Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The antioxidant effects of the hydro-alcoholic guaraná extracts (Paullinia cupana var. sorbilis Mart.) on nitric oxide (NO ) and other compounds generated from degradation of Sodium Nitroprusside (SNP) in embryonic fibroblast culture (NIH-3T3 cells) were evaluated. The guaraná bioactive compounds were initially determined by a high-performance liquid chromatography (HPLC): caffeine=12.240 mg/g, theobromine=6.733 mg/g and total catechins= 4.336 mg/g. To the experiments, initially the cells were grown in DMEM (Dulbecco s Modified Eagle Medium) medium and incubated in a humidified atmosphere of 5% CO2 and 37°C until reach 90% confluence. Cell cultures were exposed to 10μM SNP during six hours since in this concentration the cells present >90% mortality. Guaraná diluted in water was added in the cultures in five concentrations (0.5, 1, 5, 10 and 20 mg/mL). MTT and Trypan blue viability, biochemical oxidative markers and genotoxicity (DNA Comet assay) analysis were performed. Additionally, the cell oxidative stress was evaluated by 2,7 dihydrodichlorofluorescein diacetate (DCFDA) fluorescence assay by confocal microscopy. Guaraná reverted the SNP toxicity mainly in lower concentrations (<5 mg) decreasing cell mortality, lipid peroxidation, DNA damage and cell oxidative stress and increasing the SOD levels. However, guarana was unable to reverse the inhibition of catalase probably triggered by the presence of cyanide which is also produced in the decomposition of SNP. The results suggest that guarana has effects on the modulation of excessive amounts of NO probably through its antioxidant properties. These results supported previous studies that suggest guarana have a protective effect against morbidity as obesity and metabolic syndrome that are related to metabolism. / Os efeitos antioxidantes do extrato hidro-alcoólico de guaraná (Paullinia cupana var. sorbilis) sobre o Óxido Nítrico (NO ) e outros compostos gerados a partir da decomposição do Nitroprussiato de Sódio (NPS) em cultura de fibroblastos embriônicos (NIH 3T3) foram avaliados. Os compostos bioativos do guaraná foram inicialmente determinados por cromatografia líquida de alta performance (HPLC): cafeína=12,240 mg/g, teobromina=6,733 mg/g e catequinas totais=4,336 mg/g. Para os experimentos as células foram inicialmente cultivadas em meio DMEM (Dulbecco s Modified Eagle Medium) e incubadas em uma atmosfera umidificada de 5% de CO2 a 37°C até chegar a uma confluência de 90%. As culturas de células foram expostas ao NPS na concentração de 10μM durante seis horas. Nesta concentração de NPS e tempo de exposição ocorre uma taxa de mortalidade celular >90%. O guaraná diluído em água foi adicionado em cinco diferentes concentrações (0,5, 1, 5, 10 e 20 mg/mL). Os ensaios de viabilidade MTT e azul de tripan, de marcadores bioquímicos de estresse oxidativo e genotoxicidade (ensaio cometa) foram realizados. Adicionalmente, o estresse oxidativo celular foi avaliado através do ensaio da fluorescência do diacetato de 2,7 diclorofluoresceína (DCFDA) via microscopia confocal. O guaraná reverteu à toxicidade induzida pelo NPS principalmente em concentrações mais baixas (<5mg/mL), diminuindo a: mortalidade celular, peroxidação lipídica, dano de DNA e produção de espécies reativas a aumentou os níveis da enzima Super Óxido Dismutase (SOD). Entretanto, o guaraná não conseguiu reverter a inibição da catalase provavelmente desencadeada pela presença de cianeto que também são produzidos na decomposição do NPS. Os resultados sugerem que o guaraná tem efeitos na modulação das quantidades excessivas de NO provavelmente através de suas propriedades antioxidantes. Estes resultados confirmaram estudos prévios que sugerem que o guaraná tem efeito protetor contra morbidades como obesidade e síndrome metabólica que são relacionadas ao metabolismo.

Ce travail concerne l'étude de la polymérisation de l'éthylène allant de l'homopolymérisation purement radicalaire jusqu'à la copolymérisation utilisant un mécanisme hybride radicalaire/catalytique. Ce travail montre que le polyéthylène peut être synthétisé par voie radicalaire dans des conditions expérimentales beaucoup plus douces que celles utilisées industriellement (P>1000 bar et T>100°C). L'éthylène a été polymérisé à partir de 10°C et 5 bar de pression d'éthylène. Un important effet activateur du solvant a été mis en évidence. De plus la polymérisation en milieu dispersé aqueux de l'éthylène a aussi été étudiée. Des latex stables de PE avec des taux de solide de 40% ont pu être obtenus. Deux morphologies de nanoparticules, cylindre ou sphère, ont été observées. La copolymérisation radicalaire avec des monomères vinyliques polaires a été également étudiée en solution ou en émulsion. Des insertions d'éthylène jusqu'à 50% ont été obtenues. De plus l'influence du comonomère et du solvant organique utilisé sur la polymérisation radicalaire de l'éthylène a été quantifiée. Une nouvelle technique de polymérisation hybride radicalaire/catalytique a été développée pour pouvoir obtenir toute la gamme de compositions possibles de copolymères éthylène/monomère polaire à partir d'un complexe de nickel qui amorce la polymérisation radicalaire et catalyse également la polymérisation de l'éthylène. Ce complexe subit une rupture homolytique réversible de la liaison nickel carbone et permet la synthèse de copolymères multiblocs. Des insertions d'éthylène de 1% à 99% ont été obtenues en faisant varier la pression d'éthylène et la concentration en comonomères polaires / This work aims to study ethylene polymerization from the free radical polymerization process to the copolymerization by a hybrid radical/catalytic mechanism. PE is synthesized by free radical polymerization under milder experimental conditions than industrial ones (P>1000 bar and T>100°C). Indeed free radical polymerization of ethylene is efficient even down to pressure of 5 bar and temperature of 10°C. Several unexpected behaviors are observed such as a high solvent activation effect. Beside the slurry process in organic solvent, polymerization in aqueous dispersed media is also performed. Stable PE latexes are obtained with solid contents up to 40%. Two different PE particles morphologies are observed cylinder-like and sphere-like. Then free radical copolymerization is studied using a broad range of polar vinyl monomers in organic solvent and emulsion. Insertions up to 50% of ethylene are obtained under mild conditions. The ambivalent role of comonomer as monomer and activator of the polymerization is highlighted. In order to obtain a wide range of composition of polar/non-polar copolymers a new technique of polymerization has been developed. A nickel complex is used to initiate the free radical polymerization and to catalyse the coordination/insertion ethylene polymerization. This nickel complex is capable of a reversible homolytic cleavage of its nickel-carbon bond. Finally, this hybrid process is used to copolymerize efficiently ethylene with various polar vinyl monomers. Multiblock copolymers with ethylene content from 1% to 99% are obtained by simply varying the monomer feeds

Le but de ce travail de thèse est le développement d'un outil miniaturisé basé sur la millifluidique en goutte qui permet de synthétiser et d'étudier en toute sécurité des réactions de polymérisation dans des conditions difficiles ou «extrêmes».À cette fin, le réacteur de polymérisation a été réduit à la taille d'une gouttelette de quelques microlitres. A cette échelle, le microréacteurs goutte a un rapport surface sur volume plus élevé que ceux qui sont couramment obtenus avec des réacteurs discontinus classiques (~ 1500 par rapport à 10). Cette surface importante permet le transfert de chaleur efficace entre le milieu intérieur de la gouttelette (où la réaction chimique a lieu) et le milieu externe, qui est chimiquement inerte. Ici, contrairement à une approche monophasique, les caractéristiques clés d'une goutte miniaturisés permettent : (1) les gouttelettes de haute viscosité interne peuvent circuler normalement sans boucher le canal et (2) la dispersion due à la convection et la diffusion est éliminé car les réactifs sont compartimentées dans les gouttelettes. Comme toutes les gouttelettes se déplacent à la même vitesse, elles ne coalescent pas et il n'y a pas de distribution du temps de résidence. Ceci est particulièrement important étant donné que la viscosité dans des réactions de polymérisation peut augmenter à des milliers de centipoises ou même plus dans le cas des processus de gel.L'utilisation de gouttes comme microréacteurs circulant dans un tube chauffé (1/8’’ dext et 1/16’’ dint) peut permettre d’observer rapidement et en toute sécurité des réactions de polymérisation à différentes conditions. Nous avons choisi d'utiliser des conditions expérimentales où le processus de polymérisation est rapide et exothermique et/ou la viscosité peut être un problème. L'acide acrylique à faible pH et à concentrations élevées est donc un bon candidat pour obtenir un tel comportement. La composition des gouttelettes dépendant uniquement des débits, il est facile d’étudier différentes conditions expérimentales, y compris celles qui ne pouvaient pas être observées dans des réacteurs discontinus conventionnels (i.e. les concentrations de monomère et températures élevées, 40% massique et 90°C).Par ailleurs, couplé avec des systèmes appropriés d'analyse, des données cinétiques de base peuvent être obtenus en ligne à travers la paroi du tube transparent. En utilisant la spectrométrie Raman et l'équivalence temps-espace qui est spécifique à l'utilisation de dispositifs micro-et millifluidique à base de gouttes, nous avons été capables de suivre la conversion du monomère en fonction du temps. Ainsi, nous avons obtenu une cinétique d'ordre 4/3 en fonction de la concentration initiale en monomère et une demi-dépendance avec la concentration initiale de l'amorceur. Nous avons également pu mesurer une énergie d'activation globale de la vitesse de polymérisation entre 68°C et 90°C.En conclusion, la millifluidique et goutte semble être une approche prometteuse pour le criblage haut débit, l’analyse, et l’obtention de données cinétique de base en synthèse de polymères. / The aim of this thesis work is the development of a miniaturized droplet-based millifluidic tool which allows to safely synthesize and investigate polymerization reactions in harsh or “extreme” conditions.For this purpose, the polymerization reactor was reduced to the size of a droplet of a few microliters. At this scale, the droplet microreactor has a surface to volume ratio higher than those commonly obtained with conventional batch reactors (~1500 compare to 10). This important surface allows efficient heat transfer between the internal medium of the droplet (where the chemical reaction takes place) and the external one, which is chemically inert. Here, in contrast to single-phase flows, other key characteristics to a miniaturized droplet-based approach consist in: (1) droplets can manage high internal viscosity issues without plugging the channel and (2) dispersion due to convection and diffusion is eliminated because the reactants are compartmentalized within droplets. Since all droplets move at the same speed, they do not coalesce and there is no residence time distribution. This is particularly important since viscosity in polymerization reactions can increase to thousand of centipoises or even higher in the case of gel processes.The use of droplets as batch microreactors flowing within a heated tube (1/8 in. o.d. and 1/16 in. i.d.) can allow investigating quickly and safely polymerization reactions at different conditions. We choose to use experimental conditions where fast and exothermic polymerization process occurs and/or viscosity can be an issue. Acrylic acid at low pH and high concentrations is hence a good candidate to obtain such behavior. Since droplet composition depends only on flow rates, it was easy to screen different experimental conditions, including those which could not be used in conventional batch reactors (i.e., high monomer concentrations and temperatures; 40% w/v and 90 °C).Moreover, coupled with appropriate and sensitive analytical systems, basic kinetic data can be obtained in line through the wall of the transparent tube. By using Raman spectrometry and the time-space equivalence which is specific to the use of droplet-based micro- and millifluidic devices, we were capable to monitor molar conversions and monomer concentrations as a function of time. Thus, we verified the 4/3 order kinetics in initial monomer concentration and a 1/2 dependence in initial initiator concentration. We also able measured the overall activation energy for the rate of polymerization between 68°C to 90°C.In conclusion, droplet-based millifluidics seems to be a promising high throughput screening approach for investigating kinetics and possibly tailoring polymer properties.

La construction de nouvelles architectures d'aimant moléculaire basé sur l'approche métal-radical repose sur la conception de nouvelles molécules radicalaires. Dans cette optique, notre stratégie s'est concentrée sur la synthèse de porphyrins incorporant des composés radicaux libres. En effet, les porphyrines sont des composés π conjugués qui devraient favoriser la délocalisation de spin et la transmission des interactions magnétiques sur l'entier macrocycle et de plus sur l'ensemble du composé obtenu. A cause de leur excellente stabilité dans une grande diversité d'environnements chimiques et leur capacité à coordonner avec des métaux de transitions, notre choix s'est porté sur les radicaux nitroxides. Dans cette thèse, une série de porphyrines contenant des tBUNO, nitronyl and imino nitroxide directement liés sur le squelette de la molécule ont été synthétisées. Les macrocycles obtenus ont été caractérisés par UV-Vis, Masse et RPE spectroscopie. De plus, durant ce travail, des intermédiaires réactionnaires intéressant ont été obtenus et caractérisés pour la première fois. Ce fut le cas pour la meso-tetrakis(4-formylphenyl)porphyrin et ses équivalents métallés pa le Cu(II) et le Mn(II). Ainsi que pour quelques précurseurs prometteurs de macrocycle tetrapyrroliques comme 2-(3,4-dicyanophenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1oxyl, 2-(3,4-dicyanophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl and 2-(4-benzaldehyde)-4,4,5,5-tetramethylimidazoline-1-oxyl. D'après ce que nous savons, ces composés représentent le premier exemple de porphyrines substituées par des nitronyl et imino nitroxide radical, ayant été caractérisées sans ambiguïté par des méthodes spectroscopiques / The preparation of Molecule-Based Magnets is based on the assembling carriers of magnetic moment. These may be the metal ions only with diamagnetic linkers or the metal ions connected through open-shell organic molecule. The building of novel Molecule-Based Magnets architectures following the metal-radical approach relies on the design of innovative open-shell organic molecular blocks. In this regard, we focus our strategy on the synthesis of porphyrins incorporating free radicals. Indeed, porphyrins compounds are π-conjugated systems which should favor spin delocalization and the transmission of the magnetic interactions on the overall macrocycle and further over the all architecture. Due to their excellent stability in a wide variety of chemical environments, and their abilities to coordinate with transition metal we focus our attention on nitroxide radicals. In this dissertation a series of porpyrin macrocycles were synthesized, bearing tBuNO, nitronyl and imino nitroxide covalently linked to the skeleton. Characterization was done by UV-Vis, Mass and EPR spectroscopy. Moreover during this work some interesting synthetic intermediates were obtained with good yield and characterize for the first time. This was the case for meso-tetrakis(4-formylphenyl)porphyrin and its corresponding metallated derivatives by Cu(II) and Mn(II). Some novel promising tetrapyrrolic macrocycle precursors bearing nitronyl and imino nitroxides free radicals as 2-(3,4- dicyanophenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl, 2-(3,4- dicyanophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl and 2-(4-benzaldehyde)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl. To the best of our knowledge, these compounds represent the first example of nitronyl and imino nitroxide substituted porphyrin derivatives that have been unambiguously characterized by spectroscopic techniques

Espécies carbonílicas tripletes formadas quimicamente no escuro, por exemplo, durante a peroxidação de lipídios, têm reatividade química análoga à de radicais alcoxilas. Aventou-se que tais espécies possam estar implicadas na fisiopatologia de doenças degenerativas (\"estresse carbonílico\"). A pesquisa dos efeitos de espécies tripletes sobre algumas biomoléculas e consequentes respostas biológicas, propostas e pesquisadas no período 1970 - 1990 (hipótese de \"fotoquímica sem luz\" dos Profs. G. Cilento, IQUSP, e Emil H. White, Johns Hopkins University), encontrou empecilhos instrumentais e relativamente poucas propostas foram confirmadas. Com o uso de técnicas de alta resolução, tais como EPR, HPLC e MS, este trabalho teve como objetivo analisar intermediários e produtos de tais processos e estudar mecanismos de reação de acetona triplete, produzida quimicamente pela decomposição térmica de 3,3,4,4-tetrametildioxetano (TMD) ou, enzimaticamente, pela oxidação aeróbica de isobutanal (IBAL), catalisada por peroxidase de raiz forte (HRP), na presença de aminoácidos e proteínas. Este trabalho demonstra a formação de um radical acetila, presumidamente formado da clivagem &#945; de acetona triplete, e um radical terciário centrado em carbono, formado pela abstração de hidrogênio do IBAL. Resultados de espectrometria de massas demonstraram a formação de três diferentes adutos entre o radical terciário de IBAL, com L-Trp. Aventou-se que um dos produtos era resultante de alteração no nitrogênio e os outros no carbono 3, ambos no anel indólico. Observou-se também a formação de produto correspondente ao radical hidroxipropionil com L-Trp. Também se observaram dois produtos de L-Trp típicos de sua oxidação por oxigênio singlete, a formilquinurenina, e um aduto de função álcool. A formação de base de Schiff entre o L-Trp estudado e o IBAL também é apresentada. A formação de oxigênio singlete foi evidenciada indiretamente via EPR utilizando o spin trap TEMP e através de um captador de adição-9,10 (tipo Diels-Alder) em derivado de antraceno. Foram realizados, também, experimentos com precursores de melanina e demonstrou-se a formação de espécies excitadas do ácido 5,6-dihidroxi-indol-2-carboxílico (DHICA) que poderiam explicar a formação de produtos de DNA tipicamente resultantes de reação fotoquímica, mas na ausência de luz. Tais resultados corroboram a reação de espécies tripletes com biomoléculas, possibilitando a compreensão de número significativo de eventos biológicos conhecidos, mas teoricamente \"proibidos\" de ocorrer no estado fundamental, em tecidos não expostos à luz / Electronically excited triplet carbonyl species formed as products of some biochemical reactions, such as lipid peroxidation, behave similarly as alcoxyl radicals. It has long been hypothesized that such excited species could have a role in some diseases (\"carbonyl stress\"). Research of chemical lesions of triplet carbonyls over biomolecules and their biological response took place principally from 1970 to 1990 (the \"photochemistry without light\" hypothesis proposed by Profs. G. Cilento, IQUSP, and Emil H. White, Johns Hopkins University), but it suffered from the lack of required instrumentation, and just few cases of photo(bio)chemistry without light were confirmed. The aim of this work, using high resolution techniques (EPR, HPLC, and MS), is to analyze the reaction products of excited triplet acetone with aminoacid and protein targets. Triplet acetone was produced from the thermal decomposition of 3,3,4,4-tetramethyldioxetane (TMD) or from the aerobic oxidation of isobutanal (IBAL) catalyzed by horseradish peroxidase (HRP). We revealed the generation of acetyl radical, putatively originated from &#945;-cleavage of triplet acetone, and a carbon-centered tertiary radical, proposed as an IBAL radical formed by hydrogen abstraction from IBAL. Mass spectrometry showed production of three adducts from the reaction of IBAL radical with L-Trp, one of them at the nitrogen 1 and the other two at carbon 3 from the amino acid indole ring. Two adducts with m/z correspondent to the reaction between L-Trp (at carbon 3) and a hydroxypropionyl radical, and two products typically formed from singlet oxygen (formylkynurenine and an alcohol L-Trp adduct) were also observed. A Schiff base between L-Trp and IBAL was also observed. Singlet oxygen production from triplet-triplet energy transfer from excited acetone to ground state molecular oxygen was indirectly showed by EPR spin trapping with TEMP, and by MS using the anthracene derivative EAS to trap (9,10-cycloaddition) of 18O2 (1&#916;g). Other data reported here include the demonstration of excited species formed when DHICA, a melanin precursor, was oxidized. These results might explain the generation of DNA photochemical products (thymine dimers) in the absence of light. Altogether, we collect strong and significant evidence in this thesis that corroborate the reactivity of triplet excited species with a couple of biomolecules, providing insights over some reportedly known molecular events that are theoretically forbidden to occur in the ground state but happen in tissues non-exposed to light

A ce jour, le développement de textiles intelligents, de peaux artificielles, de capteurs de paramètres environnementaux et de composés optoélectroniques souples ; qui nécessite des innovations à la fois dans la synthèse des matériaux, leur conception mécanique mais aussi, à l’échelle industrielle, en stratégie de production ; présente un intérêt majeur dans le domaine du prêt-à-porter connecté. D’un point de vue mécanique, l’obtention des propriétés de flexibilité et d’étirabilité à faible coût, via un procédé simple, au sein d’un matériau léger et capable de s’expandre sur de grandes surfaces est un prérequis essentiel pour incorporer des dispositifs optoélectroniques au sein des objets connectés portables. Parmi les différents procédés couramment utilisés, l’electrospinning est une technique simple, facilement adaptable et peu onéreuse qui permet un ajustement fin et flexible des morphologies de fibres, l’assemblage de plusieurs nanofibres fonctionnelles et une production en continue à haut débit. Ces multiples avantages sont à l’origine des nombreux travaux concernant l’utilisation de l’electrospinning dans le domaine du prêt-à-porter électronique et/ou connecté. Cependant, il est nécessaire de développer des projets innovants pour ce secteur qui incluent des capteurs détectant des paramètres environnementaux (pH, température), des chemo-capteurs colorimétriques à large spectre (full-color), des composantes électroniques étirables et capteurs tactiles. / To date, the development of smart textiles, artificial skins, environmental sensory devices, and flexible/stretchable optoelectronics involve the innovation of material synthesis, mechanical design, and fabrication strategies have attracted considerable attention in wearable displays. The mechanically flexible and stretchable functions with cost-effective, facile, lightweight, and large-area expandability are essential modules to fabricate the optoelectronic devices in various wearable display applications. Among them, electrospinning is an easy, versatile, and inexpensive technique enables flexible morphology tuning, assembling various functional nanofibers, and high-throughput continuous production has motivated extensive studies on wearable electronics applications. Therefore, it is necessary to develop innovative projects including the environment-sensing elements with pH-sensing dependency, temperature-sensitive, full-color switchable chemosensors, stretchable electronics, and tactile sensors for various wearable electronics applications.

Composite materials formed from two or more functionally different materials offer a versatile avenue to create a tailored material with well defined traits. Within this dissertation research, multi-functional composites were synthesized based on organic and inorganic materials. The functionally of these composites was experimentally tested and a semi-empirical model describing the sedimentation behavior of these particles was developed. This first objective involved the fabrication of microcomposites consisting of titanium dioxide (TiO2) nanoparticles confined within porous, microgels of a thermo-responsive polymer for use in the photocatalytic treatment of wastewater. TiO2 has been shown to be an excellent photocatalyst with potential applications in advanced oxidative processes such as wastewater remediation. Upon UV irradiation, short-lived electron-hole pairs are generated, which produce oxidative species that degrade simple organic contaminants. The rapid sedimentation of these microcomposites provided an easy gravimetric separation after remediation. Methyl orange was used as a model organic contaminant to investigate the kinetics of photodegradation under a range of concentrations and pH conditions. Although after prolonged periods of UV irradiation (~8-13 hrs), the titania-microgels also degrade, regeneration of the microcomposites was straightforward via the addition of polymer microgels with no loss in photocatalytic activity of the reformed microcomposites. The second objective within this dissertation involved the systematic development of abrasive microcomposite particles containing well dispersed nanoparticles of ceria in an organic/inorganic hybrid polymeric particle for use in chemical mechanical polishing/planarization (CMP). A challenge in IC fabrication involves the defect-free planarization of silicon oxide films for successful multi-layer deposition. Planarization studies conducted with the microcomposites prepared in this research, yield very smooth, planar surfaces with removal rates that rival those of inorganic oxides slurries typically used in industry. The density and size of these ceria-microgel particles could be controlled by varying the temperature or composition during synthesis, leading to softer or harder polishing when desired.

Poly(dimethylsiloxan) (PDMS) ist ein wichtiges Polymer, das zunehmend in der Mikroelektronik aufgrund seiner hervorragenden Elastizität und thermischen Stabilität Verwendung findet. Ein limitierender Faktor für den Einsatz von PDMS ist aufgrund des Fehlens von reaktiven Gruppen und der niedrigen freien Oberflächenenergie seine geringe Adhäsion zu anderen Materialien. Zur Erhöhung der Adhäsion ist deshalb die Einführung von polaren, funktionellen Gruppen notwendig. Hier lag die Motivation der vorliegenden Arbeit, die sich eine gezielte Funktionalisierung von PDMS-Oberflächen als Aufgabe gesetzt hatte. Im ersten Teil der Arbeit wurde eine Verbesserung der Adhäsion zu einem fotostrukturierbaren Epoxidharz mittels der Sauerstoff- und Ammoniakplasmabehandlung angestrebt. In beiden Fällen führte die Plasmabehandlung zu der Einführung von unterschiedlichsten funktionellen Gruppen auf die Oberfläche und zu einer Verbesserung des Benetzungsverhaltens gegenüber Wasser. Zudem wurden Haftfestigkeiten erzielt, die um ein Vielfaches höher waren als jene zwischen Epoxidharz und einer unbehandelten PDMS-Oberfläche. Jedoch waren die hydrophilen Eigenschaften nach der Plasmabehandlung während der Lagerung an Luft zeitlich begrenzt, die PDMS-Oberfläche kehrt innerhalb kurzer Zeit in den einst hydrophoben Ausgangszustand zurück. Der Alterungsvorgang wird als „Hydrophobic Recovery“ bezeichnet und ist bei PDMS-Oberflächen, die höheren Plasmaleistungen und Behandlungszeiten ausgesetzt wurden, besonders auffällig. Die Vermeidung dieser Problematik war der Ausgangspunkt für den zweiten Teil der Arbeit. Auf der Grundlage der über die Plasmabehandlungen erzeugten funktionellen Gruppen wurden neue Konzepte für eine kovalente Anbindung von verschiedenen funktionellen Homo- und Copolymeren über die „Grafting to“-Technik entwickelt. Neben der Erhöhung der Adhäsion zu dem Epoxidharz war es möglich, das Benetzungsverhalten gegenüber Wasser durch die Unterbindung der „Hydrophobic Recovery“ zu stabilisieren. Des Weiteren gelang es, durch die Wahl der funktionellen Polymere, die PDMS-Oberfläche gezielt mit gewünschten Eigenschaften auszustatten. Somit ist der Einsatz der polymermodifizierten Oberflächen, außer in der Mikroelektronik, auch auf andere Anwendungen, wie der Biomedizin, der Mikrofluidik oder der Softlithografie übertragbar, in denen eine beständige, definierte Oberflächenfunktionalisierung ein wichtiges Kriterium darstellt.

Ceria (cerium oxide) nanomaterials, or nanoceria, have commercial catalysis and energy storage applications. The cerium atoms on the surface of nanoceria can store or release oxygen, cycling between Ce3+ and Ce4+, and can therefore act as a therapeutic to relieve oxidative stress within living systems. Nanoceria dissolution is present in acidic environments in vivo. In order to accurately define the fate of nanoceria in vivo, nanoceria dissolution or stabilization is observed in vitro using acidic aqueous environments. Nanoceria stabilization is a known problem even during its synthesis; in fact, a carboxylic acid, citric acid, is used in many synthesis protocols. Citric acid adsorbs onto nanoceria surfaces, capping particle formation and creating stable dispersions with extended shelf lives. Nanoceria was shown to agglomerate in the presence of some carboxylic acids over a time scale of up to 30 weeks, and degraded in others, at pH 4.5 (representing that of phagolysosomes). Sixteen carboxylic acids were tested: citric, glutaric, tricarballylic, α-hydroxybutyric, β-hydroxybutyric, adipic, malic, acetic, pimelic, succinic, lactic, tartronic, isocitric, tartaric, dihydroxymalonic, and glyceric acid. Each acid was introduced as 0.11 M, into pH 4.5 iso-osmotic solutions. Controls such as ammonium nitrate, sodium nitrate, and water were also tested to assess their effects on nanoceria dissolution and stabilization. To further test stability, nanoceria suspensions were subject to light and dark milieu, simulating plant environments and biological systems, respectively. Light induced nanoceria agglomeration in some, but not all ligands, and is likely to be a result of UV irradiation. Light initiates free radicals generated from the ceria nanoparticles. Some of the ligands completely dissolved the nanoceria when exposed to light. Citric and malic acids form coordination complexes with cerium on the surface of the ceria nanoparticle that can inhibit agglomeration. This approach identifies key functional groups required to prevent nanoceria agglomeration. The impact of each ligand on nanoceria was analyzed and will ultimately describe the fate of nanoceria in vivo. In addition, simulated biological fluid (SBF) exposure can change nanoceria’s surface properties and biological activity. The citrate-coated nanoceria physicochemical properties such as size, morphology, crystallinity, surface elemental composition, and charge were determined before and after exposure to simulated lung, gastric, and intestinal fluids. SBF exposure resulted in either loss or overcoating of nanoceria’s surface citrate by some of the SBF components, greater nanoceria agglomeration, and small changes in the zeta potential. Nanocomposites are comprised of a polymer matrix embedded with nanoparticles. These nanoparticles can alter material and optical properties of the polymer. SR-399 (dipentaerythritol pentaacrylate) is a fast cure, low skin irritant monomer that contains five carbon-carbon double bonds (C=C). It is a hard, flexible polymer, and also resistant to abrasion. It can be used as a sealant, binder, coating, and as a paint additive. In this case, metal oxide nanoparticles were added to the monomer prior to polymerization. Titania nanoparticles are known to absorb UV light due to their photocatalytic nature. Titania nanoparticles were chosen due to their high stability, non-toxicity, and are relatively quick, easy, and inexpensive to manufacture. Channels in thin monomer films were created using a ferrofluid manipulated by magnetic fields. The mechanical properties of a microfluidic device by rapid photopolymerization is dependent on the crosslinking gradient observed throughout the depth of the film. Quantitative information regarding the degree of polymerization of thin film polymers polymerized by free radical polymerization through the application of UV light is crucial to estimate material properties. In general, less cure leads to more flexibility, and more cure leads to brittleness. The objective was to quantify the degree of polymerization to approximate the C=C concentration and directly relate it to the mechanical properties of the polymer. Polymerization of C=C groups was conducted using a photoinitiator and an UV light source from one surface of a thin film of a multifunctional monomer. The C=C fraction in the film was found to vary with film depth and UV light intensity. The extents of conversion and crosslinking estimates were compared to local mechanical moduli and optical properties. A mathematical model linking the mechanical properties to the degree of polymerization, C=C composition, as a function of film depth and light intensity was then developed. For a given amount of light energy, one can predict the hardness and modulus of elasticity. The correlation between the photopolymerization and the mechanical properties can be used to optimize the mechanical properties of thin films within the manufacturing and energy constraints, and should be scalable to other multifunctional monomer systems.

No description available.