Universität Stuttgart
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Item Open Access Integrated process design and optimisation for the production of cellobiose lipids from Ustilago sp.(2024) Oraby, Amira; Rupp, Steffen (Prof. Dr.)Item Open Access Simulation of Electron Bernstein Waves in FLiPS with various numerical methods(2021) Rumiantsev, Kirill; Hirth, Thomas (Prof. Dr.)The plasma generation and heating by microwaves is an important research topic in the field of controlled nuclear fusion. All modern fusion plasma devices such as Wendelstein 7-X use microwave heating. The microwave plasma-heating primarily occurs at the resonances, where the microwaves are efficiently absorbed. The heating scenario must be designed such that the microwaves can reach the resonance. When the plasma exceeds the cutoff density, the microwaves will be reflected, and the resonance becomes inaccessible. However, it is possible to perform heating by Electron Bernstein Waves (EBWs), since these electrostatic waves propagate even in overdense plasmas, unlike the electromagnetic plasma waves. EBWs cannot propagate in the vacuum and must be created through a coupling process. Both O- and X-mode can couple to EBWs. The thesis investigates the coupling of the O- and X-mode to EBWs as well as the EBW propagation with various numerical methods. The application of only one numerical method is not sufficient as the coupling involves very different wavelength scales. The optimal coupling scheme for the expected plasma parameters was determined using a Finite-Difference Time-Domain (FDTD) code. Since EBWs are not included in the code, a Boundary-Value Problem (BVP) code was developed. Using the BVP code, the effect of the collisions on EBWs was studied. The field amplification at the upper-hybrid resonance (UHR), where EBWs couple to the electromagnetic waves, and the effect of the magnetic field on EBWs could be directly visualized. The propagation of the EBW was investigated using the novel ray-tracing code RiP. The ray-tracing simulations provided a clear picture of the essential features of the wave propagation. For the O- and X-mode coupling, the importance of the axial plasma inhomogeneity was shown. For the first time, the method of the Wigner function was applied to calculate the intensity distribution of EBWs. Both, ray-tracing and the Wigner function simulations showed that the inhomogeneous magnetic can cause focusing of EBWs. The focusing effect can have practical applications e.g. for controlled local heating of the plasma. Additionally, the focusing effect can cause a parametric decay due to the field enhancement in the focal regions. In this thesis, the simulations were focused on excitation and propagation of EBWs in the geometry of the linear plasma device FLiPS located at the University of Stuttgart. Measurements were carried out to study the predicted focusing of the EBWs in the FLiPS plasma with monopole antennas. The measurements provided the density profile used in the simulations. The expected amplification of the signal at the UHR was not detected, indicating either the complete collisional absorption of the X-mode at the upper-hybrid resonance, or the turbulent plasma density oscillations that reduce the coupling efficiency to EBWs. These effects can be studied further using the developed tools since they provide a complete toolbox to study the full coupling process to EBWs in an actual experimental geometry.Item Open Access Vernetzung, Permeabilität, Wasser- und Hitzebeständigkeit Polyvinylalkohol-basierter Beschichtungen(2023) Michele, Andre; Tovar, Günter E. M. (Prof. Dr.)Polyvinylalkohol (PVA) ist ein hydrophiles Polymer mit vielfältigen Anwendungsmöglichkeiten. Ein Schwerpunkt liegt auf der Nutzung von PVA als Beschichtungsmaterial. Die Beständigkeit von PVA-Schichten in Wasser ist jedoch gering, da das Polymer unter Ausdehnung des Volumens quillt oder sich vollständig auflöst. Um die Wasserbeständigkeit zu erhöhen, wird PVA deshalb üblicherweise vernetzt. Hierfür sind zahlreiche Methoden bekannt. In der Regel besitzen diese jedoch entscheidende Nachteile. Daher besteht erheblicher Forschungsbedarf, um neue Vernetzungsmethoden für PVA-Schichten zu entwickeln und bestehende Methoden zu optimieren. In dieser Arbeit wurden zwei neue Vernetzungsmethoden für PVA entwickelt. Die erste basiert auf einer Weiterentwicklung der thermischen Vernetzung von PVA, in Anwesenheit starker Säuren. Mit dem Ziel Nebenreaktionen zu minimieren, wurde hierfür p-Toluolsulfonsäure (TSA) als neuer Vernetzer untersucht. Die zweite Methode basiert auf der UV-Licht-initiierten C,H-Insertion. Hierfür wurden zwei neue Polymere, mittels polymeranaloger Umsetzung von PVA mit 4-Fluorbenzophenon und PVA mit 4-Fluorbenzphenon und 1,3-Propansulfon, synthetisiert. Die auf diese Weise erhaltenen Benzophenon-Modifizierten PVA (PVA-BP) und sulfonierten PVA-BP (sPVA-BP), wurden bezüglich ihrer UV-Licht-initiierten Vernetzung untersucht. Für die Entwicklung der thermischen Vernetzung von PVA in Anwesenheit von TSA wurde ein statistischer Versuchsplan mit den experimentellen Parametern Temperatur (ϑ), Vernetzungsdauer (tc) und Massenkonzentration an TSA (wTSA) angewandt. Mit den Ergebnissen konnten statistische Modelle des Vernetzungsprozesses erstellt werden. Bei allen angewandten Parametern wurde die Ausbildung eines unlöslichen Materials und eine Schwarzfärbung beobachtet. Diese Beobachtungen konnten, durch die parallel ablaufende Vernetzung des PVA und Zersetzung durch Dehydratation und Oxidation, erklärt werden. Die Auswertung der aufgestellten Modelle ermöglichte die Identifizierung optimaler Vernetzungsparameter bei minimaler Zersetzung des Polymers. Die Entwicklung von Synthesevorschriften für PVA-BP und sPVA-BP war erfolgreich. Durch die Bestrahlung von PVA-BP- und sPVA-BP-Schichten mit UV-Licht wurden diese vernetzt und kovalent an das Substrat angebunden. Zur Untersuchung der Vernetzungsreaktion wurde ein Modell basierend auf der Perkolationstheorie angewandt. Eine Korrelation zwischen dem Benzophenon-Modifikationsgrad und der Vernetzungsgeschwindigkeit konnte hierdurch festgestellt werden. Dieser Effekt wurde über die größere Anzahl an potenziell reaktiven Gruppen für die C,H-Insertion erklärt. Der Gleichgewichtsquellgrad (EDS) verringerte sich mit fortschreitender Bestrahlungsdauer. Dies konnte mit der Verringerung der Maschenweite des Netzwerkes erklärt werden. Zudem sank der EDS mit steigendem Benzophenon-Modifikationsgrad und sinkendem Sulfonsäure-Modifikationsgrad. Als Erklärung hierfür werden die verringerte Hydrophilie und der geringere osmotischen Druck im Netzwerk, durch die geringere Anzahl an geladenen Sulfonsäure-Gruppen, angeführt. Anwendung fanden die in dieser Arbeit vorgestellten Vernetzungsmethoden bei der Herstellung von wasser- und hitzebeständigen Komposit-Membranen mit semipermeablen PVA-Schichten. Die Membranen waren dicht gegenüber Stickstoff, jedoch gut permeabel für Wasserdampf. Folglich konnte gezeigt werden, dass die vorgestellten Vernetzungsmethoden generell für die Herstellung von Membranen für die Befeuchtung von Luft - auch Befeuchtermembranen (BM) genannt - geeignet sind.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 Modellierung und Diagnostik einer Remote-Mikrowellen-Plasmaquelle zum Hochrateätzen(2024) Pauly, Steffen; Tovar, Günter E. M. (Prof. Dr.)Bei der Herstellung von Mikrosystem-Strukturen werden Fotolacke eingesetzt, um über lithografische Verfahren Oberflächenstrukturen im Sub-Mikrometerbereich herzustellen. Der Fotolack wird als dünne Schicht auf ein Substrat aufgebracht und durch eine Maske, welche die zu erhaltende Struktur enthält, über UV-Licht ausgehärtet. Dabei dient der strukturierte und ausgehärtete Lack als Schutz für die darunterliegenden Schichten oder als formgebende Struktur der unbedeckten Bereiche. Diese Bereiche können über Ätzprozesse abgetragen oder durch galvanische Abscheidung mit einer Metallschicht überzogen werden. Im Anschluss muss der ausgehärtete Fotolack wieder entfernt werden. Das Problem dabei ist, dass dieser ein hochstabiles vernetztes Material darstellt, was nur äußerst schwer wieder entfernt werden kann, ohne dass dabei die aufgebrachten Metallstrukturen oder die geschützten darunterliegenden Schichten beschädigt werden. Die Entfernung des ausgehärteten Lacks geschieht heutzutage über Trockenätzverfahren. Diese Arbeit befasst sich deshalb mit der simulativen und experimentellen Untersuchung einer im Niederdruck arbeitende Remote Mikrowellen Plasmaquelle (RMPS) der Firma Muegge GmbH, die beim trockenchemischen Hochrateätzen von Fotolacken Anwendung findet. Dazu werden Mikrowellensimulationen durchgeführt, die die Feldverteilung in der Plasmakammer bei Zündbedingungen zeigen, welche über Mikrowellenfeldversuche verifiziert werden konnten. Mit dem Drude-Modell werden vereinfachte Plasmasimulationen durchgeführt, die den Einfluss der Elektronendichte auf das Mikrowellenfeld veranschaulichen. Der visuelle Vergleich der Drude-Modell-Simulationen mit Fotografien des Plasmas verdeutlicht auch hier eine gute Übereinstimmung. Die Erweiterung der Simulation mit dem Fluid-Modell berücksichtigt Teilchenbewegungen und Reaktionen im Plasma. Die Ergebnisse zeigen den zeitlichen Verlauf der Elektronendichte in der RMPS, welche über dreidimensionale Langmuir-Sondenmessungen quantitativ validiert werden konnten.Item Open Access UV-advanced oxidation process without additives in liquid phase : process characterization and validation(2020) Toro Santamaria, Jorge Mario; Hirth, Thomas (Prof. Dr.)Human activities are gradually generating a strong impact on the environment and the quality of natural water resources. Traces of hazardous substances are detected not only in wastewater but also already in natural water bodies (surface and ground water) around the globe. The source of these trace substances is broad, starting with chemicals from industrial production like polycyclic aromatic hydrocarbons, pesticides, food ingredients, pharmaceuticals, to components of personal care, just to mention examples. Because of their constantly growing presence in water resources, and the fact that some of those are seriously affecting natural biological processes, there is an increasing need for finding ways to impede those substances to reach water bodies. The European community has adopted the water pollution problematic as one of their main concerns. As a result, on the 23 October 2000, the Directive 2000/60/EC of the European Commission was adopted. The main purpose of the directive is the protection of European natural water resources by enhancing the status of the water bodies as well as preventing further contamination. In particular, the requirement of complying with European environmental quality standards (EQS) for priority substances (PD) became compulsory. In order to meet these requirements and directives, industry and the scientific community working in the fields of water treatment, do approach new treatment processes with the purpose of upgrading current treatment plants to destruct or reduce trace substances. One alternative are the so called Advanced Oxidation Processes (AOPs), which are able to treat persistent and hardly biodegradable pollutants by oxidation processes. Between the varieties of potential AOPs the photo-induced advanced oxidation, centred on photolysis of water by radiation below 200 nm has received special attention. The key feature of the photo induced AOP is the facts of the efficient production of hydroxyl radicals as the highest possible oxidant and the singularity of no need for aux-iliary oxidants like hydrogen peroxide, ozone, peroxydisulfate or peroxymonosulfate, needed in other AOPs. One of the most important steps to bring the photo induced AOP to be used in the real field, is to prove that the process can be operated under efficient conditions, controlling the generation of hydroxyl radicals and utilizing them efficiently for the goal of treatment. An important action to push the technology to the path of product development is therefore, the integration of efficient UV sources to a photo reactor, taking into account the peculiarities of the process. Overall, the research presented in this thesis focuses on the characterization of the photoreaction zone, the light penetration and absorption process as well as the hydroxyl radical generation and provides the understanding and database to enable different approaches for the engineering of photo induced AOP. Concretely, this thesis is structured in five parts. Part I includes the literature search and its analysis; different calculations and simulations were performed with the aim of describing the heterogeneity of the reaction zone, the theoretical penetration of radiation in water and understanding the theoretical spatial generation of hydroxyl radicals. Part II includes the reactor characterization. The photo induced AOP was first tested following the degradation of Methylene Blue (MB). Subsequently it was studied the impact of the channel dimen-sions in the oxidation process under different operational parameters and the characterization of the photo reactor in terms of radiation intensity using three different methods. Part III includes the process characterization where the investigations were focused on the penetration of radiation into water and the generation of hydroxyl radicals by means of two methodologies: the transmission measurements in thin water films and the degradation of methanol as reference substance. Part IV includes the tailor made reactor validation. In this part, the focus was directed to verify the numeric models and gain data enabling the design, construction and validation of a reactor system using flat lamps. Validation of the photo induced AOP was performed by means of degradation of the pharmaceuticals Sulfaquinoxaline (SQX) and Carbamazepin (CBZ), as well as the degradation of an organic substance coming from the chemical industry Bisphenol A (BPA) and a food ingredient Caffeine (CAF). During the validation phase the concentration of the substances, the Total Organic Carbon (TOC) and the cytotoxicity using VERO and COS cell lines for each experiments were followed. Part V summarizes the results. In general, it was found that the process shows attractive potential and advantages in comparison with other oxidation technologies. For example: the steady and local production of hydroxyl radical without the addition of supplementary oxidation agents; the not strong selectivity and the capacity of mineralization of the process; the pH independency of the oxidation process; the fact that cytotoxicity of the byproducts does not overpass the initial toxicity of the tested substances and the Dose requirements for oxidation is comparable with existing process without using any additive.Item Open Access Hydrogele aus Polyethylenglykol und methacryloylierter Gelatine für biosensorische Oberflächen(2024) Grübel, Jana; Tovar, Günter E. M. (Prof. Dr.)Item Open Access Electron cyclotron emission investigations at the stellarator TJ-K(2020) Sichardt, Gabriel; Hirth, Thomas (Prof. Dr.)Microwave diagnostics are widely used in fusion-oriented plasma research. Especially, electron cyclotron emission (ECE) measurements are routinely employed for reliable investigations of radial temperature profiles. Furthermore, an ECE diagnostic can be used to measure electron densities or detect superthermal electrons. Due to its non-invasive character, it is well suited for application to extreme conditions like in fusion plasmas since neither the plasma is perturbed nor the diagnostic harmed. Despite decades of development, ECE diagnostics are still subject of current research and development. Especially the correct interpretation of measurements at plasmas with low densities and temperatures, which are in contrast to fusion plasmas optically thin, is challenging. The stellarator experiment TJ-K in Stuttgart is operated with such thin plasmas allowing for the use of Langmuir probes for temperature measurements and thus as a benchmark for a new ECE diagnostic system. This work is about the development, optimization, construction and application of an ECE diagnostic for TJ-K. Modeling, simulation and experiment are combined to understand the processes at the specific experiment and to adapt the setup to these conditions. The first part of this thesis describes the development and test of the diagnostic. To this end, the transport and propagation of electron cyclotron radiation is simulated in the three-dimensionally modeled plasma of TJ-K. From the results, an optimization approach is derived: with a suitably positioned and optimally curved mirror for defined reflections, a tunable resonator system is built that improves the localization of the measurements significantly. After identification of the measurement signals as ECE opposed to thermal bremsstrahlung, the measurement system is calibrated with the hot-cold method. Although only about 0.2 % of the black body intensity is emitted from the optically thin plasma the temperatures obtained from the ECE diagnostic could be verified by Langmuir probe measurements. In the second part, numerical investigations of electron trajectories in the 3D magnetic field of TJ-K are employed to study their dependence on the kinetic particle energy. The trajectories form drift orbits which depend on the speed and orientation of the electron compared to the magnetic field. To what extent electrons on larger drift orbits collide with the vessel wall and thus contribute to toroidal net currents is investigated using simulations with different velocity distributions. It becomes apparent that especially electron populations additional to the thermal distribution at higher energies like for instance 1 keV, superthermal electrons, can result in large toroidal net currents. Already thermal electrons with typical energies of 10 eV provide numerically toroidal net currents that are comparable to the experimentally observed currents. The installed ECE diagnostic allows for temporally resolved measurements of local radiation temperatures for correlation with toroidal net currents.Item Open Access Synthesis and characterization of multifunctional macromonomers and photoacid generators for the modification of hydrogels(2020) Reinold, Karishma Katharina; Tovar, Günter (Prof. Dr.)Item Open Access Entwicklung eines Verfahrens zur Herstellung von Propylenoxid und Phenol mittels Ganzzellbiokatalyse unter Nutzung der Methan-Monooxygenase des Organismus Methylosinus trichosporium OB3b(2022) Derwenskus, Ilka Madeleine; Hirth, Thomas (Prof. Dr.)
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