Universität Stuttgart
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Item Open Access Proton-conducting membranes for the artificial leaf(2023) Bosson, Karell; Tovar, Günter E. M. (Prof.)With the aim of producing proton conducting membranes with improved proton conductivity and mechanical properties, the poly(pentafluorostyrene)-b-(butyl acrylate) (PPFS-b-PBuA) system was investigated. The study mainly focuses on the influence of the forming polymer nanostructures on the conductivity properties of the membranes. A series of well-defined PPFS-b-PBuA block copolymers (BCPs) were synthesized via nitroxide-mediated controlled radical polymerization (NMP). Spontaneous self-assembly of the BCP element was induced via a targeted change in polymer composition. Moreover, by adjusting the molar composition via enrichment of one of the blocks after synthesis, controlled self-assembly of the BCPs was realized. This was done by combining the corresponding homopolymer with the block copolymer to form a polymer blend - one of the blocks mixed to the BCP. Forming such polymer blends expanded the range of available techniques for tailoring the morphology for desired applications. Sulfonation of BCPs for the preparation of proton-conducting membranes was carried out by a para-fluoro thiol "click" reaction using sodium 3-mercapto-1-propanesulfonate (SMPS). The accessibility of fluorine in the para position of the phenylene group of PPFS provides countless opportunities for polymer functionalization by nucleophilic substitution. After modification of BCP, the self-assembly ability was retained, and higher conductivities were obtained compared to random copolymers. In addition, complementary studies were conducted on the use of printing techniques for membrane upscaling and evaluation of their life cycle.Item Open Access Experimental and numerical study of turbulence in fusion plasmas using reflectometry synthetic diagnostics(2018) Zadvitskiy, Georgiy; Tovar, Günter (Prof. Dr.)Anomalous energy and particle transport is closely related to micro-turbulence. Therefore plasma turbulence studies are essential for successful operation of magnetic confinement fusion devices. This thesis deals with the development of interpretative models for Ultra-Fast Swept Reflectometry (USFR), a diagnostic used for the measurement of turbulence radial wave-number spectra in fusion devices. While the interpretation of reflectometry data is quite straightforward for small levels of turbulence, it becomes much trickier for larger levels as the reflectometer answer is no longer linear with the turbulence level. It has been shown for instance that resonances due to probing field trapping can appear in turbulent plasma and produce jumps of the signal phase. In the plasma edge region the turbulence level is usually high and can lead to a non-linear regime of the reflectometer response. The loss of probing beam coherency and beam widening when the probing beam crosses the edge turbulence layer can affect USFR core measurements. Edge turbulence with a long correlation length leads to small beam widening and strong distortion of the probing wave phase. However backscattering effects from turbulence with short correlation lengths are also able to cause reflectometer signal change. To study turbulence wave-number spectra as well as reflectometer signal phase variations, signal amplitude variations can be analized. Unlike signal phase variation, amplitude does not suffer from resonant jumps, and can give more clear qualitative evaluation of turbulence structure. In the case when the turbulence amplitude peaked in the edge region, it can be detected as spectral peak near local Bragg resonance wave-number. USFR with a set of receiving antennas arranged poloidally was proposed to obtain more information on the edge turbulence properties. A displacement of the spectral peak appears when the receiving antenna is misaligned with the emitting one. Peak displacement measurements could provide additional information on probing beam shaping and turbulence properties and help in coherent mode observation as well. A 2D full wave code was applied as a synthetic diagnostic to Gysela gyro-kinetic code data to study Tore-Supra tokamak core turbulence. Radial correlation lengths computed from the amplitude of multi-channel fixed frequency reflectometry signals 5have shown good agreement with the turbulence correlation length directly computed from the simulation. The synthetic diagnostic was then applied to analyse the correlation length and wave-number spectra obtained by USFR in the ASDEX-Upgrade tokamak. A comparison between 1D and 2D results have shown different behaviour. However correlation lengths measured with UFSR signals are in the same order with turbulence ones.Item Open Access Strömungsdynamik und Stofftransport in einem Strahl-Kolonnenflotationsapparat zur Abtrennung oberflächenaktiver Substanzen aus wässrigen Stoffströmen(2020) Ziegler, Eike Eric; Hirth, Thomas (Prof. Dr. rer. nat.)Die Arbeit befasst sich mit der Untersuchung eines Strahl-Kolonnenflotationsapparates, der zur Reinigung und Konditionierung von Prozesswasser eingesetzt wird. Um den Einfluss der Strömungsdynamik auf den Stofftransport von oberflächenaktiven Substanzen (OAS) an die Phasengrenzfläche besser zu verstehen, wurden einzelne Bereiche des Apparates bezüglich der funktionalen Zusammenhänge zwischen den einzelnen Betriebsparametern näher untersucht. In einem ersten Schritt wurde die Strömungsdynamik in einem exemplarischen FSA mit Finite-Pointset-Method (FPM), einem punktbasierten Strömungssimulations-CFD-Programm, simuliert, um die Ausbreitung des Treibstrahles in der Mischkammer und dort auftretende lokale Strömungszonen zu visualisieren. Basierend auf den Simulationsergebnisse wurden fünf Treibdüsengeometrien gefertigt und für die Untersuchung der Blasenströmung im Flotationsbehälter hinzugezogen. Diese Treibdüsen wurden in ein handelsübliches Strahlapparatgehäuse eingesetzt, um zusätzlich zur Treibdüsengeometrie den Einfluss des Treibdruckes und von koaleszenzverändernden Substanzen auf die erzeugte Blasenströmung zu untersuchen. Durch Variation der Konzentration von sieben unterschiedlichen Salzen mit charakteristischen Ionenkombinationen und Fokus auf Natriumchlorid, wurde das Koaleszenzverhalten der Blasenströmung in einem Konzentrationsbereich zwischen 0 und 30 g/l unter Messung von Blasengröße und Gasanteil erfasst. Durch Definition einer Blasenaufstiegsfunktion, die den funktionalen Zusammenhang zwischen mittlerer Blasenaufstiegsgeschwindigkeit und Sauterdurchmesser in der Blasenströmung beschreibt, kann für die einzelnen Betriebszustände die Flussdichte der Phasengrenzfläche Sb approximiert werden, die als Schlüsselparameter zur Bestimmung der Flotationsrate gilt.Aufgrund der Inhibierung von Koaleszenz in der Blasenströmung fällt für kosmotrophe Salze die Blasengröße mit steigender Salzkonzentration entlang einer Exponential-Funktion. Hierdurch steigt der Gasanteil in dem Flotationsbehälter entlang einer Sigmoid-Funktion an und die Flussdichte der Phasengrenzfläche nimmt zu. Mit Sodium-Dodecyl-Sulfat (SDS) als oberflächenaktiver Modellsubstanz wurde dessen Abreicherung anhand von Batch-Versuchen unter Variation der Gasleerrohrgeschwindigkeit, der SDS-Konzentration und der NaCl-Konzentration mit einem hierfür entwickelten Gasanteilsensor messtechnisch erfasst. Aus den Messdaten wurde die Konzentrationsabnahme in Abhängigkeit der Flotationszeit berechnet und in Bezug zur Flussdichte der Phasengrenzfläche gesetzt. Die Ergebnisse wurden zur Erstellung eines Berechnungsprogramms genutzt, welches den Stofftransport an die Phasengrenzfläche durch eine flächenbezogene Anlagerungsfunktion berechnet. Diese ist entweder in ein Differentialgleichungssystem eingebettet oder wird in einer Berechnungsschleife mit thermodynamisch begründeter Adsorptionsisotherme genutzt. Damit kann der Einfluss von Gasleerrohrgeschwindigkeit und Flussdichte der Phasengrenzfläche auf die Flotation gezeigt und der Bezug zu der Abreicherung von OAS und den hierbei auftretenden Stofftransport hergestellt werden.Item Open Access Proton-conducting (blend) membranes based on sulfonated/phosphonated and basic polymers(2024) De Azpiazu Nadal, Ignasi; Tovar, Günter (Prof.)Aiming at new proton-conducting membranes, this thesis deals with the syntheses and characterizations of highly sulfonated poly(arylene sulfides) and other polysulfides for application as polymer electrolytes. The study focuses mainly on the analysis of the polymer structures that would improve the conductivity of current proton conducting membranes while maintaining their mechanical stability. In a first step, several polymers are obtained from which poly(arylene sulfide)s polymers look more promising for further functionalization. They are obtained by using mild reaction conditions of a polycondensation reaction between 4,4 ́-thiobisbenzenethiol (TBBT) and decafluorobiphenyl. Optimization of this reaction allows for the obtainment of higher molecular weights than the ones reported in the literature. In a second step, poly(arylene sulfides) were phosphonated and sulfonated by a nucleophilic aromatic substitution (SNAr) displacement reaction of the fluorine atoms of the fluorinated polymer sub-units using different agents. Highly sulfonated polymers were obtained when using sodium 3-mercapto-1-propanesulfonate and resulted in water soluble ionomers. Kinetic studies of this reaction were performed and several new sulfonated poly(arylene sulfides) were obtained. Finally, stable polymer electrolyte membrane (PEM) with enhanced mechanical and chemical stability were obtained by blending these obtained ionomers with polybenzimidazole (PBIOO). These membranes were further characterized and in the best case a PEM with new sulfonated ionomer showed a conductivity 40 % higher than Nafion 212, used as a golden reference material. The best performing PEM’s obtained were further used in an electrolytic cell being part of eSCALED, a H2020 (MSC-ITN-2017. GA# 765376) European project which aim is to obtain a device that does the artificial photosynthesis in a more efficient way than the current devices.Item Open Access Investigation of tungsten exposed to fusion relevant intense H/He particle fluxes and thermal loads(2016) Lemahieu, Nathan; Tovar, Günter (Prof. Dr.)