Application of Fluoroxy Compounds to Organic Synthesis: Electrophilic Fluorination of Unsaturated Molecules

Fluoroxy reagents are versatile and useful electrophilic fluorinating reagents. Having wide applicability in a variety of solvents they display great potential for the synthesis of specifically fluorinated analogs of bioactive molecules.     

Functional Perovskites – From Epitaxial Films to Nanostructured Arrays

Functional perovskite materials gain increasing significance due to their wide spectrum of attractive properties, including ferroelectric, ferromagnetic, conducting and multiferroic properties. Due to the developments of recent years, materials of this type can conveniently be grown, mainly by pulsed laser deposition, in the form of epitaxial films, multilayers, superlattices, and well‐ordered arrays of nanoislands. These structures allow for investigations of preparation–microstructure–property relations. A wide variation of the properties is possible, determined by strain, composition, defect contents, dimensional effects, and crystallographic orientation. An overview of our corresponding work of recent years is given, particularly focusing on epitaxial films, superlattices and nanoisland arrays of (anti)ferroelectric and multiferroic functional perovskites.     

Synchrotron-based characterization of arthroprosthetic CoCrMo particles in human bone marrow

Ti-Zr alloys have gained increasing attention as a new metallic biomaterial, being used as implants for both orthopedics and dentistry. More recently, our group found promising results for the Ti-45Zr alloy, which presented a low elastic modulus, a pronounced and excellent mechanic character, and excellent cell compatibility in vitro. However, its biocompatibility and potential to promote osteogenesis in vivo remained unclear. In the present study, the biocompatibility, osteointegration ability, and immune response effects of the Ti-45Zr alloy were evaluated in animal experiments. The results showed that the alloy had good blood compatibility and no body side effects. After implantation in vivo, the inflammation turned out well and was beneficial to the polarization of macrophages. Additionally, the Ti-45Zr alloy presented a good osteointegration ability. Overall, these results confirmed that the Ti-45Zr alloy can be used as a dental implant material.

     

Polyethylene catalytic hydrocracking by PtHZSM‐5, PtHY,and PtHMCM‐41

The mechanisms involved in polyethylene catalytic hydrocracking are investigated by monitoring temperature‐dependent evolution profiles derived from mass spectra obtained while polymer/catalyst samples were heated at a constant rate. Repetitive injection gas chromatography/mass spectrometry (GC/MS) results are used to identify class‐specific fragment ions that represent paraffins, olefins, and alkyl aromatics. Class‐specific ion signals are used to generate isoconversion‐effective activation energy plots from which mechanistic comparisons are made. Studies using PtHZSM‐5, PtHY, and PtHMCM‐41 bifunctional solid acid catalysts in helium and hydrogen are reported. The effects of hydrogen on polyethylene cracking are dramatic and result in significant changes to isoconversion‐effective activation energies. Catalytic cracking mechanisms for the three catalysts are compared and differences are explained by a combination of pore size and acidity effects. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1293–1301, 2004     

Topotaxial Formation of Mg4Nb2O9 and MgNb2O6 Thin Films on MgO (001) Single Crystals by Vapor–Solid Reaction

Thin-film solid-state reactions in the system MgO–Nb₂O₅ are experimentally investigated. MgO (001) substrates are subjected to Nb-O vapor at different temperatures in high vacuum. Thin films containing the phases Mg₄Nb₂O₉ and MgNb₂O₆ are formed by a vapor–solid reaction between the Nb-O vapor and the substrate. The crystallographic orientations of these phases are studied by X-ray diffractometry including pole figure analysis. Mg₄Nb₂O₉ grows (11.4)-, (11.6)-, and (11.9)-oriented, whereas MgNb₂O₆ grows with a preferential (241) orientation. The crystallographic relationships and their origins are discussed.     

Influence of surface diffusion on the formation of hollow nanostructures induced by the Kirkendall effect: the basic concept

The Kirkendall effect has been widely applied for fabrication of nanoscale hollow structures, which involves an unbalanced counterdiffusion through a reaction interface. Conventional treatment of this process only considers the bulk diffusion of growth species and vacancies. In this letter, a conceptual extension is proposed: the development of the hollow interior undergoes two main stages. The initial stage is the generation of small Kirkendall voids intersecting the compound interface via a bulk diffusion process; the second stage is dominated by surface diffusion of the core material (viz., the fast-diffusing species) along the pore surface. This concept applies to spherical as well as cylindrical nanometer and microscale structures, and even to macroscopic bilayers. As supporting evidence, we show the results of a spinel-forming solid-state reaction of core-shell nanowires, as well as of a planar bilayer of ZnO-Al2O3 to illustrate the influence of surface diffusion on the morphology evolution.     

The effect of mechanical stress on four viscosity improver polymers

The effect of a Bosch injector on the mass distribution function of four viscosity improver (VI) polymers has been studied. Two of these, hydrogenated styrene—isoprene (HSI) and hydrogenated styrene—butadiene (HSB), are di‐block polymers, whereas the others are either comb‐like, polyalkyl methacrylate (PMA), or linear, olefin copolymer (OCP). Measurements were performed by light scattering and viscometric techniques before and after application of mechanical stress. Only slight modifications in the physical properties were detected for HSB and HSI, which can be explained by their micellar behaviour. Conversely, a large variation in mean size and viscometric properties was observed for PMA and OCP. Finally, a model is proposed which links the variation of the mass distribution function to the intrinsic viscosity loss.