Non‐Ionic,Poly(ethylene oxide)‐Based Surfactants as Intercalants/Dispersants/Exfoliants for Poly(propylene)‐Clay Nanocomposites

Summary: Poly(propylene) (PP)‐clay nanocomposites were prepared from unmodified montmorillonite clays (NaMMT), with poly(ethylene oxide)‐based nonionic surfactants as dispersants/intercalants/exfoliants. The primary objective of this research was to find dispersants that (a) allow PP nanocomposites to be formed by direct melt mixing; (b) are effective with unmodified clays and (c) comprise of only a minor component with respect to both the clay and the overall composition. Linear, branched, gemini and sugar‐based surfactants and structures containing poly(dimethyl siloxane) and poly(methyl methacrylate) blocks were examined. These additives were found to be effective in breaking down the clay agglomerates to tactoids, giving some expansion of the clay structure and partial exfoliation and providing substantially improved clay dispersion. The properties of the derived nanocomposites depend on the level of additive and its structure. Tensile and impact properties show significant improvement over the precursor PP. Also notable are the significantly better thermal and thermo‐oxidative stabilities, as compared to both PP and “clay alone” composites. For optimal properties, it is both necessary and desirable that the surfactant should only be a minor constituent (20–50%) of the composition, with respect to the clay. A preferred surfactant is linear PE‐block‐PEO, with a short PEO block and an alkyl chain with approximately 30 carbon atoms (C₃₀).

     

X-ray photoemission spectroscopy study on the effects of functionalization in fulleropyrrolidine and pyrrolidine derivatives

Fulleropyrrolidine and pyrrolidine derivatives were studied using X-ray photoemission spectroscopy in order to determine the effects of the C₆₀-cage on the pyrrolidine nitrogen, as well as the influence of further derivatisation. Charge transfer from the carbon pyrrolidine ring to the C₆₀-cages is observed and this charge redistribution influences not only the carbon atoms but also the nitrogen. The major influence of different functionalization groups on the pyrrolidine nitrogen is whether or not they lead to quaternisation while no differences could be detected for different groups (methyl group or alkyl chain) producing one or the other configuration. However, the type of counter ion is important for the stability of the pyrrolidinium nitrogen: demethylated nitrogen, always found to be present in iodide counter balanced compounds, disappears in compounds counter balanced with anion.     

Control of Si nanowire growth by oxygen

Semiconductor nanowires formed using the vapor-liquid-solid mechanism are routinely grown in many laboratories, but a comprehensive understanding of the key factors affecting wire growth is still lacking. In this paper we show that, under conditions of low disilane pressure and higher temperature, long, untapered Si wires cannot be grown, using Au catalyst, without the presence of oxygen. Exposure to oxygen, even at low levels, reduces the diffusion of Au away from the catalyst droplets. This allows the droplet volumes to remain constant for longer times and therefore permits the growth of untapered wires. This effect is observed for both gas-phase and surface-bound oxygen, so the source of oxygen is unimportant. The control of oxygen exposure during growth provides a new tool for the fabrication of long, uniform-diameter structures, as required for many applications of nanowires.     

Wasserdampfsorptionsverhalten ausgewählter heimischer und überseeischer Holzarten

Water vapour sorption behaviour of selected domestic and overseas wood species. At 21 domestic and 11 overseas wood species the equilibrium moisture content at 20 °C and 35, 50, 65, 80 and 95% relative humidity was experimentally determined in the adsorption phase. The experimentally determined average values were computed with help of the Hailwood Horrobin model to get selected parameters such as fiber saturation point, mono‐ and polymolecular sorption, specific surface, hypothetical molecular weight as well as inaccessibility of the sorbent to the sorbate. Tables for the equilibrium moisture contents at 20 °C computed in 2% steps of relative humidity are presented. The fiber saturation point computed with the Hailwood‐Horrobin model lies for all examined wood in the range from 22% to 36%, on the average with approx. 30%. There are substantial deviations in the fiber saturation point between the individual wood species. The tendencies for the characteristics of the sorption analysis were pointed out.     

Konzept zum Nachweis der Erdbebengefährdung von Querschutzbauwerken in Wildbächen

Investigation of earthquake impacts on protection structures like torrent barriers. Protection structures with respect to settlement areas are for instance torrent barriers as often used in the mountains. In general, they can be classified in (a) sensitive and regular structures, or (b) according to their functionality in dispensing or defending structures etc. There are already numerous approaches regarding loading and combinations of loads acting on those varying types of structures. Nevertheless, earthquake impacts as loading situations on torrent barriers are only rarely investigated. Therefore, the objective of this paper is to investigate, whether neglecting loading situations resulting from earthquakes is justified. These investigations are based on a simplified dynamic method as generally used for reservoir structures of class III. Further on, the assessment is based on probability concepts as established in new design formats (e.g., JCSS model code) and the earthquake zone map.     

Stability of nutritionally important compounds and shelf life prediction of tomato ketchup

Ketchup is an important source of tomato antioxidants in human nutrition, this ambient stable product is processed using several relatively important heat treatments and can be stored for one or more years at ambient temperature. Model storage experiments were carried out with two sets of commercial ketchup produced according to the Czech recipe: (a) hot-filled without subsequent pasteurization and (b) filled and pasteurized in the jar. The samples were stored at 25, 50, 75 and 90 °C, during the storage the content of total lycopene and ascorbic acid was observed as well as the colour parameters (a*, ΔE). The obtained data were processed using the pseudo first order (total lycopene, ascorbic acid and a*) and zero order kinetics (ΔE). The obtained results corresponded with the published data, but were not consistent between the both sets of the samples. The total lycopene and ascorbic acid degradation is more dependent on the conditions in the product, mainly on the previous history of heat treatment. The colour parameters, especially ΔE seemed to be more robust criterion, which could be used for the shelf life prediction estimation. The empirically set up shelf life by the producer was confirmed.     

Identification and accurate quantitation of biological oligosaccharide mixtures

Structure-specific characterization and quantitation is often required for effective functional studies of oligosaccharides. Inside the gut, HMOs are preferentially bound and catabolized by the beneficial bacteria. HMO utility by these bacteria employs structure-specific catabolism based on a number of glycosidases. Determining the activity of these enzymes requires accurate quantitation of a large number of structures. In this study, we describe a method for the quantitation of human milk oligosaccharide (HMO) structures employing LC/MS and isotopically labeled internal standards. Data analysis was accomplished with a newly developed software tool, LC/MS Searcher, that employs a reference structure library to process LC/MS data yielding structural identification with accurate quantitation. The method was used to obtain a meta-enzyme analysis of bacteria, the simultaneous characterization of all glycosidases employed by bacteria for the catabolism of milk oligosaccharides. Analysis of consumed HMO structures confirmed the utility of a β-1,3-galactosidase in Bifidobacterium longum subsp. infantis ATCC 15697 (B. infantis). In comparison, Bifidobacterium breve ATCC 15700 showed significantly less HMO catabolic activity compared to B. infantis.     

Argon Cluster Ion Beams for Organic Depth Profiling: Results from a VAMAS Interlaboratory Study

The depth profiling of organic materials with argon cluster ion sputtering has recently become widely available with several manufacturers of surface analytical instrumentation producing sources suitable for surface analysis. In this work, we assess the performance of argon cluster sources in an interlaboratory study under the auspices of VAMAS (Versailles Project on Advanced Materials and Standards). The results are compared to a previous study that focused on C(60)(q+) cluster sources using similar reference materials. Four laboratories participated using time-of-flight secondary-ion mass spectrometry for analysis, three of them using argon cluster sputtering sources and one using a C(60)(+) cluster source. The samples used for the study were organic multilayer reference materials consisting of a ～400-nm-thick Irganox 1010 matrix with ～1 nm marker layers of Irganox 3114 at depths of ～50, 100, 200, and 300 nm. In accordance with a previous report, argon cluster sputtering is shown to provide effectively constant sputtering yields through these reference materials. The work additionally demonstrates that molecular secondary ions may be used to monitor the depth profile and depth resolutions approaching a full width at half maximum (fwhm) of 5 nm can be achieved. The participants employed energies of 2.5 and 5 keV for the argon clusters, and both the sputtering yields and depth resolutions are similar to those extrapolated from C(60)(+) cluster sputtering data. In contrast to C(60)(+) cluster sputtering, however, a negligible variation in sputtering yield with depth was observed and the repeatability of the sputtering yields obtained by two participants was better than 1%. We observe that, with argon cluster sputtering, the position of the marker layers may change by up to 3 nm, depending on which secondary ion is used to monitor the material in these layers, which is an effect not previously visible with C(60)(+) cluster sputtering. We also note that electron irradiation, used for charge compensation, can induce molecular damage to areas of the reference samples well beyond the analyzed region that significantly affects molecular secondary-ion intensities in the initial stages of a depth profile in these materials.     

Penetration of light into multiple scattering media: model calculations and reflectance experiments. Part I: the axial transfer

The article presents two general equations of radiation penetration into layers of diffuse reflectors. One of the equations describes the depth origins of reflection, the other the depth profiles of absorption. The equations are evaluated within the theory of radiative transfer applying various degrees of analytical approximations and Monte Carlo simulations. The data are presented for different scattering and absorption coefficients, arbitrary layer thicknesses, collimated and diffused irradiation, and anisotropic forward scattering. The calculated mean depths of reflection are always lower than the mean depths of absorption. For nearly non-absorbing layers, the mean depths of absorption are about one third of the physical layer thickness. In contrast, penetration saturates for strong absorbers at very low depth levels. From the simulated data, methods are derived for the determination of the penetration depth from reflectance and transmittance data of thin layers or from radially diffused reflectance profiles upon spot irradiation. The methods are experimentally verified for a series of metal oxide powders with particle sizes ranging from much smaller to much larger than the wavelength of irradiation and for microcrystalline cellulose stained with different concentrations of an organic dye.