Literatur

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Langmuir-Blodgett films of fluorinated glycolipids and polymerizable lipids and their phase separating behavior

This paper describes the phase separating behavior of Langmuir monolayers from mixtures of different lipids that (i) either carry already a glycopeptide recognition site or can be easily modified to carry one and (ii) polymerizable lipids. To ensure demixing during compression, we used fluorinated lipids for the biological headgroups and hydrocarbon based lipids as polymerizable lipids. As a representative for a lipid monomer, which can be polymerized in the hydrophilic headgroup, a methacrylic monomer was used. As a monomer, which can be polymerized in the hydrophobic tail, a lipid with a diacetylene unit was used (pentacosadiynoic acid, PDA). The fluorinated lipids were on the one hand a perfluorinated lipid with three chains and on the other hand a partially fluorinated lipid with a T(N)-antigen headgroup. The macroscopic phase separation was observed by Brewster angle microscopy, whereas the phase separation on the nanoscale level was observed by atomic force microscopy. It turned out that all lipid mixtures showed (at least) a partial miscibility of the hydrocarbon compounds in the fluorinated compounds. This is positive for pattern formation, as it allows the formation of small demixed 2D patterned structures during crystallization from the homogeneous phase. For miscibility especially a liquid analogue phase proved to be advantageous. As lipid 3 with three fluorinated lipid chains (very stable monolayer) is miscible with the polymerizable lipids 1 and 2, it was mostly used for further investigations. For all three lipid mixtures, a phase separation on both the micrometer and the nanometer level was observed. The size of the crystalline domains could be controlled not only by varying the surface pressure but also by varying the molar composition of the mixtures. Furthermore, we showed that the binary mixture can be stabilized via UV polymerization. After polymerization and subsequent expansion of the barriers, the locked-in polymerized structures are stable even at low surface pressures (10 mN/m), where the unpolymerized mixture did not show any segregation.     

Characterization of Laser-Arc deposited multilayer systems by means of AES, Factor Analysis and XPS

In a vacuum chamber at 5 · 10^–4 Pa, multilayer systems (single layer thickness 20 nm) consisting of Ti/C and Al/C, respectively, have been deposited on Si (111) disks by the laser assisted coating (Laser-Arc). Structure and composition have been investigated by means of Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and Auger Electron Spectroscopy (AES) in conjunction with Factor Analysis. AES depth profile measurements through the outermost part of the layers show for both the Ti/C and the Al/C samples a regular structure of the layer sequence metal/ carbon with a constant distance along the sample normal and sharply formed interfaces. In the metallic layers an oxygen enrichment was found, which is more intensive in the Ti/C deposit than in the Al/C one. By means of Factor Analysis in the evaluation of the differentiated spectra as a function of sputtering time, the formation of carbides at the metal/carbon interfaces has been detected. However, in the present state of the investigations it can not be decided, whether the observed carbide formation is the result of the energy impact due to ion sputtering or the coating fabrication process itself.     

Raman characterization of amorphous carbon films

Amorphous carbon films, deposited with the LASER-ARC technique, have been characterized using Raman scattering experiments at an excitation wavelength of 633 nm provided by a He-Ne laser. To distinguish between the homogeneous amorphous film and incorporated particles area resolved measurements have been carried out due to the laser spot diameter of 1 m. Typical diamondlike (DLC) films, grown near room temperature, show a broad Raman band between 1000 cm^–1 and 1800 cm^–1 fitted very well by two gaussian distributions. Films deposited at higher substrate temperatures reveal more graphitic features in the spectra. The spectra of particles consists of a graphite-like portion originated from the graphitic structure of the particle and a diamond-like portion caused by the covering DLC film. The degree of disorder and diamond-likeness in the film structure is quantified by the peak position, the full width at half maximum (FWHM) and intensity relation of the fitted D- and G-peaks.     

The Simulation of the Electrostatic Spray Painting Process with High‐Speed Rotary Bell Atomizers. Part I: Direct Charging

High‐speed rotary bell atomizers are widely used in the painting industry for high quality applications. They provide a highly uniform film thickness with reasonable transfer efficiency due to the additional electrostatic field supporting the droplet transport towards the target. A basic requirement for this type of paint atomizer is a fine and reproducible atomization of a large variety of different paints, ranging from solvent‐based materials to highly non‐Newtonian water‐borne systems. Furthermore, a broad range of paint flow rates must be covered. The present contribution summarizes investigations aiming to completely model the electrostatically supported spray painting process by means of CFD. In part I, so‐called direct charging atomizers, where high voltage is applied directly to the rotating bell, are considered. Here, charging of the droplets takes place at the bell edge and corona effects can be neglected. A powerful commercial code, in the present case Fluent in its current releases, has been extended to account for the electrostatic field and the space charge effect due to the charged paint droplets. As input conditions, the air flow from the shaping air orifices and measured droplet sizes and velocities close to the bell edge using phase‐Doppler anemometry and Fraunhofer diffraction were taken. Also, LDA measurements in front of the target were performed, yielding comparative data of the airflow field. In general, numerical and experimental results are in good agreement. This is especially true for the final film thickness on the target and the transfer efficiency, i.e. the amount of paint solids finally deposited on the target. The agreement was achieved using a droplet charge of 5% of the droplet size dependent Rayleigh limit. These results serve as a basis for a complete painting process simulation for complex work pieces, e.g. whole car bodies, in the future. This task, however, can only be successfully completed performing unsteady calculations with moving atomizers along given robot paths.     

The Simulation of Electrostatic Spray Painting Process with High‐Speed Rotary Bell Atomizers. Part II: External Charging

The present contribution summarizes investigations aiming to completely model the electrostatically supported spray painting process with high‐speed rotary bells by means of CFD. In this part II, so‐called external charging atomizers, where high voltage is applied to emitting electrode needles, are considered. Here, charging of the droplets takes place due to free ions produced from corona discharge at the electrodes. Part I [1] dealt with direct charging atomizers, where potential is applied directly to the rotating bell. The commercial CFD‐code Fluent has been extended to account for the electrostatic field and the space charge effect due to the ions. Here, a model for the time‐dependent and inhomogeneous field charging of the droplets was applied. Furthermore, the direct interaction between the ion current and the flow field, i.e., the so‐called ion wind, could be calculated. As input conditions, the airflow from the shaping air orifices and measured droplet sizes close to the bell edge using Fraunhofer diffraction were taken. In general, numerical and experimental results are in good agreement, confirming the applicability of the chosen physical approach. This is especially true for the final film thickness on the target and the transfer efficiency, i.e., the amount of paint solids that finally deposited on the target. In the near future the calculations must be extended to true unsteady simulations including the dynamic meshing procedure.     

Purification and fractionation of single-walled carbon nanotubes

This study presents the approach to the purification and subsequent metallic/semiconductive (M/S) fractionation of single-walled carbon nanotubes (SWCNTs) with diameter from 1.04 to 1.60 nm produced via laser ablation. SWCNTs were purified through 3-fold refluxing processes in nitric acid followed by the multiple washings with sodium hydroxide and hydrochloric acid. The purified-annealed SWCNTs sample was divided into seven batches. One batch was dispersed in acetone as a reference sample. Each of the remaining batches were dispersed in one of the following surface agents: sodium dodecyl sulfate, sodium cholate acid (SCA), sodium deoxycholate, cetrimonium bromide, cetylpyridinium chloride, and benzalkonium chloride (BKC). SWCNT suspensions were fractionated via free solution electrophoresis technique. The recovered fractions from electrode and control areas were analyzed via optical absorption spectroscopy in UV–Vis–NIR range to evaluate the efficiency of the separation process. Raman spectroscopy was applied to analyze the purity of the samples. The catalyst content was estimated by atomic absorption spectroscopy. The morphology of the investigated samples was observed via high-resolution transmission electron microscopy. This contribution clearly shows that among the investigated surfactants there are two promising candidates (SCA and BKC) which can efficiently enrich the bulk sample in one electronic type of carbon nanotubes when FSE is applied.