bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elektrochemie: Von der Thermodynamik zur atomaren Struktur
Authors: Kolb D. M. 
Published: July 2012

AbstractThe last decades have witnessed a remarkable change in electrochemistry: from a macroscopic, thermodynamicsoriented approach towards electrochemical problems to a microscopic, atomistic one. The latter was frequently inspired by models derived for the solid‐vacuum interface. The desire and the necessity to understand electrochemical processes on an atomic or molecular level called for new experimental and theoretical routes. Significant advances in the understanding of electrode reactions resulted from the availability of new techniques in electrochemistry, e.g., by adoption of structure‐sensitive surface‐physics techniques to electrochemical needs. Similarly important was the use of single‐crystal electrodes with well‐characterized surfaces. It was their wide‐spread use which brought to light the importance of the surface structure in electrochemical kinetics. In the following we shall demonstrate with a few selected examples how much information about the microscopic structure of electrode surfaces is nowadays available. In this respect, scanning tunneling microscopy has had a major impact. Finally, future trends in fundamental electrochemical research are discussed.
Hundred years of colloid science fascinating phenomena in surfactant solutions
Authors: Hoffmann H. 
Published: July 2012

AbstractThe lecture begins by reviewing some facts that were already known in colloid science of hundred years ago. The importance of colloid science for the development of human civilization and modern technology is then outlined. The main part of the lecture deals with surfactant science, a subdivision of colloid science:Amphiphilic molecules can assemble in aqueous solution into a variety of micellar structures such as globules, rods, disks and vesicles. For a given system the micellar structures are determined by the packing parameter of the surfactant which controls the spontaneous curvature of a micellar interface. The spontaneous curvature of micelles can be varied continuously by the addition of cosurfactant to the micellar solution. With increasing mole fraction Xc of the cosurfactant, the system develops then from micelles with interfaces that are strongly curved around the micellar core over planar interfaces towards interfaces that are curved away from the micellar core. Results are presented for the ternary systems of alkyldimethylaminoxides, n‐alcohols and water. As a consequence of the change of the spontaneous curvatures with Xc the systems undergo several macroscopic phase transitions in dilute solutions. In total eleven different single and multiphase situations are observed when one passes from the dilute surfactant to the dilute cosurfactant solution. The single phase regions are the micellar L1‐phase, two different lamellar liquid crystalline Lα‐phases (Lα1 and Lαh) and the isotropic L3 or sponge phase. The microstructures of the various phases are identified by electronmicrographs which were obtained with the freeze fracture method. The macroscopic properties of the phases are discussed on the basis of their microstructures. The influence of charges by ionic surfactants on the structures and properties of the mesophase is determined. It is found that the Lαh and the L3‐phase are transformed into a phase with multilamellar vesicles. This phase has a Theological yield stress value and can be used as a particle suspending fluid. The influence of excess salt on the microstructures and the properties of the charged phases is determined.Some of the observed phases show bright colours when illuminated with white light. Some of the phases show colour effects when viewed through crossed polarizers.
Computer simulation as a tool to analyze neutron scattering experiments: Water at supercritical temperatures
Authors: Löffler G. , Schreiber H. , Steinhauser O. 
Published: July 2012

AbstractWe present results of molecular dynamics simulations of water at supercritical conditions that correspond exactly to those of an experimental study performed by Postorino et al. (P. Postorino, R.H. Tromp, M.‐A. Ricci, A.K. Soper, and G.W. Neilson, Nature 366, 668 (1993)). The discrepancy between simulation and experiment raised by these authors is partly removed simply by considering corresponding thermodynamic states. The careful analysis of the contributions of neutron scattering experiments on the atomic radial distribution functions of water gives strong evidence that the neutron‐scattering experiment on non‐deuterated water plays a key role in determining the essential features of gOH(r) and gOO(r) and is a potential source of artifacts.
Infrared and raman study of ν4 and ν5 motions of light and deuterated nitromethane evidence of conformational equilibria
Authors: Cataliotti R. S. , Distefano M. R. , Mariani L. , Morresi A. , Paliani G. , Santini S. , Giorgini M. G. 
Published: July 2012

AbstractInfrared and Raman spectroscopy has been used to study totally symmetric ν4 and ν5 motions of CH3NO2 and CD3NO2 isotopomers, in order to ascertain the nature of the low‐frequency features appearing in these bands. A study, under high‐resolution conditions, of the gaseous phase infrared spectra and of the temperature effects, carried out on both liquid and gaseous molecules, has allowed us to proove that these features are connected to the effects of conformational population and not to hot band transitions, as it has been previously reported.
The Nucleation of Colloidal Copper in the Presence of Poly(ethyleneimine)
Authors: Sosebee T. , Giersig M. , Holzwarth A. , Mulvaney P. 
Published: July 2012

AbstractCopper colloids have been prepared by y‐radiolysis of cupric ions in the presence of poly(ethyleneimine). The reduction takes place in two, distinct steps. Copper (II) is reduced quantitatively to copper (I), and then nucleation of the colloid occurs after an induction period. The nucleation of colloidal copper is catalysed by the presence of less noble Pb(II) or T1(I) ions, which is explained by the generation of Pb and Tl nuclei in the solution, and their subsequent reoxidization by Cu(I). The formation of copper colloids is also catalysed by the presence of colloidal silver or silver ions, and radiolysis results in the formation of copper coated silver colloids. The optical shifts observed during the deposition of copper on silver cannot be explained by Mie theory. The differences are suggested to be due to weaker interband transitions in the copper monolayers than in the bulk
Viscosity Effects on the Intramolecular Fluorescence Quenching in Dipeptide Model Compounds
Authors: Sakurai Tadamitsu , Miyoshi Kenichiro , Obitsu Mitsuhiro , Inoue Hiroyasu 
Published: July 2012

AbstractThe finding that the increased solvent viscosity decreases the rate for intramolecular fluorescence quenching in the title compounds [N(n)D], giving a singlet‐exciplex intermediate, but increases the rate for the reverse process, regenerating the locally excited singlet‐state N(n)D, is explained in terms of the viscosity‐dependent free‐energy change for this fluorescence quenching process (ΔGet). A linear correlation between the ΔGet and the logarithm of solvent viscosity is found to provide a good criterion for a singlet‐exciplex mechanism in polar solvents.
A simplified DEMS Set Up for Electrocatalytic Studies of porous PtRu Alloys
Authors: Ianniello Remo , Schmidt Volkmar M. 
Published: July 2012

AbstractA simplified experimental apparatus for Differential Electrochemical Mass Spectrometry (DEMS) was constructed having only one turbomolecular pump and a modified gas inlet system. The setup allows the determination of the activity of porous PtRu electrodes for the electro‐oxidation of small organic molecules. Various PtRu alloys with defined composition can be electrodeposited onto porous gold substrates. First results on the electrooxidation of methanol in acid solution were presented.
On the Calculation of Point Defect Equilibria
Authors: Spinolo G. , Anselmi‐Tamburini U. 
Published: July 2012

AbstractA method is outlined for solving the equations describing the quasichemical equilibria of point defects, with particular reference to binary oxides. The method gives exact solutions for all defect concentrations and the oxygen activity as a function of n = [e′]. In comparison to the traditional approach, the feasibility of the method does not depend on the number of differently charged defects of the same kind. Possible extensions of the approach are briefly discussed.
The Inverted Region of Electron Transfer in Intramolecular Fluorescence Quenching of Quinolinium Betaines
Authors: Käb G. , Engel TH. , Lanig H. , Schneider F. W. 
Published: July 2012

AbstractFluorescence quenching through intramolecular electron transfer (ET) was studied in N‐(ω‐sulfonatoalkyl)‐ and N‐(ω‐carboxyalkyl)‐quinolinium betaines by stationary and time‐resolved fluorescence spectroscopy in the solvents water and acetonitrile. These substances are zwitterionic in the ground and local excited state of the quinolinium chromophore. In the sulfonato compounds fluorescence quenching through ET does not occur in water, whereas quenching is efficient in acetonitrile. A surprising opposite behaviour is observed for the carboxylato compounds: quenching is efficient in water whereas it is inefficient in acetonitrile. Semiempirical calculations were used to derive the parameters needed for the description of the quenching process by non‐adiabatic Bixon‐Efrima‐Jortner‐theory. These parameters include the solvent (λs) and the intrinsic (λv) contributions to the total reorganisation energy λ and the approximate free energy of reaction ΔG°. The vibrational motion of an aromatic C‐H bond influenced by the interaction with the negatively charged donor was taken as the major intramolecular accepting mode. ET fluorescence quenching in the present compounds and solvents may be interpreted in terms of the “normal” and the “inverted region” of Marcus theory.
A Scanning Michelson Interferometer for the Measurement of the Concentration and Temperature Derivative of the Refractive Index of Liquids
Authors: Becker A. , Köhler W. , Müller B. 
Published: July 2012

AbstractA compact scanning Michelson interferometer for the measurement of both the concentration and temperature derivative of the refractive index of liquids, liquid mixtures, and solutions has been developed. Scanning of one of the mirrors allows the extraction of the phase information and makes the instrument insensitive to intensity drifts of the light source. The refractive index noise level of the empty instrument is of the order of 10−8 for a 10 mm sample cell, and for continuously varying refractive indices there is no upper limit of the linear detection range. Accuracies of the order of 0.5% can be achieved both for (n/c)p,T and (n/T)p,c.
Phase Diagram and Dynamic Properties of the Ternary System Water – Sodium Dodecylsulfate – Aerosol OT
Authors: Muzzalupo Rita , Ranieri Giuseppe A. , Terenzi Mario , Mesa Camillo La 
Published: July 2012

AbstractThe phase diagram of the system composed by Water, Sodium Dodecylsulfate and Aerosol OT, at 25°C, has been investigated. Some physico‐chemical properties of the system were determined by optical microscopy, electrical conductance and NMR investigation on 2H and 23Na nuclei. Information on binding and counterion dynamics, as well as on the mesophases structure, were inferred by comparing quadrupole splittings and electrical conductance findings.
On the Algebraic Evaluation of the Ternary Molar Heat of Mixing HE from Calorimetric Investigations
Authors: Tomiska Josef , Wang Hai 
Published: July 2012

AbstractThe experimental effort of calorimetric investigations on ternary alloy systems is very large and evaluation of the measured data is very time‐consuming. A considerable reduction both of the time spent on evaluation and of the experimental work can be expected by applying the new overall best‐fit technique developed in this work. The suggested evaluation technique is based on the ternary “Thermodynamic Adapted Power” (TAP)‐series, requires computer assistance, but it makes possible to determine ternary molar heat of mixing HE by means of a minimum of experimental investigations: If there exist accurate HE‐data of the three binary boundary systems, only a small number (about 5 to 10) of ternary HE‐values must be determined. The application of the proposed evaluation technique is illustrated with data for liquid Fe–Co–Ti, Fe–Ni–Ti, Fe–Ni–Zr, and Cu–Sn–Ni ternary alloys. The advantages of the proposed technique are discussed in detail.
The Conformational Order and Headgroup Structure of Long‐Chain Alkanoic Acid Ester Monolayers at the Air/Water Interface
Authors: Gericke Arne , Hühnerfussf Heinrich 
Published: July 2012

AbstractThe structural properties of long‐chain alkanoic acid ester monolayers are investigated at the air/water interface by infrared reflection‐absorption spectroscopy. It is shown that the conformational order of alkanoic acid methyl ester monolayers increases with increasing acyl alkyl‐chain length and/or decreasing temperature. For expanded monolayers the alkanoic ester headgroup is E‐configured, where the alcoholic alkyl chain substantially is pointing out of the water, while for compressed states (or condensed domains) the headgroup is Z‐configured with an alcoholic alkyl component directed into the water. In the compressed states (Z‐form) the ester‐carbonyl group is found to be unprotonated, presumably as a result of a shielding by the alcoholic alkyl component of the ester. For alkanoic acid methyl ester monolayers this shielding depends on the conformational order and the tilt angle of the molecules, while for the respective ethyl‐ and n‐propyl esters an unprotonated carbonyl group was also found for states with a low conformational order. By comparing the IR‐spectra of 1‐alkanol, fatty acid and alkanoic acid ester monolayers evidence is presented that fatty acid monolayers are stabilized increasingly with decreasing chain lengths by forming hydrogen‐bridges between adjacent molecules.
The Reaction of NH2+O2 at High Temperatures
Authors: Hennig G. , Klatt M. , Spindler B. , Wagner H. G. G. 
Published: July 2012

AbstractThe reaction of NH2+O2 was investigated behind incident shock waves in the temperature range of 1450–2300 K at densities between 2·10−6 to 5·10−6 mol cm−3. The rate constant of the reaction of NH2+O2 forming products was determined by following the decay of NH2 concentration using laser absorption to be k1 = (2.2±0.5)·1014 exp (−(105±10) kJ mol−1/RT) cm3/mol s. Investigations of the possible radical products (NH, OH, O and H) showed that the contribution of the radical forming channels in the overall reaction is less than 15%. The channel leading to NO+H2O is expect to be the main reaction path.
In‐situ‐Monitoring of Electrochemical Double Layer Structure Changes at Gold with a Phase‐Controlled Quartz Microbalance
Authors: Kautek W. , Sahre M. , Soares D. M. 
Published: July 2012

AbstractContinuum hydrodynamics and no‐slip boundary conditions apply to electrochemical quartz microbalances of the thickness shear mode type with gold in aqueous contact. Electrochemical phase‐stabilized quartz micro‐balance measurements can give insight into ion adsorption, solvation, hydrogen bonding, and water clustering at charged surfaces. Species in the outer and inner Helmholtz layer can be treated as rigidly coupled masses. Frequency changes on polycrystalline gold electrodes in alkaline aqueous contact, and in the potential range from the hydrogen evolution up to the bulk oxide formation, are primarily caused by ion solvation and ion pair formation. Specifically adsorbed anions, like sulfate and hydroxide, are stripped of nearly half of their original solvation shell, and function as counter charge carriers analogously to completely solvated anions in the outer Helmholtz plane. Their saturation coverage is limited by lateral electrostatic repulsion and steric crowding by their solvation shells. Specifically adsorbed anions which form neutral ion pairs with alkali metal cations practically do not exhibit electrostatic repulsion and solvation shell crowding. They contribute much stronger to the double layer loading than specifically adsorbed partially hydrated ions and non‐specifically attracted species. In the oxide monolayer potential region, electrosorbed hydroxyl functions are deprotonated, and become neutralized by alkali metal ions at high pH. In a first order approximation, viscous fluid coupling and roughness changes do not have to be invoked to explain the observed frequency data.
Adsorption and Film Formation of Thymine on a Gold (100) Single Crystal Electrode
Authors: Roelfs B. , Baumgärtel H. 
Published: July 2012

AbstractThe film formation of thymine adsorbed at a Au (100) surface in aqueous solution has been analysed by means of cyclic voltammetrie and capacity‐potential measurements. On the freshly flame annealed and therefore reconstructed (100) surface the formation of a 2‐dimensional condensed adlayer of thymine has been observed. On the unreconstructed (100) surface exists no condensed adsorbate state.A certain amount of charge transfer from adsorbed thymine molecules is detected at potentials near to the potential of zero charge. Variation of the pH of the solution reveals a transfer of nominally 0.81 electrons per molecule. From this the surface concentration of chemisorbed thymine at positive potentials is estimated. The surface concentration correlates with an adsorption state in which the molecular plane of thymine is parallel oriented to the surface.
Specific Vibrational Sideband Changes in the Resonant Luminescence Spectrum of [Cr(urea)6]I3due to Minority‐Majority Complex Species
Authors: Schmidtke Hans‐Herbert , Schoepe Klaus E. , Degen Joachim 
Published: July 2012

AbstractThe emission spectrum of [Cr(urea)6]I3single crystals excited under resonance condition into the zero phonon4A2g→ E1/2(2Eg) absorption line, which is inhomogeneously broadened from 14210 to 14240 cm−1, is recorded at 1.9 K. The vibrational sideband spectrum is shifted in a characteristic way, the spectral profile being changed only in some minor details. All features can be explained by energy transfer processes between majority and minority complex species which have small differences of transition energies in the crystal.
Interferometric Determination of Electrooptical Effects in Liquid‐Crystalline Blue Phases
Authors: Niggemann E. , Stegemeyer H. 
Published: July 2012

AbstractIn cholesteric liquid crystals with high chirality up to three thermodynamically stable blue phases (BPI, BPII and BPIII) occur in a narrow temperature range below the isotropic phase. The BPI and BPII are characterized by a three‐dimensional helicoidal structure of cubic symmetry with lattice constants of the order of several hundred nanometers.An applied electric field causes a i) change of the BP lattice constants (electrostrictive effect) and ii) a field‐induced birefringence (electrooptical effect). At high fields, new field‐induced phases with different symmetries compared to the zero field blue phases were observed.To get further informations about the molecular arrangement within the blue phases, the electrooptical effect has been studied with a modified microscope‐interferometer in BPs of systems with positive and negative dielectric anisotropy. For the first time an electrooptical effect has been observed also in field‐induced blue phases.
Computer‐Aided Thermodynamics of Solid Ternary Fe1‐x(Ni0.86Cr0.14)x Alloys by Knudsen Cell Mass Spectrometry
Authors: Broz Pavel , Vrestal Jan , Tomiska Josef 
Published: July 2012

AbstractKnudsen cell mass spectrometry has been employed to investigate thermodynamically the fcc solid ternary Fe1‐x(Ni0.86Cr0.14)x alloys. The “Digital Intensity‐Ratio” (D.I.R.)‐method has been applied for the determination of the thermodynamic excess properties. Fcc solid ternary Fe1‐x(Ni0.86Cr0.14)x alloys are characterized by negative molar excess Gibbs energies GE, negative molar excess entropies SE, and exothermic molar heats of mixing HE. At 1673 K the minimum HE value is ‐2830 J/mol (28 at.% Fe), the minimum GE value is ‐2390 J/mol (29.5 at.% Fe), and the minimum SE value is ‐0.27 J/(mol K) (28 at.% Fe). At 1673 K the thermodynamic activities of Fe show slight negative deviations from the ideal behavior for alloys with a Fe‐content of less than 70 at.%, and ideal behavior for the Fe‐rich alloys (xFe>0.7).
Concentration Fluctuations in the Vicinity of the Liquid/Liquid Coexistence Curve of a Binary Mixture with a Lower Critical Point
Authors: Schmitz J. , Belkoura L. , Woermann D. 
Published: July 2012

AbstractExperimental evidence is presented demonstrating that the slowing down of the diffusion process in binary liquid mixtures with a miscibility gap approaching the temperature of phase separation at constant noncritical composition and approaching the critical point along the liquid/liquid coexistence curve is caused by an increase of the correlation length of local composition fluctuations. This conclusion is drawn from dynamic light scattering data obtained with the system 2‐butoxyethanol/water in the vicinity of its lower critical point. The (hydrodynamic) correlation length is calculated from the diffusion coefficient data in combination with viscosity data taken from the literature using the analogue of the Stokes‐Einstein relation.
Scavenging of Hydrocarbon Radicals from Flames with Dimethyl Disulfide. I. Characterisation and Discussion of the Method and the Scavenging Process
Authors: Hausmann M. , Homann K.‐H. 
Published: July 2012

AbstractThe method of scavenging free radicals sampled through a rarefied free‐jet from stationary low‐pressure high‐temperature reaction systems (flames, pyrolysis) in the condensed phase of dimethyl disulfide (DMDS) has been studied systematically. For this purpose the flat open condensing device originally used has been replaced by a condensation trap consisting of two stainless‐steel hemispheres cooled with liquid nitrogen. The scavenging products were separated and identified by GC/MS. The condensing efficiencies of the scavenger DMDS and condensable substances from the reaction system were so determined as to make the scavenging R+CH3SSCH3RSCH3+CH3S a quantitative method of radical analysis. It is shown that with a sufficient excess of DMDS the scavenging reaction takes place to 90‐100% for hydrocarbon radicals with two or more C atoms, with a slight interference from addition reaction of radicals to condensable unsaturated products from the reaction system. The type of reactions with mono‐ and divalent radicals and carbenes in the solid DMDS matrix are investigated. Consecutive reactions during warming‐up are also studied and discussed. It is stated that this scavenging method is well suited for the analysis of all hydrocarbon radicals heavier than ethyl, provided that the scavenging products can be separated and identified, which might become a problem with heavy polycyclic aromatic radicals.
Critical Viscosity and Ising‐to‐Mean‐Field Crossover Near the Upper Consolute Point of an Ionic Solution
Authors: Kleemeier M. , Wiegand S. , Derr T. , Weiss V. , Schröer W. , Weingärtner H. 
Published: July 2012

AbstractWe report on shear viscosity data near the upper consolute point of the ionic system tetrabutylammonium picrate+1‐tridecanol (Tc = 341.845 K) which shows a large mean‐field region in its static critical properties with crossover to Ising behavior close to the critical temperature. After suitable assessment of the non‐singular background viscosity we establish that the asymptotic scaling law η ∝ τ−y applies in the region τ < 5 ×10−3, where τ = (T‐Tc)/Tc is the reduced temperature. The value of the exponent is determined to y = 0.0434±0.001 which is close to the current best value for the 3d‐Ising model, y = 0.041. At higher reduced temperatures pronounced deviations from Ising criticality are observed. In agreement with the mean‐field prediction y = 0, the critical contribution is vanishing. This crossover is discussed in the framework of current theory.