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Climate change and global warming caused by the increasing greenhouse gases emissions (such as CO2) in the atmosphere recently attract the attention of the scientific community. These large emissions have been correlated to the Global Warming effect which has many consequences across the globe, including glacial retraction, ocean acidification and increased severity of weather events. With green technologies still in the infancy stage, it can be expected that CO2 emissions will stay this way for a long time to come. It is necessary to find an alternative way to get rid of the resulting environmentally harmful emissions. A promising solution is the use of CO2-free electrical energy produced, for example, by renewable or nuclear sources, for dissociation of CO2 or other greenhouse gases, followed by their conversion into easily storable fuels. In this context, the CO2 re-utilization to synthesize syngas, fuels or chemical compounds as well as pure CO2 dissociation into CO and O2, is of a special interest. Among the different methods to convert CO2 into added-value products (thermolysis, thermochemical cycles, electrolysis, photocatalysis, etc), the discharges sustained by microwave radiation combining high electron and low gas temperature have already demonstrated huge potential for plasma-assisted CO2 conversion. The present research work is targeted to the systematic investigation of the microwave-assisted conversion of various CO2-based gas mixtures being especially focused on plasma catalysis. The different physical effects affecting the efficiency of plasma catalysis are considered, for a better understanding of the synergistic effects between plasma and catalyst. The characterization of microwave discharges is performed by various plasma diagnostics methods, including optical spectroscopy and gas chromatography. In addition, the catalysts have been characterized by the state of art material characterization techniques, such as Transmission electron microscopy (TEM), Raman spectroscopy, etc. Such a combined characterization of both plasma and catalysts is performed for the sake of better understanding of the plasma-catalytic processes.In the first part of this study, the different dissociation pathways of the studied molecule as a function of different plasma parameters are considered by evaluating the composition with different plasma diagnostic techniques. A simple increase of Specific Energy Input (SEI) is not a promising solution since in this case the energy efficiency drops. The beneficial effects of lowering the pulse frequency for increasing CO2 conversion efficiency are observed and discussed. The obtained results are explained by the relation between the plasma pulse parameters and the rates of the relevant energy transfer mechanisms in the discharge. Simultaneous dissociation of CO2 and H2O has been investigated as well. It was clearly demonstrated that both H2 and CO productions are strongly affected by the different plasma parameters. The second part of this study deals with the effects of catalyst preparation method, nature of plasma activation gas, gas admixture, as well as NiO content and their influences on the CO2 conversion and energy efficiencies in microwave plasma. It was found throughout this work that the catalyst preparation method has a significant effect on the chemical and physical properties of the catalysts, which in turn strongly influences CO2 conversion and energy efficiencies of this process. In particular Ar plasma treatment results in a higher density of oxygen vacancies and a very favorable distribution of nickel oxide on the TiO2 surface. It is concluded that, the oxygen vacancies are the key factor explaining high catalytic activity in CO2 decomposition. The dissociative electron attachment of CO2 at the catalyst surface enhanced by the oxygen vacancies and plasma electrons can explain the observed increase of CO2 conversion efficiency as well as the energy efficiency. A mechanism explaining the observed plasma–catalyst synergy is proposed. The overall aim is to establish a model describing the interaction between highly reactive species produced in plasma discharge and supported catalyst for the conversion of CO2 into useful compounds. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

This diploma thesis was focused on the possibility of using a plasma nozzle to accelerate the wound healing process. The benefits of using low-temperature plasma in medicine or biomedical applications are known from many studies, and low-temperature plasma is already used to sterilize medical devices, materials or surgical instruments. Some studies also report a high potential of usinh plasma nozzle in the treatment of skin wounds. In the experimental part of this work, an in vitro wound healing test was performed using two different low-temperature plasma sources. Source No. 1 was a surface wave microwave discharge and source No. 2 was a torch microwave discharge. An in vitro scratch healing test was performed on a monolayer of HaCaT keratinocytes and testing was performed using various parameters. The influence of the plasma treatment time was monitored, as well as the influence of the plasma discharge power and also the influence of the argon working gas flow. Especially when using a torch microwave discharge, faster wound healing was recorded at most of the parameters used compared to the control. Thus, it can be said that this source appears to be potentially suitable for faster wound healing. Furthermore, in the work using the MTT cytotoxicity test, the viability of skin cells after their plasmination was also monitored using the same conditions as in the in vitro wound healing test. When performed in the standard MTT assay, none of the settings or sources used showed any cytotoxic effects on keratinocytes. LDH cytotoxicity tests were also performed concurrently to verify the accuracy of the MTT assays. The results of both tests agreed and the use of low-temperature plasma in skin treatment can be considered as safe. Overall, the results show that the plasma nozzle can find use in medicine in the healing of skin wounds and chronic defects as a potentially fast, inexpensive and effective method.

This master´s thesis is focused on the utilization of the sterilization effects of low temperature plasma towards the bacterial microorganisms that occur mainly on the human skin. The plasma sterilization process is fast efficient, non-toxic, environmentally friendly, cost-effective and safe for the operating staff as well as for the patient. Another advantage of using low temperature plasma is to support cell proliferation and wound healing. By combining these advantages, an effective method can be obtained, which would sterilize the wounds sparingly with regard to the surrounding healthy tissue and support the regeneration of the damaged tissue at the same time. In the experimental part, gram positive and gram negative bacteria were used to prove the sterilization effects with respect to different cell wall structure. Staphylococcus epidermidis and Propionibacterium acnes, which cause purulent skin inflammations, were used as gram-positive microorganisms. Serratia marcescens and Escherichia coli were selected from gram positive bacteria. These model organisms were inoculated at various concentrations on culture broths and treated by plasma at a distance of 1 mm from the agar surface. The microwave discharge was generated in argon at a power of 9 W, a gas flow rate of 5 l / min and water cooling to avoid thermal effects on the treated surface. Subsequently, model skin cells of HaCaT were exposed to low temperature plasma and tested for plasma cytotoxicity to demonstrate its healing effects. The obtained results make it possible to state that the sterilizing effects of low-temperature plasma in all tested gram-positive and gram-negative bacterial strains are verified in this work. Finally, tests were demonstrated using a suitable method of the treatment on human skin cells, where the safety and usefulness of the tested low-temperature plasma was demonstrated when applied to shorten the healing process.

This diploma thesis deals with the ongoing research under the auspices of the Department of Applied Physics and Technics Faculty of Education, University of South Bohemia in České Budějovice, in which the author of the work was actively participated. The thesis is divided into theoretical and experimental part. The theoretical part contains information from natural polymers, especially cellulose, plasma technology and infrared spectrometry. The subject of the experimental part of the thesis is research that deals with the functionalization of cellulose using a microwave plasma discharge on the apparatus CX-22. In the present research was also conducted to process optimization of functionalization with the liquid precursor hexamethyldisiloxane (HMDSO).

The aim of the Master thesis is the investigation of the influence of microwave discharge for skin wound healing. Microwave discharge used for this work was argon microwave plasma generated by the surface wave and direct vortex torch. The theoretical part is focused on basic information about plasma and processes that occur in plasma discharge under specific conditions. Plasma generates various active particles such as hydroxyl radicals, nitric oxide radicals, excited nitrogen molecules, atomic nitrogen, argon and oxygen. All of these particles together with plasma generated photons are usable in biomedical applications and summary of them is shown in the theoretical part. The experimental part is focused on the comparison of torch discharge and microwave plasma generated surface wave in skin wound healing. The model wounds on laboratory mousses were treated by plasma and wound healing was examined during 3 weeks after the plasma treatment. Both plasma systems showed healing acceleration. Application of torch discharge was proved to be the most effective method in the healing of skin defects. Additionally, determination of active particles was taken by optical emission spectroscopy. Based on these measurements, plasma parameters were determined: electron temparutare, rotational and vibrational temperatures. To determine role of different plasma active species, the treatment of indigo coloured artificial skin model was treated under various conditions by both plasma systems. Results show that the direct interaction between plasma particles is the main effect, role of radiation, only, is more or less negligible. Finally, the plasma vortex system was visualized using fast camera at selected powers and gas flows.

Au cours des dernières décennies, les plasmas créés par une décharge micro-ondes ont de plusen plus attiré l’attention de la communauté scientifique aérospatiale sur le sujet du contrôled’écoulements. En effet, il a été démontré expérimentalement que le dépôt d’énergie obtenu parle plasma peut modifier les propriétés aérodynamiques de l’écoulement autour d’un objet telleque la trainée de frottement. Or, la conception et l’optimisation de ces actionneurs plasma entant que technique de contrôle d’écoulements nécessitent une compréhension approfondie de laphysique sous-jacente que les seules expériences sont incapables de fournir.Dans ce contexte, nous nous intéressons à la modélisation numérique de l’interaction desondes électromagnétiques avec un plasma et le gaz afin de mieux comprendre la nature desdécharges micro-ondes et leur applicabilité. La modélisation de ces phénomènes présente desdifficultés importantes en raison du couplage multi-physique et donc de la multitude des échellesspatiales et temporelles qui apparaissent. Ce travail de thèse traite des questions de physiqueet de mathématiques appliquées soulevées par la modélisation numérique de ces plasmas.La première partie du travail se focalise sur les questions de validité du modèle physique duclaquage micro-onde fondé sur l’approximation de champ effectif local. En raison des gradientsde densité du plasma très élevés, la validité du concept de champ effectif local peut être misen doute. Pour cela, un modèle fluide du second ordre est développé en incluant une equationd’énergie électronique non-locale. Cette modélisation permet de décrire de façon plus précisele dépôt d’énergie par plasma induisant la formation d’ondes de choc dans le gaz. Une analysedimensionnelle du système d’équations fluide permet de caractériser la non-localité en espace dubilan d’énergie électronique en fonction du champ électrique réduit et de la fréquence de l’onderéduite. Une discussion est également menée sur d’autres approximations des coefficients detransport électronique. Dans une deuxième partie, la construction et l’analyse d’une méthode multi-échelles derésolution numérique du problème de propagation des ondes électromagnétiques dans le plasmasont réalisées. Il s’agit du couplage entre les équations de Maxwell dans le domaine temporel avecune équation de quantité de mouvement pour les électrons. L’approche s’appuie sur la méthodede décomposition de domaine de type Schwartz, basée sur une formulation variationnelle duschéma de Yee et utilisant deux niveaux de grilles Cartésiennes emboitées. Une grille locale,appelée patch, est utilisée pour calculer de manière itérative la solution dans la région du plasmaoù une meilleure précision est requise. La méthode proposée permet le raffinement local etdynamique du maillage spatial tout en conservant l’énergie du système. Une analyse théorique dela convergence de l’algorithme pour les résolutions temporelles explicite et implicite est égalementréalisée. Dans la dernière partie, des simulations numériques sur le claquage micro-ondes et la formation de structures filamentaires de plasma sont conduites. Les effets de différents types d’approximations sur le modèle physique du plasma sont analysés. Puis, ces expériences numériques démontre la précision et l’efficacité, en terme de temps de calcul, de la méthode multi-échelleproposée. Enfin, on étudie les effets de chauffage du gaz sur la formation et l’entretien de structures filamentaires dans l’air à pression atmosphérique. Pour cela, le modèle micro-onde-plasma développé est couplé avec les équations de Navier-Stokes instationnaires pour les écoulements compressibles. Les simulations montrent des caractéristiques intéressantes de la dynamique deces structures plasma pendant le processus de chauffage du gaz, qui sont en accord étroit avec les données expérimentales. / In recent decades, microwave discharge plasmas have attracted increasing attention of aerospace scientific community to the subject of aerodynamic flow control because of their capability of sub- stantially modifying the properties of the flow around bodies by effective energy deposition. The design and optimization of these plasma actuators as flow control technique require a compre- hensive understanding of the complex physics involved that the sole experiments are incapable to provide.In this context, we have interest in the numerical modeling of the mutual interaction of elec- tromagnetic waves with plasma and gas in order to better understand the nature of microwave discharges and their applicability. A challenging problem arises when modeling such phenomena because of the coupling of different physics and therefore the multiplicity of spatial and tempo- ral scales involved. A solution is provided by this thesis work which addresses both physics and applied mathematics questions related to microwave plasma modeling.The first part of this doctorate deals with validity matters of the physical model of microwave breakdown based on the local effective field concept. Because of large plasma density gradients, the local effective field approximation is questionable and thus a second-order plasma fluid model is developed, where the latter approximation is replaced by the local mean energy approximation. This modeling approach enables to take into account the non-locality in space of the electron energy balance that provides a more accurate description of the energy deposition by microwave plasma leading to the shock waves formation into the gas. A dimensionless analysis of the plasma fluid system is performed in order to theoretically characterize the non-locality of the introduced electron energy equation as function of the reduced electric field and wave frequency. It also discusses other approximations related to the choice and method of calculation of electron transport coefficients.Concerning the mathematical aspects, the thesis work focuses on the design and the analysis of a multiscale method for numerically solving the problem of electromagnetic wave propagation in microwave plasma. The system of interest consists of time-dependent Maxwell’s equations coupled with a momentum transfer equation for electrons. The developed approach consists of a Schwartz type domain decomposition method based on a variational formulation of the standard Yee’s scheme and using two levels of nested Cartesian grids. A local patch of finite elements is used to calculate in an iterative manner the solution in the plasma region where a better precision is required. The proposed technique enables a conservative local and dynamic refinement of the spatial mesh. The convergence behavior of the iterative resolution algorithm both in an explicit and implicit time-stepping formulation is then analyzed.In the last part of the doctorate, a series of numerical simulations of microwave breakdown and the filamentary plasma array formation in air are performed. They allow to study in detail the consequences of the different types of physical approximations adopted in the plasma fluid model. Then, these numerical experiments demonstrate the accuracy and the computational efficiency of the proposed patch correction method for the problem of interest. Lastly, a numerically investigation of the effects of gas heating on the formation and sustaining of the filamentary plasma array in atmospheric-pressure air is carried out. For doing this, the developed microwave-plasma model is coupled with unsteady Navier-Stokes equations for compressible flows. The simulations provide interesting features of the plasma array dynamics during the process of gas heating, in close agreement with experimental data.