Zum mechanismus des strahlenchemischen abbaus von polytetrafluorethylen

The present work studies the changes in polymer structure and the mechanism of the decomposition of polytetrafluoroethylene resin (PTFE) exposed to high energy radiation (electron beam). Spectroscopic and kinetic observations are used to interpret the degradation process. For the first time the decomposition of PTFE has been carried out on a preparative scale and new results obtained by analysing the degradation products. The radiation-induced degradation of PTFE is accompanied by thermal degradation under certain irradiation conditions. This is due to an increase in temperature of the polymer caused by retardation of highly accelerated electrons (heat accumulation effect).The kinetics are discussed in terms of the reactions and recombination of radicals produced by high-energy radiation both in the polymer melt and the polymer surface. These are related to the overall rate of decomposition.The primary radicals formed by decomposition of PTFE in an inert atmosphere (N₂, Ar) react to produce perfluorinated alkanes and alkenes. In the presence of reactive gases the decomposition fragments originated will react rapidly; e.g. if oxygen is present in the reactive area the radicals form perflourinated peroxyl and oxyl radicals which finally stabilize themselves by CC-scission to perfluorocarbon acid fluorides and carbonyldifluorides.     

Quantitative analysis of small pharmaceutical drugs using a high repetition rate laser matrix-assisted laser/desorption ionization source

In this work, a high repetition rate laser matrix-assisted laser desorption/ionization (MALDI) source is studied on a quadrupole-time-of-flight (QqTOF) and a triple quadrupole (QqQ) mass spectrometer for rapid quantification of small pharmaceutical drugs. The high repetition rate laser allows an up to 100-fold higher pulse frequency as compared with regular MALDI lasers, resulting in much larger sample throughput and number of accumulated spectra. This increases the reproducibility of signal intensities considerably, with average values being around 5% relative standard deviation after taking into account the area ratio of the analyte to an internal standard. Experiments were conducted in MS/MS mode to circumvent the large chemical background due to MALDI matrix ions in the low mass range. The dynamic range of calibration curves on the QqTOF mass spectrometer extended over at least two orders of magnitude, whereas on the QqQ it extended over at least three orders of magnitude. Detection limits ranged from 60-400 pg/microL on the QqTOF and from 6-70 pg/microL on the QqQ for a series of benzodiazepines. The benzodiazepine content of commercial pill formulations was quantified, and less than 5% error was obtained between the present method and the manufacturer's certified values. Furthermore, a high sample throughput was achieved with this method, so that a single MALDI spot could be quantitatively scanned in as little as 15 s, and an entire 96-well MALDI plate in 24 min.     

Effective Hamiltonian for fluid interfaces

Based on a microscopic theory of inhomogeneous fluids we derive a non-Gaussian and nonlocal effetive Hamiltonian of a liquid-vapor interface. A partial resummation of a gradient expansion yields terms proportional to the area as well as to the Gaussian and the square of the mean curvature of the interface. For van der Waals fluids the gradient expansion breaks down and leads to a singularity in the momentum dependent surface tension. The nonlocal Hamiltonian and various approximations thereof are compared quantitatively.     

Messung von Rockingkurven eines polierten CaF2-Kristalls

It is reported on the measurement of rocking-curves of a polished CaF₂ crystal after stepwise removing of thin surface-layers. The discussion leads to a completion of the Raethermodel of polished surfaces by assuming an elastic deformed region under the mosaic-crystalline layer produced by the polishing process.     

Three-dimensional linearised Euler model simulations of sound propagation in idealised urban situations with wind effects

A three-dimensional numerical time-domain model based on the linearised Euler equation is applied to idealised urban situations with elongated, isolated buildings beside a straight street with sound emissions. The paper aims at the investigation of principle relationships between the source-receiver geometry (street and building facades) and sound propagation under the consideration of ground and wind. By applying cyclic lateral boundary conditions for either one or both horizontal co-ordinates, two different idealised urban environments were considered: a single street and parallel streets. Numerical experiments were performed to elaborate the effects of different roof types, ground properties, wind flow, and turbulence in both urban environments with the focus on the back facades (‘quiet’ sides) of the buildings. As a result it was found that the back facades of flat-roof buildings are quieter than those of hip roof buildings despite equal cross-cut areas. The wind effect (resulting in quieter upwind and louder downwind facades) is more pronounced for hip-roof buildings. In the case of parallel streets upwind facades are slightly louder than downwind facades because they are simultaneously exposed to downwind propagating sound from the next parallel street.     

Low temperature synthesis of ITO nanoparticles using polyol process

A low temperature synthesis technique to prepare indium tin oxide (ITO) nanoparticles by the polyol process is proposed. On examining the phase formation of ITO nanoparticles in polyols and alcohols such as ethylene glycol, trimethylene glycol, and 1-heptanol, it was found that ITO nanoparticles could be synthesized directly without any post--annealing treatments at 175 °C in 1-heptanol. The morphology of the particles is influenced by the type of polyol. The composition of Sn in the ITO system could be easily controlled by simply varying the In/Sn precursor ratio in 1-heptanol. The low temperature synthesis method has enabled the formation of highly crystalline ITO nanoparticles with diameters less than 25 nm even at annealing temperatures as high as 700 °C.     

The effects of surfaces on dynamic critical behavior

The field theoretic renormalization-group approach for the study of critical behavior near free surfaces is generalized to dynamic properties. Time-dependent Ginzburg-Landau models with nonconserved or conserved order parameters — semi-infinite generalizations of the so-called modelsA andB — are considered. The asymptotic behavior of response and correlation functions is analyzed at the ordinary and special transitions in 4-? dimensions, and dynamic scaling laws for surface quantities are obtained. It is shown that the critical exponents can be expressed entirely in terms of static bulk and surface exponents andz, the dynamic bulk exponent. The critical exponents for the leading frequency, temperature and momentum singularities of the surface two-spin correlation function at the ordinary transition differ appreciably from the corresponding bulk analogues. In addition, the shape function which describes its frequency dependence differs qualitatively from the one of the bulk correlation function.