Publikationen

Lithium aluminum hydride combined with different amounts of aluminum chloride react with cyclopentanol under the formation of compounds with aluminum-oxygen scaffolds and hydrogen or chlorine as terminating substituents at aluminum and cyclopentyl at the oxygen atoms. H6Al4(OC5H9)6 and Cl6Al4(OC5H9)6, both displaying a central aluminum atom almost octahedrally coordinated by oxygen atoms of the cyclopentanolates with three AlH2 or AlCl2 entities bridging three oxygen edges were isolated and fully characterized. The compound dihydrido aluminum cyclopentanolate was isolated together with chloro-hydrido aluminum cyclo-pentanolate as a 6:2 aggregate, [H2Al(OC5H9)]6[H(Cl)Al(OC5H9)]2, displaying alcoholate and hydride bridges in the crystal. Structural isomers of this compound were found in the solid. Mono-hydrides could be isolated in the form of H5Al5(O)(OC5H9)8*OC4H10 and in the form of a hydride/chloride H4.5Cl0.5Al5(O)(OC5H9)8*OC4H10, which is a 1:1 mixture of H5Al5(O)(OC5H9)8 with H4ClAl5(O)(OC5H9)8 in the crystal. In both compounds an oxygen atom is in the center of an Al5 square pyramid. While in the first case the aluminum atom situated at the top of the pyramid has a hydride ligand, in the second case the ligand is a chloride.

When the majority of efforts to control adhesion from surfaces currently focus on a direct modification of the surface, either chemically or physically, perhaps a non-superficial approach where the action occurs underneath the surface can provide a competitive alternative. In this comment we highlight a methodology used to control adhesion from flexible surfaces. This is based on 'semi-closed' flexible microfluidics systems. Three basic functionalities are derived from this methodology. In one case the system is used to improve adhesion; in an extreme opposite case to prevent adhesion and in a somehow intermediate functionality it provides a switchable system in which the surface can be reversibly changed from adhesive to non-adhesive.

Fluid catalytic cracking (FCC), which currently accounts for half of the worldwide petroleum refining efforts, relies on catalytic, aluminosilicate zeolite particles which slowly deactivate. As of yet, this FCC catalyst residue (FC3R) has no commercial outlet, resulting in abundant amounts of landfill-destined refuse. However, this overlooked waste has the right ingredients for the synthesis of some of today's emerging nanomaterials. High-carbon FC3R, sourced from a Uruguayan refinery, was identified as faujasite particles encased in graphitic carbon shells. We show that pulsed laser ablation of raw FC3R produces simultaneous deposition of single-wall carbon nanotubes and silica nanowires through vapour/solid-liquid-solid self-assembly in distinct zones of an oven-laser apparatus. This is an extreme revalorisation and provides a new untapped resource for research and applications in C- and Si-based nanomaterials and mesoscopic physics.

In-stent restenosis (ISR) is one of the most common and serious complications observed after stent implantation. ISR is characterized by the inordinate proliferation of smooth muscle cells (SMC) that leads to narrowing of the blood vessels. To achieve a healthy endothelium, it is critical to selectively enhance the growth of endothelial cells (EC) while suppressing the growth of smooth muscle cells, which is still a major challenge and yet to be achieved. In this study, novel surfaces have been developed to support the selective growth of endothelial cells. Micro- and nanostructured Al2O3 surfaces with unique topographical features were fabricated and tested. Surface characterization and cellular response of endothelial cells (HUVEC) as well as smooth muscle cells (HUVSMC) has been investigated at cellular and molecular levels. A topography driven selective cell response of ECs over SMCs was demonstrated successfully. This selective response of ECs was also analyzed at protein levels in order to understand the basic mechanism.

The influence of titanium dioxide (TiO2) nanoparticles on the crystallization behavior of polypropylene was investigated by conventional differential scanning calorimetry (DSC) and fast scanning DSC measurements. The data obtained from both methods were estimated for the first time using the Lauritzen-Hoffmann equation to analyze the behavior over a wide cooling range under nonisothermal conditions. This provides more reliable values of nucleation parameters (Kg) and surface free energy (σe). The variation of the effective energy (ΔE) was determined with the Kissinger method. Regardless of the cooling rate, both Kg and σe indicate the role of titania as a nucleating agent enhances the crystallization rate. However, the ΔE denotes that TiO2 acts as an obstacle to the mobility of chain segments at cooling rates below 150 °C/s, while, in contrast, the presence of titania enhances the chain mobility at cooling rates above 150 °C/s.

In this study, the influence of surface morphology, reagent ions and surface restructuring effects on atmospheric pressure laser desorption/ionization (LDI) for small molecules after laser irradiation of palladium self-assembled nanoparticular (Pd-NP) structures has been systematically studied. The dominant role of surface morphology during the LDI process, which was previously shown for silicon-based substrates, has not been investigated for metal-based substrates before. In our experiments, we demonstrated that both the presence of reagent ions and surface reorganization effects – in particular, melting – during laser irradiation was required for LDI activity of the substrate. The synthesized Pd nanostructures with diameters ranging from 60 to 180 nm started to melt at similar temperatures, viz. 890-898 K. These materials exhibited different LDI efficiencies, however, with Pd-NP materials being the most effective surface in our experiments. Pd nanostructures of diameters >400-800 nm started to melt at higher temperatures, >1000 K, making such targets more resistant to laser irradiation, with subsequent loss of LDI activity. Our data demonstrated that both melting of the surface structures and the presence of reagent ions were essential for efficient LDI of the investigated low molecular weight compounds. This dependence of LDI on melting points was exploited further to improve the performance of Pd-NP-based sampling targets. For example, adding sodium hypophosphite as reducing agent to Pd electrolyte solutions during synthesis lowered the melting points of the Pd-NP materials and subsequently gave reduced laser fluence requirements for LDI.

In this study, the impact of analyte ablation and substrate surface acidity on ion yield in surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) from Pd nanoparticles was examined. The extent of analyte removal from the Pd material was investigated by X-ray analysis and compared to conventional desorption/ionization on silicon (DIOS) and matrix-assisted laser desorption/ionization (MALDI). Despite the different surface morphologies of the investigated materials and the widely varying ionization yields observed during the experiments, virtually the same amount of analyte was removed by laser irradiation from each of the investigated substrates at a given laser fluence. Our experiments therefore suggested that the extent of analyte ablation from the substrate was less important for SALDI efficiency than the chemical properties of the surface.

The charge storage mechanism and ion arrangement inside electrically charged carbon nanopores is a very active research field with tremendous importance for advanced electrochemical technologies, such as supercapacitors or capacitive deionization. Going far beyond the state of art, we present for the first time a comprehensive study of tracking ion electrosorption in aqueous electrolytes during charging and discharging of porous carbon electrodes using in situ X-ray scattering. We provide novel and quantitative insights into the local concentration of anions and cations and demonstrate that the global number of ions within the pores does not vary during charging and discharging. In addition, we have unique access to the spatial arrangement of ions inside carbon nanopores by using a simple, yet powerful two-phase model. Applying this model to our data, we show that double-layer formation is accomplished by a unique combination of preferred counter-ion adsorption directly at the pore wall which drains ions from their local surrounding inside carbon nanopores. Effectively, this leads to a situation which globally appears as ion swapping.

Mixtures of polyvinylpyrrolidone/polyvinyl butyral (PVP/PVB) are attractive binders for the preparation of carbon electrodes for aqueous electrolyte supercapacitors. The use of PVP/PVB offers several key advantages: They are soluble in ethanol and can be used to spray coat or drain cast activated carbon (AC) electrodes directly on a current collector. Infrared spectroscopy and contact angle measurements show that the PVP-to-PVB ratio determines the degree of binder hydrophilicity. Within our study, the most favorable performance was obtained for AC electrodes with a composition of AC + 1.5 mass% PVP + 6.0 mass% PVB; such electrodes were mechanically stabile and water resistant with a PVP release of less than 5% of total PVP while PVB itself is water insoluble. Compared to when using PVDF, the specific surface area (SSA) of the assembled electrodes was 10% higher, indicating a reduced pore blocking tendency. A good electrochemical performance was observed in different aqueous electrolytes for composite electrodes with the optimized binder composition: 160 F g−1 at 1 A g−1 for 1 M H2SO4 and 6 M KOH and 120 F g−1 for 1 M NaCl. The capacitance was slightly reduced by 2.5% after cycling to 1.2 V with 1.28 A g−1 in 1 M NaCl for 10,000 times.