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Organisationseinheit der BAM
Electron magnetic resonance (EMR) spectroscopy, X-ray-fluorescent microscopy (XFM) and thermal analysis (TGA/DTA) are used to characterize the carbon nano-phase obtained in the reaction between fine-dispersed aluminium and dichlorethane in the liquid paraffin medium and its modified with Mn(II), Fe(III), Ni(II), Cu(II) chlorides forms were studied. It was shown that the solid nano-structured functionalized carbon systems containing metals possess specific magnetic and thermal properties. Key parameters of the process, influencing on the size and structure of the formed carbon nano-phase were determined. Results and regularities established in this work create presumably the certain basis for optimization of physical and chemical properties of similar systems.
Copolymers of acrylic acid and styrene (AA/S) were prepared by pulsed plasma deposition and their structures were studied in dependence on the duty cycle (DC) for a fixed composition of 1:1. As a result, low values of DC doses preserve the structure of monomers in the plasma deposited polymers while high DC leads to a higher degree of fragmentation and a loss in regular structure. Regarding plasma copolymerisation as a feasible method to finish surfaces with a definite number of functional groups it is necessary to characterize both, the chemical nature and the physical properties of the deposited layer. Therefore, a combination of different methods was employed for the characterization of thin plasma copolymer films (FTIR, dielectric spectroscopy, differential scanning calorimetry, X-ray photoelectron spectroscopy (XPS)). Special attention was paid on the unambiguous identification of COOH groups at the surface after derivatization with trifluoroethanol by XPS and in the volume by FTIR. The glass transition temperature of the copolymer system is lower than that for the both plasma deposited homopolymers and increases with the DC in difference to plasma deposited poly(acrylic acid). The dielectric measurements showed that the plasma deposited films were not thermally stable and underwent an undesired post-plasma chemical reaction. The results obtained by dielectric spectroscopy are discussed in detail in comparison with the data from FTIR and XPS measurements.
Degradation behavior of thin polystyrene films on exposure to Ar plasma and its emitted radiation
(2013)
Spin-coated films of amorphous polystyrene (PS) were exposed to argon plasma for a few seconds to several minutes. The PS film was either in direct contact with the plasma or was shielded from the direct plasma contact by filters with different cutoff wavelengths in the vacuum UV region or by a Faraday cage (FC) made from metal mesh to prevent the impinging of charged species. Only energy-rich neutrals and plasma radiation may be operative in presence of the FC. lithium fluoride (LiF) filter protects the sample from direct contact with the plasma. Wavelengths of plasma radiation shorter than c. 105 nm (≈ 11.8 eV) were cut off. Glass filters made of fused SiO2 have a cutoff at λ ≈175?nm completely the vacuum UV radiation of plasma (ca. 175 nm ≈ 7.0 eV). These energies are sufficient to produce C–C, C–H bond scissions in case of direct Ar plasma exposure and Ar plasma exposure with use of the LiF filter. Only quartz glass shielding did not produce significant effects on the polymer surface in comparison to the reference PS, either in surface energy or O/C ratio or in IR spectra. Oxygen plasma has worked most aggressive and had etched the PS film, thus establishing a steady state between introduction of new oxygen functionalities and polymer etching. Ar plasma exposure produces also oxidation and etching of the polymer films as the oxygen plasma. Using of a FC during Ar plasma exposure or the LiF filter a slightly weaker oxidation was observed.
Brominated single-walled carbon nanotubes [(Br)n-SWCNT) produced by the plasma-chemical technique were involved in the liquid-phase process of hydrocarbons aerobic oxidation. The significant catalytic effect of the (Br)n-SWCNT was revealed at first by the cumene initiated model oxidation and then in experiments on profound aerobic oxidation of petroleum naphthenic fraction derived from the commercial Azerbaijan (Baku) oils blend diesel cut. The ability of (Br)n-SWCNT to accelerate the aerobic oxidation of the hydrocarbons was found out for the first time. Obviously this phenomenon originates from the peculiarities of electronic configuration of the (Br)n-CNT patterns. The plausible mechanism of (Br)n-SWCNT catalytic action is inclined to the formation of reactive oxygen species. The catalytic activity of (Br)n-SWCNT markedly exceeds the activity of the industrial catalysts, manganese salt of indigenous petroleum acids, used for the liquid phase petroleum hydrocarbons oxidation process.
Polystyrene (PS) spin coated thin films were modified by O2 and Ar plasma as
well as by UV irradiation treatments. The modified PS samples were compared with
plasma polymerized and commercial polystyrene. The effects of plasma (O2 and Ar) and
UV irradiation treatments on the surface and the bulk properties of the polymer layers were
discussed. The surface properties were evaluated by X-ray Photoelectron Spectroscopy and
Contact angle measurements and the bulk properties were investigated by FTIR and
dielectric relaxation spectroscopy. As a result only one second treatment time was sufficient
to modify the surface. However, this study was also dedicated to understand the effect
of plasma and plasma irradiation on the deposited layers of plasma polymers. The
dielectric measurements showed that the plasma deposited films were not thermally stable
and underwent an undesired post-plasma chemical oxidation.
Copolymers of acrylic acid and styrene (AA/S) were prepared by pulsed plasma deposition technique. Their structure–property relationships were studied in dependence on the comonomer ratio. Both, the regularity of the structure and the composition of the thin copolymer films were investigated by bulk-sensitive (dielectric spectroscopy, FTIR, and differential scanning calorimetry) as well as surface-sensitive methods such as X-ray photoelectron spectroscopy (XPS). For an unambiguous identification of the functionality of the deposited films the COOH groups were estimated by derivatization with trifluoroethanol and subsequent XPS measurement as well as by the quantitative analysis of the FTIR data. As a result, the concentration of COOH groups on the surface and in the bulk is increasing with the fraction of AA in precursor mixture in a non-monotonous way but similar to the dependence obtained by conventional free radical polymerization.
The pulsed plasma polymerization of allyl alcohol was employed under the aspect of maximal retention of OH groups and the formation of a regular polymer structure. It should be noted that earlier investigations on plasma polymers deposited from allyl alcohol did not show extensive postplasma addition of oxygen and water vapor from ambient air during storage, measuring the elemental O/C ratio by means of X-ray photoelectron spectroscopy (XPS).The identification of OH groups in the plasma polymerized polymer using FTIR spectroscopy was such an indicator for fragmentation. The peak area of OH groups in the film which was stored was increased by about 20% compared to that measured ('in situ'). These phenomenons reflected that moisture and O2 in air played an important role in scavenging the free radicals. The addition of water and more specifically chemical bonding of OH of water in the deposited plasma polymer may serve as an indicator for monomer fragmentation, poly recombination, and the remaining radicals responsible for film formation. Moreover, the dielectric measurements show that the plasma deposited films are not thermally stable but undergo a postplasma chemical reaction during heating, where the reaction kinetics depends on pressure.
Factors affecting the intrinsic anti-oxidative activity of carbon-nanofibers - Metallic impurities
(2009)
Nanotubes und Nanofasern (CNT, CNF) besitzen inhärente antioxidative Eigenschaften. Diese Fähigkeit könnte sehr nützlich für die Langzeitstabilität entsprechender Polymercomposite sein. Sie haben Elektronenaffinitäten ähnlich der von Fullerenen und sind deshalb in der Lage, Radikalfallen darzustellen und damit radikalische Kettenreaktionen zu unterbinden. Hier wurde die anti-oxidative Aktivität kommerzieller Nanofasern von Fischgrätenstruktur untersucht. Zunächst wurde der quantitative Einfluss von Ni-Verunreinigungen erfasst. Die eigentliche anti-oxidative Wirkung wurde mit einer aeroben Modelloxidation von Cumol verifiziert und deren kinetischen Parameter für kommerzielle und besonders gereinigte CNF-HBs bestimmt. CNF-HB inhibiert die Modellreaktion durch Einfangen der Peroxiradikale. Die Oxidation vollzieht sich nach einer ausgeprägten Induktionsphase in semi-logarithmischer Abhängigkeit für die speziell gereinigten Spezies. Es konnten erstmals die effektive Konzentration an inhibierenden Zentren und die Inhibierungs-Geschwindigkeitskonstante für CNF-HB bestimmt werden. Die Inhibierungs-Geschwindigkeitskonstante beträgt k7 = (6 ± 1.0) × 103lmol-1 s-1 und liegt damit in der für Anti-Oxidanzien erwarteten Größenordnung.
An experimental cold-gas study of the response of a choked convergent–divergent nozzle to swirl perturbations is presented. The perturbations were obtained by means of upstream unsteady tangential injections into initially steady flows with different values of steady background swirl. The swirl perturbations induced changes in the axial mass-flow rate, due to either their ingestion or evacuation by the nozzle. This in turn caused a downstream acoustic response. For low-intensity background swirl the responses were found to be similar to those obtained without steady background swirl. Perturbations of a high-intensity background swirl led to different effects. For long injection times, the negative mass-flow rate modulation occurred in two stages. The first stage was similar to that of the background-swirl free case. The second stage occurred after a short time delay, and induced a much stronger negative acoustic response. This unexpected behavior suggests that a significant part of the tangentially injected fluid flows upstream inducing an accumulation of swirl, which is – after tangential injection is ceased – suddenly cleared out through the nozzle. A scaling rule for the amplitudes of these acoustic responses is reported. Furthermore, quasi-steady models, based on steady-state measurements are proposed. These models predict the downstream acoustic response amplitude within a factor two. Additionally, preliminary empirical evidence of the effect of swirl on the downstream acoustic response due to the interaction of entropy patches with a choked nozzle is reported. This was obtained by comparison of sound produced by abrupt radial or tangential sonic injection, upstream from the choked nozzle, of air from a reservoir at room temperature to that from a reservoir with a higher stagnation temperature. Because the mass flow through the nozzle does not increase instantaneously, the injected higher-enthalpy air accumulates upstream of the injection-port position in the main flow. This eventually induces a large downstream acoustic pulse when tangential injection is interrupted. The magnitude of the resulting sound pulse can reach that of a quasi-steady response of the nozzle to a large air patch with a uniform stagnation temperature equal to that of the upstream-injected heated air. This hypothesis is consistent with the fact that the initial indirect-sound pulse is identical to one obtained with unheated air injection. The authors posit that – given all of the insight gleaned from them in this case – acoustic measurements of indirect sound appear to be a potentially useful diagnostic tool.