bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion and Thermodynamic Properties of Polyvinylchloride‐ and Polymethylmethacrylate‐Solutions
Authors: Roßkopf G. , Polawka J. , Rehage G. , Borchard W. 
Published: September 2012

AbstractDiffusion coefficients of different polyvinylchloride (PVC)‐samples have been measured in solvents of varying quality up to polymer concentrations which were still experimentally tractable. The samples differed by polymerization conditions and thus by the stereospecific microstructure. The thermodynamic factor of the diffusion coefficient was determined osmotically and the mobility of the polymer was calculated. In the semi‐dilute concentration range, the diffusion coefficient does no more depend on the molar mass of the polymer but is strongly influenced by the stereospecific microstructure of the PVC. The concentration dependence of the diffusion coefficients in all systems under investigation can be described by the relationship D ∼ ρα2. This was predicted by a new theory of De Gennes.
Absolute Molekulargewichte und molekulare Heterogenitäten aus der Sedimentationsgeschwindigkeit
Authors: Woblschiess R. , Elgert K. F. , Cantow H.‐J. , Bantle S. 
Published: September 2012

AbstractIm Zusammenhang mit der Bestimmung absoluter Molekulargewichte in der Ultrazentrifuge auf der Basis der experimentellen Lösung der Lammschen Differentialgleichung werden drei Verfahren bezüglich der Ermittlung des Diffusionskoeffizienten beschrieben. Ein Lösungsweg zur Ermittlung absoluter Molekulargewichtsverteilungen aus den Sedimentationsdiagrammen wird vorgeschlagen.
Techniques for the Measurement of the Gas Permeability in High Polymers
Authors: Schuch H. 
Published: September 2012

AbstractThe knowledge of the barrier properties of high polymers is necessary e. g. for the application in packaging. This requires reliable and fast permeability measurement techniques. During the last few years the traditional setup using mercury manometers as a gas detector has been replaced, e. g. by capacitance manometers with higher resolution and accuracy, by detectors used in gaschromatography (thermal conductivity detector and flame ionization detector), a detector specific for H2O and electrochemical detectors specific for O2. Sensitivity, response time and calibration procedure of different methods are compared. For practical applications the electrochemical detector specific for O2 seems to be the best compromise.
Dynamical Scaling in Polymer Solutions Investigated by the Neutron Spin Echo Technique
Authors: Richter D. , Hayter J. B. , Mezei F. , Ewen B. 
Published: September 2012

AbstractChain dynamics in polymer solutions was investigated by means of the recently developed neutron spin echo spectroscopy. — By this technique, it was possible for the first time to verify unambiguously the scaling predictions of the Zimm model in the case of single chain behaviour and to observe the cross over to many chain behaviour. The segmental diffusion of single chains exhibits deviations from a simple exponential law, indicating the importance of memory effects.
Inelastische Lichtstreuung von Polymeren in Lösung, Schwerpunktstransport und Polymolekularität
Authors: Raczek J. , Meyerhoff G. 
Published: September 2012

AbstractMittels der inelastischen Lichtstreuung wurden zwei Polystyrol‐Präparate mit M = 200000 und 670000 und vier aus diesen Substanzen zusammengesetzte Mischungen in Toluol bei 20 °C vermessen. Die im Winkelbereich 11° ≤ ϑ≤40° aufgenommenen Autokorrelationsfunktionen wurden dazu benutzt, verschiedene Bestimmungsverfahren von z‐Mitteln von Potenzen des Reibungs‐ und Diffusionskoeffizienten zu testen. Experimentell gelang es bei den Mischungen lediglich die ersten Potenzen dieser Größen zu ermitteln. Diese werden zusammen mit den Reibungs‐ bzw. Diffusionskoeffizienten der einzelnen Komponenten zur Charakterisierung der Parameter der Molekulargewichtsverteilung der Mischungen benutzt.
Charge Transport in Polydiacetylenes
Authors: Spannring W. , Bässler H. 
Published: September 2012

AbstractThe photoconductivity action spectrum of PTS consists of an intrinsic region in the blue and an extrinsic region in the red. The latter is due to defect excitation followed by ionization. The absorption profile is Gaussian with a width of 0.24 eV and a peak at hw = 1.75 eV. A kinetic analysis shows that defects must also be responsible for darkconductivity although its activation energy is about half of the band‐gap. No indication of carrier generation via host excitons is found.
Charge Carrier Transport in Oxidized Polyethylene
Authors: Fischer Peter , Röhl Peter 
Published: September 2012

AbstractThe conduction currents of low‐density polyethylene containing additionally introduced C = O‐groups pass through maxima when stressed by a constant de‐voltage. This maximum is shifted to shorter times after application of the electric field with increasing temperature and field strength. The normalized current/time relationships are identical and they may be described in terms of a hopping process with a distribution of event times according to Scher/ Montroll. The shift of the maximum with temperature and independently the absolute current density both yield a thermal activation energy of 1.1 eV. This value is not to be understood as a mean activation energy characterizing the relaxation or event time spectrum, but represents essentially the depth of the dipolar traps (C = O‐groups) out of which the charge carriers have to be activated prior to their motion in the electric field.
An NMR investigation of anion and cation diffusion in solid lithium hydride
Authors: Oei Y. S. , Richtering H. , Wiemhöfer H. D. 
Published: September 2012

AbstractNuclear spin‐lattice relaxation rates and nmr absorption linewidths of 1H and 7Li in solid LiH have been measured up to 620 C. For both species motional narrowing is observed which is shifted under the influence of MgH2 additions in opposite directions. Above 300°C spin‐lattice relaxation is exclusively determined by dipole interactions originating from translational diffusion. The calculated peak relaxation rates are in excellent agreement with the observed ones. ‐ For LiH containing Li2O or small additions of MgH2, the mean jump frequency of hydrogen by far exceeds that of lithium in the whole temperature range. Between 400 and 620°C for LiH in equilibrium with Li2O the mean jump frequencies are given bymagnified imageFor the “pure” material investigated (with an estimated oxygen content of 300 ppm) the activation energy for v(H) is (0.97 ± 0.07) eV. The numerical values of v(H) and v(Li) are not very sensitive to variations in oxygen content. With large additions of MgH2 (> 1000 ppm), v(Li) by far exceeds v(H) in the whole temperature range; the activation energy for v(Li) above 250°C is 0.55 eV in agreement with results derived from conductivity data for LiH doped with MgH2. — For LiH without MgH2 additions, the nmr results are in agreement with diffusion data but deviate from conductivity measurements in temperature dependence and in numerical value. — The present results are interpreted on the basis of Schottky disorder with an enthalpy of formation of 2eV and migration enthalpies of 0.3–0.4eV and 0.55 eV for H− and Li+ ions, respectively. Strong association between O2− impurities and anion vacancies must be assumed. With O2− impurities present, the H− jumps by means of associated vacancies probably play an important role for the diffusion process. For this type of diffusion a nmr correlation factor is to be expected which differs by a factor of 0.5 from the corresponding correlation factor for tracer diffusion.
Kinetics of the topochemical solid‐state polymerization of diacetylenes as studied by a flash photochemical experiment
Authors: Leyrer R. J. , Wegner G. 
Published: September 2012

AbstractThe kinetics of an organic solid‐state reaction is studied by a flash‐photochemical experiment. A set‐up is described which allows the detection of a photoreaction monitoring the change in reflectivity of a polycrystalline sample reacting upon photoinitiation with a laser light pulse. The time scale of the measurement extends from 5 ns to several hundred ms. The topochemical polymerization of two different diacetylenes is investigated measuring the formation of the polymer as a function of time after the initiating light pulse of wavelength λ = 337.1 nm. The first polymer is formed after a timelag of 300 ns. The total conversion per light pulse is less than 1 percent. The time conversion curve is described by an exp √t‐law for virgin samples suggesting a kinetic model which includes a strongly scattering random walk of photo‐excited states to randomly distributed reaction centers as the rate determining factor of the photopolymerization. The average life time of the photoexcited state is 758.5 ps. The overall quantum yield of the polymerization is approximately 10 and the frequency of addition of a monomer unit to a reactive chain end is va, ≤ 3.3 · 107 s−1.
Photoelectrochemical study on copper phthalocyanine films
Authors: Minami Nobutsugu , Watanabe Tadashi , Fujishima Akira , Honda Ken‐Ichi 
Published: September 2012

AbstractCopper phthalocyanine (CuPc) films vacuum‐deposited on SnO2 electrodes develop photocurrents by illumination with monochromatic light. Their action spectra reflect the absorption spectrum of the CuPc film. The effect of the thickness of the CuPc film and the illumination direction dependence of photocurrent action spectra are observed. Anodic photocurrents arise from excitons generated near the SnO2/CuPc interface and are consistent with the ordinary dye sensitization scheme. Cathodic photocurrents are attributable to excitons which are generated and dissociate in the bulk of CuPc. Hydroquinone, p‐quinone, and O2 act as a reducing or an oxidizing agent. p‐Quinone interacts with CuPc preferentially. Transient behaviors and open circuit photovoltages are also discussed.
The triplet state in trans → cis‐photoisomerization of thioindigo
Authors: Karstens T. , Kobs K. , Memming R. 
Published: September 2012

AbstractThe triplet state processes in thioindigo have been investigated with respect to the mechanism of the trans → cis photoisomerization by laser flash photolysis. According to our experimental results the intersystem crossing takes place from the trans singlet to the trans triplet. This is also the only transient, which is detected spectroscopically. An activation energy barrier between the trans‐ and a twisted triplet determines the internal rotation. The twisted triplet decays nonradiatively to the cis and trans groundstates. A model for the mechanism of the trans → cis photoisomerization is proposed. — Preliminary results for the cis → trans photoisomerization indicate an internal rotation in the excited singlet state to a transoid configuration followed by intersystem crossing to the trans triplet from which the molecule decays into the ground state.
1H and13C NMR‐spectroscopic studies on acetone exchange of nickel and magnesium ions
Authors: Dickert F. L. 
Published: September 2012

AbstractWith13C PFT‐NMR‐spectroscopy it is possible to determine the acetone exchange rate of magnesium ions. This was done with nickel ions using both1H and13C NMR‐spectroscopy. At low enough temperatures separate signals can be obtained for the coordinated acetone molecules. ‐ The data for the acetone exchange of the nickel ions confirms an earlier theory concerning solvent exchange rates as function of donicity.
Nuclear magnetic relaxation studies of benzene in ultrapure NaX zeolite
Authors: Lechert H. , Wittern K. P. 
Published: September 2012

AbstractIn a sample of NaX zeolite with very low paramagnetic impurity the temperature behaviour of the proton relaxation timesT1andT2has been studied for different coverages of benzene, 1,3,5‐trideuterobenzene and different mixtures of benzene and hexadeuterobenzene. For temperatures above 200 K,T1is determined by the interaction of the protons with the residual paramagnetic impurities, which allows the estimation of translational diffusion coefficient of about 10−7cm2s−1at room temperature. From the frequency dependence of theT1‐minimum average activation energies of 15 kJ/mol can be drawn for intermediate and 34 kJ/mol for full coverage. The data for the deuterated samples give the intra‐ and the intermolecular part and the contribution of the interaction with the paramagnetic impurities to the longitudinal relaxation rate can be drawn below 200 K. — From these results for 3.6 molecules in a large cavity a mechanism of motion can be drawn the freedoms of which lie in the range of an isotropic rotational reorientation. For 5.3 molecules in a large cavity below 220 K only a rotation around the sixfold axis is observed. From the results a model of the mobility mechanism to all coverages is developed.
Beziehungen zwischen der Kompressibilität und der Druckabhängigkeit der Dielektrizitätskonstante. Wasser‐Acetonitril‐Mischungen bei 25°C und Drücken bis 850 bar
Authors: Lührs C. , Schwitzgebel G. 
Published: September 2012

AbstractZur simultanen Messung der Dichte und der DK eignet sich ein Schutzringkondensator mit einem Trennkolben, dessen Verschiebung bei Druckänderungen (p< 850 bar) sehr genau registriert werden kann. Die Meßergebnissed(p) und ε(p) von Wasser‐Acetonitril‐Mischungen lassen sich durch quadratische Druckpolynome darstellen. In einer separaten Auswertung, die eine bessere Extrapolation von Elektrolytvolumina anstrebt, werden drei verschiedene Formeln, die den Zusammenhang zwischen der Kompressibilität und der Druckabhängigkeit der DK wiedergeben, auf Genauigkeit und Invarianz geprüft. Die Vorzüge einer Kombination der Tait‐Gleichung mit der Gleichung von Owen und Brinkley werden diskutiert.
Untersuchungen zur Temperaturabhängigkeit der Eigenschaften von Elektrolytlösungen II. Bestimmung der Leitfähigkeit über einen großen Temperaturbereich
Authors: Wachter R. , Barthel J. 
Published: September 2012

AbstractEs wird eine Meßanordnung zur genauen Bestimmung (Präzision: 0,01%, Genauigkeit: 0,02%) der Temperatur‐ und Konzentrations‐abhängigkeit der Elektrolytleitfähigkeit über einen großen Temperaturbereich (ΔT > 100 K) beschrieben. Mittels einer Methode isologer Schnitte werden A‐c‐T‐Diagramme von Elektrolytlösungen erstellt, aus denen die Koeffizienten Λx, J1 und J2 der vollständigen Leitfähigkeitsgleichung und der Assoziationsgrad (1 ‐ α) der Elektrolyte gewonnen werden. Die Auswertung der Bestimmungsgrößen J1 = J1 (R1), J2 = J2 (R2) und α = α (R) liefern Abstandsparameter, R1 = R2 = R, mit denen sich Aussagen über die kurzreichenden Ion‐Ion‐ und Ion‐Lösungsmittel‐Wechselwirkungen in der Lösung machen lassen.
Photoreactions of Small Organic Molecules VII Photoionization Studies on the Ion‐Pair Formation of the Fluorochloromethanes CF2Cl2, CF3Cl, and CFCl3
Authors: Schenk H. , Oertel H. , Baumgärtel H. 
Published: September 2012

AbstractIon‐pair processes were studied applying photoionization mass spectroscopy in the photon energy range 8 — 30 eV. The investigation of the fluorochloromethanes CF2Cl2, CF3Cl, and CFCl3 revealed that the fragments F−, CF−, Cl−, CCl−, CF−2, FCl−, CFCl−, Cl−2, CF−3, CF2Cl−, and CFCl−2 are formed in unimolecular reactions. The Cl−‐yield of CFCl3 is strongly influenced by the attachment of photoelectrons. The ion efficiency curves of the halides show that a variety of ion‐pair processes leads to the formation of F− and Cl−. The interpretation has been confirmed by the corresponding efficiency curves of the positive ions.
NMR Spectra of the [AX2]2and [A[X]2]2Types: The X Transitions when |JAX| is Large, as in the Case of Tetrafluorodiazadiphosphetidines
Authors: Harris Robin K. , Wazeer Mohamed I. M. 
Published: September 2012

AbstractExplicit expressions for X transition frequencies in NMR spectra of [A[X]2]2spin systems are derived for the case where one of the (A. X) coupling constants is much larger in magnitude than any of the other couplings, as is commonly encountered for molecules containing PF2groups. The spectra to be expected are compared with those for the corresponding magnetic equivalence [AX2]2case. Emphasis is placed on the determination of relative signs of coupling constants, and examples of spectra for fluorinated diazadiphosphetidines are discussed.
Neuere Untersuchungen zur Bindung von Ethidiumbromid an DNA 3. Mitteilung: Tetramethylethidiumbromid. Beteiligung von Wasserstoffbrücken an der nicht‐kompetitiven und der kompetitiven Bindung
Authors: Pauluhn Jürgen , Grezes Rene , Zimmermann Herbert W. 
Published: September 2012

AbstractDie Bindung des Farbstoffs Tetramethylethidiumbromid TME (2,7‐Bis(dimethylamino)‐9‐phenyl‐10‐äthyl‐phenanthridinium‐bromid) an Kalbsthymus‐DNA wurde absorptionsspektroskopisch untersucht. Der Farbstoff kann durch Na⊕‐ und Mg2⊕‐Ionen aus seiner Bindung an DNA vollständig verdrängt werden. Er geht nur eine kompetitive Bindung ein (Ks2 = 1,6 · 105 m−1), die gegenüber Ethidiumbromid E (Ks2 ≈︁ 5,6 · 105 m−1) deutlich geschwächt ist. Die nicht‐kompetitive Bindung von TME an DNA war nicht nachweisbar (Ks1 ∼ 0). Dieser Befund zeigt, daß Ersatz von Aminogruppen (E) durch Dimethylaminogruppen (TME) wesentliche Veränderungen im Bindungsverhalten verursacht. Er spricht für die Beteiligung von Wasserstoffbrücken an der nicht‐kompetitiven und der kompetitiven Bindung von E an DNA.
High‐Pressure High‐Resolution Nuclear Magnetic Resonance III: Concentration Dependence of ΔV≠ and ΔG≠ for the Rotation of the Dimethylaminogroup in Aqueous Solutions of Some N, N‐Dimethylamides
Authors: Völkel G. , Lang E. , Lüdemann H.hyphen;D. 
Published: September 2012

AbstractThe concentration dependence of the activation volume ΔV≠ and the free activation enthalpy ΔG≠ for the inversion of the dimethylamino‐group has been determined in a series of dimethylamides in aqueous solution by high pressure HRNMR (pmax = 150 M Pa). The compounds studied are the N, N‐dimethylamides of formic‐, acetic‐, propionic‐, isobutyric‐, valerianic‐ and benzoic acid. In all nonaqueous solvents ΔV≠ is only slightly concentration dependent, ΔV≠ being in the range of +10 ± 2 cm3·mol−1. For all compounds studied, ΔV≠ in the dilute aqueous solutions (x ≥ 0.9) decreases very rapidly to values around + 2 cm3·mol−1. It is attempted to explain this decrease by the formation of an open hydration shell around the dimethylaminogroup and to correlate the concentration effects with the hydro‐phobic character of the amides.
Pyrolysis of 1.3.5.7‐Cyclooctatetraene, Semibullvalene, and 1.5‐Dihydropentalene in Shock Waves and in a Flow System (Part I)
Authors: Dudek D. , Glänzer K. , Troe J. 
Published: September 2012

AbstractProduct distributions in the flow system pyrolysis of cyclooctatetraene and dihydropentalene have been measured in the temperature range 700–900 K. Furthermore the thermal reactions of cyclooctatetraene leading to the isomer dihydropentalene or the decomposition products benzene + acetylene have been studied in shock wave experiments. Rate constants of the two parallel reaction channels have been determined in the temperature range 1000–1400 K. By the same technique, the isomerizations of dihydropentalene to styrene (T = 1200–1600 K) and of semibullvalene to dihydropentalene (T = 740–900 K) have been investigated; rate constants of these reactions have also been determined. The thermal rate data in particular of the reactions of cyclooctatetraene are compared with results of our study of reactions of photoactivated cyclooctatetraene molecules (Part II) by means of unimolecular reaction rate theory.
Thermochemistry, Kinetic Energy, and Compton Profiles of the Electrons in Molecules and Solids
Authors: Weyrich Wolf 
Published: September 2012

AbstractAs a consequence of the virial theorem, Compton profiles are connected to the energetics of matter. While the relationship for spherically symmetric and isotropic systems is already known, in this paper the corresponding relations for anisotropic systems such as molecules and solids are presented. The introduction of a tensor τ = (1/2me){pipj} for the kinetic energy of the electrons turns out to be useful, the properties of which are analysed. In order to be able to test the experimental significance, the influence of experimental errors on kinetic‐energy data is investigated. Results for diamond, LiH, LiF, NaF, Be, graphite, and urea are presented and discussed.
ESR‐Untersuchung von Protonenaustauschreaktionen der Radikale N‐Hydropyridinylcarbonsäure‐(4) und N‐Hydropyridinylcarboxylat‐(4)
Authors: Mehnert Michael , Dohrmann Jürgen K. 
Published: September 2012

AbstractESR‐Spektren der kurzlebigen Radikale N‐Hydropyridinylcarboxylat‐(4), HI−, und N‐Hydropyridinylcarbonsäure‐(4), H2I. die durch in‐situ‐Photolyse wäßriger Lösungen von Isonicotinsäure in Gegenwart von Boranmorpholin oder Propanol‐(2) erzeugt wurden, sind bei verschiedenen pH‐Werten gemessen worden. In gepufferter Lösung (KH2PO4/K2HPO4/KCl) bei 4, 5 < pH < 9, 0 wird ein Spektrum erhalten, das pH‐abhängige Aufspaltungen und Linienbreiteneffekte zeigt. Aus der pH‐Abhängigkeit der Aufspaltungen wird ein pKs‐Wert von 6, 57 ± 0, 04 für die Dissoziation des COOH‐Protons bei 25°C und Ionenstärke 2, 0 mol/l bestimmt. Die Analyse der Linienbreiteneffekte ergibt zwei schnelle Austauschreaktionen des COOH‐Protons, in denen die Anionen HPO2‐4 und Isonicotinat als Protonenakzeptoren wirken. Die Geschwindigkeitskostanten für die Hin‐und Rückreaktion bei der Protonenübertragung auf HPO2‐4 sind (1.1 ± 0.3) · 108 1/mol · s bzw. (1.4 ± 0, 5) · 108 1/mol · s und bei der Protonenübertragung auf Isonicotinat (9, 8 ± 3, 2) · 1071/mol · s bzw. (5, 0 ± 1.4) · 109 1/mol · s jeweils bei 25°C und Ionenstärke 2, 0mol/1. Bei 9 < pH < 13 bewirkt der basenkatalysierte Austausch des NH‐Protons in HI− eine Linienverbreiterung. Die Austauschhäufigkeit ist klein im Vergleich zur Frequenz der Hyperfeinkopplung des NH‐Protons. Die Geschwindigkeitskonstante der basenkatalysierten Deprotonierung von HI− ist (8, 5 ± 0, 5) · 1071/mol · s bei 25°C und Ionenstärke 2.0 mol/1. Der pKs‐Wert für die Dissoziation des NH‐Protons ist größer als 13. Ein Spektrum von H2I mit scharfen Linien wird bei pH 5 in wäßriger Lösung mit 50 Vol.‐% Propanol‐(2) erhalten. Linienverbreiterung, Verschmelzen der Dubletts des COOH‐Protons und Linienverschärfung werden in Richtung abnehmenden pH‐Werts beobachtet. Die Linienformeffekte werden durch intermediäre Bildung des protonierten Radikals H3I+ erklärt (pK s < 2), welche zu einem säurekatalysierten Austausch des COOH‐Protons führt. Die Geschwindigkeitskonstante der Protonierung von H2I ist (4, 40 ± 0, 04) · 109 1/mol · s bei 24°C. In allen Fällen wurden die mittleren Austauschlebensdauern der Spezies sowohl mittels der modifizierten Bloch‐Gleichungen als auch mittels Spektrensimulation bestimmt. ‐ pKs‐Werte und Geschwindigkeitskonstanten werden diskutiert. Bildungsenthalpien und Ionisierungspotentiale aus MINDO/3‐Rechnungen und freie Solvatationsenthalpien aus der Born‐Näherung wurden zur Abschätzung der Differenz der pKs‐Werte von H2I und zwei Referenzsäuren (Benzoesäure und protonierte Isonicotinsäure) benutzt. Die Abschätzungen stimmen mit dem Experiment befriedigend überein.