bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

The 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

Continuum 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

The 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

The 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

In 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

Knudsen 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

Experimental 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

The 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

We 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.
Thermal Electric Polarization of Molecules
Authors: Borovikov Yu. Ya. , Makovetskii V. P. , Pivovarova N. S.
Published: July 2012

The problem of molecular thermal (Pq) polarization estimation in the substances with different forms of aggregation and using different experimental techniques is discussed. It is shown on the base of numerous experimental data analysis that Pq includes both rotational (Prot) and orientational (Por) components, which may be commensurable in magnitude in gases and gasiform condensed media. The principle of equal distribution of molecules' thermal polarization over their kinetic degrees of freedom is being satisfied, so Prot term should not be neglected. The neglect of this fact on estimation of the molecular dipole moments using the first method of Debye results in √(5/3) or √(4/3) times overestimated dipole moment values.
Photochemical Formation of Colloidal Gold Particles in Chitosan Films
Authors: Yonezawa Y. , Kawabata I. , Sato T.
Published: July 2012

Thin films of chloroauric acid salt of chitosan (CTOAu films) were photolyzed with 253.7 nm light. On irradiating with UV light in air at room temperature, the CTOAu film first became yellow‐blue colored due to the formation of colloidal gold. When irradiation was continued, the irradiated surface of the film finally changed into clear gold mirror. Primary photochemical products are assumed to be gold atom, quaternary ammonium chloride of chitosan and chlorine. With aids of UV‐visible absorption spectroscopy, X‐ray photoelectron spectroscopy, and scanning electron microscopy, aggregation of small gold particles to form colloidal gold and gold metal film has been investigated. It has been found that the aggregation state of small gold particles is controlled by reaction conditions; temperature, evacuation, the amount of chloroauric acid. When the CTOAu film was photolyzed in vacuum at room temperature, the gold particulate film was formed. Irradiation at liquid nitrogen temperature resulted in absorption spectrum characterized by the structureless absorption extending from λ = 400 nm to shorter wavelength. However, an introduction of air after photolysis brought about the development of the broad colloidal absorption band.
Tracking Unstable Periodic Orbits in a Model for Electrochemical Corrosion
Authors: Parmananda P.
Published: July 2012

We continuously track the unstable period one orbit through various bifurcations in a numerical model for electrochemical corrosion. The tracking strategy used is a combination of a continuation method and the map‐based control strategy (SPF) [1, 2] to stabilise periodic orbits in deterministic chaotic systems. After achieving control on the unstable periodic orbit using the control strategy (SPF), we use a continuation method to maintain control on the orbit as one of the system parameters is allowed to drift. This allows us to track the stabilised orbit over long ranges of parameters and through various bifurcations. Tracking could prove to be advantageous in controlling the dynamical behavior of experimental situations where the system response drifts with time
Topologically disordered hubbard models and the electronic structure of expanded Cs: A numerical study
Authors: Koslowski Thorsten , Rowan David G. , Logan David E.
Published: July 2012

We present a numerical study of the electronic properties of simple models of expanded alkali metals. An Anderson‐Hubbard model incorporating on‐site electron‐electron repulsion and liquid‐like disorder is solved within the unrestricted Hartree‐Fock approximation. We focus on the proper determination of the localization properties deciding the metallic or nonmetallic character of the model and on the computation of the electrical conductivity within the random phase model.

With a realistic set of parameters we obtain good quantitative agreement with experiments on expanded Cs for i) the density at which the metal‐nonmetal transition occurs and ii) the electrical conductivity throughout the entire density interval accessible by experiments. The transport properties thus computed give additional support to recent claims that the description of liquid expanded metals requires the incorporation of both disorder and interaction effects.
Phenomenological Description for a Formation of Cylindrolites in Co‐Operative and Dynamic 2D‐(Bio)Polymeric Systems
Authors: Gadomski Adam
Published: July 2012

A phenomenological description for the formation of cylindrolites in cooperative 2d‐(bio)polymeric systems in terms of the modified normal grain growth concept and stretched exponential kinetics in a linear regime is offered. As the principal result, a linear dependence of the cylindrolite radius as a function of time has been obtained which is in excellent accord with experimental data reported.
The Film Formation in Electrode Processes at the Electrode/Electrolyte Interface
Authors: Ivanov S. V. , Ivanova N. D.
Published: July 2012

The formation of a film at the electrode in aqueous electrolytes with organic ligands is shown. This film is presumed to be an intermediate product in the overall mechanism of the reduction or oxidation of metal ions. It consists of oxide‐hydroxide compounds with mixed conductivity as it takes place in electrolyte with inorganic ligand.
Phasendiagramm mit S‐förmigen Labilgrenzen
Authors: Bärner K. , Zavadskii E. A.
Published: July 2012

Metastable regions which are bounded by S‐shaped lability lines can become infinitely large at temperatures which are significantly lower than a chosen critical point temperature. Such a behaviour is found in at first sight totally different systems: CoSiF6 (6H2O), MnAs0.96P0.04, β‐(ET)2I3, and is explained in the framework of the Landau‐theory.
The Effect of Temperature on the Adsorption of Dodecane onto Nonionic and Ionic Surfactant Monolayers at the Air‐Water Surface
Authors: Aveyard R. , Binks B. P. , Fletcher P. D. I. , Macnab J. R.
Published: July 2012

We have measured the adsorption isotherms for dodecane adsorption at the solution‐vapour surface for surfactant monolayer covered aqueous surfactant solutions at concentrations in excess of their critical micelle concentration (cmc) values. The temperature dependence of the adsorption have been determined for both a nonionic surfactant (H(CH2)12(OCH2CH2)5OH, abbreviated to C12E5) and an ionic surfactant (n‐dodecyltrimethyl‐ammonium bromide, abbreviated to DoTAB). For the nonionic surfactant, dodecane adsorption decreases with increasing temperature at low surface concentration of the oil whereas it increases at high surface concentrations. With the ionic surfactant DoTAB, the temperature effect shows a similar crossover in behaviour but the changes in adsorption are opposite in direction to those seen for the nonionic surfactant. The adsorption data are correlated to the effects of temperature on the microemulsion phase behaviour of ionic and nonionic surfactants and discussed in relation to the microstructures of the mixed oil/surfactant films as determined by neutron reflection methods.
Shape Similarities of Ultra‐Low Interfacial Tension Curves in Ternary Microemulsion Systems of the Water‐Alkane‐CiEj Type
Authors: Sottmann T. , Strey R.
Published: July 2012

The interfacial tensions between water‐ and oil‐rich phases in microemulsion systems have been measured for a series of ternary water‐alkane‐CiEj systems. It is found that interfacial tensions vary over orders of magnitude with temperature displaying a pronounced minimum for each surfactant. The center of the three‐phase temperature interval, Tu‐T1, i.e. the phase inversion temperature (PIT), corresponds to the temperature Tm of the minimum in interfacial tension. Increasing the surfactant chain length the minimum value decreases by 3 orders of magnitude for a change of i from 6 to 12. Interestingly, all interfacial tension curves have a similar shape. Centering the curves around Tm and reducing the temperature scale by Tu‐T1 permits determining the factors, by which the individual interfacial tension curves differ. The factors are found to be proportional, respectively, to square of the maximum length scale ζ or the inverse surfactant volume fraction Φc,i in the interface. Accordingly, plotting σab/Φc, j2 vs. 2(T‐Tm)/(Tu‐T1) an almost perfect superposition of all interfacial tension curves is observed.
Calculation of the Rigidity Constant in a Landau Model for Microemulsions
Authors: Blokhuis Edgar M.
Published: July 2012

A theoretical investigation into the validity of different mean‐field formulas for the rigidity constant of a microemulsion system is presented. As a theoretical model for the microemulsion system we use a Landau‐theory‐like expression for the free‐energy in which, besides the usual gradient of the density squared term, a term proportional to the square of the second derivative is present, while the coefficient of the squared gradient term is taken to be negative in the microemulsion phase. Gompper and Zschocke (Phys. Rev. A 46, 4386 (1992)) used this model and derived mean‐field expressions for the surface tension, spontaneous curvature and rigidity constants. The formula for the rigidity constant of bending features the curvature dependent density profile. It was observed that approximating the curvature dependent density profile with the density profile of the planar interface, yields approximate values for the rigidity constant which are in good agreement with a numerical calculation of the free energy of the curved surface. This is somewhat surprising since the same approximation for the rigidity constant of a simple liquid‐vapour interface was shown to be incorrect. In this paper we investigate the differences and similarities between the two systems by calculating the approximate and exact values of the rigidity constant. We investigate when the approximate value of the rigidity constant is a good approximation to the exact one.
Transmission Electron Microscopy of Complex Fluids: The State of the Art
Authors: Talmon Y.
Published: July 2012

Transmission electron microscopy (TEM) is potentially one of the most useful techniques in the study of micro‐structured fluid systems. It is the one technique that provides high resolution direct images, thus the interpretation of the data is not model‐dependent. But at the same time electron microscopy is probably the most abused experimental technique, and as such, a rather problematic one. People have taken liberties with the technique as with no other. In a critical review of the field, the inherent limitations on TEM of liquid systems are described, together with the technical solutions that have been developed to overcome them. Sample results of recent data that illustrate the potential of the techniques, as well as novel technical extensions of the basic technique are described. Also, artifacts, the result of improper specimen preparation, are demonstrated.
Microemulsions: A Medium for Polymerization Reactions
Authors: Lusvardi K. M. , Schubert K.‐V. , Kaler E. W.
Published: July 2012

Aqueous and nonaqueous microemulsions containing either of the monomers styrene or hexyl methacrylate polymerize when initiated with potassium persulfate. Reactions in both types of microemulsions lead to stable, bluish dispersions of latex particles with diameters ranging from 40 to 90 nm. By substituting formamide for water, one can investigate the effect of the monomer solubility in the continuous domain on the microemulsion polymerization mechanism in a way independent of the monomer type. When the monomer solubility in the polar domain is high, the latex particles are larger and have a larger number of polymer chains than when the monomer solubility is low. If the monomer solubility in the continuous domain is greater than the overall monomer concentration in the microemulsion, the reaction mechanism shifts from that of a microemulsion polymerization to one of a solution polymerization in the presence of empty micelles.
Nonfaradaic Two‐Dimensional Phase Transition on Smooth Surfaces ‐ An Example for Time‐Dependent Homogeneous Nucleation
Authors: Donner C. , Baumgärtel H. , Pohlmann L. , Retter U. , Philipp R.
Published: July 2012

Two dimensional film formation on smooth surfaces has been investigated theoretically. The commonly used exponential law for nucleation and its limiting cases in connection with the Avrami theorem are examined critically.

A new model for describing nucleation on surfaces on the basis of the classical nucleation theory is proposed. This model takes into account the time‐dependent supersaturation caused by the simultaneous processes of adsorption of molecules from the bulk to the surface and the real phase transition. The model was proofed experimentally by the investigation of condensation of 5‐bromocytosine on mercury electrodes in aqueous Na2SO4‐electrolyte solution. On the basis of the new model the experimental results can be for the first time explained consistently.
Electron‐Deficient Palladium Clusters in Zeolites and Their Complexes with Probe CO Molecules. A Density Functional Model Cluster Study
Authors: Yakovlev Alexey L. , Zhidomirov Georgy M. , Neyman Konstantin M. , Nasluzov Vladimir A. , Rösch Notker
Published: July 2012

Tetrahedral and octahedral palladium clusters with an entrapped proton, [Pd4H]+ and [Pd6H]+, were considered as models of electron‐deficient palladium species encaged in a zeolite matrix. Density functional studies employing a gradient‐corrected exchange‐correlation potential have been carried out on the bare and protonated Pd4 and Pd6 clusters as well as on their complexes with a CO molecule adsorbed at the three‐fold hollow position. In line with the experimental data it is found that the protonation of palladium clusters leads to a reduced CO adsorption energy and an increased vibrational frequency of the adsorbed CO. The protonation energies of the clusters Pd4 and Pd6 were calculated to 9.4 eV and 9.9 eV, respectively. These large values are comparable to the proton affinity of such a strong base as NH3 (calc. 9.2 eV) and support the hypothesis that, as a result of the interaction of the guest metal particles with zeolitic protons, electron‐deficient [PdnHx]x+ species are formed.
Thermodynamic Activities in the Alloys of the Ti‐Al System
Authors: Eckert M. , Bencze L. , Kath D. , Nickel H. , Hilpert K.
Published: July 2012

The vaporization of the solid alloys of the Ti‐Al system has been extensively studied for the complete composition range of the system by using Knudsen effusion mass spectrometry at temperatures between 1113 and 1664 K. 19 alloy samples of different compositions covering the complete composition range were investigated and their Ti and Al partial pressures determined. Thermodynamic activities and chemical potentials of Ti and Al as well as Gibbs energies were evaluated for a temperature of 1473 K. Two independent methods were used for the determination of the Ti activities yielding consistent results. The large temperature range of the partial pressure measurement for three alloys in the homogeneity range of the TiAl phase rendered possible the determination of partial and integral thermodynamic functions (ΔH, ΔG) for the formation of this phase. The data obtained are discussed.
Phase Transitions and Ionic Motions in Solid Trimethylethylammonium Iodide Studied by 1H and 127I NMR, Electrical Conductivity, X‐ray Diffraction, and Thermal Analysis
Authors: Ishida Hiroyuki , Furukawa Yoshihiro , Kashino Setsuo , Sato Setsuko , Ikeda Ryuichi
Published: July 2012

1H and 127I NMR, differential thermal analysis (DTA), differential scanning calorimetry (DSC), electrical conductivity, and powder and single crystal X‐ray diffractions were studied for trimethylethylammonium iodide. Three solid phases, named I, II, and III, were obtained above 410 K, between 336 and 410 K, and below 336 K, respectively. Powder X‐ray patterns showed that Phase I and II have a NaCl‐type cubic structure (a = 10.00(1) Å, Z = 4) and a tetragonal structure (a = 8.430(5), c = 6.216(4) Å, Z = 2), respectively. The structure of Phase III was determined to be orthorhombic (Pnam (#62), a = 11.294(4), b = 10.729(2), c = 7.158(6) Å, Z = 4) by single crystal X‐ray diffraction. In Phase III, the C3 reorientation of CH3 groups and the C3 reorientation of the whole (CH3)3N group in the cation were observed by 1H NMR. In Phase II, the cation is expected to perform the quasi‐isotropic reorientation. In Phase I, the cation was found to carry out the isotropic reorientation, while the spherical anion the translational self‐diffusion, as evidenced by 1H and 127I NMR, and electrical conductivity. Phase II and I are, therefore, dynamically disordered phases; especially, Phase I is highly disordered. From the dynamical behaviour of the cation and anion, and thermal properties, Phase I can be classified into an ionic plastic phase with a NaCl‐type structure.
Gaseous Diffusion Coefficients of ZnSe in Argon and Helium at 1140–1280 K and 70–100 mbar
Authors: Schönherr E. , Freiberg M. , Hartmann H.
Published: July 2012

The diffusion of subliming ZnSe in argon and helium gas has been investigated by a modified entrainment method with a flowing gas at a reduced pressure between 70 and 100 mbar. From the weight loss measurements an effective diffusion coefficient results for the (Zn+0.5 Se2, Ar) system as 0.0828 (T/273)1.47 cm2/s and for the (Zn+0.5 Se2, He) system as 0.177 (T/273)1.88 cm2/s between 1140 and 1280 K. With a simplified gas collision theory, rigid sphere diameters are estimated as 4.11×10−8 cm for Zn and 5.97 × 10−8 cm for Se2.
A Gaskinetic Investigation of HOBr Reactions with CI(2P), O(3P) and OH(2II). The Reaction of BrCl with OH(2II)
Authors: Kukui A. , Kirchner U. , Benter Th. , Schindler R. N.
Published: July 2012

The reactions of HOBr with atomic chlorine (1), with oxygen (2) and with hydroxyl radicals (3) have been investigated at 300 K using the discharge flow technique with mass‐spectrometric detection. The rate constants based on HOBr consumption have been determined to be k1 = (8.0±0.4)·10−11 and k2 = (3.1±0.2)·10−11. For the reaction with OH radicals k3<5×10−13 was obtained. All rate constants are given in units cm3 molecule−1 s−1.

The reactions of HOBr with Cl and with O are shown to proceed via bromine abstraction with formation of BrCl and BrO, respectively. The predominant channel in the reaction of OH with BrCl was identified to be step (4a) OH+BrCl → HOBr+Cl (4a) Based on the present kinetic investigation the heat of formation for HOBr at T = 300 K was evaluated to be ΔH0f (HOBr) = −(60.22±2) kJ · mol−1.
Reaction of NO3 Radicals with 1,3‐Cyclohexadiene, α‐Terpinene, and α‐Phellandrene: Kinetics and Products
Authors: Berndt T. , Böge O. , Kind I. , Rolle W.
Published: July 2012

The gas‐phase reaction of NO3 radicals with 1,3‐cyclohexadiene, α‐terpinene, and α‐phellandrene has been studied in a flow system at 298 K in the pressure range 8<P(mbar)<250 using GC‐MS/FID, MS, and long‐path FT‐IR as detection techniques. At a total pressure of 15 mbar N2 rate constants for the primary attack of NO3 were determined with the relative rate method to be (1.08±0.02) 10−11, (1.03±0.06) 10−10, and (5.98±0.20) 10−11, respectively (unit: cm3 molecule−1 s−1).

As buffer gas in the product studies served N2 or He as well as O2/N2 mixtures. In the case of 1,3‐cyclohexadiene the formation of the corresponding oxirane (7‐oxa‐bicyclo[4.1.0]hept‐2‐ene) up to a yield of 90% at P<35 mbar and the formation of benzene (about 6%) was observed. The oxirane yield was independent on the amount of added O2 and decreased with increasing total pressure. In the case of α‐terpinene and α‐phellandrene no indication of oxirane formation was found. However, the corresponding aromatic compound (p‐cymene) was detected for both terpenes, maximum yield 6% for α‐terpinene and 22% for α‐phellandrene. For all reaction systems investigated the formation of organic nitrate‐compounds was proved by means of long‐path FT‐IR measurements. In the case of the 1,3‐cyclohexadiene degradation with [O2]>5·1015 molecule cm−3 an absorption band was detected in addition assigned to a carbonylic group. There were no indications for a reaction of O2 with the adduct radical (NO3/diene).
Liquid‐Liquid Extraction of Rare Earth Metals Using 25,27‐Dicarboxy‐26,28‐Dimethoxy‐5,11,17,23‐Tetra‐tert‐Butylcalix[4]Arene
Authors: Soedarsono J. , Hagège A. , Burgard M. , Asfari Z. , Vicens J.
Published: July 2012

The extraction of lanthane, erbium and yttrium by dicarboxy‐dimethoxy‐calix[4]arene in 1,2‐dichloroethane has been studied. Rare earth metal extraction has been shown to be accompanied by an important co‐extraction of alkali ions. The extraction takes place via the formation of a mixed complex L2(RE)M, where L is the ligand, RE a rare earth metal and M an alkali ion. The stoichiometry of the extracted species has been confirmed by mass spectrometry. A poor selectivity is observed.
Mixed‐Mode Oscillations in the Peroxodisulfate Reduction on Platinum and Gold Rotating Disk Electrodes
Authors: Koper Marc T. M.
Published: July 2012

It is shown experimentally that mixed‐mode oscillations may be observed in the peroxodisulfate reduction on platinum and gold rotating disk electrodes, in addition to previously reported monoperiodic (relaxation) oscillations. If account is made for the internal drift of the system, the typical features of the mixed‐mode oscillations are in good agreement with the predictions of a model which combines the negative faradaic impedance characteristics with a treatment of the mass transport that goes beyond the stationary diffusion layer approximation. Although the actual observation of mixed‐mode oscillations requires a pretreatment procedure the precise effect of which is poorly understood, these results may be interpreted as evidence for the importance of slow mass transport in the explanation of multiperiodic and chaotic electrochemical oscillations.
Rate and Mechanism of the Atmospheric Degradation of 1,1,1,2‐Tetrafluoroethane (HFC‐134a)
Authors: Bednarek G. , Breil M. , Hoffmann A. , Kohlmann J. P. , Mörs V. , Zellner R.
Published: July 2012

The atmospheric chemical behaviour of 1,1,1,2‐tetrafluoroethane (CF3CFH2, HFC‐134a) with respect to its rate and mechanism of degradation in the troposphere has been investigated. The rate coefficient for the reaction of (1 a) CF3CFH2 + OH→CF3CFH + H2O has been determined in direct time‐resolved experiments using laser‐pulse initiation and laser long‐path absorption. A value of k1a = (4.6±0.5)×10−15 cm3/s at T = 295K has been found. The ratio of the rate coefficients for the reactions of the CF3CFHO‐radical with O2, (4) CF3CFHO + O2→CF3CFO + HO2, and C‐C bond fission, (5) CF3CFHO + M→CFHO + CF3 + M, for T = 295 K and ptotal = 50 mbar (O2) has been obtained to be k4/(k5 [M]) = 1.5×10−19 cm3, with the individual values being k4 = 2.7×10−15 cm3/s and k5 [M] = 1.8×104 s−1. The mechanism of the atmospheric degradation of HFC‐134a has been investigated in the temperature range 244‐295 K and ptotal = 1000 mbar using UV photolysis/FTIR product studies. From these experiments the Arrhenius expression k4/(k5 [M]) = 8.7±10−25 exp ((3240+990−610) K/T) cm3 was determined. Moreover, it is concluded that the major carbonyl products are CF3CFO, CFHO and CF2O which result from the two possible reactions of the oxy radical CF3CFHO. As a consequence the yield of these carbonyl products is dependent on temperature, O2 partial pressure and total pressure. For the reaction of CFHO with Cl atoms the Arrhenius expression k18 = 5.7×10−14exp (−(1130 ± 160) K/T) cm3/s was determined in the temperature range 244‐298 K.
Time Resolved Studies of Intermediate Products in the Oxidation of HCFC 141b (CFCl2CH3) and HCFC 142 b (CF2ClCH3)
Authors: Mörs V. , Hoffmann A. , Malms W. , Zellner R.
Published: July 2012

The oxidative degradation of HCFC 141 b (CFCl2CH3) and HCFC 142 b (CF2ClCH3) in the presence of NO at T = 293 K and p = 50 mbar has been studied using laser pulse initiation combined with cw laser long path absorption/LiF for the detection of OH and NO2. The absolute yield and temporal behaviour of these products have been found to be sensitive indicators for the reaction behaviour of the alkoxy radicals CFCl2CH2O and CF2ClCH2O, respectively. The rate coefficients for the reactions of the alkoxy radicals with O2 were determined to be k(CFCl2CH2O+O2→CFCl2CHO+HO2) = (2.0±1.0)×10−15 cm3/s and k(CF2ClCH2O+O2→CF2ClCHO+HO2) = (2.5±1.5)×10−15 cm3/s. Upper limits for the rate coefficients for unimolecular decomposition of the alkoxy radicals by C‐C‐bond fission of k(CFCl2CH2O+M→CFCl2+CH2O+M)×1.0±103 s−1 and k(CF2ClCH2O+M→CF2Cl+CH2O+M)≤1.5 T≤ 103 s−1 were derived. We conclude from these data that CFCl2CHO and CF2ClCHO will be formed as the dominant primary carbonyl products in the oxidation of HCFC 141 b and 142 b throughout the troposphere. Moreover, the rate coefficients for the reactions of the HCFCs with OH radicals at T = 293 K have been measured. The values k(CFCl2CH3+OH→CFCl2CH2+H2O) = (4.6±0.8)×10−15 cm3/s and k(CF2ClCH3+OH→CF2ClCH2+H2O) = (2.6±0.4)×10−15 cm3/s were obtained.
Determination of the Pressure‐Dependent Rate Constant CFO+O2 in a F/F2/CHFO/O2 Gas Mixture at 298 K
Authors: Behr Peter , Heydtmann Horst
Published: July 2012

Homogeneous gas phase reactions in F/F2/CHFO mixtures with helium as a bath gas were studied pure and with addition of oxygen at ambient temperature. A computer‐controlled discharge flow system with mass spectrometric detection was used. The accessible pressure range was 1.6–3.5 mbar. A more precise value for the reaction CFO+CFO→CF2O+CO was determined: k(2a)=(1.7+0.4−0.3)·10−11 cm3 molecules−1 s−1. No discernible pressure dependence was found for CFO+F→CF2O: k(3a) = (5.0+3.3−1.4)·10−12 cm3 molecules−1 s−1. Fluoroformyl peroxy radicals were formed by CFO+O2+M→CF(O)O2+M. The pressure dependence of this reaction could be described by k0(4) = (4.5+2.2−1.1)·10−31 cm−6 molecules−2 s−1 and k·(4) = (1.7±0.3)×10−12 cm3 molecules−1 s−1. A small bath gas dependence of k(4) was noted.
Growth of Nanocrystalline Platinum in a Zeolite Host ‐ An in Situ X‐Ray Powder Diffraction Study
Authors: Schnell Ralf , Fuess Hartmut
Published: July 2012

The growth of nanocrystalline platinum particles in zeolite [Pt(NH3)4]NAX was investigated by in situ X‐ray diffraction in combination with Rietveld refinement atT= 509, 519, 530 and 562 K. The reaction was directly followed by the gradual decrease of the Pt2+‐occupation and the simultaneous increase of the metallic platinum particles, which grow up to an average size of 4 nm. An increase of the zeolite lattice constant and a gradual decomposition of the framework up to 20% were simultaneously observed.

The process of crystal growth can be influenced by the preparation conditions of the zeolite. After dehydration up to 383 K at 10−7bar more than 90% of the platinum cations are located near the centre of the 12‐ring‐window. Dehydration in the temperature range from 403 to 443 K under vacuo results in a partial shift of the platinum cations to a second position and to an increase of the reactivity.
Copolymers of acrylamide and quaternary ammonium cationic monomers: Characterization by HPLC and copolymer composition control
Authors: Hernández‐Barajas Jose , Hunkeler David
Published: July 2012

Copolymers of acrylamide with quaternary ammonium cationic monomers (dimethylaminoethylacrylate‐methyl chloride, DMAEA and dimethylaminoethylmethacrylate‐methyl chloride, DMAEM) have been synthesized by inverse‐emulsion copolymerization using both sorbitan monoleate (SMO) and a block copolymeric surfactant (HB246) whose hydrophilic moiety is polyethylene oxide and whose hydrophobic moiety is poly‐12 hydroxy stearic acid. Residual monomer concentrations were determined by means of an optimized HPLC method using a CN coated column. The optimized conditions consist of an acetonitrile‐water mobile phase with a ratio of 50:50 vol% with dibutylamine used as an additive to reduce the adsorption of the cationic monomer at a concentration of 0.01 M and phosphoric acid to adjust the pH. The results indicate that the choice of surfactant influences strongly the quality of the copolymers produced. For example, more uniform copolymers of acrylamide and DMAEA can be synthesized using the block copolymeric surfactant (HB246) at faster production rates in comparison with sorbitan monoleate (SMO). However, a composition drift is observed in the inverse‐emulsion copolymerization of acrylamide and DMAEM using HB246. It is shown that uniform water soluble copolymers of acrylamide and DMAEM can be produced by implementing semi‐batch policies with non time‐varying feed‐rates.
Charge transport in polyelectrolyte solutions
Authors: Turq P. , Bernard O. , Simonin J. P. , Durand‐Vidal S. , Barthel J. , Blum L.
Published: July 2012

The concept of apparent charge is a convenient tool for the description of electrical effects on polyelectrolytes in solution. The apparent charge can be significantly lower than the structural charge. The difference between these two parameters provides information on the interactions between the particle and the surrounding medium. Assessment of the physical contribution to the apparent charge can be made with the use of modern electrolyte theories; chemical speciation processes can be described by suitable chemical models.
Polyelectrolyte simulation
Authors: Seidel Christian
Published: July 2012

We present results of a Monte Carlo simulation of weakly charged chains at infinite dilution but with added salt. The charges on the chain interact with a screened Coulomb potential of the Debye‐Hückel type. Trial chain configurations are generated by means of the Pivot algorithm which is shown to exhibit short relaxation times also with Coulomb interaction. The extension of the coils as well as their shape is discussed for varying solution conditions characterized by the screening parameter ζ = 2λD/b where λD is the Debye length and b is the contour distance between neighbouring charged segments. There is an evident influence of the flexibility of the underlying neutral chain on properties of the charged chain. The resulting behaviour of the electrostatic persistence length is compared with predictions recently made by Barrat and Joanny.
Ising models and acid‐base properties of weak polyelectrolytes
Authors: Borkovec Michal , Koper Ger J. M.
Published: July 2012

Ionization equilibria of weak polyelectrolytes and their oligomeric analogs are discussed in terms of the Ising model. Within the Ising model one treats the thermal statistics of a collection of interacting sites, which can be either protonated or deprotonated. The basic parameters of the model are microscopic pK values of individual groups and various interaction parameters between pairs and possibly triplets of sites. By performing the appropriate thermal average, one can obtain the titration curve of the system considered. For systems with finite number of ionizable sites, we recover the classical description in terms of successive protonation equilibria. Thereby one can express the ionization constants in terms of the interaction parameters. For system with infinite number of sites, such as linear polyelectrolytes, the titration curves can be also calculated explicitly. We discuss three illustrative examples in more detail: (i) a simple model for linear, weak polyelectrolytes; (ii) a refined model for same type of system which describes poly(ethylene imine) and its oligomeric analogs quantitatively; (iii) simple mean‐filed model for polymeric interfaces, such as the surface carboxylated latex particles.
Polarized and depolarized dynamic light scattering of a rodlike polyelectrolyte in a strong acid
Authors: Sohn D. , Russo P. S. , Roitman D. B.
Published: July 2012

Unusual dynamic light scattering behavior of poly(benzoxazole), a stiff backbone rodlike polymer, has been found in methane sulfonic acid/methane sulfonic acid anhydride. A very rapid, angle‐independent decay mode characterized the short‐time autocorrelation functions at various levels of added salt, sodium methane sulfonate, in both polarized and depolarized dynamic light scattering experiments. In some ways, the behavior qualitatively resembles the long‐predicted “plasmon” mode, which has never been seen in more conventional polyelectrolyte systems. However, calculations based on a point charge model are inconsistent with the plasmon mode, even allowing for the high viscosity of the methane sulfonic acid solvent. The absence of angle dependence means that the rapid decay mode cannot be explained by the diffusion of oligomers. The meaning of the rapid, angle‐independent decay mode remains unclear.
Structure and dynamics of polyelectrolyte solutions with multivalent salts
Authors: Drifford Maurice , Dalbiez Jean‐Pierre , Delsanti Michel , Belloni Luc
Published: July 2012

Aqueous solutions of highly charged polyelectrolyte solutions phase separate in the presence of multivalent salts. Phase diagrams of sodium polystyrene sulfonate (Na+PSS−) with LaCl3, Th(NO3)4 were studied over a wide range of polyelectrolyte and salt concentrations. The concentration of salt at the transition C was found to be proportional to the monomer concentration Cm and nearly molecular weight independent: C/Cm≅0.23 for La3+ and C/Cm≅0.12 for Th4+. With further addition of salt a new transition from a two phase system back to a single phase was observed at constant salt concentration independent of NaPSS concentration but sensitive to molecular weight. A theoretical model which explains this behavior in termes of electrostatic attractive interaction between monomers due to the high valency of condensated counterions has been developped recently. The form of the phase diagram results from a competition between the classical long range Coulombic interaction, the short range bridging attraction via the condensed counterion and the electrostatic screening.

Dynamic light scattering measurements were performed in the lower monophase solution as a function of NaPSS concentration and over a wide LaCl3 concentration range. Two relaxation times were observed at very low salt concentration.

The dynamic studies reveal some interesting behaviours of apparent diffusion coefficient as a function of polyelectrolyte and salt concentrations (Cm, Cs): i) a q2 dependence of the fast mode and a q3 dependence of the slow mode; ii) the power law Dfast varies approximately as C1/2m at constant low salt concentration. This mode can be explained assuming cooperative diffusion in a transient polyelectrolyte network.

The slow mode of the bimodal decay disappears increasing the added salt (LaCl3) concentration at constant Cm. It is concluded that the slow mode is related to labile clusters or temporal domains of polyelectrolyte chains which are formed in solutions at low concentration of added salt. Both the disappearance of the slow mode on a very long time scale and the non reappearance of this mode when cycling at constant Cs/Cm between high and low salt concentration indicate that low salt or salt free polyelectrolyte solutions tend very slowly to thermodynamic equilibrium.
Ion‐ion correlations and effective charges in electrolyte and macroion systems
Authors: Kjellander Roland
Published: July 2012

Various ion‐ion correlation mechanisms that affect double layer interactions between charged macroparticles in electrolyte solutions are reviewed and discussed. Such effects give rise to quantitative and sometimes qualitative deviation from the prediction of the Poisson‐Boltzmann theory. Special attention is given to the attractive double layer interactions that can appear between equally charged surfaces at short surface separations for aqueous systems with divalent counterions. The long‐range behaviour of the double layer interaction is also treated. It is efficiently described in terms of effective surface charge densities, which summarizes how the inner parts of the diffuse double layer affects the distant parts. The magnitude as well as the sign of the effective charge depends on the state of the system. Charge reversal can occur for aqueous systems with divalent counterions. A major objective of the paper is to describe and illustrate the mechanisms in a simple and graphical manner.