a wide range of temperature. The study has been focused on the temperature dependence of the two following characteristic quantities: the effective volume of the hard convex body ν*, which represents the molecules of the fluid, and the attractive van der Waals parameter (a/ν*). It has been confirmed that the nearly universal relation found between the medium densities correction to the compressibility factor (in the formulation of Móritz and Kohler) and the limiting value of the attractive parameter at high densities (a0/ν*) holds for tetramethylsilane. In addition, it has been studied the general form of the low density correction, which can be directly related to third virial coefficient.
Thermophysical properties of alkali metal vapours part II ‐ assessment of experimental data on thermal conductivity and viscosity
Authors: Fialho P. S. , Ramires M. L. V. , De Castro C. A. Nieto , Fareleira J. M. N. A. , Mardolcar U. V.
Published: July 2012

An analysis of the available data on the viscosity and thermal conductivity coefficients of the alkali metal vapours is presented. The analysis is based upon theoretical calculations of the properties of the monatomic systems, described in the preceeding parts I and I.A of the present paper, and making use of the kinetic theory of a binary gas reacting mixture. A summary of the measurement techniques used, including, whenever possible, the magnitude of the corrections performed on the raw data and the nominal precision of the results, complements the analysis.

It is concluded that it is possible to select precise and mutually consistent sets of experimental results for both viscosity and thermal conductivity coefficients of lithium, sodium and potassium vapours among the available literature data and to classify all the data in uncertainty classes. Regarding rubidium and cesium no systematic discussion is possible due to a lack of experimental data with sufficient precision.
DISQUAC predictions on VLE andHEfor ternary mixtures containing 1‐alkanols and hydrocarbons
Authors: González Juan Antonio , La De Fuente Isaias Garcia , Cobos José Carlos , Casanova Carlos
Published: July 2012

Thermodynamic properties, vapor‐liquid equilibrium or excess enthalpy, for a set of 13 ternary mixtures including one or two 1‐alkanols and hydrocarbons are studied in the framework of the DISQUAC group contribution model. The study is extended for the binaries involved. The DISQUAC analysis is developed using interchange coefficients available in the literature. No ternary interactions are taken into account.

The average relative standard deviations are 0.02 for pressure in the vapor‐liquid equilibria (4 systems); and 0.07 for the excess enthalpy (9 systems).
Rate and mechanism of the atmospheric degradation of 2H‐heptafluoropropane (HFC‐227)
Authors: Zellner R. , Bednarek G. , Hoffmann A. , Kohlmann J. P. , Mörs V. , Saathoff H.
Published: July 2012

The atmospheric chemical behaviour of 2H‐Heptafluoropropane (CF3CHFCF3, HFC‐227) with respect to its rate and mechanism of degradation in the troposphere has been investigated. The rate coefficient for the reaction of HFC‐227 with OH radicals has been determined in direct time resolved experiments using a combination of laser‐pulse initiation and LIF. In the temperature range T=298‐463 K the Arrhenius expression k(T) = (3.8±0.8) 10−13 exp(‐1596±77K/T) cm3/s, which corresponds to k (298 K) = (1.8±0.3) 10−15cm3/s, was found. The mechanism of the atmospheric degradation of HFC‐227 has been investigated using both, laser‐pulse initiated/time resolved and UV photolysis/FTIR product studies. It is concluded that the major carbonyl products are CF3COF and CF2O which result from the decomposition of the oxy radical CF3CF(O)CF3 by C‐C bond fission. The rate coefficient for this decomposition process has been determined to be k = (2±1) 103s−1 at 298K. Based on the reactivity of HFC‐227 with respect to the reaction with OH radicals, the atmospheric lifetime and the GWP value for HFC‐227 are estimated to be ∼40 years and 0.6±0.2, respectively.
On the alignment of thermotropic nematic and smectic liquid crystals on lecithin coated surfaces
Authors: Hiltrop K. , Hasse J. , Stegemeyer H.
Published: July 2012

The orientation of thermotropic nematic and smectic liquid crystals at monomolecular films of lecithin on glass as well as germanium substrates has been studied by polarizing microscopy and FTIR spectroscopy. Nematic liquid crystals with only a weak tendency to form smectic phases exhibit a dependence of their orientation on the temperature and the packing density of the monolayer which can be explained by a sterical model. Liquid crystals in the smectic A phase as well as nematics with a strong tendency to build up smectic layers, however, align homeotropically, independent on the packing density of the lecithin film and the temperature. This can be understood as a screening of the lecithin film properties by the smectic‐like boundary layers of the nematic liquid crystal.
Interdiffusion in the quasibinary systems Cd3Te3/Ga2Te3 and Hg3Te3/Ga2Te3
Authors: Leute Volkmar , Zeppenfeld Astrid
Published: July 2012

The quasibinary systems Cd3Te3/Ga2Te3 (I) and Hg3Te3/Ga2Te3 (II) form regions of extended solid solution. The interdiffusion of the cationic components in these regions is coupled with a flux of so‐called structural vacancies. Peculiarities in the composition and temperature dependence of the interdiffusion coefficient, measured by an electron microprobe, are due to the effect of the thermodynamic factor. The calculation of the thermodynamic factor is based on a model of tetrahedral clusters. Special features of the phase diagrams of systems I and II are used to estimate the cluster energies. By use of these cluster energies the free excess enthalpy of the solid solution is calculated, and therefrom the thermodynamic factor can be derived. The course of the interdiffusion coefficient is caused by totally different influencies: in system I by a trend towards spinodal demixing, in system II by a trend towards ordering.
Ultrafiltration of an aqueous polymer solution in a hollow fiber dialyzer with a semipermeable membrane: Internal filtration
Authors: Wüpper A. , Röttger H. , Kreuser H. , Woermann D. , Baldamus C. A.
Published: July 2012

An experimental method is described to study internal filtration (back filtration) in a hollow fiber dialyzer during ultrafiltration of an aqueous polymer solution. This process takes place within a hollow fiber module if there exists a location along the axis of the fibers forming the module at which the radial volume flow density across the wall of the fibers changes its direction: Near the influx of the solution into the hollow fiber the radial volume flow density is directed into the external phase and near the efflux of the solution out of the hollow fiber it is directed into the lumen.
Microscopic derivation of the low‐T myoglobin‐CO recombination rate law by estimating statistical parameters of folding relaxation
Authors: Fernández Ariel
Published: July 2012

The low‐T recombination of carbon monoxide (CO) to myoglobin (Mb) obeys a rate law interpreted as a superposition of appropriately‐weighted Arrhenius‐type relaxations. We derive this rate law from microscopic principles by determining the random activation energy landscape for short timescale interconversion of myoglobin conformational substates that preserve CO‐storage capacity. Thus, the random energy model (REM) first introduced in the context of protein folding by Bryngelson and Wolynes is applied here to derive the nonexponential rate law of a reaction ‐ Mb‐CO recombination — built upon an REM‐type distribution of substate reactants.
Wetting in fluid systems. Wetting and capillary condensation of lattice gases in thin film geometry
Authors: Binder K. , Ferrenberg A. M. , Landau D. P.
Published: July 2012

Monte Carlo studies of lattice gas models with attractive interactions between nearest neighbors on a simple cubic lattice are carried out for a L×L×D geometry with two hard walls of size L×L and periodic boundary conditions parallel to the wall. Two types of short‐range forces at the walls are considered:

(i) Both walls are of the same type and exert an attractive force of the same strength (in Ising model terminology, surface fields HD = H1 occur). (ii) The walls differ, one attracts and the other repels particles, again with the same strength (HD = −H1). In the first case, capillary condensation occurs at a chemical potential differing from its value for phase coexistence in the bulk, and the (second‐order) wetting transition that occurs for D→∞ is rounded off. In the second case, an interface parallel to the walls is stabilized and we observe the interface delocalization transition predicted by Parry and Evans. A first attempt to study the nature of this “quasi wetting transition” by finite size scaling methods is reported, and discussed in the context of recent theories.
Critical point wetting from binary polymer mixtures
Authors: Steiner Ullrich , Eiser Erika , Budkowski Andrzej , Fetters Lewis , Klein Jacob
Published: July 2012

Critical point wetting generally occurs whenever a binary fluid system in the demixed region of phase space, in contact with a surface, approaches its critical temperature. For the case of polymeric mixtures the segmental interaction parameter, which determines the interfacial tension between the coexisting phases, can be very low even far from the critical point. This suggests that polymer blends should be likely candidates to exhibit complete wetting even far below the critical point. Using nuclear reaction analysis, we have now observed such complete wetting behaviour from two different classes of binary polymer mixtures. These are mixtures of statistical olefinic copolymers, with slightly different chemical microstructures; and an isotopic pair of deuterated and protonated polymers. In the former case we have been able to follow the growth with time t of the wetting layer thickness l; our results indicate l ∼ log t.
Ellipsometric studies of wetting on low‐energy surfaces
Authors: Lawnik Wolfgang H. , Findenegg Gerhard H.
Published: July 2012

The physisorption of the vapor of pure nonpolar liquids (alkanes and cycloalkanes) and water onto a thermally oxidized silicon wafer was studied by means of a phase modulation ellipsometer. The resulting film thickness isotherms show complete wetting for all studied nonpolar liquids (n‐pentane, n‐hexane, cyclopentane, and cyclohexane) and incomplete wetting for water on the SiO2(27 nm)/Si‐wafer.

The film thickness isotherms of the wetting systems were analysed in terms of the Frenkel‐Halsey‐Hill (FHH) equation, In (p/p0) = –(α/kT)·d−n, where n is expected to have a value of 3 for non‐retarded dispersion force interactions. The present systems, however, exhibit a much smaller value, n = 1.5±0.2. It appears that for small film thickness (a few monolayers) the exponent n depends on the nature of the adsorbent surface and increases with the strength of the adsorbate‐adsorbent interaction; in this regime the FHH equation can be taken merely as an empirical relation.
Some specific features of spreading at the molecular scale: Wetting transition and molecular self‐assembly
Authors: Valignat M. P. , Cazabat A. M. , Tiberg F.
Published: July 2012

Profiles of microdroplets spreading on solid surfaces are studied in the molecular range of thickness using spatially resolved ellipsometry. Surface induced layering leads to stepped profiles for nonvolatile liquids, the thickness of the successive molecular layers giving information on the configuration of the molecules at the solid surface. For example, the worm‐like molecules of polydimethylsiloxane (PDMS) lay flat on the substrate, while the bulk configuration is a coil. On the same way, surfactant molecules behave differently on hydrophobic and hydrophilic surfaces.

After a general discussion of drop behaviour on finite or infinite substrates, we present two examples illustrating the specificity of the molecule‐surface interactions. The first case could be referred to as a “wetting transition”: A hydrophobic layer is grafted on a high energy surface, and the liquids are a series of PDMS. The lighter oils wet the surface, the heavier do not. The approach to transition is clearly observed in the droplets shape: The thickness of the film which grows at the bottom of the drop increases when transition is approached and diverges at transition, where the liquid becomes nonwetting. This is the “pancake” first predicted by de Gennes.

The second case concerns nonionic trisiloxane surfactants, which do not wet the substrates, but build an extended autophobic film on it. The profile of the film strongly depends on the surface energy: it looks like a “sand pile” on high‐energy surfaces, but the molecules self‐assemble into a perfect bilayer on low‐energy ones. These phenomena are understood by considering the chemical structure of the molecules, and the dynamics of the films is related to the “superspreading” properties of these surfactants.
Critical adsorption of fluids and the equivalence of extraordinary to normal surface transitions
Authors: Diehl H. W.
Published: July 2012

The current understanding of the critical adsorption of fluids on walls or interfaces is reviewed, with the emphasis put on a description of what can be learned from field‐theoretic renormalization group (RG) approaches. In particular, results of a recent RG calculation of the universal order‐parameter profile are presented. The prototypical continuum model describing critical adsorption is a standard semi‐infinite ϕ4 model with surface terms ∫ dS(−1/2g0ϕ2‐h1ϕ). For h1, = 0, this model describes surface phase transitions called ordinary, special, and extraordinary depending on whether the surface enhancement g0 is less than, equal, or greater than a certain critical value. For typical chemical systems one expects g0 to be subcritical and h1 to be nonvanishing. Under those conditions the model describes a so‐called normal surface transition or, equivalently, critical adsorption of fluids. The critical behavior at this normal transition (and hence at critical adsorption) is the same as at the extraordinary transition. This can be shown by an explicit mapping of appropriate lattice models.
The potentiality for tm elevation of dipalmitoylphosphatidylcholine liposomes
Authors: Fernández Marta S.
Published: July 2012

In a previous article from this laboratory [M.S. Fernández and E. Calderón, Ber. Bunsenges. Phys. Chem. 95, 1669 (1991)], the interfacial acid‐base ionization of dipalmitoylphosphatidylcholine (DPPC) was studied by applying the concept of potentiality for tm elevation to experimental results of the increase in the phase transition temperature of DPPC liposomes upon incorporation of cationic stearylamine, at different bulk pH values. In this way, an intrinsic interfacial pK of 4 was determined for the phosphodiester group of DPPC. In this work, a modified form of the theoretical treatment developed previously, is applied to the analysis of the ionization of the same phospholipid using data from the literature for the phase transition temperatures (tm) of lamellar phases of DPPC mixed with cetyl alcohol at neutral and acidic pH, as compared to tm values of pure DPPC liposomes. The intrinsic interfacial pK of lecithin phosphate determined in this way is 3.75, very close to that found using stearylamine as an additive. The similarity between the intrinsic interfacial pK values for lecithin phosphate group estimated from the pH dependent tm shifts induced in DPPC bilayers by additives with quite different polar groups such as stearylamine and cetyl alcohol, gives additional support to the concept of potentiality for tm elevation as correlated with the dissociation degree of DPPC bilayers, that we proposed previously.
Monolayers, critical layers and wetting films in a liquid‐liquid‐solid system undergoing a wetting transition. Experimental study
Authors: Privat M. , Amara M. , Hamraoui A. , Sellami H. , Mear A. M.
Published: July 2012

Experimental adsorption isotherms have been drawn for the water‐2,5 lutidine liquid system against silica, at several temperatures, on both sides of the liquid‐liquid coexistence curve and for the coexisting phases. In the two‐phase liquid system, perfect wetting, probably due to long range interactions is made by the water rich phase, whereas lutidine, probably due to chemical forces is preferentially adsorbed.

In water rich monophases, at very low lutidine concentrations, lutidine forms monolayers on silica. Close to the phase separation, lutidine adsorption strongly increases and diverges for T→Tc, the critical temperature of the liquid system: a critical behaviour.

In lutidine rich phases, adsorption behaviour is quite different, and Tw, the wetting transition temperature is the important parameter for the behaviour of the adsorption at coexistence.

The set of experimental results is very similar to the results of the theoretical literature, and both can be used as a guide for further experimental exploration of the so‐called “prewetting” transition.
Electrotransport in ionic crystals: I. Application of liquid electrolyte theory
Authors: Janek J. , Martin M. , Yoo H. I.
Published: July 2012

Transport of matter and charge in ionic crystals is only possible by the existence of irregular structure elements (defects) which are often charged relative to the crystal lattice. A comparison between the transport behaviour of a crystalline matrix containing such charged defects and a liquid electrolyte containing dissolved ions shows a lot of similarities. As is well known the transport properties of liquid electrolytes are strongly affected by interactions between the dissolved ions. We have applied the well elaborated concept of mixed electrolytes by Onsager and Fuoss which was originally devoted to liquid electrolytes to ionic crystals containing charged point defects. The equations of Onsager and Fuoss allow in principle the calculation of the concentration dependence of the phenomenological transport coefficients Lij of all charge carriers of n‐component electrolytes. We will use these equations to predict the transport behaviour of ionic crystals containing differently charged point defects.

As examples we have calculated transport coefficients for electrolyte systems which can be regarded as models for the transition metal oxides Co1‐δO and Cu2‐δO. One major result concerns the magnitude of the cross effect between the ionic and electronic fluxes in those materials. The implications of these results with respect to experimental observations are discussed.
Influence of electrochemical activation and surface orientation on the photoresponse of single crystalline pyrite/electrolyte and pyrite/metal junctions
Authors: Büker K. , Alonso‐Vante N. , Scheer R. , Tributsch H.
Published: July 2012

The current/voltage curves of crystalline (100)‐ and (111)‐oriented surfaces of n‐pyrite/electrolyte and n‐pyrite/Pt junctions in darkness and under illumination are strongly influenced by cathodic hydrogen evolution before junction formation. Higher dark current and lower photocurrent on n‐pyrite (111)‐oriented surfaces in comparison to (100)‐oriented surfaces were obtained. The junction properties of the untreated surfaces change from a metal‐like behaviour to a rectifying one. During electrochemical treatment different etching patterns develop according to the exposed surface orientation. In the case of (111)‐oriented crystals these patterns are identified as new (100)‐surfaces. Quantum yields of ca. 0.7 at photon energies of 1.4 eV and almost similar photocurrent action spectra are obtained on n‐pyrite/electrolyte and n‐pyrite/metal junctions. The energetical position of the subbandgap response at 0.68 eV is not changed during etching. The increase of the quantum yield for photon energies higher than 1.4 eV on both types of junction points towards a reduction of surface recombination centers on etched samples. EBIC analysis on previously etched n‐pyrite in contact to vacuum deposited platinum films of 120 to 1000 Å thickness (Schottky barriers) indicate that the charge carrier collection efficiency is higher on etched areas. The role of surface recombination processes for photocurrent generation is demonstrated and discussed.
Observation of an H/D‐isotope exchange channel in the reaction D + H2CO
Authors: Dóbé S. , Oehlers C. , Temps F. , Wagner H. Gg. , Ziemer H.
Published: July 2012

The reactions of H and D atoms with H2CO,

H + H2CO → H2 + HCO , (1)

D + H2CO → HD + HCO , (2a)

→ HD + HDCO , (2b)

were studied in an isothermal discharge flow reactor at room temperature with EPR detection of H and D atoms and LIF detection of HCO radicals. Simultaneous measurements of the absolute concentration‐versus‐time profiles of D, H, and HCO in the D + H2CO system established the occurrence of the H/D isotope exchange reaction (2b), which competes with the usually assumed direct H atom abstraction channel (2a). The room temperature rate constants of the two reaction channels were found to be

k2a (296 K) = (1.9±0.5) × 1010 cm3/mol s ,

k2b (296 K) = (1.5∓0.4) × 1010 cm3/mol s .
Vapor pressure determination of liquid PCl3 by the Knudsen effusion method
Authors: Matsumoto K. , Schönherr E. , Wojnowski M.
Published: July 2012

The vapor pressure of liquid PCl3 was determined by the Knudsen effusion method. The pressure was found to follow the relation log10 P[kPa] = −1800/T+7.371 between 240 and 278 K.
Crystal structures, molecular conformations, hydrogen bonds, and 35Cl NQR in some chloral hemiacetals
Authors: Hashimoto Masao , Isono Takahiro , Mano Koichi
Published: July 2012

Crystal structures of chloral 4‐bromo‐, 4‐methyl‐, 2,4‐dichlorobenzylhemiacetals, and iso‐butylhemiacetal were determined by the single crystal X‐ray method at room temperature. Two modifications were found for the 2,4‐dichlorobenzyl derivative. A chiral chain of molecules formed by OH … O hydrogen bonds (H‐bonds) along a 21 axis is common to the crystals studied, except for iso‐butyl derivative where a centrosymmetric dimer is formed by H‐bonds. Conformation analyses were made using molecular mechanics. The crystal structures and IR spectra indicated that the H‐bonds in these crystals except for the 2,4‐dichlorobenzyl derivate were bifurcated ones. An intramolecular OH…Cl interaction was found in the iso‐butyl derivative. The relationship between the 35Cl NQR spectrum and the molecular structure are discussed.
A Nuclear magnetic resonance investigation of proton dynamics in α‐D‐glucose
Authors: Latanowicz L. , Reynhardt E. C.
Published: July 2012

It has been shown that the trans‐gauche rearrangement of the CH2OH group and the jump motion of an OH group proton between two equilibrium sites in a hydrogen bond are the motions contributing to the observed proton spin‐lattice relaxation times of anhydrous polycrystalline α‐D‐glucose.
Electrochemical oxidation of anthracenes on poly(vinylferrocenium) coated pt electrodes in acetonitrile
Authors: Gülce Handan , Özyörük Haluk , Yildiz Attila
Published: July 2012

The electrooxidation behaviour of anthracene and 9,10‐diphenylanthracene on poly(vinylferrocenium) coated Pt electrodes was investigated and compared with that on uncoated Pt surface using cyclic voltammetry in acetonitrile/0.1 M TBAP solutions. IR spectroscopy was used to detect the changes occurring in the structure after the electrode reaction. The formation of the quinone and hydroxy substituted type products was revealed if the electrode potential was cycled between + 1.50 and 0.00 V. The catalytic oxidation of anthracene rings were observed if the potential cycling was kept between + 1.50 V and −2.30 V.
From vesicles to micelles
Authors: Schönfelder E. , Hoffmann H.
Published: July 2012

On the system soybean lecithin (Epicuron 200)/tetradecyldimethylaminoxide C14DMAO/water the aggregation behavior of mixtures composed of surfactant and phospholipid in a dilute solution was studied. The lipid was dispersed into water as vesicles, which were prepared by sonication. By varying the surfactant‐to‐lipid‐ratio at a constant total concentration the whole spectrum of properties from vesicles to micelles with its transition properties could be investigated. Most of the measurements were carried out at a total concentration of 10 mM.

Three different regions exist in this system: a micellar region on the surfactant rich side, a vesicular region on the lipid rich side and a two‐phase‐region between these two phases. In the micellar region there are spherical micelles, which grow to rodlike micelles with increasing molefraction of lipid XL. This region was investigated by electric birefringence, by rheology and by measuring the interfacial tension.

In the lipid rich solution vesicles are the dominant structures. Vesicles in this region can exist with a large molefraction of surfactant. These vesicles were examined by electron microscopy, dynamic light scattering, electric birefringence and conductivity measurements. We found that the vesicles in the region XL = 1–0.27 will grow only a small amount with added surfactant. For XL<0.27 the vesicles grow rapidly.

A two‐phase‐region exists between the micellar and the vesicular region. One of these phases contains nearly the whole amount of lipid and surfactant in a very small volume of the solution. In this phase the lipid and surfactant molecules are present in the form of rodlike micelles. The other phase contains almost pure water. The two‐phase‐region shows a very strong temperature dependence.
A kinetic study about the reactions of NH(X3Σ−) with hydrocarbons part 1: Saturated hydrocarbons and acetaldehyde
Authors: Röhrig Michael , Wagner Heinz Georg
Published: July 2012

The reactions of NH in its electronic ground state with the hydrocarbons methane (1), ethane (2), propane (3) and with acetaldehyde (4) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ−). The experiments were performed with very low initial concentrations of HN3 which was used as NH source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH(X3Σ−) with hydrocarbons directly. The following rate constants were obtained:

k1 = (9±3)·1013 exp (−(84±5) kJ mol−1/RT) cm3/ mol s ( 1150 K < T < 1500 K)

k2 = (7±3)·1013 exp (−(70±5) kJ mol−1/RT) cm3/ mol s ( 1010 K < T < 1170 K)

k3 = (6±3)·1013 exp (−(61±5) kJ mol−1/RT) cm3/ mol s ( 980 K < T < 1150 K)

k4 = (5±3)·1013 exp (−(48±5) kJ mol−1/RT) cm3/ mol s ( 1000 K < T < 1200 K)

The apparent energies of activation fit rather well into an Evans Polanyi plot. They correlate with the energies of activation of the corresponding reactions of O(3P) and therefore also with (CH2(X̃3B1) radicals.
A kinetic study about the reactions of NH(X3Σ−) with hydrocarbons part 2: Ethene, propene, and 2,3‐dimethyl‐2‐butene
Authors: Röhrig Michael , Wagner Heinz Georg
Published: July 2012

The reactions of NH in its electronic ground state with the alkenes ethene (1), propene (2), and 2,3‐dimethyl‐2‐butene (TME) (3) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ−). The experiments were performed with very low initial concentrations of HN3 which was used as NH source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH(X3Σ−) with these alkenes directly. The following rate constants were obtained for T>1000 K:

C2H4: k1 = (1.8±0.4)·13 exp (−(56±4) kJ/mol/RT) cm3/mol s

C3II46: k2 = (3.3±1.0)·13 exp (−(50±4) kJ/mol/RT) cm3/mol s

TME: k3 = (4.1±1.5)·13 exp (−(40±6) kJ/mol/RT)

The apparent energies of activation correlate well with the ionisation potentials of the alkenes and with the energies of activation of the corresponding reactions of O(3P) and can therefore be used for the extrapolation to the addition reactions of the higher alkenes. The reaction of NH(X3Σ−) with ethene proceeds via an intermediate triplet diradical ethylenimin which then decomposes into several reaction channels. For the reaction of propene and TME with NH(X3Σ−) a contribution of an abstraction reaction channel besides electrophilic addition cannot be excluded.
Kinetics of oxirane formation in the reaction of nitrate radicals with tetramethylethylene
Authors: Berndt T. , Böge O.
Published: July 2012

The kinetics of oxirane formation in the reaction of nitrate radicals with tetramethylethylene was investigated in a flow system at room temperature. Total pressure ranged from 5 to 1000 mbar. Using inert gas (He, N2) tetramethyloxirane only was detected as reaction product. In the case of synthetic air acetone also is formed in dependence of the system pressure. With increasing pressure the oxirane yield decreases and the acetone yield increases. Under tropospheric conditions 20% tetramethyloxirane was found.

It is concluded that the oxirane observed results from the excited adduct formed in the electrophilic addition of the nitrate radical to the double bond. In the absence of O2 the quenched adduct radical formes oxirane in a thermal reaction also.

Kinetic parameters were estimated.
On the metallic droplet model for successive ionization potentials of metal clusters ‐ relativistic electronic structure investigations of the icosahedral gold cluster Au55
Authors: Häberlen Oliver D. , Chung Sai‐Cheong , Rösch Notker
Published: July 2012

We have carried out relativistic electronic structure calculations on the naked cluster Au55 in icosahedral geometry using the linear combination of Gaussian‐type orbitals density functional (LCGTO‐DF) method. The one‐electron level spectrum is discussed and compared to that of the jellium model which is able to reproduce the s‐type level manifold of Au55 only qualitatively. Furthermore, a series of successive ionization potentials and electron affinities of the cluster has been calculated. The remarkable agreement of the all‐electron LCGTO‐DF results with those of the metallic droplet model indicates that the naked cluster Au55 acts like an almost perfect electron reservoir. In this respect a gold particle of about 50 atoms may mark the onset of the metallic regime.
Investigation of the electronic spectra of arylidene‐, arylethylidene‐ and heterocyclicmethylene‐malononitriles. MNDO‐CI treatment
Authors: Moustafa H. , Hamed Maher M. , El‐Taher S. , Hilal R.
Published: July 2012

The electronic absorption spectra of some arylidene‐, arylethylidene‐ and heterocyclicmethylenemalononitriles have been investigated qualitatively and quantitatively. MNDO‐CI calculations were performed to predict the suitable conformer for the studied compounds. The conformer adopted by arylethylidene derivatives is found to be the non‐planar one, while the other two groups of compounds had the planar conformer. The observed transitions are assigned as charge transfer (CT), localized and delocalized according to the contribution of the various configurations in the CI‐states. The correspondence between the calculated and experimental transition energies was satisfactory.
The mitotic oscillator: Temporal self‐organization in a phosphorylation‐dephosphorylation enzymatic cascade
Authors: Romond P.‐C. , Guilmot J.‐M. , Goldbeter A.
Published: July 2012

The conditions for temporal self‐organization in the form of sustained oscillations are determined in a minimal cascade model previously proposed (A. Goldbeter, Proc. Natl. Acad. Sci. USA 88, 9107–9111 (1991)) for the mitotic oscillator driving the embryonic cell division cycle. The model is based on a phosphorylation‐dephosphorylation cascade involving cyclin and cdc2 kinase. In the first cycle of the cascade, cdc2 kinase is activated through dephosphorylation triggered by the accumulation of cyclin, while in a second cycle the activation of a cyclin protease is brought about through phosphorylation by cdc2 kinase. The fact that cyclin promotes the activation of cdc2 kinase while the latter enzyme triggers cyclin degradation introduces a negative feedback loop which is at the core of the periodic operation of the cascade. We analyze the mechanism of oscillatory behavior by constructing stability diagrams as a function of some of the main parameters of the model. Investigated in turn are the roles of negative feedback and of phosphorylation‐dephosphorylation thresholds. Such thresholds arise from the phenomenon of zero‐order ultrasensitivity associated with the kinetics of covalent modification cycles. An extension of the minimal model allows one to address the effect of additional phosphorylation‐dephosphorylation cycles and the possible role of autocatalysis by cdc2 kinase in the generation of periodic behavior. The analysis shows that the existence of thresholds as well as an increase in the number of cycles in the cascade favor the occurrence of sustained oscillations. The results further indicate that negative and positive feedback may both contribute to the repetitive activation of cdc2 kinase.
On the existence of bicontinuous cubic phases in dioleoylphosphatidylethanolamine
Authors: Erbes J. , Czeslik C. , Hahn W. , Winter R. , Rappolt M. , Rapp G.
Published: July 2012

Aqueous dispersions of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphatidylethanolamine (DOPE) exhibit a well‐known phase transition from a lamellar liquid‐crystalline (Lα) to an inverted hexagonal (HII) phase as the temperature is raised above 13°C. Recently, it has been reported [1, 2] that a bicontinuous cubic phase can be induced in this system, when the lipid is rapidly cycled between these two phases. Their X‐ray diffraction results indicated that the cubic lattice is most consistent with either the Pn3m or Pn3 space group. In studies on similar systems [3, 4], two cubic phases could be detected in the Lα‐HII transition region, however. One aim of the present study was to investigate, if still further bicontinuous cubic phases can be induced in simple DOPE dispersions by changing the experimental conditions. Indeed, we found that two cubic lattices may be induced when the lipid system is cycled between –5 and 15°C more than thousand times. The second goal of the present investigation was to study the temperature dependence of the lattice parameters, the stability and transformations of these cubic phases over a wide temperature range. It has been discussed that the presence of cubic phases may be a general feature of HII‐forming lipids in the region of their lamellar to hexagonal phase transition region and that non‐lamellar lipid structures might play an important role as transient intermediates in biochemical processes.
Scanning electrochemical microscopy: A new scanning mode based on convective effects
Authors: Borgwarth K. , Ebling D. G. , Heinze J.
Published: July 2012

A new measuring technique for the scanning electrochemical microscope (SECM) is presented, which we call picking mode. The influence of the tip‐surface distance on the current signal is separated from the current due to the electrochemical properties of the surface by this new method. Based on convective effects, the fast approach of the tip towards samples revealed a sharp increase of the tip current close to the samples' surface. During this strongly instationary stage, the current is dominated by convective flows and the influence of the electrochemical surface properties is negligible. Using this convective current, the tip‐surface distance can be adjusted within a few microns. In a second step after reaching the steady‐state transport conditions again, the electrochemical processes are characterised by the current at this position. The capability of the new mode is proven by scanning a bended platinum sheet and a PVC sample. The new method enables the separate acquisition of the height profile due to the surface's morphology and of the topology due to local variations of electrochemical properties.