Zur Bestimmung von Doppelbindungsanteilen in Polyolefinen durch FTIR-Analyse

Zusammenfassung Im Rahmen von kinetischen Untersuchungen zur Olefinpolymerisation mußten geringe Doppelbindungskonzentrationen in Polymeren mit stark differierender Struktur und Konsistenz exakt bestimmt werden. Die quantitative FTIR-Analyse der unterschiedlichen Doppelbindungen wurde dadurch optimiert, daß die Substanzen in der Schmelze vermessen wurden, die IR-Bandengruppen mittels rechnerisch erzeugter Bandenprofile entzerrt und die integralen Absorbanzen der olefinischen Banden bestimmt wurden. Die durch Analyse von Modellsubstanzen ermittelten integralen Extinktionskoeffizienten, bezogen auf 1 cm Schichtdicke und auf eine Doppelbindung pro 10⁵ C-Atome liegen bei 0.93 (Vinyl), 0.95 (trans-Vinylen) und 1.04 (Vinyliden).

---

Determination of double bond concentrations in polyolefines by FTIR analysis

Summary In the course of kinetic investigations on olefin polymerization it was necessary to measure the concentration of double bonds in polymers with very variable structure and consistency as exactly as possible. For that purpose, the quantitative FTIR-analysis of the different double bonds was optimized by measuring the melted substances, by analysis of the groups of IR-bands with the help of computer generated band profiles and by determing the integral absorbances of the olefinic bands. The integral extinction coefficients of the vinyl, the trans-vinylene and the vinylidene double bonds were determined by the analysis of model compounds and values of 0.93, 0.95 and 1.04, respectively, for a sample of 1 cm thickness with one double bond per 10⁵ carbon atoms were obtained.

     

Untersuchungen über die Konzentration von D2O in natürlichem Eis. II

Ohne Zusammenfassung     

Über einen neuen aromatischen Kohlenwasserstoff C24H18 aus Erdölen

Ohne Zusammenfassung     

Is Nd2−xCexCuO4 an electron-superconductor?

We present results from electron energy-loss spectroscopy on Nd_2–xCe_xCuO₄. There is no clear evidence for Cu¹⁺ but for holes at the oxygen sites. The valency of Ce is found to be close to 3.4. Thus our results do not corroboraten-type superconductivity in this compound.     

Large tunable Rashba spin splitting of a two-dimensional electron gas in Bi2Se3

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi(2)Se(3) from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.     

Exploiting the time-reversal operator for adaptive optics, selective focusing, and scattering pattern analysis

We report on the experimental measurement of the backscattering matrix of a weakly scattering medium in optics, composed of a few dispersed gold nanobeads. The decomposition of the time-reversal operator is applied to this matrix and we demonstrate selective and efficient focusing on individual scatterers, even through an aberrating layer. Moreover, we show that this approach provides the decomposition of the scattering pattern of a single nanoparticle. These results open important perspectives for optical imaging, characterization, and selective excitation of nanoparticles.     

Determination of metal additives and bromine in recycled thermoplasts from electronic waste by TXRF analysis

A new method for analysis of metal additives in recycled thermoplasts from electronic waste was developed, based on dissolving the samples in an organic solvent and subsequent analysis of the corresponding solutions or suspensions by total-reflection X-ray fluorescence spectroscopy (TXRF). The procedure proved to be considerably less time consuming than the conventional digestion of the polymer matrix. Additives containing Ti, Zn, Br, Cd, Sn, Sb, and Pb were analyzed in a hundred randomly selected samples from recycling, which provided an overview of the range of elemental concentrations in thermoplasts utilized for consumer electronics. The results were validated independently by instrumental neutron activation analysis (INAA), subsequent regression analysis confirmed the trueness of the chosen approach. Received: 7 February 2000 / Revised: 25 February 2000 / Accepted: 1 March 2000     

Dielectric function of YBa2Cu3O7-δ between 50 meV and 50 eV

Electronic excitations with polarization parallel to the CuO₂-planes in single-crystalline YBa₂Cu₃O₇ and YBa₂Cu₃O₆ have been investigated by optical reflectance and by highenergy electron energy-loss spectroscopy in transmission in the energy ranges from 50 meV to 6 eV and 0.2 eV to 150 eV, respectively. From a combination of these experimental data the dielectric function, the reflectivity and the optical conductivity have been obtained in a wide energy range. The observed spectra are interpreted in terms of optical phonons, free-carrier absorption, transitions across the charge-transfer gap, further interband transitions, low-lying core-level excitations, excitonic transitions and valence conservingd-d transitions within the Cu 3d shell combined with O 2p intraband transitions. The charge carrier plasmon and the 4 eV-excitation in YBa₂Cu₃O₆ show quadratic dispersions in momentum transfer. From the dispersion constant of the plasmon a mean value of the Fermi velocity of the charge carriers parallel to the CuO₂ planes has been derived.