Fabes Forschungs (Germany)

A multi-tip scanning tunneling microscope (STM) specifically designed for charge transport measurements at the nanoscale is described. Complementing the instrument with a versatile measurement electronics creates a powerful tool to give insight into fundamental transport properties at the nanoscale. We demonstrate the capabilities of the instrument by measuring resistance profiles along freestanding GaAs nanowires, by the acquisition of nanoscale potential maps, and by the identification of an anisotropy in the surface conductivity at a silicon surface. Ein Multimeter auf der Nanoskala Wir prasentieren ein Multispitzen-Rastertunnelmikroskop (STM), das speziell fur Ladungstransportmessungen auf der Nanoskala konzipiert ist. Erganzt um eine vielseitige Messelektronik ergibt sich ein leistungsstarkes Instrument, mit dem wesentliche Erkenntnisse uber grundlegende Transporteigenschaften auf der Nanoskala gewonnen werden konnen. Wir demonstrieren die Leistungsfahigkeit dieses Instruments anhand von Messungen des Widerstandsprofiles entlang von freistehenden GaAs Nanodrahten, durch die Aufnahme von Potential-Karten an Nanostrukturen sowie durch die Messung der Anisotropie der Oberflachenleitfahigkeit an Silizium Oberflachen.

Essential oils (EOs) are promising substances to be incorporated in food packaging materials as antioxidant and/or antimicrobial agents in active packaging systems. Once incorporated into the materials, their constituent compounds diffuse through the material. However, there is little information about the diffusion behaviour of EOs in plastics, and this is one of the major drawbacks in the design of active packaging relying on EOs as active agents. This study presents a new method for studying the diffusion of basil, citronella, oregano and rosemary EOs into plastic films. Diffusion assays of EOs from a coated polypropylene (PP) film into a stack of virgin PP films were conducted by the Moisan method using up to 10 layers of PP. Direct quantification of diffused analytes from the plastic sheets was performed by multiple headspace solid phase microextraction–gas chromatography–mass spectrometry. The fitting of experimental data for the main EO components with a Fickian model gave diffusion and partition (between active and virgin PP) coefficients, which are discussed under the light of some intrinsic factors contributing to the diffusion process. The results demonstrate the dependence of diffusion and partition coefficients on the initial concentration of EO components in the coated films, on their molecular weight and on their polarity. In particular, for similar molecular weight and initial concentration, a higher polarity is responsible for a faster diffusion, whereas lower polarity determines the retention of the EO component in the coating layer. Copyright © 2012 John Wiley & Sons, Ltd.

This study carried out migration investigations with different spiked and non-spiked paper and board packaging materials in contact with foodstuffs and food simulants in the temperature range between −18°C and 40°C. The aim was to deepen the understanding of the migration behaviour of target substances in paper and board fibres. Components and contaminants of paper and board with different molecular weight and chemical structure were selected as target migrants. From the kinetic migration studies, diffusion and partition coefficients were derived by using software for modelling migration in multilayer materials. On the basis of these results, for the first time a model for the migration from paper and board into foods and simulants was developed by adapting the validated diffusion model for plastics. In contrast to the migration in plastic materials, where the migrants are solved and homogeneously distributed in the polymer matrix, mass transfer in paper and board is a more complex phenomenon, because the migrants can be adsorbed on the cellulose surface with different strength. The most important finding of the study was that for a correct modelling of the experimental results in many cases paper and board must be regarded as a two-layer system: the main mass of paper and board (B1) defines the core layer with high diffusion rates, and a thin second layer (B2) represents the surface region of the paper and board with decreased diffusion rates due to the slow desorption.

A summary of experimental results from nanoindentation, strain rate-controlled tension, in-situ bending and high pressure torsion on bulk electrodeposited nanocrystalline nickel, focusing on the effects of grain size on the mechanical behaviour and deformation mechanisms is presented. The interaction between dislocations and grain boundaries was locally examined by studying the dependence of nanohardness on grain size and indentation size; this is done by always performing nanoindents in the center of individual grains and by varying the grain size and indentation depth systematically. The grain size effects on the different deformation mechanisms of nanocrystalline nickel were revealed by strain rate-controlled tension and nanoindentation experiments, which show that with decreasing grain size the strain rate sensitivity increases and the activation volume decreases, indicating increased grain boundary mediated deformation processes in nanocrystalline nickel. Creep experiments at room temperature revealed that in nanocrystalline nickel grain boundary sliding or diffusion along the interface may dominate at lower stress levels, but with increasing stresses the deformation process is mainly controlled by dislocation creep. In-situ bending experiments in an atomic force microscope revealed directly that grain boundary mediated deformation processes play a significant role in nanocrystalline nickel, which is also supported by the observation of grain coarsening and softening of nanocrystalline nickel caused by high pressure torsion.

The migration behaviour of polymer additives in 17 polypropylene (PP) samples is described. These samples cover the major types of PP used in food packaging. The diffusion coefficients of additives with relatively small molecular masses, M r = 136 (limonene), as well as the migration of typical antioxidants used in PP up to M r = 1178 (IRGANOX 1010), were measured at different temperatures. In addition, the diffusion data and percentages of xylene-soluble fractions were correlated. This enables a prediction of the migration behaviour of a PP sample by testing its ‘isotactic index’ with xylene. The results clearly indicate that PP can be subdivided, from the migration point of view, into the monophasic homopolymer (h-PP), the monophasic random copolymer (r-PP), and the heterophasic copolymer (heco-PP). The diffusion coefficients for r-PP are at least one order of magnitude higher than those of h-PP and comparable with the values for heco-PP. Upper limits for the diffusion values can be calculated based on the safety margin required by consumer protection laws.

A finite difference method to solve the one‐dimensional diffusion of impurities in a multilayer system was developed for the special case in which a partition coefficient K impose a ratio of the concentrations at the interface between two adiacent layers. The fictitious point method was applied to derive the algebraic equations for the mesh points at the interface, while for the non‐uniform mesh points within the layers a combined method was used. The method was tested and then applied to calculate migration of impurities from multilayer systems into liquids or solids samples, in migration experiments performed for quality testing purposes. An application was developed in the field of impurities migrations from multilayer plastic packagings into food, a problem of increasing importance in food industry.

C’est à une étude minutieuse des rapports au corps dans cinquante textes manuscrits inédits à teneur autobiographique – autobiographies, diaires, récits de vie, livres de raison – de la Suisse alémanique du XVIIIe s. (seulement un quart des textes ont été rédigés avant 1750, et seulement un d’entre eux l’est par une femme) que se livre G.P. Évitant les pièges du linguistic turn, elle souligne que le langage sur le corps est certes codé, sans toutefois faire écran avec une réalité vécue. Le co...