bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dyestuff Diffusion in Partly Crystalline Polymers
Authors: Schollmeyer Eckhard , Kühnle Gerhard 
Published: September 2012

AbstractThe change of the racial structure during the diffusion of dyestuffs in fibres of poly(ethylene terephthalate), [poly(oxyethylenoxytere‐phthaloyl)], is studied with regard to the relationship between the dyestuff diffusion and the structure of high polymers. The fibre structure is described by interferometric measurements, which allow statements about order and orientation as a function of the diffusion path. The experimental results show that C. I. Disperse Red 60 raises the parameters which describe the order and orientation and that C. I. Disperse Blue 139 lowers these structure parameters. — An interpretation of concentration distributions of dyestuffs in microtomic cuttings gives informations about the diffusion process. It is shown, that the diffusion of dyestuffs in high polymers depends — in a complicated way ‐ on fibre structure (as a function of the diffusion path), fibre history and experimental conditions: C. I. Disperse Red 60 shows a lower diffusion rate at higher radial orientations, whereas the diffusion rate of C.I. Disperse Blue 139 does not depend on the radial dependence of these structure parameters.
Diffusion in Macromolecular Solutions
Authors: Sundelöf Lars‐Olof 
Published: September 2012

AbstractDiffusion is a very fundamental phenomenon which plays an important role in the most varied physical and chemical processes. In living matter, in industrial production, in material science it is in many cases basic to our understanding of what happens. Often the systems of interest are macromolecular in nature: the “solute” or the “solvent” or both may consist of big molecules. Very often the concentrations are high and sometimes the system is in a condition close to phase separation. Not unfrequently there may be more than one solute component present. ‐ Against this background some more recent results will be reviewed and discussed especially concerning diffusion and self‐diffusion in more concentrated solutions, the frictional coefficient and its concentration dependence, the diffusion behaviour of systems close to a critical point of mixing, diffusion under conditions where reactions (e.g. aggregation or dissociation) occur and in multicomponent systems. Some newer experimental techniques which have influenced the recent development will be briefly mentioned.
The Diffusion Coefficient of Branched Polyvinylacetates and of Polyvinylacetate Microgels Measured by Quasielastic Light Scattering
Authors: Burchard Walter , Schmidt Manfred 
Published: September 2012

AbstractThe principles of quasielastic light scattering are outlined. The theoretically predicted behaviour of the initial decay constant Γ of the time correlation function of the scattered light is compared for two types of branched molecules and for linear chains of different polydispersity. The apparent diffusion coefficient Dapp = Γ/q2, (where q = (4π/λ) sin Θ/2), shows for small q2 in any case a linear increase with q2, but the slope depends on the architecture of the molecule. At large q the apparent diffusion coefficient shows for all of the three types of flexible chain molecules a linear asymptote, where the slope now depends also on the polydispersity in addition to the molecular architecture. — These results from theory are taken as basis for the interpretation of quasielastic light scattering measurements from polyvinylacetate that was polymerized within latex particles (emulsion polymerization). The translational diffusion coefficient Dz = lim Dapp as function of the molecular weight is found to decrease like Dz = 9.17 · 10−5 · Mw−0.48 until a molecular weight of Mw = 14 · 106 is reached; on further increase of Mw the diffusion coefficient Dz remains constant. This effect is shown being caused by gelformation within the latex particle. ‐ The observed concentration dependence of Dz is satisfactorily explained by a theory of Pyun and Fixman. A best fit of the experimental points of the gelled samples is obtained with a parameter which characterizes the microgels as not fully rigid spheres.
Mobility of Small Molecules in Polymer Systems
Authors: Kosfeld R. , Zumkley L. 
Published: September 2012

AbstractSeveral theoretical correlations between glass temperature depression and concentration of plasticizer, known from literature, were examined on their use in describing self‐diffusion processes with the non‐linear extension of the Fujita theory [1 ‐3, 8]. — The experiments involved measurements of the self‐diffusion in various polymer‐solvent systems with the spin‐echo technique as well as glass temperature measurements conducted on a differential scanning calorimeter. ‐ The results show that both the theories of Kanig [13–15] and Kilian [16, 17] and especially the theory of Mandelkern [18] can be successfully used in describing the experimentally observed glass temperature and self‐diffusion dependence. ‐ The calculated free volume shows a non‐linear dependence in the range of high polymer concentrations.—The self‐diffusion behaviour could be correlated to the free volume by a nearly temperature‐independent relationship.
NMR Matrix Technique for Detecting Self Diffusion in Polymers
Authors: Sillescu H. , Zimmer G. 
Published: September 2012

AbstractA technique is discussed where monodisperse small spheres or cylindrical fibers of a polymer are embedded in a matrix of the corresponding fully deuterated polymer. On annealing the sample at a temperature above the glass transition the protonated macromolecules diffuse into the deuterated matrix and vice versa. Since the NMR spectrum depends upon the intermolecular proton proton dipolar coupling, the decrease of this coupling can be used to monitor the diffusion process. For particle diameters d ∼ 10−4 cm and annealing times t ∼ 105 s, extremely small diffusion constants D < d2/t are attainable. The NMR analysis of prospective diffusion experiments with polystyrene is discussed in some detail.
Synthesis, Structure, and Electrical Properties of Doped Polyacetylene
Authors: Chiang C. K. , Heeger A. J. , Macdiarmid A. G. 
Published: September 2012

AbstractPolyacetylene, (CH)x is the simplest organic polymer. Through chemical doping, the electrical conductivity of films of (CH)x can be varied over twelve orders of magnitude with properties ranging from insulator (σ < 10−10Ω−1 cm−1) to semiconductor to metal (σ > 103 Ω−1 cm−1). Both donors and acceptors can be used with these flexible, free‐standing polycrystalline polymer films (thickness 10−5 cm to 0.5 cm) to yield n‐type or p‐type material. In this review we summarize some of the more important chemical and physical properties of (CH)x and its doped derivatives.
Photoconducting, Metallic, and Superconducting Polymers — Polyacetylenes, Polymeric Sulfur Nitride, and Adducts and Analogues
Authors: Baughman Ray H. 
Published: September 2012

AbstractRecently investigated conductive linear polymers are discussed, with special emphasis on the relationship between electronic properties and defect and periodic structural aspects. The electronic properties of either semiconducting, metallic, or superconducting states of presently available linear polymers are strongly effected by prevalent defect structures. The origin and nature of these defects and the effect of defect and periodic structures on interchain and charge transfer interactions will be examined.
Elektrisch leitfähige Polyaromaten
Authors: Naarmann H. 
Published: September 2012

AbstractIn einer Übersicht werden konjugierte aromatische Systeme in Herstellung und Eigenschaften, speziell der elektrischen Leitfähigkeit, vorgestellt. ‐ Eine interessante Substanzklasse sind die Polyphenylene, die aus Benzol unter den Bedingungen der oxidativen Kupplung erhalten werden und in Abhängigkeit von den Synthesebedingungen längere Ketten und dementsprechend bessere Leitfähigkeit aufweisen. ‐ Eine weitere Substanzklasse sind die Perylenimide, die als hochkondensierte Systeme nach Ausbildung von Charge‐Transfer‐Komplexen in Abhängigkeit vom zugesetzten Elektronenakzeptor einen gewissen Anstieg der elektrischen Leitfähigkeit zeigen.
Energy Transfer in Poly(N‐Vinylcarbazole) Films
Authors: Rippen G. , Klöpffer W. 
Published: September 2012

AbstractThe fluorescence spectra of poly(N‐vinylcarbazole) films consist of two bands that are emitted by traps of differing structure. The relative proportion of the components is determined by the mode of polymerisation. The film phosphorescence, which is structureless and redshifted compared with monomer phosphorescence, is assigned to a triplet excimer whose structure is not identical with that of the two singlet traps. The kinetics is described on the basis of a three‐trap model.
Charge Transport in Atactic Polystyrene
Authors: Hofmann R. , Fuhrmann J. 
Published: September 2012

AbstractA range of different experimental evidence is presented showing the electrical properties of atactic polystyrene bulk as well as in the surface. — Charge transfer in polystyrene depends on the injection of excess electrons by metals and is discussed within the concept of a two level energy system. Through contact charging and dark conductivity measurements it is shown that one of these localized levels depends on the state of order in the polymer. — Finally the measurements of the frequency dependent dielectric constant show that the bulk properties of polystyrene, in the case of pressed‐leaf gold electrodes, and the properties of the polystyrene/gold contact, in the case of evaporated gold electrodes, can be investigated.
The Diffusion of Short Polymer Chains in Dilute Solution
Authors: Mokrys I. J. , Rigby D. , Stepto R. F. T. 
Published: September 2012

AbstractThe variation of diffusion coefficient with chain length predicted by the Kirkwood‐Riseman theory is discussed using various models for polymethylene chains. The relative magnitudes of the free‐draining and impermeable contributions to the molecular friction coefficient are evaluated, and, for the range of chain lengths studied, less than 40 chain atoms, the details of the chain model are shown to be less important than the value of the friction coefficient per segment (ζ). — Diffusion data on short polymethylene chains in various solvents are analysed according to the Kirkwood‐Riseman theory and variations of ζ with both chain length and solvent are necessary for their interpretation. The significance of these variations with respect to segmental motion and solvent structure is discussed. — Diffusion data on poly(ethylene oxide) (PEO) in water and in quinoline and on poly(hexamethylene oxide) in quinoline are also considered. These systems do not show Kirkwood‐Riseman behaviour in that impermeability remains at short chain lengths. The behaviour observed is analysed and found to be consistent with solvent molecules diffusing with the solute molecules, through hydrogen bonds at the terminal hydroxyl groups, and, for the system PEO/ water, through additional hydrogen bonds at the ether oxygen atoms along the chain.
Charge transfer and consecutive kinetics of azide‐anion oxidation at platinum, glassy carbon and carbon anodes in acetonitrile, an analogy to Kolbe synthesis
Authors: Plzak V. , Wendt H. 
Published: September 2012

AbstractBy evaluating potential‐shifts and slopes of the anodic polarographic wave which is associated with the azide‐anion oxidation in acetonitrile, standard charge transfer rates for N·3 ⇌ N3 + e− were determined at graphitic carbon, glassy carbon and platinum electrodes. This standard exchange rate decreases from carbon to platinum by more than an order of magnitude. Furthermore the rate constants for the consecutive irreversible radical‐dimerization (2N·3 → N6) and competing addition reaction to olefinsmagnified imagewere evaluated by the same means. Dimerization as well as addition reaction are essentially of heterogeneous nature and are heterogeneously catalyzed at carbon electrodes. They are however of a homogeneous character at platinum electrodes due to a relatively poor adsorbability of azide‐and carbon‐radicals at platinum anodes compared to carbon anodes. — It is this special non‐catalytic nature of platinum anodes which favours typical radical dimerization reactions in Kolbe‐synthesis as well as in anodic radical‐addition‐reactions to olefins.
The photovoltaic effect at the interface between semiconductor and electrolyte
Authors: Sakata Tadayoshi , Kawai Tomoji , Tanimura Katsumi 
Published: September 2012

AbstractA phenomenological theory of the photovoltage at a semiconductor/electrolyte interface is proposed. This theory was found to explain well the dependence of the photovoltage on the light intensity. The validity of the theory was proved experimentally. The slope of the curve of the photovoltage plotted against the logarithmic light intensity was found to be inversely proportional to the sum of the transfer coefficient and the corresponding coefficient of the photocurrent, which can explain the dependence of the slope on the kind of electrode and redox system.
Formation and properties of sandwich oxides
Authors: Lohrengel M. M. , Richter P. K. , Schultze J. W. 
Published: September 2012

AbstractThe formation, reduction, and the properties of “sandwich oxides” of the type metal/oxide 1/oxide 2/electrolyte were investigated by potentiostatic and potentiodynamic techniques, using the system Au/Au2O3/γy‐FeOOH/borate buffer, pH = 7.2.Gold oxide layers (up to 5 Å) were formed by anodic oxidation, the γ‐FeOOH‐layers (up to 200 Å) by anodic deposition from a 10−3 M Fe2+‐solution. The two oxide layers could be formed in arbitrary sequence and varied independently in layer thickness. ‐ Kinetic investigations of formation and reduction were completed by capacity and redox measurements. The results are explained by a model of a semi‐conducting γ‐FeOOH‐layer with an underlying insulating gold oxide layer.
Electron spin resonance study of methyl‐substituted N‐hydropyridinyl and N, N′‐dihydrodiazinyl radicals in solution
Authors: Rakowsky Thomas , Dohrmann Jürgen K. 
Published: September 2012

AbstractESR spectra of a number of methyl‐substituted N‐hydropyridinyl, N, N′‐dihydropyrazinyl, and N, N′‐dihydropyrimidinyl radicals have been measured in solution at room temperature. The radicals were produced by in‐situ photolytic reduction of the parent azaaromatic compounds. The hyperfine coupling constants have been analyzed in terms of the Karplus‐Fraenkel relation and the McConnell‐type relations for the CH, CH3, and NH proton splittings and using the condition for conservation of π‐spin population. Consistent values of the spin polarization parameters QN, QNCN, QHCH, and QHCCH3, but not of QHNH, were obtained virtually independently of calculated spin populations. Experimental and calculated π‐spin populations have been compared for the N‐protonated azaaromatic radicals from this and other work. There is no correlation between the NH proton coupling constant and the experimental π‐spin population on the nitrogen atom in substituted N‐hydropyridinyl radicals. The non‐transferability of the McConnell‐type parameter QHNH is attributed to a contribution of the out‐of‐plane vibration of the NH proton.
Trans/cis photoisomerization of 4‐stilbenecarboxylate coordinated to rhodium (III) and iridium(III)
Authors: Vogler Arnd , Kern Alfred 
Published: September 2012

AbstractThe electronic absorption spectra of trans‐4‐stilbenecarboxylic acid HTSC, its sodium salt NaTSC, [Rh(NH3)5TSC]2+, and [Ir(NH3)5TSC]2+ dissolved in different solvents, all show a nearly identical long wavelength absorption band at 319 nm. This band is assigned to the first spin‐allowed (So → S1)ππ* transition of TSC− and appears as an isolated intraligand chromophore in the complexes. Whereas HTSC and TSC− emit a fluorescence, this emission is completely quenched in the complexes. Not only HTSC, but also [Rh(NH3)5TSC]2+, and [Ir(NH3)5TSC]2+ undergo trans/cis photoisomerization of the stilbene moiety upon So → S1 intraligand excitation. While the S1 state of the free ligand is assumed to initiate the isomerization, the results support the first triplet (T1) of the coordinated TSC− as the photoactive excited state. In the complexes, the heavy metals seem to induce S1 → T1 intersystem crossing.
Depolarized rayleigh scattering: Orientational correlation functions of acetonitrile and carbon disulfide
Authors: Langer H. , Versmold H. 
Published: September 2012

AbstractDepolarized Rayleigh scattering from acetonitrile and carbon disulfide has been studied in the temperature range from — 40 °C to 74.5°C and from −40°C to 33.5° C, respectively. Orientational correlation functions, cross angular momentum‐orientation correlation functions, and memory functions have been calculated and are compared with J‐diffusion model predictions. At short times the J‐diffusion model gives a poor description of the experimental correlation functions. It is concluded that a more complicated memory of the dynamical state during the collision than the J‐diffusion assumption of a random walk in angular momentum space is necessary for an adequate description of the molecular reorientation at short times in these liquids.
Untersuchungen zur Reaktion von Wasserstoffatomen mit Dimethyläther, Diäthyläther und tert. Butyl‐Methyl‐Äther in der Gasphase
Authors: Faubel C. , Hoyermann K. , Ströfer E. , Wagner H. Gg. 
Published: September 2012

AbstractDie Reaktionen von H‐Atomen mit Dimethyläther, Diäthyläther und tert. Butyl‐Methyläther wurden zwischen 250 K und 620 K in Strömungssystemen verschiedener Oberflächenbeschaffenheit und verschiedenen Durchmessers untersucht. Die Konzentrationsmessungen wurden mit Elektronenspinresonanz, Massenspektrometrie und Gaschromatographie ausgeführt. Die Geschwindigkeitskonstante k des Elementarschrittes H + CH3OCH3 → Produkte ergab sich in Arrhenius‐Darstellung zumagnified imageBei der Reaktion H + (C2H5)2O → Produkte wurde die Geschwindigkeitskonstante des Primärschrittes in Arrhenius‐Darstellung zumagnified imagebestimmt. ‐ Für die Reaktion H + (CH3)3COCH3 kann eine obere Grenze für die Geschwindigkeitskonstante des Einleitungsschrittes angegeben werden:magnified imageDer Einleitungsschritt der beiden ersten Reaktionen lautetmagnified imageEin Gesamtmechanismus, der die beobachteten Produkte befriedigend erklärt, wird diskutiert.
Schwingungsenergiefluß in Methylisocyanid
Authors: Kleinermanns C. , Wagner H. Gg. 
Published: September 2012

AbstractDer Schwingungsenergiefluß in CH3NC wurde mit Hilfe der laserinduzierten Fluoreszenz und der Messung der absorbierten Energie nach Anregung der v4‐C‐N‐Streckschwingung untersucht. ‐ Die Anregung der C‐H‐Streckschwingungen v1, v5 und der CH3‐Deformationsschwingungen v3, v6 dauert ca. 15, die der N = C‐Streckschwingung v2 etwa 8 Stöße. Fluoreszenzen der 2 v4‐Schwingung und der v2 + v8‐, v4 + v6‐Kombinationsschwingungen wurden ebenfalls gefunden. ‐ Ein Schema für den Schwingungsenergiefluß in CH3NC wird vorgeschlagen.
A kinetic model for reppe synthesis in dimethyl formamide
Authors: Ghosh S. , Hugo P. 
Published: September 2012

AbstractInvestigations were undertaken on the reaction between formaldehyde and acetylene in DMF using supported copper acetylide catalyst in a stirred reactor. It was found that the reaction is mostly chemically controlled below 100°C. The kinetic modelling of the reactor was undertaken at temperatures below 100°C. The experimental data fits adequately to the proposed model assuming a surface reaction between adsorbed acetylene and formaldehyde in the liquid phase.
The viscosity of three polar gases
Authors: Kestin J. , Wakeham W. A. 
Published: September 2012

AbstractThe paper reports on new, accurate measurements of the viscosity of three polar gases: nitrous oxide (N2O), trichlorofluoromethane (CCl3F) and chlorodifluoromethane (CHClF2). The measurements were performed at atmospheric pressure in the temperature range 27.5–200°C, and the accuracy of the reported viscosities is estimated to be one of ± 0.2%. ‐ It is shown that the results can be represented by the extended law of corresponding states developed by Kestin, Ro, and Wakeham, despite the polar nature of the gases. The scaling factors σ and ε which secure the best representation of this kind are determined. That the three polar gases can be included in a correlation scheme developed originally for non‐polar gases is shown to be due to the relative weakness of the dipole‐dipole interaction term in their intermolecular potentials.
Messungen zur Hochtemperaturpyrolyse von Äthan
Authors: Roth P. , Just Th. 
Published: September 2012

AbstractDurch direkte Messung des zeitlichen Verlaufes der H‐Atomkonzentration in der Reaktionszone hinter Stoßwellen konnte in Gemischen aus Argon mit geringen relativen Konzentrationen an C2H6(1 ÷ 50 ppm) die Geschwindigkeitskonstante der Reaktion magnified image in einem Temperaturbereich 1650 ≤ T ≤ 2100 K direkt bestimmt werden. Durch Computersimulation gelang es, für die Geschwindigkeitskoeffizienten der Einleitungsreaktionen des thermischen C2H6‐Zerfalles magnified image aufgrund von H‐Atommessungen für Temperaturen T > 1420 K plausible Wertepaare zu bestimmen. Die beiden Koeffizienten k1 und k2 sind unter unseren Bedingungen nicht unabhängig voneinander meßbar. Die Gesamtdichten, bei denen die Versuche ausgeführt wurden, lagen zwischen 1,7 · 1018 und 2,3 · 1019 cm−3.
Adsorption of adenine at the mercury/water interface. Effects of pH and ionic strength
Authors: Katz Michael , Cummings Timothy E. , Elving Philip J. 
Published: September 2012

AbstractThe adsorption of adenine at the mercury/aqueous solution interface has been examined by phase‐selective a. c. polarography. Surface charge, surface tension and adsorption isotherms have been derived from the capacity curves. At all pH, adenine molecules are adsorbed in a flat orientation due to specific π‐orbital interaction, which, in acidic media, predominates over electrostatic repulsion between protonated adenine and positively charged electrode. The extent of adsorption increases with pH in Mcllvaine buffer (pH 2.6 to 7.2); it is less in pH 9.0 carbonate buffer than in pH 7.2 Mcllvaine buffer. With increasingly negative electrode potential or charge, the surface excess of adenine steadily decreases; adenine is not adsorbed negative of ‐1.6V. There is neither potential‐ nor surface‐charge‐dependent reorientation beyond about ‐ 1.1 V; a concentration‐dependent‐reorientation occurs before monolayer coverage is complete. Adsorption can be described by a Frumkin isotherm with an interaction factor corresponding to attraction between adsorbed molecules for potentials positive of ‐0.7 V at pH 7.2 and ‐ 0.5 V at pH 9.0. Repulsion between adsorbed molecules at pH 3.8 implies that protonated adenine is present on the surface. The standard free energy of adsorption varies from ‐ 29 to ‐ 38 kJ/mol.
Substitution reactions of beryllium(II) ion in mixed solvents III. Beryllium sulphate complexes in water‐dimethylsulphoxide mixtures
Authors: Devia D. H. , Strehlow H. 
Published: September 2012

AbstractUsing conductivity as well as pressure jump relaxation measurements the thermodynamic and kinetic behaviour of BeSO4in water‐dimethylsulphoxide (DMSO) mixtures has been studied. The existence of a rather stable Be(SO4)2−2complex (KD= 400 atxDMSO= 0.392) was established in mixtures of DMSO mole fraction larger than about 0.3. Up to five relaxation processes were observed in some of the mixtures. Whereas only one relaxation process is attributed for the substitution of water molecules by SO2−2in the solvation sheath of the Be2+ion the corresponding substitution of DMSO occurred with different rates depending on the composition of the species Be(DMSO)i(H2O)2+4 ‐i. The analysis of the relaxation data not only explained the relaxation times but also sign and magnitude of the relaxation amplitudes. The behaviour of the system is understood in terms of the poor solvating power of DMSO (and of DMSO · 2H2O) for the sulphate anion.