Herwig Peterlik

Efficient Air‐Stable Organometallic Low‐Molecular‐Mass Gelators for Ionic Liquids: Synthesis, Aggregation and Application of Pyridine‐Bridged Bis(benzimidazolylidene)–Palladium Complexes

Novel pincer-type, pyridine-bridged bis(benzimidazolylidene)-palladium complexes 5-7 were synthesised from cheap commercial precursors under microwave assistance. Although simple in structure, carbene complexes 5a,b are efficient low-molecular-mass metallogelators. They gelate not only a broad variety of protic and aprotic organic solvents, but also different types of customary ionic liquids (such as imidazolium, pyridinium, pyrazolidinium, piperidinium and ammonium salts) at concentrations as low as 0.5 mg mL(-1). The morphologies of the resulting 3D gel networks composed from long and thin fibres were studied by TEM and light microscopy for a selection of organic and ionic liquids. The achiral gelators are able to induce the formation of helical fibres. The thermal stability of the gel samples increases with the gelator concentration as demonstrated by thermoreversible DSC studies. Temperature-dependent NMR and X-ray diffraction studies, as well as comparisons with pincer complex analogues bearing shorter alkyl chains, suggest that the 3D networks responsible for gelation are based on non-covalent interactions, such as pi-stacking, van der Waals interactions, and hydrogen and metal-metal bonding. Ionic liquids and gels obtained from them and 5a,b display comparable high conductivities, which characterises pyridine-bridged bis(benzimidazolylidene)-palladium pincer complexes as air-stable metallo gelators that efficiently immobilise ionic liquids in low gelator concentration indicating--beyond catalysis--their potential applications in electrochemical devices.

Age- and genotype-dependence of bone material properties in the osteogenesis imperfecta murine model (oim)

Cortical mineralization of long bones was studied in collagen alpha2(I)-deficient mice (oim) used as a model for human osteogenesis imperfecta. Aspects of the age development of the mice were characterized by combining nanometer- to micrometer-scale structural analysis with microhardness measurements. Bone structure was determined from homozygous (oim/oim) and heterozygous (oim/+) mice and their normal (+/+) littermates as a function of animal age by small-angle X-ray scattering (SAXS) and quantitative backscattered electron imaging (qBEI) measurements. SAXS studies found anomalies in the size and arrangement of bone mineral crystals in both homozygous and heterozygous mice aged 1-14 months. Generally, the crystals were smaller in thickness and less well aligned in these mice compared with control animals. An increase in the mean crystal thickness of the bone was found within all three genotypes up to an age of 3 months. Vickers hardness measurements were significantly enhanced for oim bone (homozygotes and heterozygotes) compared with controls. The microhardness values were correlated directly with increased mineral content of homozygous and heterozygous compared with control bone, as determined by qBEI analysis. There was also a significant increase of mineral content with age. Two possibilities for collagen-mineral association are discussed for explaining the increased hardness and mineral content of oim/oim bone, together with its decreased toughness and thinner mineral crystals. As a consequence of the present measurements, one model for oim bone could incorporate small and densely packed mineral crystals. A second model for possible collagen-mineral association in oim material would consist of two families of mineral crystals, one being smaller and the other being much larger than the crystals found in normal mouse long bones.

Confined linear carbon chains as a route to bulk carbyne

Strong chemical activity and extreme instability in ambient conditions characterize carbyne, an infinite sp(1) hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for production, and even more so for application. We report a method for the bulk production of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk production of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbynes bulk production.

Texture of PAN- and pitch-based carbon fibers

The new technique of scanning microbeam X-ray diffraction is used to get information about the axial as well as the cross-sectional crystallographic texture of single PAN- and mesophase-pitch-based carbon fibers. The resulting preferred orientation in the axial direction is considerably higher than the values obtained from conventional X-ray diffraction measurements on fiber bundles. A change in azimuthal width of the 002 reflection was observed across some of the fibers, which can be attributed to a radial folded cross-sectional texture for pitch-based fibers, and to a different preferred orientation of skin and core layers for PAN-based fibers.

Elastic moduli of nanocrystallites in carbon fibers measured by in-situ X-ray microbeam diffraction

Abstract The in-plane Young’s modulus and the shear modulus of carbon nanocrystallites were investigated during in-situ tension tests of single carbon fibers by X-ray diffraction using the shift of the 10 band in the meridional direction and the change in the azimuthal width of the 002 reflection. The limiting value for the Young’s modulus was found to be 1140 GPa, which is higher than the value for graphite obtained from macroscopic specimens, but coincides with recent measurements on nanotubes. Furthermore, the shear modulus was evaluated using a uniform stress approach and was found to increase with increasing misorientation of the crystallites. It turns out that both the in-plane Young’s modulus and the shear modulus are not constant, but dependent on the orientation parameter.

Magnetic behaviour of a hybrid polymer obtained from ethyl acrylate and the magnetic cluster Mn12O12(acrylate)16

The magnetic properties of polymers prepared by polymerization of the magnetic cluster Mn12O12(acrylate)16 with various portions of ethyl acrylate as co-monomer are reported. According to SAXS studies, the clusters are homogeneously distributed in the polymer. Ac susceptibility measurements show superparamagnet-like behaviour of the cluster-crosslinked polymers with relaxation following an Arrhenius law with τ0 = 4–8 × 10−8 s and an energy barrier in the range 45–65 K.

A novel resonant beam technique to determine the elastic moduli in dependence on orientation and temperature up to 2000 °C

A new equipment was developed to determine the elastic moduli from the resonance frequencies of the flexural vibrations of a beam up to temperatures of 2000 °C. The elastic moduli are calculated by minimizing the difference of the experimental versus the theoretical resonance frequencies. The theoretical frequencies are obtained by numerically solving Timoshenko’s equation, which takes into account the influence of the shear deformation and the rotatory inertia. From the fundamental frequency and the higher modes of vibration, one Young’s modulus and two shear moduli (e.g., E11, G12, and G13) are obtained, the latter two coincide for an elastically isotropic material. With the additional effort of cutting out specimens in specific directions, the complete elastic tensor of anisotropic materials can be measured at high temperatures. The limits and the precision of the method are discussed.

Chairside CAD/CAM materials Part 1: Measurement of elastic constants and microstructural characterization

OBJECTIVE A deeper understanding of the mechanical behavior of dental restorative materials requires an insight into the materials elastic constants and microstructure. Here we aim to use complementary methodologies to thoroughly characterize chairside CAD/CAM materials and discuss the benefits and limitations of different analytical strategies. METHODS Eight commercial CAM/CAM materials, ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Elastic constants were evaluated using three methods: Resonant Ultrasound Spectroscopy (RUS), Resonant Beam Technique (RBT) and Ultrasonic Pulse-Echo (PE). The microstructures were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Raman Spectroscopy and X-ray Diffraction (XRD). RESULTS Youngs modulus (E), Shear modulus (G), Bulk modulus (B) and Poissons ratio (ν) were obtained for each material. E and ν reached values ranging from 10.9 (Lava Ultimate) to 201.4 (e.max ZirCAD) and 0.173 (Empress CAD) to 0.47 (Lava Ultimate), respectively. RUS showed to be the most complex and reliable method, while the PE method the easiest to perform but most unreliable. All dynamic methods have shown limitations in measuring the elastic constants of materials showing high damping behavior (hybrid materials). SEM images, Raman spectra and XRD patterns were made available for each material, showing to be complementary tools in the characterization of their crystal phases. SIGNIFICANCE Here different methodologies are compared for the measurement of elastic constants and microstructural characterization of CAD/CAM restorative materials. The elastic properties and crystal phases of eight materials are herein fully characterized.

Simultaneous drying and chemical modification of hierarchically organized silica monoliths with organofunctional silanes

Large, low density silica monoliths with a hierarchical organisation of macro- and periodically arranged mesopores are prepared by a true liquid crystal templating approach of an ethylene glycol-modified silane in the presence of a non-ionic block copolymer surfactant and subsequent drying of the wet gels with organosilanes. In this approach the silanes serve two functions: first, the silylation reactions allow for non-destructive drying of the monolithic gels and simultaneous extraction of the block copolymer template; second, they serve as surface functionalization agent. A variety of organofunctional silanes such as trimethylchlorosilane, 3-mercaptopropyltrimethoxysilane, phenyl-trimethoxysilane, 3-[(2,2-dimethyl-1-aza-2-silacyclopent-1-yl)dimethylsilyl]-1-propanamine, a cyclic silazane resulting in aminopropyldimethylsilyl groups on the silica surface, and (methylmethacryloyl)dimethyl-methoxysilane, has been successfully applied in the interfacial modification of the silica surface. The resulting silica monoliths were characterized with respect to their structure by SEM, SAXS, and nitrogen sorption and with respect to their chemical composition by elemental analysis, titrations and MAS-NMR spectroscopy.

The validity of Weibull estimators

The parameters of the two-parametric Weibull distribution, the Weibull modulus and the scale parameter, were estimated by using not only analytical means but also Monte-Carlo simulations. The precision of the measurement of both parameters, i.e. their variation coefficient, has been calculated. It is shown that the variation coefficient of the scale parameter is dependent on the number of experiments, M, which were performed, and on the Weibull modulus itself, whereas the variation coefficient of the Weibull modulus is only dependent on M. Furthermore, the correctly interpreted results show that each single measurement gives the statistically correct Weibull parameters and the biasing arises only from the method of adding single measurements to obtain a mean value. Thus, in practice, when only one set of experiments for further evaluation is available, there is no need for adjustment factors.