Rozprawy doktorskie na temat „Atmospheric plasma applications”

Plasma chemistry is a rapidly growing field which covers applications ranging from technological processing of materials, including biological tissues, to environmental remediation and energy production. The so called atmospheric plasma, produced by electric corona or dielectric barrier discharges in a gas at atmospheric pressure, is particularly attractive for the low costs and ease of operation and maintenance involved. The high concentrations of energetic and chemically active species (e.g. electrons, ions, atoms and radicals, excited states, photons) present in such plasmas can promote chemical reactions which are otherwise hardly possible under such mild temperature conditions. This thesis deals with the use of atmospheric plasma to activate two different processes: water purification from organic pollutants and carbon dioxide reforming of methane to produce syngas. Both address major environmental issues, specifically the ever growing demand for drinking water and the need to control carbon emissions in the atmosphere. Due to the very different nature of the two investigated processes, different plasma sources, types of discharge, reactors, experimental conditions and analytical procedures had to be developed and adopted. Despite such differences, however, both lines of research stem from a common background and share a common goal: to understand and exploit the great chemical potential of atmospheric plasma. Thus, a common research approach was used, based on extensive investigation of the discharge and plasma features, notably of its reactive species, and of the process efficiency, products and intermediates. The mechanistic investigations involved quantitative product and kinetic studies, spectroscopic determinations and some modeling. An already available prototype reactor was used for water treatment, in which dielectric barrier discharges (DBD) are generated in the air above the liquid. The strong oxidants formed in humid air plasma (OH radicals, atomic oxygen, ozone) interact with the aqueous solution and induce the oxidation of even the most resistant organic pollutants. Phenol was used as a model organic pollutant and found to be decomposed quite efficiently, especially in dilute solutions, the rate of reaction increasing linearly with the reciprocal of phenol initial concentration. Despite its high reactivity air plasma displays some selectivity. The rate of oxidation of monosubstituted phenols (m-(CH3)2N-, m-Cl-, p-NO2- and m-NO2-) depends linearly on the Hammett substituents constant yielding a rho value of -0.48 which is characteristic of electrophilic attack by the OH radical. The main products and intermediates of phenol decomposition were determined quantitatively. The behavior of two such intermediates, maleic acid and fumaric acid, was investigated in detail since they are very common water secondary pollutants formed in the oxidative degradation of most aromatic compounds. The reaction mechanisms and the role of the major oxidizing species – hydroxyl radical and ozone – were investigated in experiments in which the two acids were treated separately and also in mixture under different pH conditions. Most interesting and useful was also the comparison with the results obtained in experiments of ozonation conducted under the same experimental conditions except for the fact that ozone was produced ex situ. These experiments show that under any conditions plasma treatment is more efficient due to the contribution of short lived highly reactive species. As for the oxidation mechanism of the two acids in the plasma system, it is concluded that due to their high reactivity with ozone, the decomposition process of maleic and fumaric acids is mainly due to this species. Depending on the pH of the solution, ozone reacts directly with the organic molecules or is converted to OH radicals. However, additional OH radicals produced directly by the electrical discharge also contribute to the oxidation of maleic and fumaric acids in the air-liquid plasma system, independently on the pH used. Thus, the direct formation of •OH by the discharge in situ constitutes a big advantage of plasma treatment over reaction with ozone produced ex-situ, in particular at acidic pH values for compounds which do not react with ozone itself. In fact, contrary to ozone, OH radicals react efficiently with any organic compound and when directly produced by the discharge their concentration is independent on pH. The obtained results are also very useful to show the importance of ozone mass transfer from the gas phase to the solution. Both in plasma treatment and in ozonation ozone is not accumulated into the solution but reacts as it is transferred in water or directly on its surface. However, comparing the behavior of maleic and fumaric acids in plasma treatment and in ozonation, it was demonstrated that the ion wind present in the DBD reactor, due to the charged species formed by the discharge, plays an important role in mixing the solution. In fact, when ozone produced ex-situ is used magnetic stirring of the solution is required to allow the reaction to take place also in the bulk and not only on the surface of water, while in the case of plasma treatment magnetic stirring increases the rate of the reaction but does not change significantly the shape of the oxidation curves. The reactor and experimental apparatus for performing plasma driven carbon dioxide reforming of methane and product analysis had to be designed and developed from scratch since this line of research started with this Thesis. To allow emission spectroscopy measurements and in view of future investigations on the combination of plasma with heterogeneous catalysis, the reactor was made of quartz: two flanges are welded on the extremities of a tube of 570 mm of length and 37 mm of diameter, while a ring is welded in the middle of the tube to support a stainless steel tip which constitutes the high voltage electrode. The grounded counter electrode has the shape of a funnel and is covered by a stainless steel mesh. Most of the quartz tube is filled with ceramic cylinders, while the plasma zone occupies a volume of about 40 cm3 in the middle of the tube for allowing its heating in a vertical furnace for future investigations with heterogeneous catalysts. The setting-up of the experimental apparatus was a major task which was followed by preliminary tests with different types of discharge for determining the most efficient regime for transformation of methane and carbon dioxide to the mixture of hydrogen and CO. The best results in terms of efficiency and product selectivity were obtained with a spark discharge, self-triggered by a simple and efficient power supplying. The average electron density of the plasma, 5.7 x 1014 cm-3, was measured by emission spectroscopy techniques and the temperature of the bulk gas, approaching 100°C, by a thermocouple. However, the main characteristic of spark is the development of discharge filaments, in which the electron density and the temperature of the species, such as electrons, radicals, ions, but also atoms and molecules, are significantly higher than those of the bulk. In the present reactor these filaments fill completely the plasma zone. Thus, it is assumed that the elementary processes of the reaction between methane and carbon dioxide take place inside the discharge filaments. The major products, hydrogen and carbon monoxide were determined quantitatively by GC/FID/TCD. A few byproducts were also detected in low percentages and identified by means of GC/MS analysis. These include ethane, ethylene and acetylene. Based on quantitative product data and on precise measurements of the input and output flows, the reagents conversion, the products yield and selectivity and the energy efficiency of the process were calculated. The quite high conversion of CH4 (74%) and CO2 (69%), the high selectivity for the desired products (78% H2 and 86% CO) and the good energy efficiency (2.4 mmol/kJ) obtained make this system competitive with other reactors/processes described in the literature. Moreover, no carbon deposition was observed and CO2/CH4 ratios between 0.5 and 1.5 could be used without significant changes in the characteristics of the process. Easy power control and self-triggering of the system eliminate the need for expensive high-voltage switches, making this setup attractive for scaling up and further development.
La chimica dei plasmi è un settore in rapida espansione che conta un gran numero di applicazioni, dal trattamento di materiali, inclusi materiali biologici, alla decomposizione di inquinanti e produzione di energia. Il cosiddetto plasma atmosferico, prodotto da scariche elettriche corona o a barriera di dielettrico in un gas a pressione atmosferica, è particolarmente attraente grazie ai costi contenuti e alla facilità di impiego e manutenzione. L’elevata concentrazione di specie ad alta energia chimicamente attive (ad esempio elettroni, ioni, atomi, radicali, specie eccitate, fotoni) presenti in questi plasmi può promuovere reazioni chimiche che in condizioni più blande sarebbero difficilmente realizzabili. La Tesi riguarda l’impiego del plasma atmosferico per attivare due diversi processi: la purificazione dell’acqua da inquinanti organici e il reforming di metano con anidride carbonica per produrre gas di sintesi. Entrambi i processi mirano a dare un contributo nella risoluzione di un problema ambientale, la crescente domanda di acqua potabile in un caso, la necessità di limitare le emissioni di carbonio nell’atmosfera nell’altro. A causa della natura molto diversa dei due processi indagati, essi richiedono lo sviluppo e l’impiego di sorgenti di plasma, tipi di scarica, reattori, condizioni e procedure sperimentali diversi. Tuttavia, nonostante queste differenze, entrambe le linee di ricerca derivano da conoscenze comuni e condividono lo stesso obiettivo: comprendere e sfruttare l’enorme potenziale chimico dei plasmi atmosferici. Anche nella ricerca è stato quindi applicato un approccio comune, basato su uno studio approfondito delle caratteristiche della scarica elettrica e del plasma, in particolare per quanto riguarda le specie reattive, dell’efficienza del processo e dei prodotti e degli intermedi che si formano nel processo. Gli studi meccanicistici sono basati sull’analisi quantitativa dei prodotti, sulla cinetica del processo, su misure spettroscopiche e su simulazioni. Il reattore impiegato per il trattamento delle acque è un prototipo realizzato in precedenza, in cui vengono generate scariche a barriera di dielettrico (DBD) nell’aria sovrastante la soluzione. I potenti ossidanti formati nel plasma in aria umida (radicale OH, ossigeno atomico, ozono) interagiscono con la soluzione acquosa e inducono l’ossidazione anche dei più resistenti inquinanti organici. Il fenolo, usato come inquinante organico modello, viene decomposto efficacemente, soprattutto in soluzioni diluite. La sua velocità di scomparsa aumenta linearmente con il reciproco della sua concentrazione iniziale. Nonostante l’elevata reattività, il plasma in aria mostra una certa selettività. La velocità di ossidazione di fenoli monosostituiti m-((CH3)2N-, m-Cl-, p-NO2- and m-NO2-) dipende linearmente dalle costanti di Hammett. Il valore di rho ottenuto, pari a -0.48, è caratteristico dell’attacco elettrofilo da parte del radicale OH. I principali prodotti ed intermedi della decomposizione del fenolo sono stati determinati quantitativamente. Il comportamento di due di questi intermedi, l’acido maleico e l’acido fumarico, è stato analizzato in dettaglio poiché si tratta di comuni inquinanti secondari delle acque derivanti dalla degradazione ossidativa della maggior parte dei composti aromatici. Esperimenti in cui i due acidi sono stati trattati separatamente e in miscela a diversi pH hanno permesso di indagare i meccanismi di reazione e il ruolo delle principali specie ossidanti – radicale ossidrile e ozono - nella decomposizione dei due acidi. Molto interessante ed utile è stato anche il confronto con i risultati ottenuti in esperimenti di ozonizzazione realizzati nelle stesse condizioni sperimentali ma in cui l’ozono veniva prodotto ex situ. Questi esperimenti dimostrano che in tutte le condizioni sperimentali il trattamento al plasma è più efficiente del trattamento con solo ozono grazie al contributo aggiuntivo da parte di specie a vita breve altamente reattive. Per quanto riguarda il meccanismo di ossidazione dei due acidi nel plasma, è stato concluso che a causa dell’elevata reattività con ozono, il processo di decomposizione degli acidi maleico e fumarico è dovuto principalmente a questa specie. A seconda del pH della soluzione, l’ozono reagisce con le molecole organiche come tale oppure viene convertito in radicali OH. Nel sistema al plasma, radicali OH vengono prodotti anche direttamente dalla scarica elettrica e contribuiscono anch’essi all’ossidazione degli acidi maleico e fumarico, indipendentemente dal pH della soluzione. E’ quindi evidente che la formazione diretta di •OH in situ da parte della scarica costituisce un enorme vantaggio del trattamento al plasma rispetto al caso in cui l’ozono venga prodotto ex-situ, in particolare nel caso di composti che a pH acidi non siano in grado di reagire direttamente con l’ozono. Infatti, contrariamente all’ozono, il radicale OH reagisce in modo efficiente con qualsiasi composto organico, inoltre, quando viene prodotto direttamente dalla scarica la sua concentrazione è indipendente dal pH. I risultati ottenuti si sono rivelati molto utili anche per dimostrare l’importanza del trasferimento di massa dell’ozono dalla fase gas alla soluzione. Sia nel trattamento al plasma che nell’ozonizzazione l’ozono non si accumula nella soluzione ma reagisce non appena viene trasferito in acqua o direttamente sulla superficie dell’acqua. Comunque, confrontando il comportamento degli acidi maleico e fumarico nel trattamento al plasma e nell’ozonizzazione, è stato dimostrato che il vento ionico attivo nel reattore DBD e dovuto al trasferimento di specie cariche generate dalla scarica, svolge un ruolo importante nel mescolamento della soluzione. Infatti, quando l’ozono viene prodotto ex-situ è necessario agitare la soluzione con un’ancoretta magnetica perché la reazione abbia luogo nell’intera massa di acqua e non solo sulla sua superficie; al contrario, nel caso del trattamento al plasma il mescolamento magnetico aumenta la velocità della reazione ma non cambia significativamente la forma dell’andamento dell’ossidazione in funzione del tempo. Nel caso del processo di reforming di metano con CO2 attivato da plasma è stato necessario progettare e sviluppare il reattore e l’intero sistema sperimentale da zero poiché questa linea di ricerca è stata iniziata con questa Tesi. Per poter realizzare misure di spettroscopia di emissione e in vista di studi futuri sulla combinazione del plasma con la catalisi eterogenea, il reattore è stato realizzato in quarzo: due flange sono saldate alle estremità di un tubo lungo 570 mm e largo 37 mm (diametro interno), mentre un anello è saldato nel mezzo del tubo per supportare una punta di acciaio inossidabile che costituisce l’elettrodo ad alto voltaggio. Il controelettrodo, posto al potenziale di terra, ha la forma di un imbuto ed è ricoperto da una retina di acciaio. Il tubo è in buona parte riempito con cilindri di ceramica forati, mentre la zona del plasma occupa un volume di circa 40 cm3 nel mezzo del tubo, soluzione che ne permetterebbe il riscaldamento in una fornace verticale in eventuali studi futuri con catalizzatori eterogenei. La realizzazione dell’apparato sperimentale ha richiesto un grosso impegno. Il passo successivo è stato l’esecuzione di esperimenti di prova con diversi tipi di scarica per determinare il regime più efficiente per realizzare la trasformazione di metano e anidride carbonica in una miscela di idrogeno e monossido di carbonio. I risultati migliori in termini di efficienza e selettività dei prodotti sono stati ottenuti con una scarica di tipo spark, auto-innescante grazie ad un sistema di alimentazione elettrica semplice ed efficiente. La densità elettronica media del plasma, pari a 5.7 x 1014 cm-3, è stata misurata tramite tecniche di spettroscopia di emissione e la temperatura del gas, poco inferiore a 100°C, tramite una termocoppia. La caratteristica principale della scarica di tipo spark è lo sviluppo di canali filamentari di scarica, in cui la densità degli elettroni e la temperatura delle specie, vale a dire elettroni, radicali, ioni, ma anche atomi e molecole, sono significativamente maggiori di quelle della massa del gas. Nel reattore in questione questi canali filamentari di scarica occupano interamente la regione in cui si sviluppa il plasma. Di conseguenza, si può assumere che i processi elementari della reazione tra metano e anidride carbonica si verifichino all’interno di tali canali. I prodotti principali della reazione, idrogeno e monossido di carbonio, sono stati determinati quantitativamente tramite GC/FID/TCD. Alcuni sottoprodotti sono stati rivelati in basse percentuali e identificati tramite analisi GC/MS: si tratta di etano, etilene ed acetilene. Sulla base dei dati quantitativi relativi alla formazione dei prodotti e delle misure precise dei flussi di entrata ed uscita del gas nel e dal reattore, sono state calcolate le percentuali di conversione dei reagenti e di resa e selettività dei prodotti. I risultati di conversione di CH4 (74%) e CO2 (69%), di selettività per i prodotti desiderati (78% H2 and 86% CO) e di efficienza energetica sono risultati molto buoni e rendono il sistema competitivo con altri reattori e processi descritti nella letteratura. Non viene inoltre osservata deposizione di carbone e il rapporto CO2/CH4 può essere variato tra 0.5 e 1.5 senza variazioni significative delle caratteristiche del processo. La facilità di controllo della potenza e la caratteristica di auto-innesco del sistema fanno sì che non siano necessari costosi sistemi di controllo che lavorano ad alto voltaggio e rendono promettente il ridimensionamento dell’apparato sperimentale e interessante il suo impiego in ricerche future.

Les plasmas froids produits par les décharges électriques sont des gaz faiblement ionisés, ce qui maintient la température du gaz à une température proche de la température ambiante, contrairement à la température de l'électron qui peut atteindre plusieurs électron-volts. Les applications des plasmas froids en médecine et en agriculture sont des nouveaux domaines de recherche multidisciplinaires basés sur les interactions de ces plasmas avec des organismes vivants. Le champ électrique ainsi que les espèces réactives de l’oxygène et de l'azote peuvent inactiver les bactéries, stimuler la régénération de la peau (dermatologie), la réduction tumorale (oncologie) et la germination des graines (agriculture). Ces nouveaux domaines de recherche, basé sur la chimie produite par l’interaction plasma-liquide est très prometteur et se développe rapidement. L’objectif de ce travail est d’étudier les interactions entre les plasmas froids et l’eau pour les applications biologiques, d’une part la promotion de la germination des graines au moyen d’une décharge à barrière diélectrique (DBD) et, d’autre part, l’effet ex vivo d’un traitement par jet de plasma froid sur la peau.Ce manuscrit est divisé en cinq chapitres: i) On présente tout d'abord une revue de la littérature présentant l'état de l’art concernant l'interaction plasma-liquide et les principales avancées en matière d'applications des plasmas froids à la germination des semences. Ii) Deuxièmement, les dispisitifs expérimentaux sont décrits, en particulier la fabrication de réacteurs à plasma utilisant l’impression 3D. Iii) Ensuite, la production d'espèces réactives gazeuses et aqueuses formées par des plasmas de type DBD a été mesurée quantitativement et l'interaction plasma-liquide a été analysée. Iv) Puis, plusieurs variétés de graines ont été sélectionnées pour évaluer l’effet un traitement par plasma DBD ; l'étude des mécanismes de promotion de la germination du plasma a été spécifiquement étudiée en traitant les graines de soja vert dans différentes conditions de décharge, dans différents milieux, avec un champ électrique seul et dans différentes conditions de cultures ou de niveau d'hydratation des graines.v) Enfin, l'imagerie paramétrique de Muller (MPI) a été appliquée pour la modification de la peau de souris ex vivo traitées par un plasma à jet d'hélium
Non-Thermal-Plasmas (NTP) produced by electric discharges are weakly ionized gases, which keeps the gas temperature at near room temperature contrary to the electron temperature which can reach several electron-Volts. Applications of NTP to medicine and agriculture are new multidisciplinary research fields based on interactions of the Non-Thermal-Plasmas with living organisms. Electric field as well as Reactive Oxygen and Nitrogen Species produced by NTP may inactivate bacteria, stimulate skin regeneration (dermatology), tumor reduction (oncology) and seeds germination (agriculture). These new fields of research are based on the plasma-liquid chemistry. The objective of this work is to study the NTP interacting with water for biological applications including on one hand, the promotion of the germination of seeds using a Dielectric Barrier Discharge (DBD) and on the other hand, the effect of a plasma jet treatment ex vivo on skinThis manuscript is divided in five chapters: i) First a literature review is presented showing the state of the art of the plasma-liquid interaction, and the main advances of the application of non thermal plasmas to seed germination. Ii) Second, experimental set ups are described, in particular the manufacturing of plasma reactors using 3D printing. Iii) then , the production of gaseous and aqueous reactive species formed by DBD plasmas was measured quantitatively and plasma-liquid interaction was analyzed. Iv) Next, different varieties of seeds were selected to evaluate the effect of a DBD plasma treatment and the study of the mechanisms of plasma germination promotion was specifically investigated by treating mung bean seeds in different discharge conditions, in different mediums, in electric field alone and in different hydration levels of seeds.v) Finally, Muller parametric imaging (MPI) was applied to study the modification of ex vivo mice skin treated by a helium jet plasma

In this study, an in-house built atmospheric. pressure non-thermal plasma jet has been investigated for its potential utilisation as a new alternative antimicrobial tool for a variety of medical applications. Anti - biofilm activity of this plasma jet has been evaluated against biofilms of a selected panel of bacterial species, grown on different abiotic surfaces, where complete eradication of all tested bacterial biofilms was achieved after relatively short plasma exposures of up to 10 minutes. Multiple approaches of cell viability evaluation were adopted to show the nature, extent and distribution of the remarkable anti-biofilm activity of the plasma jet including colony counting, XTT metabolic assay, scanning electron microscopy examination and differential Live/Dead fluorescent staining followed by confocal laser scanning microscopy examination. Antibacterial efficacy of the plasma jet has also been evaluated against similar bacterial species in their planktonic mode of growth where plasma exposures even shorter than those required for biofilm eradication were sufficient to cause complete inactivation of these planktonic bacteria. Such excellent bactericidal activity resulted from the ability of plasma exposure to mediate an oxidative damage to multiple cellular targets including cellular membrane, DNA and proteins of bacterial cells. However, damage of cellular membrane and the resultant disruption of its integrity and permeability were shown to be the primary rate-determining step in the plasma mediated bacterial cell death. Furthermore, in depth investigation of the plasma- mediated bacterial destruction mechanism has been carried out to identify the plasma-produced reactive species that were responsible for mediating its bactericidal activity. Based on the findings of this study, a hypothesis was formulated to describe the mechanism of bacterial cell destruction after plasma exposure. This hypothesis assumed a two-part mechanism; one part was a rapid H20 2-dependent mechanism associated with Fenton's or Fenton's-like reaction that was catalysed by metal ions released from the bacterial cells initially damaged by another proposed H20 2 - independent mechanism.

My Ph.D. activity developed along four lines of research dealing with non-thermal plasma (NTP) induced chemical processes for water remediation and biomedical applications. Specifically, I studied the effectiveness of atmospheric air plasma treatment in decomposing emerging organic contaminants (EOCs). The experimental setup used was a dielectric barrier discharge (DBD) reactor, a prototype developed in collaboration with the Department of Industrial Engineering of the University of Padova. Among EOCs, I chose six different contaminants, notably sulfamethoxazole, a veterinary antibiotic, triclosan, an antibacterial agent, perfluorooctanoic acid (PFOA), a perfluorinated organic contaminant, and the herbicides irgarol, metolachlor and mesotrione. Kinetics of their removal by plasma, intermediates of oxidation, possible degradation pathways and conversion to CO2 were evaluated. The achievement of more than 93% of conversion was observed for all the contaminants used at the initial concentration of 5 μM, except for PFOA (42%). An important advancement in my research involved the assessment of residual toxicity of plasma treated water samples. For this purpose, in collaboration with Prof. Giovanni Libralato (University of Naples), we tested the efficiency of plasma treatment in producing water free from ecotoxicological effects due to potentially toxic by-product residues. We tested one of the pollutants mentioned above, sulfamethoxazole (SMZ), an antibiotic listed among the most important emerging organic contaminants. A battery of acute and chronic toxicological test were employed: Daphnia magna, Raphidocaeilis Subcapitata and Vibrio Fischeri. It was found that toxicity of SMZ 5×10-4 M is minimized (V.fischeri) or reduced to zero (D. magna, R. Subcapitata) after 4 h of plasma treatment. To improve the efficiency of our DBD reactor, we tested the effect of addition of a photocatalyst, TiO2. We compared the kinetics of degradation of Irgarol in photocatalytic plasma process with those obtained when TiO2 was not included. The results obtained suggest that the effect of photoactivation by titanium dioxide in our reactor was negligible under the conditions employed. Possible reciprocal effects of different organic pollutants dissolved in water subjected to plasma induced advanced oxidation in our dielectric barrier discharge (DBD) reactor were then evaluated. As case study for this investigation, I chose the herbicides S-metolachlor and mesotrione, which are commonly applied in mixture. Results revealed that metolachlor does not affect mesotrione kinetics and viceversa when they are in solution, in 1:1 ratio. A new reactor was developed in our lab, in collaboration with Dr. Bosi from the Department of Industrial Engineering (University of Padova) with improved design and features with respect to the existing DBD reactor. The new reactor, operating in streamer discharge regime, was exhaustively characterized in collaboration with Dr. Gabriele Neretti (University of Bologna) and Dr. Barbara Zaniol (Consorzio RFX), and tested on phenol and metolachlor. Finally, during a four-month stage at the University of Bochum (Germany) I had the opportunity to work on a project dealing with plasma applications in the biomedical field under the supervision of Profs. Julia Bandow and Jan Benedikt. In particular, the effects of two plasma sources were tested in vitro on glyceraldehyde 3-phosphate dehydrogenase and E. coli. The results obtained for the enzyme suggest the importance of oxidation of the thiol group of the active site in plasma mode of action. The same approach was applied to assess the effect of ionic components of plasma by a new source developed by Prof. Benedikt (University of Bochum). The study of inactivation of the enzyme via plasma, with and without ions, showed a synergic effect between radicals and ions.
La Tesi riporta e discute i risultati ottenuti nell’applicazione di plasmi non termici per il trattamento ossidativo di inquinanti modello e ulteriori risultati relativi all’utilizzo del plasma in campo biomedico. L’apparato sperimentale impiegato è stato progettato e realizzato in collaborazione con il Dipartimento di Ingegneria Elettrica e produce una scarica a barriera di dielettrico (reattore DBD). Il sistema era già in uso nel periodo antecedente l’inizio della mia attività di dottorato. Le specie reattive che si generano a causa della scarica elettrica nell’aria umida sovrastante la fase liquida entrano in contatto con essa e possono reagire con l’inquinante organico in soluzione. Le specie reattive possono essere distinte in primarie, cioè generate direttamente dalla scarica per reazione del gas con gli elettroni energetici formando radicali, ioni e specie eccitate altamente reattive ed instabili, e secondarie prodotte per reazione delle stesse specie con le molecole del gas oppure con l’umidità presente. Il primo passo è stato quello di applicare tali scariche elettriche per il trattamento di diverse categorie di inquinanti emergenti allo scopo di valutare le potenziali applicazioni di questa tecnologia in relazione alle proprietà chimico fisiche degli inquinanti trattati. Sono stati selezionati i seguenti contaminanti organici persistenti: il sulfametossazolo, un antibiotico veterinario, il triclosan, un antibatterico, l’acido perfluoroacetico e tre erbicidi, l’irgarol, il metolachlor ed il mesotrione. Per tutti i composti in esame ho ottenuto profili esponenziali di degradazione in funzione del tempo di trattamento, da cui sono state ricavate le costanti cinetiche di pseudo-primo ordine. L’analisi HPLC-MS ha consentito l’identificazione degli intermedi e prodotti di degradazione, compatibili con possibili reazioni dovute all’azione dell’ozono e dei radicali ∙OH. Sono stati proposti inoltre i meccanismi di degradazione dei composti organici trattati. Lo scopo finale nell’uso di processi di degradazione avanzata è la completa conversione della componente organica a CO2. In seguito al trattamento al plasma, sono state riscontrate percentuali di mineralizzazione pari o maggiori al 93% per tutti gli inquinanti considerati, usati in concentrazione pari a 5 μM, fatta eccezione per l’acido perfluoroottanoico per cui la percentuale di mineralizzazione è stata considerevolmente più bassa (42%). Lo studio dei processi di degradazione al plasma è inoltre servito in alcuni casi da punto di partenza per ulteriori approfondimenti. È questo il caso dell’irgarol, in cui si è cercato di implementare l’effetto del plasma aggiungendo un fotocatalizzatore ampiamente utilizzato, TiO2. Non sono stati riscontrati tuttavia miglioramenti nell’effetto della scarica su tale inquinante indicando un trascurabile effetto fotocatalitico nelle condizioni sperimentali adottate. Un ulteriore avanzamento nelle ricerche in questo ambito è consistito nell’applicazione della scarica DBD su una miscela di inquinanti, il metolachlor e il mesotrione, solitamente utilizzati in combinazione in diverse formulazioni agricole. Gli studi cinetici effettuati hanno evidenziato che i due composti non si influenzano reciprocamente quando subiscono il trattamento al plasma in soluzioni miste in cui sono presenti in rapporto molare 1:1. Un importante parametro nella valutazione di una tecnica di depurazione consiste nell’analisi ecotossicologica del campione acquoso dopo il trattamento. A tale scopo, in collaborazione con il Prof. Giovanni Libralato del Dipartimento di Biologia dell’Università di Napoli, sono stati effettuati test tossicologici su campioni contenenti sulfametossazolo (SMZ), prima e dopo il trattamento nel reattore DBD. Allo scopo è stata utilizzata una batteria di test acuti e cronici per Vibrio Fischeri, Daphnia magna e Raphidocaelis subcapitata. I dati ottenuti a partire da una soluzione di SMZ 5·10-4 M hanno mostrato un elevato livello di tossicità della soluzione iniziale e la riduzione (V.fischeri) o l’azzeramento di tali effetti (D.magna e R.subcapitata) a seguito del trattamento nel reattore al plasma. Un nuovo reattore è stato inoltre ideato e realizzato in collaborazione con il Dr. Franco Bosi, del Dipartimento di Ingegneria Industriale dell’Università di Padova. La sorgente di plasma utilizza una scarica di tipo streamer ed è stata realizzata allo scopo di favorire un migliore trasporto delle specie reattive prodotte dalla scarica e ottimizzare la loro interazione con la soluzione da trattare. Il reattore è stato quindi caratterizzato in collaborazione con il Dr. Gabriele Neretti (Università di Bologna) e la Dr.ssa Barbara Zaniol (Consorzio RFX, Padova) e collaudato nel trattamento di due inquinanti organici, il fenolo ed il metolachlor. Infine nel corso di un periodo di quattro mesi di attività di ricerca presso il laboratorio della Prof.ssa Bandow dell’Università di Bochum (Germania) ho avuto modo di approfondire alcuni aspetti legati alle applicazioni del plasma atmosferico in campo biomedico. In particolare ho partecipato a studi sugli effetti di due diverse sorgenti al plasma su un enzima, gliceraldeide-3-fosfato deidrogenasi, in vitro e sul batterio E. coli. Il sito di attacco principale è risultato essere il sito attivo cisteina con conseguente ossidazione del gruppo -SH. Lo stesso approccio è stato applicato, in collaborazione con il Prof. Benedikt per lo studio degli effetti del plasma, in assenza e in presenza delle specie ioniche. I risultati ottenuti hanno evidenziato un effetto sinergico dovuto alla copresenza di specie neutre e ioniche.

The use of plasmas in aerodynamics has become a recent topic of interest. In particular, over the last ten years, plasma actuation has received much attention as a promising active method for airflow control. Flow control consists of manipulating the properties of a generic moving fluid with the aim of achieving a desired change, but flow dynamics in proximity of a solid object is usually considered, being a consistent and significant issue in many engineering applications, such as engine, automobile or airplane design. Plasma control of airflows along surfaces has been the subject of several experimental studies whose aim was to reduce turbulence, to decrease drag, to enhance airfoil lift or to prevent flow detachment. The fast temporal response and the absence of moving parts are the most promising features from which plasma actuators could benefit. Different types of plasma sources are currently studied as good candidates for plasma actuation, but Dielectric Barrier Discharges (DBDs) are usually preferred, being characterized by the presence of an insulating barrier between the electrodes. This allows the generation of a non-thermal plasma at atmospheric pressure and prevents the discharge from collapsing into an arc. Surface Dielectric Barrier Discharges (SDBDs) are particularly suitable for these kinds of applications, since plasma is created by ionizing a thin portion of air nearby the surface of the dielectric barrier and this can effectively influence the local properties of the boundary layer associated to an external flow. This thesis deals with SDBDs in an asymmetric configuration where one electrode is glued into an insulating material and to other one is exposed to air, so that plasma is created in correspondence of just one side of the dielectric barrier. The buried electrode is connected to the ground, whereas a sinusoidal high-voltage is applied to the exposed one. It has been noticed that, when these discharges are operated in quiescent air, an airflow of several metres per second is observed above the dielectric sheet and near the plasma region. This is usually called ionic wind because the main mechanism responsible for its generation is believed to be momentum transfer from the ions drifting in the discharge electric field to the surrounding fluid, by particle-particle collisions. When the electric field imposed by the voltage difference between the electrodes is sufficiently high, plasma is created and electrical charges are transported through the gap and accumulated on the insulating surfaces. This charge accumulation generates an electric field that locally weakens the external one. When the total electric field falls below the threshold necessary for plasma ignition, the discharge extinguishes. If the voltage imposed to the fed electrode is increased, the discharge can be locally initiated again, and that is the reason why a sinusoidal high-voltage supply is adopted instead of a continuous one. Consequently, the presence of the insulating barrier usually leads to a regime where charge is mainly transported in sub-millimetre regions consisting of current filaments with temporal duration limited to a few tens of nanoseconds. These plasma microdischarges are concentrated into two phase intervals of the sinusoidal voltage supply, when the modulus of the applied voltage difference is high enough and is increasing in time. These two phases of plasma activity are often called Backward Stroke (BD) and Forward Stroke (FD), depending if the high-voltage signal is rising from its minimum to its maximum or decreasing from its maximum to its minimum. This thesis is motivated by the fact new studies focusing on plasma properties and dynamics are required in order to get better and better aerodynamic results, to understand which parameters mainly affect the actuator performances and to validate numerical models trying to forecast the aerodynamic effects induced by the discharge. This has brought to a scientific collaboration between the Centre of Excellence PlasmaPrometeo of University of Milano-Bicocca and the Aerodynamics and Wind Tunnel Department of the aerospace company Alenia Aermacchi. During these years I have studied the properties of these discharges by means of electrical and optical diagnostics (mainly Rogowski coils, capacitive probes, a photomultiplier tube and a thermal camera). With some of them a temporal resolution high enough for studying several characteristics of plasma microdischarges has been achieved. This is important because these strokes manifest as series of current and light pulses, lasting tens of nanoseconds and a few nanoseconds respectively. I have first of all carried out a detailed investigation of the properties of these events and of their evolution in space and time in the course of the FD and BD. It has been pointed out that there are several analogies between the BD and FD, but that not all plasma properties are identical for the two semi-cycles, because of the asymmetrical configuration adopted. These investigations let think that light and current signals give insights about different microdischarge properties. Light is presumably ascribable to electrons that excite nitrogen immediately after the passage of the ionizing wave that initiates the microdischarge. In contrast, the current signal is due to the movement of charges into the plasma channel and thus reflects the microdischarge temporal evolution, rather than its formation. In the following experiments I have thus focused mainly on the electrical properties of plasma microdicharges, with the aim of better understanding which plasma characteristics are responsible for the ionic wind generation and properties. Several SDBDs with different geometrical configurations and operating parameters have been considered. It has been found that both the discharge and ionic wind characteristics are mainly affected by the dielectric thickness, whereas other properties of the SDBD are less decisive. These studies are of practical interest because optimizations of SDBD characteristics are still needed for adopting these discharges as plasma actuators for active flow control. In particular, it has been found that at first the speed of the induced wind increases quite linearly with the voltage amplitude, but then this velocity and thus the aerodynamic effects induced by the discharge tend to saturate. This is particularly evident when thin panels are adopted as dielectric barriers. I thus focused on this topic and I found that an asymmetry in the total charge transported by plasma microdischarges during the backward and forward strokes is favourable for obtaining a ionic wind with a greater velocity, and that the velocity saturation at the highest voltages is associated to a change in discharge regime, which is visible first of all because a pattern of plasma filaments appears superimposed to the more homogeneous plasma. I have thus characterized how this regime transition affects the dynamics of the backward and forward strokes. Three groups of microdischarges have been identified, depending on their temporal duration, and results let think that they don't contribute equally to the electric wind generation. These studies pave the way to a better understanding of the discharge peculiarities and ionic wind formation, with the aim of understanding if an intrinsic limit exists in plasma actuator potentialities or if new optimization strategies are possible. Eventually, I proposed to implement the Background Oriented Schlieren (BOS) technique for the visualization and characterization of the airflow induced by the discharge. The potentialities of this technique have been evaluated in relation to the specifics of the available scientific equipment. The technique has then been proved to be able to visualize density changes induced by plasma. A spatial characterization of the air near the discharge was made in stationary wall jet conditions as well as in the transient period following the discharge ignition when a starting vortex is generated.

This PhD thesis is focused on cold atmospheric plasma treatments (GP) for microbial inactivation in food applications. In fact GP represents a promising emerging technology alternative to the traditional methods for the decontamination of foods. The objectives of this work were to evaluate: - the effects of GP treatments on microbial inactivation in model systems and in real foods; - the stress response in L. monocytogenes following exposure to different GP treatments. As far as the first aspect, inactivation curves were obtained for some target pathogens, i.e. Listeria monocytogenes and Escherichia coli, by exposing microbial cells to GP generated with two different DBD equipments and processing conditions (exposure time, material of the electrodes). Concerning food applications, the effects of different GP treatments on the inactivation of natural microflora and Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli on the surface of Fuji apples, soya sprouts and black pepper were evaluated. In particular the efficacy of the exposure to gas plasma was assessed immediately after treatments and during storage. Moreover, also possible changes in quality parameters such as colour, pH, Aw, moisture content, oxidation, polyphenol-oxidase activity, antioxidant activity were investigated. Since the lack of knowledge of cell targets of GP may limit its application, the possible mechanism of action of GP was studied against 2 strains of Listeria monocytogenes by evaluating modifications in the fatty acids of the cytoplasmic membrane (through GC/MS analysis) and metabolites detected by SPME-GC/MS and 1H-NMR analyses. Moreover, changes induced by different treatments on the expression of selected genes related to general stress response, virulence or to the metabolism were detected with Reverse Transcription-qPCR. In collaboration with the Scripps Research Institute (La Jolla, CA, USA) also proteomic profiles following gas plasma exposure were analysed through Multidimensional Protein Identification Technology (MudPIT) to evaluate possible changes in metabolic processes.

This PhD thesis is focused on cold atmospheric plasma treatments (GP) for microbial inactivation in food applications. In fact GP represents a promising emerging technology alternative to the traditional methods for the decontamination of foods. The objectives of this work were to evaluate: - the effects of GP treatments on microbial inactivation in model systems and in real foods; - the stress response in L. monocytogenes following exposure to different GP treatments. As far as the first aspect, inactivation curves were obtained for some target pathogens, i.e. Listeria monocytogenes and Escherichia coli, by exposing microbial cells to GP generated with two different DBD equipments and processing conditions (exposure time, material of the electrodes). Concerning food applications, the effects of different GP treatments on the inactivation of natural microflora and Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli on the surface of Fuji apples, soya sprouts and black pepper were evaluated. In particular the efficacy of the exposure to gas plasma was assessed immediately after treatments and during storage. Moreover, also possible changes in quality parameters such as colour, pH, Aw, moisture content, oxidation, polyphenol-oxidase activity, antioxidant activity were investigated. Since the lack of knowledge of cell targets of GP may limit its application, the possible mechanism of action of GP was studied against 2 strains of Listeria monocytogenes by evaluating modifications in the fatty acids of the cytoplasmic membrane (through GC/MS analysis) and metabolites detected by SPME-GC/MS and 1H-NMR analyses. Moreover, changes induced by different treatments on the expression of selected genes related to general stress response, virulence or to the metabolism were detected with Reverse Transcription-qPCR. In collaboration with the Scripps Research Institute (La Jolla, CA, USA) also proteomic profiles following gas plasma exposure were analysed through Multidimensional Protein Identification Technology (MudPIT) to evaluate possible changes in metabolic processes.

In this dissertation are reported the most relevant results obtained during my three years Ph.D. project. An open-air plasma source has been developed to treat plastic and metallic films typically used in food packaging manufacturing. Among others, the DBD configuration was chosen due to its many advantages such as high intensity and uniformity of the treatment, possibility of operating in ambient air as well as ease of scale up. Biological experiments were performed to assess the microbial reduction induced by the plasma treatment. Different operative conditions have been tested in order to identify the most efficient configuration and two distinct behaviours have been observed: low-power density treatment allowed to achieve microbial inactivation values below log 2 independently on treatment time; high-power density treatment where the microbial reduction grew with increasing treatment time. Subsequently, the plasma discharge has been characterized by means of three investigation methods: thermal, electrical and optical absorption spectroscopy (OAS) analysis. The thermal and electrical analyses were employed to identify the best dielectric materials for food packaging manufacturing purposes. Once defined the optimal DBD configuration, OAS was used to measure the absolute concentration of ozone and nitrogen dioxide. Results showed that at low-power density the chemistry is governed by ozone; while at high-power density ozone is consumed by the poisoning effect and only nitrogen dioxide is detectable. Lastly, a numerical simulation has been used to deeper investigate the chemistry governing the plasma discharge; by means of PLASIMO a global model and a fluid model were implemented.

This thesis is the study of cold atmospheric plasma (CAP) applications in cancer, anti-viral treatments, and nano-biotechnology. The optimal treatment strategy, potential molecular mechanism and methods to increase selectivity and efficiency of plasma treatment were investigated for each application. In the near future, CAP or plasma activated medium (PAM) would likely become a widely used, high-efficiency and targeted clinical therapeutic tool.

This thesis presents experimental and modelling research on atmospheric pressure hollow cathodes and hollow electrodes. Experiments with the hybrid hollow electrode activated discharge (H-HEAD), which is a combination of a hollow cathode and a microwave plasma source, is presented. The experiments show that this source is able to produce long plasma columns in air and nitrogen at atmospheric pressure and at very low gas flow rates. Measurements of the vibrational temperature of the nitrogen molecules are also presented in this thesis. The vibrational temperature is an indication of the electron temperature in the plasma, an important characteristic of the plasma. Modelling work on the hollow cathode at atmospheric pressure with fluid equations is also presented. It is shown that the inclusion of fast and secondary electrons, characteristic of the hollow cathode plasmas, increases the sheath width. The sheath width was found to be of the order of 100 μm. By modelling the plasma as highly collisional by using the drift-diffusion approximation, it was shown that the increase in sheath thickness was larger at lower pressures than at higher pressures. Still, the sheath width can be of the order of 100 μm. A pulsed atmospheric plasma in a hollow electrode geometry was also modelled by the drift-diffusion fluid equations, with the addition of the energy equation for electrons. Rate and transport coefficients for the electrons were calculated from the solution to the Boltzmann equation as functions of mean electron energy. The dynamics of the plasma at pulse rise time showed large electron density and mean energy peaks at the cathode ends, but also that these quantities were enhanced at the centre of the discharge, between the cathode plates.

Since last century, the rising interest of value-added and advanced functional materials has spurred a ceaseless development in terms of industrial processes and applications. Among the emerging technologies, thanks to their unique features and versatility in terms of supported processes, non-equilibrium plasma discharges appear as a key solvent-free, high-throughput and cost-efficient technique. Nevertheless, applied research studies are needed with the aim of addressing plasma potentialities optimizing devices and processes for future industrial applications. In this framework, the aim of this dissertation is to report on the activities carried out and the results achieved concerning the development and optimization of plasma techniques for nanomaterial synthesis and processing to be applied in the biomedical field. In the first section, the design and investigation of a plasma assisted process for the production of silver (Ag) nanostructured multilayer coatings exhibiting anti-biofilm and anti-clot properties is described. With the aim on enabling in-situ and on-demand deposition of Ag nanoparticles (NPs), the optimization of a continuous in-flight aerosol process for particle synthesis is reported. The stability and promising biological performances of deposited coatings spurred further investigation through in-vitro and in-vivo tests which results are reported and discussed. With the aim of addressing the unanswered questions and tuning NPs functionalities, the second section concerns the study of silver containing droplet conversion in a flow-through plasma reactor. The presented results, obtained combining different analysis techniques, support a formation mechanism based on droplet to particle conversion driven by plasma induced precursor reduction. Finally, the third section deals with the development of a simulative and experimental approach used to investigate the in-situ droplet evaporation inside the plasma discharge addressing the main contributions to liquid evaporation in the perspective of process industrial scale up.

In the last decades, the possibility to generate plasma at atmospheric pressure gave rise to a new emerging field called plasma medicine; it deals with the application of cold atmospheric pressure plasmas (CAPs) or plasma-activated solutions on or in the human body for therapeutic effects. Thanks to a blend of synergic biologically active agents and biocompatible temperatures, different CAP sources were successfully employed in many different biomedical applications such as dentistry, dermatology, wound healing, cancer treatment, blood coagulation, etc.… Despite their effectiveness has been verified in the above-mentioned biomedical applications, over the years, researchers throughout the world described numerous CAP sources which are still laboratory devices not optimized for the specific application. In this perspective, the aim of this dissertation was the development and the optimization of techniques and design parameters for the engineering of CAP sources for different biomedical applications and plasma medicine among which cancer treatment, dentistry and bioaerosol decontamination. In the first section, the discharge electrical parameters, the behavior of the plasma streamers and the liquid and the gas phase chemistry of a multiwire device for the treatment of liquids were performed. Moreover, two different plasma-activated liquids were used for the treatment of Epithelial Ovarian Cancer cells and fibroblasts to assess their selectivity. In the second section, in accordance with the most important standard regulations for medical devices, were reported the realization steps of a Plasma Gun device easy to handle and expected to be mounted on a tabletop device that could be used for dental clinical applications. In the third section, in relation to the current COVID-19 pandemic, were reported the first steps for the design, realization, and optimization of a dielectric barrier discharge source suitable for the treatment of different types of bioaerosol.

The research described in this doctoral thesis work was mainly focused towards the low pressure inductively excited PECVD of organic precursors for biomaterials. An open air atmospheric pressure DBD plasma jet was also studied for the antifouling applications. Systematic studies were carried out in order to optimize the deposition of plasma polymerized (PP) coatings which were deposited at different process parameters for biomedical applications. The optimized amphiphilic PFDA-DEGVE coatings, presented no adhesion with respect to BSA as well as Lysozyme proteins. The plasma processing parameters were optimized using DoE methodology. By adjusting the process parameters, the chemical compositions of the PCL- PEG coatings were tailored to be cell adherent, convenient for biomedical implants such as artificial skin substrates, or cell repellent which could be used for antibiofouling surfaces for urethral catheters, stents etc. Multilayer biodegradable coatings based on PCL- PEG polymers were successfully used for controlled delivery of anticancer drug and tested in vitro. PP Poly (2-ethyl 2-oxazoline), having a peptidomimetic structure was deposited by LP. Such polymers are considered to be a prime candidate for an alternative of PEG like surfaces for antibiofouling applications. The last chapter was devoted to open air AP argon plasma jet. The deposited PEG coatings had 56. 3% of ether functions and were cell repellent as compared to a positive control (PS). This study has shown the capability of plasma processes for the deposition of (co-) polymer coatings with tailorable surface chemical compositions, with considerable promises for the variety of biomedical applications
Les recherches effectuées dans cette thèse se concentrent essentiellement sur la PECVD par plasma basse pression à partir de précurseurs organiques pour la synthèse de biomatériaux. Un procédé à jet de plasma hors équilibre à couplage DBD a aussi été développé pour élaborer des surfaces anti-bioadhésives. Les conditions opératoires ont été optimisées afin de pouvoir répondre à plusieurs applications biomédicales. Des copolymères amphiphiles à base de PFDA-PEG, élaborés et optimisés par des plans d’expériences, n’ont montré aucune adhésion vis à vis des protéines BSA et Lysozyme. Les polymères PCL-PEG ont aussi été étudiés, et les différentes compositions ont permis d’obtenir soit de bonnes propriétés d’adhésion cellulaire, permettant ainsi d’envisager des applications en ingénierie tissulaire, soit des surfaces anti-bioadhésives, intéressantes pour élaborer des cathéters ou des stents. Les copolymères PCL-PEG déposés en multicouches ont permis de contrôler les cinétiques de relargage de médicaments et de réaliser des tests in vitro. Nous avons aussi travaillé sur le remplacement des PEG en déposant un polymère mimant la structure des peptides ; le polyoxazoline. Les résultats obtenus ont donné de bonnes propriétés anti-fouling. Enfin, des surfaces anti-bioadhésives ont été élaborées par PECVD à pression atmosphérique. Les résultats obtenus ont montré une rétention des fonctions éthers de 56. 3% et les surfaces correspondantes repoussent les cellules. En conclusion, les travaux menés au cours de cette thèse ont montré que les procédés plasma permettent de déposer des (co)polymères permettant de répondre à une large palette d’applications dans le domaine biomédical

Durant la dernière décennie, un nouveau type de décharge hors équilibre thermodynamique à pression atmosphérique a suscité un engouement croissant compte tenu de sa capacité de produire un plasma s'étendant dans l'air ambiant à une température proche de l'ambiante. Ces jets de plasma, souvent basés sur un réacteur de type décharge à barrière diélectrique, sont intéressants du point de vue de leurs propriétés physico-chimiques. De plus, ces jets de plasmas ont l'avantage de permettre des applications des matériaux thermosensibles, ouvrant ainsi un nouveau domaine de recherche, Plasma Médecine. Au GREMI le Plasma Gun, a été développé tant pour l'étude de la physique des jets de plasma que pour les applications biomédicales notamment dans le domaine de la cancérologie. Dans une première étape, des traitements par Plasma Gun in vitro et in vivo, dans le cadre d'un modèle murin du carcinome pancréatique, ont été effectués. L'action anti-tumorale du plasma a été démontrée ainsi que la combinaison bénéfique avec un traitement chimiothérapique. Fondée sur ces résultats encourageants, l'objectif principal de cette étude porte sur l'influence drastique de la cible de l'application sur les propriétés du plasma (propagation et production des espèces réactives) ainsi que l'interaction du gaz et du plasma. Des diagnostiques tels que l'imagerie rapide et filtrée en longueur d'onde, la spectroscopie d'émission optique, l'imagerie Schlieren ainsi que la spectroscopie infrarouge à transformée de Fourier ont été utilisés pour caractériser le jet de plasma. Une étude quantitative de la distribution spatiale et temporelle du radical hydroxyle (densité comprise entre 5.1011 et 1.1014 cm-3) a été réalisée par fluorescence induite par laser. L'étude de l'OH en combinaison avec un modèle numérique a permis une meilleure compréhension de la pénétration de l'air dans le jet de gaz et de l'interaction avec les surfaces humides. L'interaction complexe entre le comportement du gaz, du plasma et la nature de la cible est mise en avant en vue d'optimiser les applications biomédicales
Over the past decade, a new type of non-equilibrium discharge at atmospheric pressure has attracted growing interest, given the ability to produce a plasma extending in ambient air close to room temperatures. These plasma jets, often based on a dielectric barrier discharge type of reactor, are interesting on their physicochemical property perspectives. In addition, these cold plasma jets have the advantage of allowing applications to heat sensitive materials, creating a new field of research, Plasma Medicine. At GREMI the Plasma Gun, has been developed for both the study of the physics of plasma jets and for biomedical applications particularly in the field of cancerology. In a first step, in vitro and in vivo were performed, within a rodent model of pancreatic carcinoma. The anti-tumor action of the plasma has been demonstrated as well as its benefic combination with a chemotherapeutic treatment. Based on these encouraging biomedical results, the main focus of this study is to report on the drastic influence of the application target on the plasma properties (propagation and production of reactive species) and on the strong coupling between gas jet and plasma discharge. Diagnostics such as fast, wavelength-filtered and Schlieren imaging, optical emission spectroscopy as well as Fourier transform infrared spectroscopy were used to characterize the plasma. A quantitative study on spatial and temporal distribution of hydroxyl radicals (OH density ranging between 5.1011 and 1.1014 cm-3) was performed by laser-induced fluorescence. The study of the OH in combination with a numerical model allowed a better understanding of the moist air penetration into the gas jet and the interaction with wet surfaces. This PhD work enlightened the complex interaction between the gas flow, the plasma and the nature of the target which has to be taken into account for further optimization of biomedical applications

L’utilisation de plasmas, qu’ils soient thermiques ou basse pression, dans le domaine biomédical remonte aux années 1970. Au cours de ces dernières années, les développements concernant des jets de plasma froid à pression atmosphérique, ont permis un élargissement des domaines d’applications biomédicales des plasmas. Au sein du GREMI, un type de jet de plasma a été développé : le Plasma Gun. Le plasma généré par le Plasma Gun se propage sur de longues distances à l’intérieur de capillaires. L’optimisation des traitements visés nécessite une étude approfondie des décharges créées par le Plasma Gun. La caractérisation du Plasma Gun a mis en évidence la génération de Pulsed Atmospheric pressure Plasma Streams ou PAPS, ces derniers se propageant du réacteur jusque dans l’air ambiant où ils génèrent une plume plasma. Ces PAPS présentent deux modes de propagation, au cours desquels une connexion entre le front d’ionisation et le réacteur est présente en permanence. Ces deux modes nommés respectivement Wall-hugging et Homogène, diffèrent principalement par la morphologie et la vitesse de propagation des PAPS qui leur sont associés. Chacun de ces modes présentent donc des caractéristiques qui leur sont propres mais certaines propriétés de propagation leur sont communes, telles que la possibilité de division ou de réunion de PAPS, ainsi que du transfert de PAPS à travers une barrière diélectrique ou via un capillaire métallique creux. L’étude de la plume plasma, propagation des PAPS dans l’air ambiant, a souligné l’importance de la longueur des capillaires sur la longueur du jet plasma. De plus, la génération du plasma a une très forte influence sur l’écoulement du gaz et la structuration du jet lors de son expansion dans l’air
The use of plasmas, thermic or low pressure, in biomedical goes back up to 1970s. During these last years, atmospheric pressure cold plasma jets have been developed, allowed an increase of biomedical applications of plasmas. In GREMI, a plasma jet was developed : the Plasma Gun (PG). The plasma generated by the PG propagates on long distances inside capillaries. The optimization of the aimed treatments requires a detailed study of the discharges created by the PG. The characterization of the PG highlights the generation of Pulsed Atmospheric pressure Plasma Streams or PAPS, these last ones propagating from the reactor to the capillary outlet (ambient air) where they generate a plasma plume. These PAPS present two propagation modes, during which a connection between the ionization front and the reactor is present permanently. These two modes named respectively Wall-hugging and Homogeneous, differ mainly by the morphology and their propagation velocity. These modes have common characteristics, such as the possibility of division or meeting of PAPS, as well as the transfer of PAPS through a dielectric barrier or via a hollow metal capillary. The study of the plasma plume underlined the importance of the length of capillaries on the length of the plasma jet. Furthermore, the generation of the plasma has a very strong influence on the gas flow and the jet structuration during air expansion

El present treball es basa en l'estudi de la modificació de la superfície del negre de carboni (NC) per mitjà de tècniques de plasma. Tot i que aquest tipus de tractament s'utilitza de manera comú sobre superfícies planes, tanmateix encara existeixen problemes a l'hora de treballar en materials en pols degut a la dificultat que suposa la seva manipulació. En aquest treball s'ha modificat NC tant per tècniques de plasma a baixa pressió com per mitjà de tècniques de plasma atmosfèric. Per tal d'assolir aquest objectiu s'han posat a punt tres reactors de plasma capaços de modificar aquest tipus de material; dos reactors treballen a baixa pressió mentre que el tercer es tracta d'un equip a pressió atmosfèrica.

Els sistemes de plasma a baixa pressió utilitzats han estat un reactor down-stream i un reactor de llit fluiditzat. Ambdós sistemes utilitzen un generador de radio freqüències a 13,56MHz per tal de general el plasma. Tots dos sistemes han estat optimitzats per la modificació de materials en pols. En el cas del reactor down-stream, s'ha estudiat a posició d'entrada del gas reactiu, la potència del generador i el temps de modificació per a tres tipus de tractament: oxigen, nitrogen i amoníac. En el cas del reactor de llit fluiditzat, els paràmetres que s'han estudiat han estat la distància entre la pols i la zona de generació de plasma, la mida de la partícula i la porositat de la placa suport.

Pel que fa a la modificació mitjançant la utilització de plasma atmosfèric, s'ha dissenyat un sistema que permet utilitzar una torxa de plasma atmosfèric comercial (Openair® de Plasmatreat GmbH) per tal de modificar materials en pols. Aquest sistema consisteix en un reactor adaptable a la torxa de plasma atmosfèric on té lloc la modificació, un sistema d'introducció de la pols dins de la zona de reacció així com també un sistema de refredament i col·lecció del material modificat que conjuntament permeten un funcionament quasi-continu del tractament.

S'ha utilitzat el reactor down-stream i el reactor a pressió atmosfèrica per tal de modificar tres tipus diferents de negre de carboni (N134, XPB 171 i Vulcan XC-72). D'altra banda, s'ha grafititzat i extret el N134 prèviament a la modificació per tal de realitzar un estudi sobre la influència de l'estructura superficial així com també de la presència d'impureses sobre la superfície del NC. L'oxidació i l'augment de nitrogen en superfície han estat les dues modificacions que s'han estudiat principalment per tal de comparar el resultat obtingut per les tècniques presentades.

El NC s'ha caracteritzat mitjançant diverses tècniques analítiques per tal de poder obtenir informació sobre els canvis produïts durant la modificació per plasma. Aquestes tècniques inclouen superfície específica, XRD, WAXS, STM per tal d'estudiar els canvis en la seva morfologia i estructura de la superfície. D'altra banda, per tal d'estudiar els canvis en la composició química s'han emprat mesures de pH, valoracions àcid/base i XPS.

Finalment, alguns dels negres de caboni modificats han estat seleccionats per tal de ser avaluats en aplicacions finals tal i com són el reforçament d'elastòmers i la seva activitat vers la reducció d'oxigen utilitzada en les PEMFC per tal d'eliminar els metalls nobles. En el primer cas, s'ha estudiat l'efecte sobre la cinètica i el mecanisme de vulcanització del negre de carboni modificat mitjançant el plasma atmosfèric. Aquest estudi s'ha dut a terme utilitzant dues tècniques complementaries com són les corbes reomètriques i la vulcanització de molècules model (MCV). També s'han realitzat mesures d'adsorció de polímer sobre el NC i Bound Rubber per tal d'estudiar la interacció polímer-càrrega la qual presenta una gran influència en les propietats finals dels materials. D'altra banda, s'ha estudiat també la capacitat del NC modificat vers a la reducció d'oxigen a partir de voltametria cíclica i s'han determinat les propietats del NC que poden influir de manera rellevant en l'activitat cataítica final del NC per a aquesta reacció. Tot i que es necessari fer una preparació posterior al tractament de plasma per a aquesta aplicació, el material final pot contribuir notablement a la eliminació de metalls nobles com a catalitzadors de reducció d'oxigen en les Piles de Combustible.
The present works deals with plasma modification of carbon black (CB). Although this type of treatment is widely used on flat surfaces handling problems should be overcome in order to treat powders as CB. In this study CB has been modified both by means of low-pressure and atmospheric pressure non-equilibrium plasmas. In order to accomplish this objective three different plasma reactors have been set-up; two at low pressure and one at atmospheric pressure working conditions.

Low pressure plasma reactors utilised in this work consist in a down-stream and a fluidised bed system working at Radio Frequency generation power (RF 13,56 MHz). Both reactors have been optimized to treat powder materials. For the down-stream reactor, position of the reactive gas inlet, and treatment conditions such as generator power and time have been studied for oxygen, nitrogen and ammonia treatments. For the fluidized bed reactor the distance of the powder sample to the plasma generation zone, particle size and support porosity have been taken into account.

Concerning atmospheric plasma, a device has been set up in order to adapt a commercial plasma torch (Openair® from Plasmatreat GmbH), for powder modification. An adaptable reactor, a method to introduce the powder in the plasma zone as well as a collecting system had been developed in order to obtain a quasi-continuous modification treatment.

Three types of CBs, N134, XPB 171 and Vulcan XC-72 have been modified in both the down-stream and the atmospheric plasma system. Graphitization and extraction of N134 were also carried out before plasma modification in order to study the effect of both impurities and surface structure of the CB during plasma modification. Surface oxidation and nitrogen enrichment were the two main studied treatments in both systems which allowed comparing their performances.

Unmodified and Modified CBs have been characterised from several points of view. Specific surface area, XRD, WAXS and STM have been used in order to study morphological and surface structure changes. On the other hand, pH measurements, acid/base titration and XPS were employed in order to study the surface chemistry composition changes that had taken place during plasma modification.

Some of the modified CB grades were selected in order to be tested in final applications such as rubber reinforcement and oxygen reduction non-noble metal catalyst for PEMFC. In the first case, the effect of atmospheric plasma treatment on the vulcanization kinetics and mechanism has been evaluated both by rheometre curves and the model compounding approach. Studies about the polymer-filler interaction have been also carried out by calculating bound rubber and adsorption from polymer solution. Last but not least, plasma modification capacity to enhance the oxygen reduction activity to obtain non-noble metal catalysts for PEMFC has been evaluated after the correspondent preparation. Oxygen reduction activity has been studied by means of cyclic voltammetry. The main CB properties which could play an important role in such applications have been analyzed.

Chaque année, environ 1,5 million de patients requièrent un remplacement vasculaire en réponse à une athérosclérose avancée, causant le rétrécissement interne des vaisseaux sanguins. Malheureusement, encore aujourd'hui les matériaux synthétiques utilisés pour remplacer les artères de petits diamètres (inférieurs à 6 mm) restent associés à un haut taux d'échecs, démontrant ainsi un manque de biocompatibilité certain. L'une des principales complications observées est l'hyperplasie néointimale artérielle caractérisée par l'obstruction du vaisseau sanguin due à la prolifération tridimensionnelle de cellules sur la paroi interne de la prothèse. Différentes stratégies visant à limiter cette réaction naturelle sont aujourd'hui envisagées, notamment l'utilisation d'un système à libération contrôlée de médicament intégré localement aux prothèses vasculaires. En parallèle, l'essor des technologies plasma a permis de montrer qu'il était possible de revêtir la surface de matériel biomédical pour améliorer son interaction avec un environnement biologique. La stratégie consiste à utiliser l'énergie et la réactivité d'un plasma pour polymériser un précurseur gazeux. En sélectionnant la structure moléculaire du précurseur et les conditions expérimentales du plasma appropriées, il est possible de déposer un polymère plasma à la surface du matériel sélectionné pour lui conférer des propriétés sur mesure. C'est dans ce contexte que cette thèse a consisté à synthétiser, à l'aide d'un plasma, une matrice polymère plasma biodégradable pour revêtir la paroi interne d'une prothèse vasculaire, dans le but d'y incorporer un médicament choisi de façon à limiter l'hyperplasie néointimale. Ce projet a permis d'une part de réaliser une preuve de concept en déposant un revêtement polymère plasma dégradable par décharge à barrière diélectrique en configuration planaire. En utilisant le lactate d'éthyle en tant que précurseur et après de nombreuses analyses, des conditions de dépôt optimales ont pu être élues pour leur potentiel dans le cadre d'applications vasculaires. D'autre part, grâce à une caractérisation approfondie de la décharge, une corrélation étroite entre la physico-chimie du plasma et les dépôts dégradables obtenus a pu être établie. Afin d'élargir les possibilités de vitesse de dégradation, l'influence d'une alimentation impulsionnelle sur la décharge et sur le dépôt a de plus été étudiée. Si la manière d'apporter l'énergie a eu une forte influence sur la décharge, aucune influence majeure n'a été notée sur la chimie et la morphologie des dépôts faits à partir de lactate d'éthyle. Enfin, la construction d'un réacteur plasma tubulaire permettant de déposer la matrice développée à l'intérieur de prothèses artérielles a permis de s'étendre aux conditions réelles de dépôt. Dans l'ensemble, ce projet de recherche a mis en évidence le potentiel des procédés plasma pour le développement de matrices polymères plasma dégradables, notamment dans le cadre de systèmes à libération contrôlée et locale de médicaments pour des applications en chirurgie vasculaire. D'un point de vue de la physique des plasmas, ce travail a de plus souligné l'importance de l'étude de la décharge dans de véritables conditions de dépôt de couches minces
Every year, about 1.5 million patients need a vascular replacement due to advanced arteriosclerosis, which causes the internal narrowing of blood vessels. Unfortunately, even today the synthetic materials used to replace small diameter arteries (below 6 mm) remain associated with low patency rate, which demonstrates an evident lack of biocompatibility. One of the main observed complications is arterial neointimal hyperplasia, which is characterized by the blood vessel obstruction due to the tridimensional proliferation of cells on the graft internal wall. Different strategies aiming at limiting this body reaction are currently considered, in particular the use of a drug delivery system locally integrated to the vascular grafts. Concurrently, the rise of plasma technologies enabled to demonstrate the possibility to coat the surface of biomedical devices to improve their interaction with a biological environment. The strategy consists in using the plasma energy and reactivity to polymerize a gaseous precursor. By selecting the appropriate precursor molecular structure and plasma experimental conditions, one can build up a plasma polymer with tailored properties. It is in this context that this thesis consisted in synthesizing, using plasma, a biodegradable polymeric plasma polymer matrix to coat the internal wall of a vascular graft, with the goal to incorporate a drug chosen to limit neointimal hyperplasia. On one hand, this project acted as proof of concept by developing a degradable plasma polymer coating using a planar dielectric barrier discharge. After extensive studies using ethyl lactate as precursor, optimal chemical vapor deposition conditions were elected for their potential in terms of vascular applications. On the other hand, thanks to an extended discharge characterization, a strong correlation was established between the plasma physico-chemistry and the properties of the degradable coatings synthesized. In addition, to broaden possibilities in terms of degradation rate, the influence of a squared pulse power supply on the discharge and the coating was studied. If changing the way to bring the energy had a strong influence on the discharge, no major influence was noticed on the ethyl lactate-based coatings' chemistry and morphology. Finally, a tubular plasma reactor was build up to empower the internal wall of vascular prosthesis to be coated, which enabled to extend this project to the deposition conditions of its final application. Overall, this research project highlighted the potential of plasma processes for the development of degradable plasma polymer matrices, particularly for local drug delivery systems for vascular applications. On a physics perspective, this work emphasized the importance of studying the discharge under actual thin layer deposition conditions

Les dispositifs plasma à la pression atmosphérique (PA) produisent de nombreuses espèces actives physiques (photons, particules chargées, champ électriques etc.) et chimiques (radicaux libres, espèces réactives de l'oxygène, espèces réactives de l'azote etc.). Ces espèces connues pour leurs effets biologiques directs ou indirects font de l'utilisation des jets de plasmas froids à la PA pour des traitements biomédicaux un sujet de recherche en plein développement. La recrudescence des cas de radiorésistance et chimiorésistance chez les micro-organismes et les cellules cancéreuses impose la recherche de nouveaux modes de traitements innovants. C'est dans ce contexte général que s'inscrit les travaux présentés ici dont l'enjeu majeur est la compréhension des mécanismes d'actions des plasmas froids à la PA sur le cancer colorectal (deuxième cause de mortalité par cancer en France). Le travail de thèse présenté concerne l'utilisation d'un modèle biologique in-vitro (sphéroïde tumoraux multicellulaire du cancer du côlon HCT116) en 3 dimensions qui permet de prendre en compte des paramètres déterminants dans la prolifération tumorale. Ce modèle permet ainsi une meilleure prédiction des résultats in vivo dans l'objectif d'une étude clinique ultérieure. De plus les cinétiques de créations des espèces actives ont été étudiées dans leur globalité depuis le dispositif plasma jusqu'aux interactions intracellulaires à partir d'analyses physiques, biologiques et chimiques. Le traitement indirect par utilisation de liquides activés par jet de plasma d'hélium a été privilégié pour élaborer un traitement endoscopique du cancer colorectal. L'ensemble des travaux menés sur l'observation des interactions des liquides activés par plasma sur les sphéroïdes tumoraux multicellulaires a permis de révéler deux modes d'actions distincts. Le premier étant une génotoxicité du liquide activé induite par la présence de peroxyde d'hydrogène dont l'action induit une cassure double brin de l'ADN intracellulaire conduisant les cellules à la mort par apoptose. Une interaction directe des radicaux libres produits dans le milieu avec les composants de ce dernier (acides aminés, glucose, etc.) ainsi que la présence de nitrites et nitrates induisent également un effet antiprolifératif à long terme du milieu activé par plasma sur les tumeurs HCT116. Différentes méthodes comme la résonance paramagnétique électronique et la spectroscopie d'émission optique ont permis de révéler des voies de création possibles conduisant à la formation de ces espèces actives. Des campagnes d'essais thérapeutiques ont permis d'évaluer la capacité des liquides activés par plasma à cibler davantage les cellules cancéreuses plutôt que les cellules saines ce qui en fait une méthode de traitement sélectif particulièrement prometteuse. Le développement et la caractérisation d'un second jet de plasma d'argon a été réalisé avec l'objectif d'optimiser l'effet antiprolifératif des plasmas sur les tumeurs tout en tenant compte des contraintes imposées par l'utilisation d'un tel dispositif pour le traitement du cancer colorectal
Plasma devices at atmospheric pressure (AP) generate many physical active species (photons, charged particles, electric field, etc.) and chemical (free radicals, reactive oxygen species, reactive nitrogen species, etc...). This species are well known for their direct or indirect biological effects thus biomedical treatment by low temperature plasma jets at AP is currently a hot research topic. The upsurge of radioresistance and chemoresistance of microorganisms and cancer cells requires the development of new biomedical treatment. In this general context, the present work is a step towards the understanding of the effect induced by low temperature plasma jets at atmospheric pressure on colorectal cancer (second leading cause of death by cancer in France). This thesis focuses on the implementation of an in vitro biological model (multicellular tumor spheroid of colorectal cancer HCT116) in 3 dimensions which allows to take into account key parameters in tumor proliferation. This model is also well suited for the prediction of in vivo results in the aim of a subsequent clinical study. Further research about kinetic reactions of active species has been studied from the plasma device up to intracellular interactions through physical, biological and chemical analyses. Indirect treatment of tumors was carried out through helium plasma jet activated liquids. This solution was chosen for its relevance for endoscopic treatment of colorectal cancer. Interaction between plasma activated liquid and multicellular tumor spheroids has shown two distinct pathways. The first one is the genotoxicity of activated medium induced by the occurrence of hydrogen peroxide which induced DNA damages once penetrated in intracellular medium and leading to cell death by apoptosis. A direct interaction between free radicals generated in liquid medium and the latter components (amino acids, glucose, etc.) associated with the occurrence of nitrites and nitrates induces a long-term antiproliferative effect of plasma activated liquid. Chemical pathways of the formation of these active species were identified by using different analysis techniques such as electron paramagnetic resonance and optical emission spectroscopy. Therapeutic analysis have also demonstrated that plasma activated liquid damage preferentially colon cancer cells rather than healthy cells making it a particularly promising selective treatment method. The design and the characterization of a second plasma jet using argon as a carrier gas was carried out with the aim to improve the antiproliferative effect of plasmas on tumors while taking into account the requirement for the use of such device for colorectal cancer treatment

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.

Le manuscrit porte sur l'élaboration de couches minces ayant des propriétés barrières aux liquides, aux gaz et aux ultra-violets. Pour réaliser nos différents systèmes, la technologie plasma à décharge à barrière diélectrique à la pression atmosphérique (DBD) a été utilisée. Dans la première partie, des films polymère plasma à base de 1H, 1H, 2H, 2H, Perfluorodecyl acrylate ont été développé. En fonction des paramètres plasma une surface dîtes superhydrophobe en une étape a été obtenue grâce à l'obtention d'un film composé de nanoparticules fluorés. La seconde partie des travaux a consisté à développer des films barrières aux gaz à partir de l'hexamethyldisiloxane. Ainsi, des films minces SiOx et multicouches SiOxHyCz/SiOx ont pu être obtenue afin d'améliorer les performances barrières de substrat PET et PEN. Enfin, l'obtention de film barrière aux UV a consisté à une croissance in-situ de nanoparticules de dioxyde de titane (TiO2) à partir du film polymère plasma. La matrice polymère constitué d'une structure siloxane et aminée plasma joue le rôle de nano-réacteur pour la croissance de cristaux de TiO2.

Surface modification techniques using plasmas have generally been completed in a low pressure environment due to Pd (pressure x gap distance) considerations influencing the behavior of plasma generation. Generally, plasmas produced in a low pressure environment are of a non-thermal or cold nature. The basic feature of non-thermal plasmas is the majority of electrical energy used to generate the plasma is primarily used to produce energetic electrons for generating chemical species. Low pressure plasmas serve many purposes for materials processing. Since the plasma environment is contained within a closed vessel, the plasma can be controlled very easily. Low pressure plasmas have been used in many industries but the complexity associated with the large pumping stations and limitation to batch processing has motivated new work in the area of atmospheric plasmas. Atmospheric plasmas offer both economic and technical justification for use over low pressure plasmas. Since atmospheric plasmas can be operated at ambient conditions, lower costs associated with continuous processing and a decrease in the complexity of equipment validate atmospheric plasma processing as a next generation plasma-aided manufacturing processes. In an effort to advance acceptance of atmospheric plasma processing into industry, a process was developed, the dielectric barrier discharge (DBD), in order to generate a homogeneous and non-thermal plasma discharge at ambient conditions. The discharge was applied to the reduction of known food borne pathogens, deposition of thin film materials, and modification of lignocellulosic biomass.

This work is focused on modelling of atmospheric pressure high frequency (HF) discharges operated at relatively low power densities. Two types of devices are considered – the radio frequency capacitively coupled atmospheric pressure plasma jet and the microwave discharge sustained by surface electromagnetic waves. They are addresses as the plasma shower and the surface-wave discharge (SWD). Both of the considered devices operate in argon at atmospheric pressure (p = 1 bar). However, the difference in the frequency of the power coupling mechanism induces a big difference in plasma properties. This implies also that different modelling approaches have to be employed.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

La réponse biologique d'un matériau est essentiellement reliée à sa surface : cela souligne l'importance du rôle des techniques de modification de surface dans la réalisation d'une réponse biologique adaptée. Ainsi les surfaces fonctionnalisées par des 'hydrogels' minces possèdent un énorme potentiel dans diverses applications. En effet, les hydrogels sensibles au pH et à la température peuvent être utilisés dans le but de libérer de façon contrôlée une molécule dans l'environnement biologique. Ces hydrogels peuvent aussi être utilisés en tant que biocapteur de par leurs fonctions disponibles permettant la reconnaissance spécifique de biomolécules cibles. Différents procédés, choisis principalement en fonction du type de matériau et de la surface à fonctionnaliser, peuvent être utilisés pour l'obtention de ce genre de films. Parmi ces procédés, le choix s'est tourné vers l'utilisation de la polymérisation par plasma dont les propriétés de surfaces peuvent être ajustées en fonction des paramètres de la décharge tel que la puissance électrique, le temps de traitement, la composition et la pression du gaz.

En l’espace d’une dizaine d’années, les jets de plasma froid à pression atmosphérique ont su s’imposer comme un outil pertinent pour les applications biomédicales. La simplicité de conception et d’utilisation de ces dispositifs, combinée à leurs facultés de produire des espèces réactives (NO, OH, O …), ont significativement contribué au développement rapide du domaine. Beaucoup d’efforts ont été entrepris dans le développement de diagnostics quantitatifs, pour mesurer la production des espèces réactives dans la plume plasma d’un jet donné. Toutefois, la diversité des géométries de décharge, des sources d’alimentations électriques ou des conditions d’utilisation, rendent les comparaisons d’un jet à l’autre, difficiles. Cette thèse a porté sur l’étude du jet de plasma froid à pression atmosphérique développé au GREMI, le Plasma Gun (hélium, impulsion de tension microseconde). Nous avons étudié les mécanismes de décharge susceptibles de considérablement affecter la production d’espèces réactives, dans des conditions approchantes d’applications biomédicales. La thèse s’articule en trois chapitres principaux : l’étude de la modification de l’écoulement de l’hélium par plasma (par strioscopie) ; l’étude de la propagation du plasma dans le capillaire diélectrique (étude expérimentale et numérique de la dynamique de propagation rapide du plasma et de l’évolution du champ électrique en mélange hélium-azote) ; l’étude de l’interaction du plasma avec une cible conductrice (mesures dans le capillaire et dans la plume de l’évolution spatiale et temporelle de la concentration des métastables de l’hélium, corrélées à des mesures du champ électrique). Ce dernier point est en particulier représentatif de tout jet plasma en condition traitement biomédical in vivo et tend à faire une distinction fondamentale avec les mécanismes de décharge du jet plasma dit « libre », sans obstacle entravant la plume plasma
Over the past ten years, the cold atmospheric pressure plasma jets (CAPPJ) became useful devices for biomedical applications. Their relatively simple design and use, combine with their ability to produce reactive species (NO, OH, O, …), led to a rapid research growth in this field. A lot of studies have been devoted to quantitative diagnostics development for the reactive species production measurements in the plasma plume. However, it is difficult to compare one jet with another because of the huge variety of discharge geometries, electric power supplies or operating conditions. This thesis deals with the study of the CAPPJ developed in GREMI, the Plasma Gun (helium feeded, microsecond voltage pulse). We have studied discharge mechanisms which strongly impact the reactive species production in near target biomedical application conditions. This study is divided in three parts : the study of helium flow modifications induced by the plasma (strioscopy visualization); the study of plasma propagation inside dielectric capillary (experimental and numerical study of fast plasma propagation dynamic and electric field evolution for helium-nitrogen mixtures); the study of conductive target-plasma interaction (space and time resolved measurements inside the capillary and the plasma plume of helium metastable production, correlated with electric field evolution). The conductive target contact concerns any in vivo biomedical treatments. CAPPJ in front of such a conductive target leads to fundamentally different discharge mechanisms compare to the free jet case

Les thérapies anticancéreuses basées sur des principes physiques (radiofréquences, ultrasons, laser, électroporation...) ont considérablement augmenté lors de la dernière décennie. Leurs objectifs sont de détruire directement les cellules cancéreuses, de favoriser l'entrée ciblée de molécules thérapeutiques ou encore de stimuler le système immunitaire du patient afin d'éliminer la tumeur. Le plasma froid suscite l'intérêt dans le domaine de l'oncologie grâce à sa capacité à générer des espèces réactives oxygénées (ROS) et azotées (RNS) qui peuvent être génotoxiques et cytotoxiques pour les cellules cancéreuses. Deux approches d'utilisation du plasma sont étudiées : soit l'exposition directe de cellules au jet plasma, soit l'exposition indirecte via l'utilisation d'un Milieu Activé par Plasma (PAM). Le PAM étant plus facile à délivrer par injection dans la tumeur, c'est cette approche qui est choisie lors de ces travaux. Le travail de thèse présenté consiste à étudier l'effet génotoxique et cytotoxique du PAM, obtenu après exposition du milieu au jet de plasma d'hélium, sur des tumeurs in vitro et in vivo. Pour les études in vitro, nous avons choisi d'utiliser un modèle 3D : le sphéroïde (MCTS - MultiCellular Tumor Spheroid). Ce modèle présente des caractéristiques proches du modèle in vivo grâce à son organisation en sphéroïde. Les MCTS présentent en effet des gradients de pénétration d'oxygène, de nutriments et de prolifération cellulaire. La première partie de la thèse concerne l'identification et la quantification des espèces générées dans le PAM. Les méthodes d'analyses utilisées sont la résonance paramagnétique électronique, la fluorimétrie, la colorimétrie, la chromatographie en phase liquide et la spectrométrie de masse. Ces analyses ont mis en évidence que la toxicité du PAM était due à plusieurs facteurs : d'un côté la génération de ROS et RNS mais aussi à la dégradation des nutriments pour les cellules contenues dans le milieu via par exemple l'oxydation et la nitrosylation des acides aminés. La deuxième partie est dédiée à l'étude des effets du PAM sur les MCTS HCT-116 (cancer du côlon).[...]
Cancer therapies based on physical principles (radiofrequency, ultrasound, laser, electroporation...) have considerably increased in the last decade. Their objectives are to directly destroy cancer cells, to favor the targeted entry of therapeutic molecules or to stimulate the patient's immune system in order to eliminate the tumor. Cold plasma still arouses interest in the field of oncology through its ability to generate reactive oxygen species (ROS) and nitrogen species (RNS) which can be genotoxic and cytotoxic for cancer cells. Two approaches to the use of plasma are studied: either direct exposure of cells to the plasma jet, or indirect exposure via the use of a Plasma Activated Medium (PAM). The PAM being easier to deliver by injection into the tumor, this approach was chosen in this work. The work presented consists in studying the genotoxic and cytotoxic effects of PAM resulting from exposure of the medium to the helium plasma jet on in vitro and in vivo tumors. For in vitro studies, we chose to use a 3D model: the spheroid (MCTS - MultiCellular Tumor Spheroid). This model has similar characteristics to the in vivo model thanks to its spheroidal organization. The spheroids have indeed gradients of oxygen penetration, nutrients and cell proliferation. The first part of the thesis concerns the identification and quantification of the species generated in PAM. The analytical methods used are paramagnetic electronic resonance, fluorimetry, colorimetry, liquid chromatography and mass spectrometry. These analyses revealed that the toxicity of PAM was due to several factors: on the one hand to the generation of ROS and RNS and on the other hand to the degradation of cell nutrients contained in the medium via, for example, the oxidation and nitrosylation of the amino acids. The second part is dedicated to the study of the effects of PAM on HCT-116 (colon cancer) spheroids[...]

Atmospheric pressure plasma, APP, jets, are now attracting great interest because of their potential uses in many applications; for example surface modification and plasma medicine. These applications require an insight into their plasma chemistry, which is strongly influenced by the electron energy distribution function. In this work the dynamic behaviour of a 20 kHz-driven APP jet operating with helium as the main gas and oxygen as an additive is investigated. The jet has a commonly used configuration, a cylindrical quartz tube with two electrodes used to form a dielectric barrier discharge. This atmospheric pressure plasma jet was used to generate non thermal plasma bullets away from the production region. The characteristics of the plasma plume and streamer were diagnosed using, current-voltage measurements, ICCD imaging, and optical emission spectroscopy. Here, the use of Thomson scattering to measure the electron properties in the plasma plume created by 20 kHz was reported. The investigation reveals a "ring-like" radial distribution of both the electron density and temperature. A 532nm Nd:YAG laser beam was focused into the plasma plume. The temporally and spatially resolved spectra of light at 900 to the laser direction were detected. The spectra contain light from Thomson Scattering from electrons, along with Rayleigh and Raman scattering from atoms and molecules. The use of a atmospheric pressure helium non-thermal plasma jet to assist a SCR deNOx reaction over a silver-based catalyst at low temperature using simulated diesel fuels was explored. A coupled IR-plasma reactor was developed allowing direct interaction of the plasma with the catalyst bed whilst accommodating a FTIR spectrometer and NOx analyzer. Two KHz, quartz tube jet designs were developed to operate at low gas flows, one with a circular copper electrode but with a grounded electrode in the reaction area, and the other with a central powered electrode with the vessel as a ground. The catalyst was prepared by the impregnation of ?-AI203 with a silver nitrate solution. NOx and hydrocarbon conversions were studied with toluene and octane on an Ag-catalyst at two different temperatures.

This dissertation will be focused on the characterization of an atmospheric pressure plasma jet source with an application oriented diagnostic approach and the description of processes supported by this plasma source. The plasma source investigated is a single electrode plasma jet. Schlieren images, optical emission spectra, temperature and heat flux profiles are analyzed to deeply investigate the fluid dynamic, the chemical composition and the thermal output of the plasma generated with a nanosecond-pulsed high voltage generator. The maximum temperature measured is about 45 °C and values close to the room temperature are reached 10 mm down the source outlet, ensuring the possibility to use the plasma jet for the treatment of thermosensitive materials, such as, for example, biological substrate or polymers. Electrospinning of polymeric solution allows the production of nanofibrous non-woven mats and the plasma pre-treatment of the solutions leads to the realization of defect free nanofibers. The use of the plasma jet allows the electrospinnability of a non-spinnable poly(L-lactic acid) (PLLA) solution, suitable for the production of biological scaffold for the wound dressing.

This dissertation will be focused on the characterization of an atmospheric pressure plasma jet source with an application oriented diagnostic approach and the description of processes supported by this plasma source. The plasma source investigated is a single electrode plasma jet. Schlieren images, optical emission spectra, temperature and heat flux profiles are analyzed to deeply investigate the fluid dynamic, the chemical composition and the thermal output of the plasma generated with a nanosecond-pulsed high voltage generator. The maximum temperature measured is about 45 °C and values close to the room temperature are reached 10 mm down the source outlet, ensuring the possibility to use the plasma jet for the treatment of thermosensitive materials, such as, for example, biological substrate or polymers. Electrospinning of polymeric solution allows the production of nanofibrous non-woven mats and the plasma pre-treatment of the solutions leads to the realization of defect free nanofibers. The use of the plasma jet allows the electrospinnability of a non-spinnable poly(L-lactic acid) (PLLA) solution, suitable for the production of biological scaffold for the wound dressing.

Le développement dans l'industrie aéronautique des composites à matrices organiques renforcés par des fibres de carbone se justifie entre autres par leur très bonne capacité à transférer les efforts mécaniques élevés en rapport de leur faible masse. Les matrices Poly-EtherEtherCétone (PEEK) sont des candidates idéales pour les applications structurales en raison de leurs bonnes propriétés chimiques, mécaniques, ainsi que d'une stabilité thermique supérieure à d'autres polymères. Cependant celles-ci présentent des inconvénients majeurs pour la phase de mise en peinture, à savoir une faible réactivité de surface et une inertie chimique importante qui impliquent le développement d'un procédé d'activation de surface avant toute étape de revêtement. Ce travail se concentre sur une technologie de plasma froid à la pression atmosphérique développée par la société AcXys Technologie(r) : le module ULS en post-décharge. Cette technologie, choisie sur la base de considérations industrielles et environnementales, vise à garantir une activation de surface efficace, sans détérioration des propriétés intrinsèques de la matrice polymère. L'objectif de ce travail est alors d'améliorer la compréhension des mécanismes d'activation par plasma menant à une meilleure adhésion à l'interface composite PEEK/revêtement industriel. Des caractérisations électriques et optiques de la décharge et de la post-décharge nous permettront de mieux comprendre le fonctionnement intrinsèque de l'équipement. Tandis que la caractérisation des modifications de surface (de nature chimiques, physiques et/ou physico-chimiques), notamment au travers de la mouillabilité et de l'acido-basicité, permet d'appréhender l'influence des paramètres opératoires et du gaz plasmagène utilisé. Dans la perspective de mieux spécifier les conditions optimales d'utilisation industrielles, nous évaluons dans cette étude la pertinence de l'utilisation de la notion de dose plasma pour ce procédé, notion représentative de l'ensemble des paramètres opératoires. Cette notion, communément rencontrée dans d'autres procédés, est revue et développée pour correspondre à notre cas d'étude. Son utilisation permet une juste comparaison entre des configurations d'activation différentes puisqu'elle rend compte à la fois de la puissance dissipée sur le substrat et du temps d'interaction plasma/surface. Afin de valider la dose plasma exprimée pour notre équipement, nous introduisons des mesures d'adhérence effectuées entre le composite activé et le revêtement. Les résultats laissent entrevoir des perspectives d'améliorations dans les procédés industriels d'activation de surface
Carbon Fiber Reinforced Polymer (CFRP) using thermoplastic polymer matrices as Poly-EtherEtherKetone (PEEK) for example, are increasingly being used in structural engineering due to their light weight coupled with good mechanical properties. In aeronautic industry, the adhesive bonding of these composites is often required. However, their low surface energy motivates the development of robust and reliable surface activation treatments aiming at increasing the surface reactivity before painting. For this reason, we have used an atmospheric pressure plasma torch developed by AcXys Technologies(r). It is a remote plasma, well known to be an effective process to improve surface reactivity without deterioration of the bulk matrix properties. This easily implementable technology attracts many industries looking for a cost-effective and eco-friendly surface activation process. The aim of this work is to contribute to the understanding of plasma activation mechanisms leading to a greater and a more durable adhesion between PEEK matrix and an industrial painting. This study provides some insight into the effects of process parameters (device power, distance between nozzle and substrate, etc) on adhesion improvement. Mechanisms which are attributed to it are investigated by means of three point bending and crosscut adhesion standard tests. Results are discussed with respect to surface properties characterized by wettability measurements including acid-base approach, X-ray Photoelectrons Spectroscopy and Atomic Force Microscopy. In order to facilitate industrialization of atmospheric pressure remote plasma as surface activation technique, this study proposes a new approach aiming at allowing a better and more equitable comparison between atmospheric pressure plasma processes. This comparison is made through the "plasma dose" expression, similar to the one commonly used in Corona process. It is applicable for one plasma gas and accounts for both received energy and interaction time of the post-discharge with the surface. Mechanisms assigned to improvement of adhesion will be more appreciated and their characterization will contribute to a greater definition of industrial surface preparation range by remote plasma

In this Ph.D. thesis, we have carried out numerical simulations to study nanosecond repetitively pulsed discharges (NRPD) in a point-to-point geometry at atmospheric pressure in air and in H2-air mixtures. Experimentally, three discharge regimes have been observed for NRPD in air at atmospheric pressure for the temperature range Tg = 300 to 1000 K: corona, glow and spark. To study these regimes, first, we have considered a discharge occurring during one of the nanosecond voltage pulses. We have shown that a key parameter for the transition between the discharge regimes is the ratio between the connection-time of positive and negative discharges initiated at point electrodes and the pulse duration. In a second step, we have studied the dynamics of charged species during the interpulse at Tg = 300 and 1000 K and we have shown that the discharge characteristics during a given voltage pulse remain rather close whatever the preionization level (in the range 109-1011 cm��3) left by previous discharges. Then, we have simulated several consecutive nanosecond voltage pulses at Tg = 1000 K at a repetition frequency of 10 kHz. We have shown that in a few voltage pulses, the discharge reaches a stable quasi-periodic glow regime observed in the experiments. We have studied the nanosecond spark discharge regime. We have shown that the fraction of the discharge energy going to fast heating is in the range 20%- 30%. Due to this fast heating, we have observed the propagation of a cylindrical shockwave followed by the formation of a hot channel in the path of the discharge that expands radially on short timescales (t < 1 _s), as observed in experiments. Then we have taken into account an external circuit model to limit the current and then, we have simulated several consecutive pulses to study the transition from multipulse nanosecond glow to spark discharges. Finally the results of this Ph.D. have been used to find conditions to obtain a stable glow regime in air at 300 K and atmospheric pressure. Second we have studied on short time-scales (t_ 100_s) the ignition by a nanosecond spark discharge of a lean H2-air mixture at 1000 K and atmospheric pressure with an equivalence ratio of _ = 0:3. We have compared the relative importance for ignition of the fast-heating of the discharge and of the production of atomic oxygen. We have shown that the ignition with atomic oxygen seems to be slightly more efficient and has a completely different dynamics.

La capacité de modéliser, simuler et prédire le phénomène de reconnexion magnétique est un enjeu crucial pour de nombreuses applications (ITER, plasmas astrophysiques) et impacte la prédiction du « temps solaire » et des « orages magnétiques » pouvant perturber les satellites. L’enjeu scientifique fondamental est la description du transfert instationnaire d’énergie magnétique en énergie cinétique et thermique, encore hors d’atteinte des modèles magnéto-hydrodynamique (MHD) actuels. L’objectif premier de la thèse est le développement d’un modèle fluide cohérent de plasma magnétisé hors équilibrethermique et chimique avec une description détaillée des effets dissipatifs basée sur la théorie cinétique des gaz et une bonne structure mathématique. Le second repose sur le développement d’une stratégie numérique innovante, précise et robuste, dans un code de calcul massivement parallèle avec adaptation demaillage permettant de capturer tout le spectre d’échelle en jeu et la raideur numérique en résultant. L’ensemble des coefficients de transport, la thermodynamique et la chimie correspondante seront étudiés et comparés aux données préalablement utilisées dans le domaine. Puis on montrera que le modèle et sa simulation, issus d’un travail transdisciplinaire impliquant ingénierie, physique des plasmas, physique solaire, mathématique, et calcul scientifique et parallèle, est capable de reproduire correctement la physique du phénomène. La validation de l’approche à travers une série de cas test issus de l’application à la dynamique de l’atmosphère solaire en lien avec la NASA et le VKI permettra de disposer d’un outil, ouvert à la communauté, capable de lever plusieurs verrous scientifiques et technologiques
The ability to model, simulate and predict magnetic reconnection (MR) is a stumbling block in order to predict space weather and geomagnetic storms, which can lead to great perturbation of satellites. Some fundamental aspects of MR are not yet well understood. The scientific issue at stake is the proper description of the unsteady energy transfer from magnetic energy to kinetic and thermal energy, which is still out of reach for the standard Magneto-hydrodynamics (MHD) models. The first objective of the present project is to develop a coherent fluid model for magnetized plasmas out of thermal and chemical equilibrium with a detailed description of the dissipative effects based on kinetic theory of gases, which thus inherits a proper mathematical structure. The second goal is the development of a new numerical strategy, with high accuracy and robustness, based on a massively parallel code with adaptive mesh refinement able to cope with the full spectrum of scales of the model and related stiffness. The whole set of transport coefficients, thermodynamics relations and chemical rates in this magnetized two-temperature setting will be studied and compared to the one in the literature used in the field. Then, we will show that the model and related numerical strategy, obtained from this transdisciplinary work involving engineering, plasma physics, solar physics, mathematics, scientific computing and HPC, is able to properly reproduce the physics of MR. The validation of the approach through a series of test-cases relevant for the application to the dynamics of solar atmosphere in connection with VKI and NASA will provide a tool, open to the community, capable of resolving several critical scientific and technological issues

Les travaux présentés dans ce mémoire portent sur l’étude des plasmas d’hélium générés par micro-ondes en cavité résonnante à la pression atmosphérique et sur leurs applications en traitement de surfaces. Tout d’abord, un état de l’art sur les plasmas micro-ondes à la pression atmosphérique et leurs applications est présenté. Ensuite, un modèle collisionnel-radiatif de la décharge et de la post-décharge d’hélium pur est établi. Les résultats du modèle sont comparés aux mesures expérimentales obtenues à 2500 K et un jeu de sections efficaces et de constantes cinétiques valables pour ces conditions est proposé. Expérimentalement, des analyses par spectroscopie d’émission et d’absorption sont employées. La température du gaz est déterminée par la méthode du spectre rotationnel synthétique en fonction de la puissance, de la concentration et de la nature des impuretés introduites dans l’hélium. Il s’avère que le volume du plasma est un paramètre déterminant sur la température du gaz. La concentration du métastable He(23S), en décharge continue et pulsée, est déterminée par absorption laser. En décharge continue, la concentration du métastable est divisée par trois avec 360 ppm d’impureté, la nature de l’impureté n’ayant pas d’importance. En revanche, en post-décharge la nature de l’impureté est déterminante. Les mesures réalisées indiquent que He+ et non He2+ serait l’ion majoritaire. Concernant les applications de ce type de plasma, nous avons travaillé en post-décharge uniquement. Nous avons démontré la faisabilité du procédé de dépôt de SiOx à partir d’hexaméthyldisiloxane. Nous avons aussi montré que la nitruration du titane à haute température était possible
The present work deals with the study of helium microwave plasmas at atmospheric pressure generated in a resonant cavity and their applications in surface treatment. First of all, a state of art of microwave atmospheric pressure plasmas and their applications is presented. Next, a collisional-radiative model for pure helium discharge and post-discharge is described. The results of the model are compared to experimental data obtained at 2500 K and a coherent set of cross-sections and rate constants is obtained for these conditions. Emission and absorption spectroscopy diagnostics are employed to characterize the helium plasma. The gas temperature is determined by the rotational synthetic spectra method. The evolution of the gas temperature, as a function of the input power, the concentration and the nature of impurities in helium, is measured. It turns out that the plasma volume plays a significant role on the gas temperature. The He(23S) concentration is determined by laser absorption in pulsed and continuous mode. In continuous mode, the metastable concentration is divided by 3 with 360 ppm of impurity, regardless of the nature of the impurity. Nevertheless, during the post-discharge, in pulsed mode, the nature of the impurity plays an important role. These measurements support the idea that He+ and not He2+ is the main ion. Concerning the applications, only post-discharges are utilized. We demonstrate that deposition of SiOx using hexamethyldisiloxane as precursor can be efficient. We show that titanium nitriding at high temperature is possible

Les plasmas froids sont des gaz partiellement ionisés, très riches d’un point de vue physico-chimique. Cette propriété se retrouve dans des plasmas froids aujourd’hui générés à pression atmosphérique et température ambiante et a été mise à profit depuis une quinzaine d’années environ pour des applications biomédicales (hématologie, dermatologie, cancérologie, odontologie etc…). L’efficacité de ces plasmas froids dans le domaine de la médecine a été prouvée par de nombreuses études. Cependant, les phénomènes biologiques mis en jeu ne sont pas encore bien compris, et il primordial de savoir quels pourraient être les éventuels effets secondaires indésirables de ces milieux ionisés réactifs. Le premier niveau d’interaction des plasmas avec le vivant est celui avec les milieux liquides, qui sont présents en surface des tissus, des cellules in vivo ou en culture. Depuis une décennie, une attention particulière a donc été portée aux interactions des plasmas avec les liquides, pour apporter un niveau de compréhension supplémentaire. La compréhension de ces interactions a constitué l’axe de ce travail. Différents réacteurs à plasmas froids (générés à pression atmosphérique et température ambiante) ont été développés, notamment afin de contrôler les interactions du plasma avec l’air ambiant qui peuvent être problématiques pour les applications visées. La nature du gaz servant à initier le plasma a été modifiée, pour connaître son influence sur la réactivité chimique de la phase gaz. Pour cela, des mesures de spectroscopie d’émission optique (SEO) ont été nécessaires. Par ailleurs, de nouveaux capteurs électrochimiques et des approches méthodologiques ont été développés pour identifier et quantifier les espèces réactives de l’oxygène et de l’azote (RONS) produites dans des milieux liquides physiologiques, exposés à ces gaz ionisés. Les analyses électrochimiques ont été combinées à de la spectroscopie d’absorption UV-visible ainsi qu’à d’autres méthodes de chimie (pH-métrie/conductimétrie). Un des objectifs visés est d’établir une corrélation entre les espèces réactives générées dans la phase gaz et dans la phase liquide. Enfin, des expérimentations nous ont permis d’analyser la production des RONS dans des liquides in situ en temps réel. Les mesures de SEO montrent qu’il existe de nombreuses espèces chimiques excitées au sein des différents plasmas (NO°, HO°, O, N2+ (FNS) etc…). Les analyses de la phase liquide ont révélé la présence d’espèces stables de l’oxygène et de l’azote (H2O2, NO2-, NO3-), directement reliées aux espèces détectées dans les plasmas. De plus, les diverses méthodologies d’analyse chimique mises en place ont permis la détection et la quantification de RONS tels que l’anion peroxynitrite ONOO-. L’ensemble des résultats obtenus devrait permettre d’appréhender de façon plus fine les effets induits par différents plasmas froids dans des milieux liquides physiologiques afin d’établir un lien avec les études menées sur des cellules en culture et sur la peau dans le cadre d’un programme de recherche financé par l’ANR, Agence Nationale de la recherche
Cold plasmas are partially ionized gases, very rich in a physico-chemical point of view. This property characterizes cold plasmas today generated at atmospheric pressure and ambient temperature and was used since about fifteen years approximately for biomedical applications (haematology, dermatology, cancer research, odontology etc.). The efficiency of these cold plasmas in the field of the medicine was proved by numerous studies. However, the involved biological phenomena are not still well included, and it is essential to know what could be the possible unwanted side effects of these reactive ionized gases. The first level of interaction of plasmas with living matter is the one with the liquid phase, which is present on the tissue surface, in vivo cells or in culture. For a decade, a particular attention was thus worn in the interactions of plasmas with liquids, to bring a level of additional understanding. The understanding of these interactions constituted the axis of this work. Various cold plasmas reactors (generated at atmospheric pressure and ambient temperature) were developed, in order to control the interactions of these plasmas with the ambient air which can be problematic for the aimed applications. The nature of the gas used to initiate the plasma was modified, to know its influence on the chemical reactivity of the gas phase. For that purpose, measurements of optical emissive spectroscopy (OES) were necessary. Besides, new electrochemical sensors and methodological approaches were developed in order to identify and quantify the reactive nitrogen and oxygen (RONS) produced in physiological liquid media, exposed to these ionized gases. The electrochemical analyses were combined UV-visible absorption spectroscopy as well as other methods of chemistry (pH-metry/conductimetry). One of the aimed objectives is to establish a correlation between the reactive species generated in the gas phase and in the liquid phase. Finally, experiments allowed us to analyze the production of RONS in liquids in situ and in real time. OES measurements showed that there are numerous chemical species generated in various plasmas (NO°, HO°, O, N2+ (FNS) etc.). The analyses of the liquid phase revealed the presence of stable oxygen and nitrogen species (H2O2, NO2-, NO3-), directly correlated with the species detected in plasmas. Furthermore, the diverse methodologies of chemical analysis allowed the detection and quantification of RONS such as the peroxynitrite anion ONOO-. The obtained results should allow to arrest in a finer way the effects led by various cold plasmas in physiological liquid media to establish links with the studies led on cultured cells and on skin within the framework of a research program financed by the ANR, National Agency of the Research

Cette thèse porte sur l'étude de micro-plasmas froids à la pression atmosphérique générés à partir de différents réacteurs des configurations basées sur le principe des Décharges à Barrière Diélectrique (DBD) et alimentés par des générateurs de tension impulsionnelle et sinusoïdale. Les plasmas sont formés dans des gaz nobles tels que l'hélium et l'argon (gaz vecteurs), et également dans des mélanges réalisés avec des gaz moléculaires tels que l'azote et l'oxygène afin de produire des Espèces Réactives de l’Azote et de l’Oxygène (ERA, ERO). La (ré)activité chimique du plasma est ainsi supposée être accrue, permettant le traitement de matériaux inertes ou vivants pour diverses applications (fonctionnalisation de surfaces, inactivation de cellules, régénération de tissus vivants, etc.). La caractérisation des plasmas étudiés est réalisée en enregistrant les aspects électriques et optiques en fonction des paramètres élémentaires, comme l’amplitude et la fréquence de la tension, le débit du gaz, la configuration des électrodes, et le rapport cyclique dans le cas du régime pulsé. Ainsi, la (ré)activité chimique des plasmas est évaluée tandis que au même temps les mécanismes de la génération des plasmas et les façons de l’optimisation de la chimie sont dévoilées. Finalement, nous examinons l'efficacité du plasma dans le domaine biomédical en traitant divers systèmes biologiques (bactéries, liposomes, cellules) sans effets thermiques
The present PhD thesis is devoted to the study of atmospheric pressure cold micro-plasmas produced in different Dielectric Barrier Discharge (DBD) reactors which are driven by pulsed or sinusoidal high voltages. Noble gases such as helium and argon are used as carrier gases, whereas admixtures with nitrogen and oxygen are studied as well. The formation of Reactive Nitrogen and Oxygen Species (RNS, ROS) is thus achieved, and the possibility of improving the chemical (re)activity of the plasmas is demonstrated. This is of interest in the treatment of inert or living materials (e.g. surface functionalization, cell inactivation, living tissue regeneration, etc.). Plasmas are characterized by recording electrical and optical features as a function of principal operational parameters, including voltage amplitude and frequency, gas flow rate, electrode configuration, and voltage duty cycle in the case of pulsed waveform. The physico-chemical (re)activity of the plasmas is thus evaluated, while at the same time mechanisms on the plasma generation and paths for chemistry optimization are unveiled. Finally, the efficiency of the plasma in relation to biomedical applications is tested by treating different biological systems (bacteria, liposomes, cells) while preventing any thermal effect

Depuis près d'un siècle, les chercheurs déploient des efforts importants pour apporter de nouvelles propriétés aux matériaux et aujourd'hui la modification de surface des matériaux est plus que jamais un sujet de recherche très attractif lié à une variété d'applications industrielles prometteuses. Le développement d'une méthodologie simple pour caractériser les interactions biomoléculaires a été, au fil des ans, une technologie indispensable pour soutenir les recherches dans les domaines de la biologie et de la microbiologie en raison de son haut degré de sensibilité. La fonctionnalisation de surface par revêtement chimique est une solution prometteuse pour obtenir de nombreuses propriétés bien définies. Cette étude présente la faisabilité de la fonctionnalisation de la surface de l'or en utilisant une chimie basée sur les sels d'aryldiazonium pour le développement de biocapteurs appliqués à la technologie de résonance plasmonique de surface (SPR). Une technique de haute qualité utilisée pour mesurer les interactions biomoléculaires en temps réel dans un environnement label-free. Depuis de nombreuses années, les activités industrielles sont responsables de la pollution de l'atmosphère. Bien que différents gaz à effet de serre soient impliqués dans la pollution atmosphérique, le CO2 reste l'un des plus importants en raison de ses concentrations élevées dans l'atmosphère et de sa capacité à provoquer des maladies graves. Plusieurs études dans la littérature ont démontré que certains adsorbants tels que les charbons actifs, les tamis basiques de silice fonctionnalisés, les zéolithes, etc. bien que disponibles dans le commerce sont encore sophistiqués et coûteux limitant leur application. Cependant, il est toujours nécessaire de capter le CO2 pour des activités à coûts d'exploitation limités. L'objectif de cette étude est de valoriser l’écorce du cacao, une ressource d'agro-déchets prête à l'emploi et facile à modifier, en tant que matériaux peu coûteux pour l'adsorption du CO2 et l'élimination des toxines des déchets industriels en solution appliquant un traitement chimique à partir des sels de diazonium et des composés de silane pour modifier ses propriétés physico-chimiques
For almost a century, the researchers have been making important efforts in order to bring new properties to materials and nowadays surface modification of materials is more than ever a very attractive research subject related to a variety of promising industrial applications. The development of simple methodology to characterize biomolecular interactions has been, over the years, an indispensable technology to support researches in the areas of biology and microbiology due its high degree of sensitivity. Surface functionalization by chemical coating is a promising solution to obtain numerous well-defined properties. This study presents the feasibility of gold surface functionalization using a chemistry based on aryldiazonium salts to the biosensors development applied to Surface Plasmon Resonance (SPR) technology. A high-quality technique used to measure biomolecular interactions in real time in a label free environment. Since many years, industrial activities are responsible to the pollution of the atmosphere. Although different greenhouse gases being involved in atmospheric pollution, CO2 is still one of the most important due its high concentrations in the atmosphere and due to its ability to induce serious health disease. Several studies in the literature have demonstrated that some adsorbents such as activated carbons, basic functionalized silica sieves, zeolites, etc.. although commercially available are still sophisticated and expensive limiting their application. However, there is still a need to capture CO2 for activities with limited operating cost. The objective of this study is to promote the cocoa shell, an agro-waste resource ready to use and easy to modify, as low-cost materials for CO2 adsorption and toxins removal from industrial waste in solution applying a chemical treatment from diazonium salts and silane compounds to modify its physic-chemical properties

碩士
聖約翰科技大學
自動化及機電整合研究所
97
In industrial application, usually the plasma is used to surface modification to improve the surface function and quality or yield rates for products. Since an atmospheric pressure plasma could be applied to surface modification for products with complex geometry in a lack of vacuum environment, it definitely saves a lot of operation cost. The pulsed atmospheric pressure plasma supply system (PAPPS) has unique features in lower surface charge accumulation and higher processing repeatability due to pulsed parameter adjustment from clever tuning technique in manufacturing recipes. There are two important sections described in this thesis. First section, the practical design is performed for one set of a pulsed high-voltage power supply involved a high-frequency pulsed transformer which was adapted a DC power supply and a pulsed power controller. Its electrical specifications are maximum output power of 2 kW, the operating frequencies within 25 kHz, and limited working voltage at 20 kV with a bipolar pulsed output mode. Through RS232 interface, the PC remote control system was built for setting the pulsed parameters and for monitoring the variation of electrical power outputs, which also consisted of an oscilloscope, a high voltage differentiate probe, and a current probe. Next, under appropriate dry-pressure air and high-pulsed voltage supply, the atmospheric pressure plasma jet was generated via a plasma jetting nozzle. This low-temperature plasma jet would be employed as the tool of surface treatment for work pieces at an atmospheric chamber. Through measured instruments of contact angles and 3D surface profiles, the surface characteristics were detected after surface treatment. Experimental results have demonstrated that the pulsed atmospheric pressure plasma supply system is able to offer a stable plasma stream while a tunable DC power source, pulsed parameters and air pressures. One of optimal parameters includes the operating frequency of 25 kHz and 50％ duty cycle, air pressure in 0.4 kg∕cm2, and electrical power of 0.77 kW, resulting in contact angles of drop-shape varied from 65.1° fallen into 34.1° after 12 second plasma surface treatment. Also, the surface average roughness (Ra) was carried from 1.19 μm levitated to 2.17 μm after surface modification in 10 seconds. It is an obvious proof of the PAPPS system useful capability in PCB surface cleaning and activating. After plasma surface treatment, the hydrophilic feature of PCB plates has been enhanced that meaning of adherent substance ability on PCB surface is improved for component welding and in robust yield rate.

The properties of materials, especially of solids, can be attributed mainly to the phenomena occurring at the surface. Surface engineering deals with altering the surface properties of materials to realize useful functionalities like wear and corrosion resistance, biocompatibility, hardening etc. Among the various methods adopted, plasma surface modification stands out, because of the inherent dry processing nature and little amount of left over chemicals. In conventional plasma systems, the process is carried out in a low pressure environment. This restricts its use in treating vacuum incompatible materials including tissues and bio-medical samples. Moreover, the batch processing nature and use of expensive vacuum pumps put a bottle-neck in the throughput of any production line. The subject matter of this thesis is about developing and optimizing an atmospheric pressure (760 torr) plasma system and to use it for surface modification of polymers. The experimental system developed, consists of two parallel electrodes facing each other, each of which is covered with a dielectric plate. A gap of 4mm exists between the dielectric surfaces, through which an axial flow of the working gas is maintained. When a high voltage is applied across the electrodes, the gas breaks down, creating plasma. The surface of the sample kept in this plasma, undergoes various phenomena, depending on the power applied, type of gas used and gas flow rate. To drive the plasma a high voltage power supply, which is able to generate 10 kV at 5.8 kHz, was developed in the laboratory. By varying the process parameters, the inherent filamentary nature of discharge can be converted to a diffuse uniform glow. The purity of plasma was studied and established by analyzing the optical emission from the plasma. After optimizing the system, it was used to modify the surface properties of polyester sheets. The wetting nature was altered using fluorocarbon and oxygen plasmas, realizing hydrophobic and hydrophilic surfaces. The contact angle of a water droplet made with the surface changed from 72° to 84° degree for hydrophobic and to 22° for hydrophilic surfaces respectively. Through this investigation, an insight to the procedure for developing an Atmospheric glow discharge system was developed. The details about system frame work, the power supply, electrical and optical characterization of the plasma, are well studied and recorded. The work establishes the various parameters to be varied to convert the filamentary discharge to a uniform glow. Purity of the plasma has been studied extensively and the system design and process values essential for maintaining the purity have been dealt with. Finally the plasma was put in use for surface modification of polymers, and the surface wetting nature alteration was studied and quantified.

The properties of materials, especially of solids, can be attributed mainly to the phenomena occurring at the surface. Surface engineering deals with altering the surface properties of materials to realize useful functionalities like wear and corrosion resistance, biocompatibility, hardening etc. Among the various methods adopted, plasma surface modification stands out, because of the inherent dry processing nature and little amount of left over chemicals. In conventional plasma systems, the process is carried out in a low pressure environment. This restricts its use in treating vacuum incompatible materials including tissues and bio-medical samples. Moreover, the batch processing nature and use of expensive vacuum pumps put a bottle-neck in the throughput of any production line. The subject matter of this thesis is about developing and optimizing an atmospheric pressure (760 torr) plasma system and to use it for surface modification of polymers. The experimental system developed, consists of two parallel electrodes facing each other, each of which is covered with a dielectric plate. A gap of 4mm exists between the dielectric surfaces, through which an axial flow of the working gas is maintained. When a high voltage is applied across the electrodes, the gas breaks down, creating plasma. The surface of the sample kept in this plasma, undergoes various phenomena, depending on the power applied, type of gas used and gas flow rate. To drive the plasma a high voltage power supply, which is able to generate 10 kV at 5.8 kHz, was developed in the laboratory. By varying the process parameters, the inherent filamentary nature of discharge can be converted to a diffuse uniform glow. The purity of plasma was studied and established by analyzing the optical emission from the plasma. After optimizing the system, it was used to modify the surface properties of polyester sheets. The wetting nature was altered using fluorocarbon and oxygen plasmas, realizing hydrophobic and hydrophilic surfaces. The contact angle of a water droplet made with the surface changed from 72° to 84° degree for hydrophobic and to 22° for hydrophilic surfaces respectively. Through this investigation, an insight to the procedure for developing an Atmospheric glow discharge system was developed. The details about system frame work, the power supply, electrical and optical characterization of the plasma, are well studied and recorded. The work establishes the various parameters to be varied to convert the filamentary discharge to a uniform glow. Purity of the plasma has been studied extensively and the system design and process values essential for maintaining the purity have been dealt with. Finally the plasma was put in use for surface modification of polymers, and the surface wetting nature alteration was studied and quantified.

博士
國立清華大學
物理系
101
In study, we used atmospheric pressure plasma source (APPS) to study the effect of driving frequency on the characteristic of plasma, the effect of gas flow on the deposition process and plasma density distribution, deposition of organic silicon film, and controlling the pretilt angle of liquid crystals (LCs). The study was to investigate the driving frequency effects on the characteristics of atmospheric plasma jets system. The discharge gas is the helium. We change the power source frequency range from 10 MHz to 20 MHz. As the driving frequency is increased, we can observe the several phenomena. (1) gas breakdown voltage from 256 V down to 204 V, (2) plasma density from 0.798×〖10〗^12 〖cm〗^(-3) rose to 2.218×〖10〗^12 〖cm〗^(-3) and increase the current from 0.125 A to 0.224 A when the plasma state at highest α mode discharge, (3) sheath thickness decreased from 0.348 mm to 0.257 mm before discharge mode transition, (4) the electron excitation temperature dropped from 0.535 ev 0.316 ev when the plasma power of 25 W. Collectively, these results suggest that the high driving frequency help to improve the quality of plasma, enhance discharge efficiency, and make the atmospheric plasma jets systems have a wider application space. From the results, the gas flow distribution became non-uniform at helium flow rate of 5 slm. By modifying the structure of nozzle, the gas flow distribution became more uniform so that film deposition became uniform. Because the uniformity of film deposition is related to the plasma density distribution, the gas flow distribution effected the plasma density distribution. In study, the APPS was used to deposited the organic silicon film, HMDSO as the material. The process could control the structure and properties of the film. Results showed main bonds (Si–CH¬3 and Si–O–Si) can be controlled by molecular average energy (W/FM). The ratio of Si–O–Si increased when W/FM became large. The ratio of Si–CH¬3 was increasing with decreasing the W/FM. Si–O–Si are polar bonds, and Si–CH¬3 are non-polar bonds. Thus, if the ratio of Si–O–Si was higher than Si–CH¬3, the film became hydrophilic (surface energy could be 68 mJ/m2) and surface hardness became hard. If the ratio of Si–CH¬3 was higher than Si–CH¬3, the film became hydrophobic (surface energy could be 25 mJ/m2) and surface hardness became soft. The pretilt angle of LCs could be controlled by adjusting the surface energy of the film. When the surface energy was smaller than 34 mJ/m2, the pretilt angle approached 90o. When the surface energy was larger than 60 mJ/m2, the pretilt angle approached 0o. Therefore, the pretilt angle could be controlled by the range of surface energy from 34 to 60 mJ/m2.