Resumo: Materiais poliméricos têm sido amplamente utilizados em várias áreas tecnológicas e biomédicas, devido às suas excelentes propriedades mecânicas, térmicas e elétricas. No entanto, estes materiais têm baixa energia de superfície e, portanto, não aderem facilmente a outros materiais. Por isso, para muitas aplicações é necessário modificar a superfície do polímero, a fim de aumentar a sua energia de superfície. Tratamentos a plasma à pressão atmosférica têm sido muito utilizados para modificar as propriedades superficiais de polímeros comerciais, devido aos baixos custos do processo. Este trabalho apresenta os resultados do tratamento de tereftalato de polietileno (PET), poliuretano (PU) e de politetrafluoretileno (PTFE) em plasma de descargas com barreira dielétrica (DBD) em ar, nitrogênio e argônio, à pressão atmosférica. As superfícies tratadas foram caracterizadas por medidas de ângulo de contato, espectroscopia de fotoelétrons de raios-X (XPS) e microscopia de força atômica (AFM). A superfície polimérica, modificada nas DBD a pressão atmosférica, mostraram uma redução significativa no ângulo de contato da água, embora uma recuperação parcial da molhabilidade ocorresse nos primeiros dias após o tratamento. Todavia, a recuperação foi insuficiente para que as amostras tratadas recuperassem a sua molhabilidade original. Análises de XPS mostraram um aumento na concentração de oxigênio na superfície, devido à formação de grupos polares, tais como C-O e OC= O. Um pequeno aumento na concentração de nitrogênio também foi observada. Imagens de AFM mostraram um aumento da rugosidade de polímeros tratados, decorrentes da interação física entre as espécies geradas na descarga e a superfície do polímero. A superfície ativada e a elevada tensão superficial dos polímeros tratados devem levar a um aumento da aderência do polímero. / Abstract: Polymeric materials have been widely used in various biomedical and technological applications, due to their excellent mechanical, thermal and electric properties. However, these materials have low surface energy, and thus not easily adhere to other materials. Therefore, for many applications it is necessary to modify the polymer surface in order to increase its surface energy. Plasma treatments at atmospheric pressure have been frequently used to modify the surface properties of commercial polymers, due to their low process costs. This work reports the results of polyethylene terephthalate (PET), polyurethane (PU) and polytetrafluoroethylene (PTFE) treatments in plasma by dielectric barrier discharges (DBDs) in air, nitrogen and argon at atmospheric pressure. The plasma-modified surfaces were characterized by contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The polymer surface, modified by DBD at atmospheric pressure, showed a significant decrease in water contact angle although a partial recovery of the surface wettability occurred during the first few days after the treatment. However, the process of hydrophobic recovery was insufficient for complete recovering of the samples original wettability. XPS analysis showed an increase of the oxygen concentration on the surface, due to the formation of polar groups, such as C-O and OC= O. A small increase in the concentration of nitrogen was also observed. AFM images exhibit an increased roughness of the treated polymers because of the physical interaction between the species generated in the discharge and the polymer surface. The activated surface and high surface tension of treated polymers should promote an enhancement of the polymer adhesion to paints and coatings. / Orientador: Konstantin Georgiev Kostov / Coorientador: Roberto Yzumi Honda / Banca: Konstantin Georgiev Kostov / Banca: Rogério Pinto Mota / Banca: Gilberto Petraconi Filho / Mestre

Le dioxyde de carbone, principal gaz à effet de serre lié aux activités humaines, est considéré comme l’un des gaz les plus problématiques pour notre environnement ces dernières années, principalement à cause du réchauffement climatique qu’il engendre. C’est pour cette raison que l’augmentation de sa teneur dans l’atmosphère nous concerne tous quant aux conséquences futures pour notre planète. Afin de limiter l’émission de CO2, sa conversion en composés à valeur ajoutée présente un grand intérêt et est possible notamment via des procédés plasmas. Plus particulièrement, les décharges à barrière diélectrique (DBD) sont utilisées depuis quelques années pour générer des plasmas froids opérant à pression atmosphérique, principalement pour des applications en traitement de surface, mais également pour le traitement d’effluents gazeux.Lors de cette thèse, nous nous sommes focalisés sur le processus de dissociation du CO2 en CO et O2 via un réacteur DBD à flux continu et avons analysé sa conversion et son efficacité énergétique via différentes études. Celles-ci ont été réalisées grâce à plusieurs méthodes de diagnostic, comme par exemple la spectrométrie de masse utilisée pour déterminer la conversion et l’efficacité du processus, la spectroscopie d’émission optique, l’oscilloscope pour une caractérisation électrique, etc. afin d’avoir une meilleure compréhension du comportement des décharges CO2.Dans un premier temps, nous avons réalisé une étude détaillée d’un plasma CO2 pur où nous avons fait varier différents paramètres, tels que le temps de résidence, la fréquence, la puissance, la pulsation de la haute tension et l’épaisseur et la nature du diélectrique. Le CO2 donne lieu généralement à une décharge filamentaire, consistant en de nombreuses microdécharges réparties au niveau de la zone du plasma. Celles-ci constituent la principale source de réactivité dans une DBD. Un aperçu détaillé de l’aspect physique de ces microdécharges a été réalisé grâce à la caractérisation électrique, permettant de mieux comprendre les propriétés électriques de la décharge et des microdécharges. En effet, nous avons pu déterminer l’importance de la tension présente au niveau du plasma, de l’intensité du courant plasma, du nombre de microdécharges et de leur temps de vie sur l’efficacité du processus de dissociation de CO2.Ensuite, nous avons conclu ce travail avec des études combinant le CO2 en phase plasma avec de l’eau ou du méthane afin de produire des molécules à valeur ajoutée telles que les syngas (CO et H2), mais aussi des hydrocarbures (C2H6, C2H4, C2H2 et CH2O) dans le cas de l’ajout du méthane. A travers ces études, nous avons obtenu une meilleure connaissance de la chimie et de la physique qui ont lieu dans ce type de plasma. / Carbon dioxide appears as one of the most problematic gases for the environment, mostly because it is responsible for global warming. This is why its increasing concentration into the atmosphere, mainly due to anthropogenic activities, is a real concern for planet Earth. In order to prevent the release of large amounts of CO2, its conversion into value-added products is of great interest. In this context, plasma-based treatments using dielectric barrier discharges (DBDs) are nowadays more and more used for the conversion of this gas. In this thesis, we investigated the CO2 splitting process into CO and O2 via a flowing cylindrical DBD and we studied its conversion and energy efficiency by means of several diagnostic methods, such as mass spectrometry to determine the conversion and energy efficiency of the process, optical emission spectroscopy for gas temperature measurements, and an oscilloscope for electrical characterization, in order to obtain a better understanding of the CO2 discharge itself.First, we focused on an extensive experimental study of a pure CO2 plasma where different parameters were varied, such as the gas residence time, the operating frequency, the applied power, the pulsation of the AC signal, the thickness and the nature of the dielectric. CO2 discharges typically exhibit a filamentary behavior, consisting of many microdischarges, which act as the main source of reactivity in a DBD. A detailed insight in the physical aspects was achieved by means of an in-depth electrical characterization, allowing more insight in the electrical properties of the discharge and more specifically in the microdischarges, which are spread out throughout the active zone of the plasma. It was found throughout this work that the plasma voltage, which reflects the electric field and thus determines how the charged particles are accelerated, the plasma current, which reflects the electron density, but also the number of microdischarges and their average lifetime, play an important role in the efficiency of the CO2 dissociation process. It was revealed that the microdischarge number is important as it represents the repartition of the locations of reactivity. Indeed, as the microfilaments are more spread out in the same discharge volume, the probability for the CO2 molecules to pass through the reactor and interact with at least one microdischarge filament becomes more important at a larger number of microfilaments.The second part of the thesis was dedicated to discharges combining CO2 and H2O or CH4, both being hydrogen source molecules. The combined CO2/H2O or CO2/CH4 conversion allows forming value-added products like syngas (CO and H2), but also hydrocarbons (C2H6, C2H4, C2H2 and CH2O), at least in the presence of methane. Throughout this study, we tried to obtain a better knowledge of the chemistry and physic behind these conversion processes. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

<div>Plasma treatment of polymers has been a rapidly growing area of research due to its broad applications, homogenous and repeatable surface properties, low cost, and environmental friendliness when compared to alternative techniques. Only recently have significant developments been made in the application of atmospheric pressure plasma in polymer surface treatment. The use of atmospheric pressure plasma enables further reductions in cost and mechanical complexity. Of particular interest in this work is the application of atmospheric pressure plasma for the isolated modification of the inner surfaces of small diameter polymer tubing to improve the wetting and adhesion characteristics compared to untreated polymer.</div><div>This work focuses on the development, characterization, and implementation of an atmospheric pressure dielectric barrier discharge (DBD) plasma apparatus for the treatment of the inner surface of polymer tubes. The iterative process of the development of this system is detailed, with two finalized designs established and defined. These two designs are then applied to low density polyethylene (LDPE) tubing of 0.38 mm inner diameter (ID), and characteristics for surface morphology and wettability are analyzed.</div><div>Investigation of the relationship between plasma power and treatment time with morphology characteristics of protrusion density and size and surface roughness parameter, R_a is presented. Treatment times of 5, 10, 15, 30 and 45 minutes are performed on tubing samples at a power level of 35 mW. From 5 to 15 minutes, protusion density increases rapidly, from n_p=4*10^4- 10^7 protrusions/(mm^2 ), and small variation in protrusion size, with 0.1< A_p<0.2 μm^2. At treatment times of 30 and 45 minutes, coalescence of protrusions was observed, resulting in a decrease in protrusion density, down to n≈4*10^4 protrusions/(mm^2 ), and substantial increases in mean protrusion size, up to A_P=5-9 μm^2. Plasma powers of 9, 12, 16, 25, 35, and 45 mW were also investigated, at a treatment time of 15 minutes. As power level was increased, protrusion density was observed to increase, with an inverse relationship with mean protrusion size. Protrusion density was observed to increase from n_p=2*10^5-10^7 protrusions/(mm^2 ), with diminishing increases in density observed between power levels of 35 and 45 mW. Protrusion mean size was observed to decrease from A_p= .25-0.025 μm^2, with similar diminishing reductions observed at 35 and 45 mW. Surface roughness, R_a, was observed to vary from .01-0.3 μm, or ISO roughness grades N1 to N5, in the treated samples.</div><div>Wettability characteristics were measured and characterized relative to plasma power and linear feed rate. Wettability was measured by measurement of contact angles of the meniscus formed from water introduced into the tubing volume by capillary action. On all samples treated, a duality of mechanisms for surface wetting were observed. After initial treatment, samples were observed to have a lower contact angle, indicating higher wettability, but after 12 hours samples were observed to have reduced wetting characteristics, indicating a transient mechanism for surface wetting in addition to permanent effects induced my surface morphology. Samples were treated at plasma powers of 7, 10, 15, 20, and 40 mW. At all power levels, initial contact angle was generally consistent, with 20^o< θ_0<30^o. Permanent wetting features measured on these samples indicated almost complete reversing of wettability at 7 and 10 mW, with θ_SS measured at ~75^o, comparable to the average measurement of an untreated sample of ~80^o. Conversely, at higher powers of 15, 20 and 40 mW, significant retention of wettability was observed, with 45^o<θ_SS<55^o for those samples.</div><div><br></div>

This diploma thesis is focused on studying of the effect of the dielectric barrier discharge (DBD) on eucaryotic microorganisms. Plasma sterilization is considered to be an alternative method to conventional sterilization processes. Contrary to standard decontamination methods it doesn´t stress exposed material by heat, pressure and chemicals. Plasma acts on eucaryotic and procaryotic systems by means of synergy of three inactivation mechanisms. They are various reactive species, UV radiation and heat. The Aspergillus niger has been chosen as a bio-indicator enabling to evaluate the effect of plasma assisted microbial inactivation. Plasma was generated in dielectric barrier discharge (DBD) at atmospheric pressure. Nitrogen and argon were used as working gases, paper and PET foil were used as carrying media. The influence of various working conditions on the sterilization effect was studied. Namely it was the influence of plasma exposition time, plasma power density, the type of operating gas and type of supporting medium. The effect of UV radiation in combination with temperature, temperature and direct plasma were studied separately. According to our results the efficiency of DBD increases with plasma power density, resp. plasma exposition time. When comparing sterilization efficiency of nitrogen and argon operating at the same conditions, the higher sterilization effect was observed in argon. The influence of the carrying medium on sterilization effectiveness was proved. It was caused by the different structure of surface. It was found out, that in our experimental setup the active species are probably the main inactivation mechanism. The influence of temperature on inactivation of microorganisms was negligible. The combination of UV radiation and temperature reached the decontamination level about 2 orders. The discharge parameters were studied by means of optical emmision spectroscopy. Scanning electron microscopy enabled to evaluate possible damage of exposed materials through DBD.

<p>  </p> <p>In the time after their conception, Dielectric Barrier Discharge (DBD) systems have become highly utilized in the field of plasma research, with applications ranging from medicine to water treatments to airfoil design. One of the more recent applications for DBD systems has been the plasma treatment of polymers, overcoming the deficits of previously used chemical treatment systems such as environmental hazards, high cost, and other complexities. A novel development occurring within the past three years was the use of a DBD system to treat the inner surface of small-diameter polymer tubing to improve the wettability and adhesion characteristics as compared to untreated polymer tubing. This work is interested in improving that DBD system.</p> <p>This thesis focuses on the development and implementation of two additional systems for an atmospheric pressure DBD system that treats the inner surface of narrow-diameter polymer tubes. The first, a pulsed-DC HV generator, will improve the plasma treatment. The fast rise times of the applied voltage prevent any stochastic behavior in plasma ignition and reignition, the resulting homogeneity of the plasma means that the plasma conditions of the treatment are more easily reproduced, and the increase in plasma intensity allows for quicker treatment of the tubing, the feed rates can reach the level of industrial production without lessening the effects induced by the treatment. The second, a Capstan-driven spooling system, will also improve the industrial capabilities of the DBD system. The higher feed rates that the spooling system reaches provide a means to rapidly produce treated tubing at a continuous rate, and the user-friendly interface means that system operation increases to a broader range of potential personnel. </p> <p>Investigation of the effect that tube feed rate (plasma exposure time) has on surface wettability was performed for the feed rates of the spooling systems. Feed rates of 2.5, 10, 50, 200, and 800 mm/min were performed on tubing samples for a 100% Helium plasma at a power level of 5 mW and a 98%He-2%O2 plasma at a power level of 20 mW. The temporal evolution of wettability was determined by taking the water contact angle (θ) of the treated tubing surface 0, 1, 2, 4, 16, 24, and 120 hours after plasma treatment. The resulting water contact angles initially fluctuate but eventually decay to reach a steady-state hydrophilicity that remains up to five days. The steady-state contact angles ranged from 42.3o < θss < 70.2o for a Helium plasma and 39.9o < θss < 62.7o for a Helium-Oxygen plasma. </p> <p>Investigation of the plasma power achieved with a pulsed-DC HV generator was also performed. The pulsed DC-driven plasma, which has a characteristic rise time of ~300 ns, ignites at Vbd = 4.5 kV. This breakdown voltage is 1.3 times higher than the minimum for the system, Vbd,min = 3.45 kV, so the resulting overvoltage of the pulsed-DC generator is approximately 1.3 times the minimum breakdown voltage. The electrical power deposited to the discharge for the pulsed-DC driven discharge (133.2 mW) is 6 times the power of the previous AC-driven discharge (21.4 mW). Resulting surface wettability was also calculated for the two generators. The stronger plasma treatment of the pulsed-DC HV generator resulted in a steady-state contact angle 11.4o more hydrophilic than the AC HV generator (θss = 44.6o for pulsed-DC-driven discharge compared to θss = 56o for AC-driven discharge).</p>

This dissertation presents an experimentally supported multi-physics model of a dielectric barrier discharge boundary layer flow control actuator. The model is independent of empirical data about the specific behavior of the system. This model contributes to the understanding of the specific mechanisms that enable the actuator to induce flow control. The multi-physics numerical model couples a fluid model, a chemistry model, and an electrostatics model. The chemistry model has been experimentally validated against known spectroscopic techniques, and the fluid model has been experimentally validated against the time-resolved shadowgraphy. The model demonstrates the capability to replicate emergent flow structures near a wall. These structures contribute to momentum transport that enhance the boundary layer’s wall attachment and provide for better flow control. An experiment was designed to validate the model predictions. The spectroscopic results confirmed the model predictions of an electron temperature of 0.282eV and an electron number density of 65.5 × 10⁻¹²kmol/m³ matching to within a relative error of 12.4% and 14.8%, respectively. The shadowgraphic results also confirmed the model predicted velocities of flow structures of 3.75m/s with a relative error of 10.9%. The distribution of results from both experimental and model velocity calculations strongly overlap each other. This validated model provides new and useful information on the effect of Dielectric Barrier Discharge actuators on flow control and performance. This work was supported in part by NSF grant CNS-0960081 and the HokieSpeed supercomputer at Virginia Tech. / Ph. D.

No description available.

Plasma actuators are devices that with two electrodesand a dielectric material can ionize the air around itand thus control the airflow. They have considerable potentialfor a multitude of reasons, one of which being that they haveno moving parts, making them easy to produce and hard tobreak. Using this technology on the front of vehicles like truckscould be revolutionary in increasing fuel efficiency and thusreducing emissions. A model of a plasma actuator in COMSOLMultiphysics was used to simulate the effect it has on the airaround it. The focus of the project has been to optimize thedesign of an actuator for increased velocity in the air around it.This has been done with regards to properties of the appliedvoltage, the distance between the electrodes and material ofthe dielectric. Parametric analyses of all the above propertieswas performed. Close-to-optimal values of some of the abovementioned parameters were successfully calculated. However,other parameters, such as the horizontal distance between theelectrodes, were beyond the model’s capability to determine usingthe described method. / Plasmaställdon är anordningar som medtvå elektroder och ett dielektriskt material kan jonisera luftenrunt sig och på detta sätt styra luftflödet. De har betydandepotential av en mängd anledningar, varav en är att de inte har några rörliga delar, vilket gör dem lätta att producera och ochsvåra att förstöra. Användande av denna teknologi på fronterav fordon som lastbilar skulle kunna vara revolutionerande förökad bränsleeffektivitet och därmed minska utsläpp. En modellav ett plasmaställdon i COMSOL Multiphysics användes för attsimulera effekterna den har på luften runt sig. Projektets fokushar varit på att optimera ett ställdons design för ökad hastigheti luften runt den. Detta har gjorts med avseende på egenskaperhos den tillförda spänningen, avståndet mellan elektroderna ochdielektrikumets material. Parametriska analyser för alla dessaegenskaper har genomförts. Nästintill optimala värden för någraav de ovan nämnda parametrarna beräknades med framgång.Andra parametrar, som det horisontella avståndet mellan elektroderna,var bortom modellens förmåga att bestämma vidanvändande av den beskrivna metoden. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm

Dans ces travaux de recherche nous avons cherché à développer et optimiser un procédé d'oxydation avancée dédié au traitement de l'eau. Pour cela, nous avons développé un procédé combinant la génération de radicaux hydroxyles par décharge plasma à pression atmosphérique et un catalyseur fixe. L'originalité de ce travail a été d'utiliser un système d'écoulement permettant l'obtention d'un film liquide (épaisseur<1mm) afin de permettre une interaction entre le plasma, le liquide et la surface catalytique. Les résultats ont montré que l'utilisation d'une décharge de type DBD était préférable au Glidarc, thermique, énergétique et produisant trop de NOx. Les valeurs d'efficacité respectives étaient de 0,67g.kWh-1 pour la DBD et 0,23g.kWh-1 pour le Glidarc. Les résultats ont également montré que le matériau de la contre-électrode/plaque d'écoulement pouvait influencer l'efficacité du procédé. Ainsi dans le cas du laiton, la présence de réactions de corrosion produisant des NO2- réduit l'efficacité de moitié comparée à une plaque d'acier. Le développement d'un modèle CFD 1D à partir des données expérimentales du procédé a été effectué. Ce modèle a permis d'estimer que l'efficacité énergétique de production des HO est de 4,4.10-9 molHO.J-1 pour la décharge DBD. Il a également permis de montrer que le facteur majoritairement limitant était la diffusion moléculaire des espèces dans le liquide. En effet les réactions chimiques ne dure pas plus de 1µs après l'impact du streamer et n'ont lieu que dans les premiers 5% d'épaisseur de liquide. Enfin, un dépôt catalytique de DLC dopé à l'argent et réalisé par rf-PECVD a permis d'améliorer de près de 10% l'efficacité maximale du procédé. / The aim of this research lies in the development and optimization of an advanced oxidation process dedicated to wastewater treatment. This process combines an atmospheric plasma discharge with an immobilized catalyst (Ag-DLC) in order to generate hydroxyl radicals. The novelty of this work relies in the use of a falling thin film system (thickness < 1mm) to promote the interaction between plasma discharge, the solution and the catalytic surface. The results demonstrate the interest of employing a Dielectric Barrier Discharge configuration instead of a Glidarc system. Indeed, the Glidarc system leads to a too high production level of NOx. The efficiencies of these two processes were respectively 0,67 g.kWh-1 and 0,23 g.kWh-1 for the DBD and the Glidarc system. Moreover, the influence of the counter-electrode / flowing plate material on the process efficiency was pointed out. Compared to stainless steel, the presence of corrosion reactions on the brass surface produced NO2- and thus, reduced the process efficiency. The production of HO??radicals at the plasma / water interface was estimated to be 4,4.10-9 molHO.J-1 by the use of 1D CFD modeling. Side reactions such as HO? recombinaison appear as the major limiting factors. Futhermore the model demonstrates that the time needed to complete all the chemical reactions was less than 1 µs and these reactions occurred only in the first 5% of the top liquid film. Finally with an Ag-DLC based catalytic coating elaborated by RF-PECVD, the efficiency was increased to 10% compared to the best efficiency observed with the non-catalytic system.

Forças eletro-hidrodinâmicas apresentam boas qualidades para a utilização como meio de produzir e manipular escoamentos. Um de seus grandes méritos consiste na falta de partes móveis para a introdução de quantidade de movimento em escoamentos. Foi realizado um estudo experimental para a investigação e comparação de três diferentes configurações dos eletrodos usados para a produção de dispositivos eletro-hidrodinâmicos gerados por descarga de barreira dielétrica. Uma configuração é composta de eletrodos retangulares planos e a outra de um fio e um eletrodo retangular plano. A outra configuração usa uma nova configuração com um eletrodo plano de borda serrilhada, como eletrodo ativo, e um eletrodo retangular plano isolado. Todas as configurações foram investigados para entender o comportamento na produção de escoamento. Medições de tubo Pitot dos perfis de velocidade dos jatos de parede foram feitas em várias distâncias a partir da região da descarga elétrica. Na sequência, a medição do escoamento ao longo do eletrodo serrilhado foi realizada. Assim, pretende-se determinar as características de escoamento tridimensionais produzidas por esta configuração. Os resultados mostram melhores características da configuração serrilhado para ser utilizado na produção de escoamento mais intensos. / Electro-hydrodynamic forces have good qualities to be used to produce and manipulate flows. One of its great merits is the lack of moving parts to introduce momentum in flows. An experimental study for measure and comparing three different configurations of electrodes used for the production of electro-hydrodynamic devices generated by dielectric barrier discharge was performed. One configuration is composed of rectangular at electrodes and the other of a wire electrode and a rectangular at electrode. The other uses a new configuration with a serrated edge flat plane electrode, as the active electrode and an isolated rectangular flat. All configurations are investigated to understand the behavior in the production of the flow. Pitot tube measurements of velocity profiles of the wall jets are made at various distances away from the electrical discharge region. Further, the measurement of the flow along the serrated electrod is performed. Thus, it is intended to determine the three-dimensional flow characteristics produced by this configuration. The results show the best features of serrated configuration to be used in the production of more intense flow.