Ingenieurwissenschaften und zugeordnete Tätigkeiten
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In this study, the molecular dynamics of a series of dipole functionalized triphenylene-based discotics, forming a columnar mesophase, were investigated by broadband dielectric spectroscopy (BDS). In addition to conductivity and localized dynamics, glassy dynamics were also observed. At higher temperatures an α1-processes and at low temperatures an α2 processes were detected having a completely different temperature dependence of its relaxation times. Different molecular assignments of α1- and α2-processes are suggested. The phase behavior of the material was explored under helium purge down to 100 K by differential scanning calorimetry (DSC). Besides the phase transition temperatures and enthalpies, one or two thermal glass transitions were found for all the materials. Moreover, the glassy dynamics were further investigated by Flash DSC, which is a chip-based calorimetry technique allowing for fast heating and cooling rates as high as 10000K/s.
High performance polymers of intrinsic microporosity (PIMs) have emerged as novel materials with broad applications from gas separation to electronic devices. Sufficiently rigid, even contorted polymer chains show only limited molecular mobility, therefore undergo inefficient packing and give rise to intrinsic microporosity with pore size generally smaller than 1 nm and BET surface areas larger than 700 m2/g. Further performance optimization and long-term stability of devices incorporating PIMs rely on our understanding of structure-processing-property relationships and physical aging, in which glass transition plays a key role. Up to now no glass transition temperature (Tg) of PIMs could be detected with conventional thermal analysis techniques before degradation. Decoupling the time scales responsible for the glass transition and the thermal decomposition is a reliable strategy to overcome this. This was achieved by employing fast scanning calorimetry (FSC) based on a chip sensor, which is capable to heat and cool a small sample (ng-range) with ultrafast rates of several ten thousand K/s. FSC provides definitive evidence of glass transition of a series of PIMs with a special consideration on the chain rigidity. The determined glass transition temperature of these PIMs follows the order of the rigidity of their backbone structures. FSC provides the first clear-cut experimental evidence of the glass transition of PIM-EA-TB with a Tg of 663 K, PIM-1 of 644 K and PIM-DMDPH-TB of 630 K at a heating rate of 1Χ104 K/s. Local fluctuations are featured in glass transition of highly rigid PIMs. As conformational changes are prevented by the backbone rigidity, the glass transition must rather be assigned to local small scale fluctuations.
Ultrashort laser pulse micromachining features a high precision. By increasing the repetition rate of the applied laser to several 100 kHz, laser processing becomes quick and cost-effective and make this method attractive for industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose becomes significant for high-repetition-rate laser systems so that radiation safety must be considered.
In well-annealed thin polymer films, with non-repulsive polymer/substrate interactions, an irreversibly adsorbed layer is formed. These adsorbed layers have shown enormous potential for technological applications. Due to the hard accessibility of these layers, their growth kinetics and molecular dynamics are still not fully understood. Here, the irreversibly adsorbed layers of Poly(2-vinylpyridine) (P2VP) and Poly(vinyl methyl ether) (PVME) thin films are revealed by solvent-leaching experiments. The growth kinetics of these layers is investigated as a function of original film thickness and annealing times. The thickness, topography and quality of the adsorbed layer is determined with Atomic Force Microscopy (AFM) and spectroscopic ellipsometry. Additionally, the molecular mobility of the adsorbed layer is investigated with Broadband Dielectric Spectroscopy (BDS). A recently developed nanostructured capacitor (NSC) is employed to measure the adsorbed layers with a free surface layer depending on annealing and solvent-leaching time. The results are quantitatively compared and discussed with respect to recently published work.
For inorganic/polymer nanocomposites a so-called Rigid Amorphous Phase (RAF) is formed in the interfacial region by adsorption of polymer segments onto the nanoparticles. The segmental dynamics of RAF is expected to be altered, as compared to the pure matrix, which might percolate to the entire system, affecting the overall nanocomposite properties. A combination of two relaxation spectroscopy techniques (Broadband Dielectric Spectroscopy (BDS) and Temperature Modulated DSC (TMDSC)) as well as Fast Scanning Calorimetry (FSC) was employed to investigate the structure and molecular mobility of nanocomposites based on Epoxy and Layered Doubled Hydroxides with different nanoparticle content. First, BDS investigations proved the existence of a process, which is present only for nanocomposites, assigned to the dynamics of polymer segments within RAF. Second, the amount of RAF was quantified by analyzing the change of specific heat capacity step of nanocomposites, comparing to the pure material. Thirdly, the glass transition of nanocomposites was studied with FSC, applying high heating rates (0.5-10 kK/s). Considering that all techniques probe essentially the same molecular process, an activation plot was constructed, delivering a complete picture of the molecular mobility and structure of the polymer nanocomposites including RAF.
Microbiologically influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) in offshore industries, such as the oil and gas pipelines, due to the high concentrations of sulfate in the seawater. SRM act upon the metal by the reactiveness of hydrogen sulfide (HS-), and by withdrawal of the available electrons (Fe --> Fe2+ + 2e-; E° = -0.47 V) in electrical contact with the metal (EMIC). However, methanogenic archaea can also cause MIC. Because they do not produce HS-, withdrawal of electrons may be their main corrosive mechanism; however, mechanistic details and kinetics of the overall process are poorly understood.
To investigate the corrosion potential of methanogens, we studied the EMIC methanogenic strains isolated from marine sediments (Methanobacterium-affiliated strain IM1) and crude oil tanks (Methanococcus maripaludis Mic1c10), in an in-house developed flow-through cell to simulate a fluctuating environment. A co-culture of M. maripaludis and D. alaskensis was also established to study the effect of syntrophic growth on metal corrosion that may occur in industrial pipelines. Results indicate that the rates of iron corrosion due to coupled methanogenesis (up to 0.4 mm/yr) are higher to that caused by the marine SRM Desulfovibrio alaskensis (0.15 mm/yr). Surface analyses of the metal showed severe pitting with high methane production. Genomic analysis of the EMIC methanogen M. maripaludis Mic1c10 will provide an insight on the mechanisms of MIC. Such knowledge and deeper understanding also from an electrokinetic point of view may not only provide further models in microbial electrophysiology, but also contribute to mitigation strategies in MIC.
Permitted explosives have a tradition of many decades in Germany and had been designed to the needs of the underground coal mining in the Ruhr. In neighboring countries of Germany similar provisions were made to prevent hazards from fire damp and coal dust explosions in underground coal mines. Due to the termination of coal mining in Germany and most other European countries, also the testing facilities are disappearing. This presentation outlines the current situation of testing regimes and facilities.
During a European convention of the authorities for market surveillance (AdCO) for explosives the activities of the notified bodies are presented, putting a focus on matters concerning market surveillance.
The presentation outlined in detail, which verifications are possible
with explosives, while practical tests involving initiation of
explosives are excluded. Elements of labeling and the conclusions in
view of quality control were explained, and typical failures by
manufacturers to comply were orally described.
The reassessment of bridges is becoming increasingly important. The basic requirement for analyses of structural safety is reliable knowledge about individual structures. This paper introduces the new approach to evaluate the quality of measured data gained from non-destructive testing (NDT) to provide reliable, objective, and relevant information about existing bridges. The purpose is to relate this validated knowledge to probabilistic analyses. Bridging the gap between NDT and numerical reassessments indicates reduced numerical uncertainties and residual service time extensions. This paper deals with an application of this approach using measurement data collected by ultrasonic technique at a prestressed concrete bridge.
While today, engineers can choose from a wide range of rheology modifying admixtures, in some parts of the world, these are difficult to access, due to their complex processing. However, alternatives can be bio-based polymers such as polysaccharides from various sources. These are easily accessible all over the world, do not demand for complicated processing, and typically they are more sustainable than many established materials, which are crude oil-based.
The paper presents the effects of acacia gum, cassava starch and the gum of triumfetta pendrata A. Rich on the rheological performance of cementitious systems. It is shown that acacia gum can be as efficient as polycarboxylate based superplasticisers, cassava starch can reduce the yield stress slightly with little effect on the plastic viscosity, and the gum of triumfetta pendrata A. Rich increases the thixotropy of cement pastes with plasticizing polymers significantly.