• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 124
  • 56
  • 51
  • 18
  • 11
  • 8
  • 4
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 323
  • 323
  • 93
  • 44
  • 42
  • 40
  • 35
  • 34
  • 33
  • 29
  • 28
  • 28
  • 25
  • 24
  • 24
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

Conception rationnelle de nano-hybrides de carbone 1D pour l'application de nanocomposites diélectriques / Rational design of 1D carbon nano-hybrids for dielectric nanocomposites application

Yang, Minhao 08 November 2018 (has links)
Les nanocomposites polymères diélectriques ayant une constante diélectrique élevée et une faible perte diélectrique ont reçu un grand intérêt pour une utilisation dans le domaine du condensateur électrostatique. De manière générale, les performances diélectriques améliorées des nanocomposites sont déterminées par le type et la nature des polymères et des nanocharges sélectionnés, ainsi que par l'effet de couplage interfacial entre les matrices et les nanocharges. Parmi ces facteurs, les propriétés physiques, les géométries et les structures des composants des nanocharges jouent un rôle essentiel dans la détermination des performances diélectriques des nanocomposites. Selon les conductivités des nanocharges, les nanocomposites polymères diélectriques peuvent être classés en deux types: les nanocomposites polymères diélectriques conducteurs (CDPN) et les nanocomposites polymères diélectriques-diélectriques (DDPN). Cependant, la perte diélectrique élevée accompagnée au voisinage du seuil de percolation pour les CDPN et la charge élevée de nanocharges en céramique entravent le développement de nanocomposites polymères diélectriques à haute performance.Tout d'abord, des nanocomposites ternaires BNNS/CNT/PVDF ont été fabriqués. L'incorporation de BNNS dans les nanocomposites binaires CNT/PVDF a amélioré la dispersion des NTC et optimisé le réseau conducteur. La connexion directe entre les CNT pourrait être entravée en augmentant le contenu de BNNS.Deuxièmement, des hybrides CNT@AC à structure cœur-coquille ont été préparés par méthode CVD. La couche de carbone amorphe entrave non seulement le contact direct des NTC, mais améliore également la dispersibilité des NTC dans la matrice de PVDF. Le seuil de percolation augmente avec la prolongation du temps de dépôt du carbone. Plus important encore, la perte diélectrique a subi une forte diminution après le processus de revêtement. Troisièmement, les hybrides BNNSs@C avec des teneurs en carbone différentes ont été synthétisés par la méthode CVD. La fraction de carbone dans les hybrides BNNSs@C pourrait être ajustée avec précision en contrôlant le temps de dépôt de carbone. Les propriétés diélectriques des nanocomposites BNNSs@C/PVDF pourraient être ajustées avec précision en ajustant la teneur en carbone. Les polarisations interfaciales améliorées des interfaces BNNS/C et C/PVDF ont doté les nanocomposites de performances diélectriques améliorées.Quatrièmement, les hybrides TiO2@C NW structurés en noyau et en coquille ont été synthétisés par une combinaison d'une réaction hydrothermale et du procédé CVD. L'épaisseur de la couche de carbone dans les hybrides TiO2@C NW obtenus pourrait être précisément ajustée en contrôlant le temps de dépôt du carbone. De plus, les propriétés diélectriques des nanocomposites TiO2@C NWs/PVDF pourraient être ajustées avec précision en ajustant l'épaisseur de la coque en carbone. Les polarisations interfaciales améliorées des interfaces TiO2/C et C/PVDF ont doté les nanocomposites d'excellentes performances diélectriques.Enfin, des nanofils structurés de TiO2@C@SiO2 structurés à double coques ont été synthétisés par une combinaison de réactions hydrothermales modifiées, de CVD et de réactions sol-gel. L'introduction de carbone comme enveloppe interne entre le noyau de TiO2 et l'enveloppe externe de SiO2 a induit deux types supplémentaires de polarisation interfaciale. Les nanocomposites de PVDF obtenus avec TiO2@C@SiO2 NWs présentaient simultanément une constante diélectrique améliorée et des caractéristiques de perte diélectrique supprimées. La constante diélectrique et la perte de nanocomposites ont augmenté avec l'augmentation de l'épaisseur de la couche interne de carbone et ont diminué avec l'augmentation de l'épaisseur de la couche externe de SiO2. La relation entre la perte diélectrique et l'épaisseur de l'enveloppe extérieure en SiO2 a été démontrée par les résultats de la simulation finie. / Dielectric polymer nanocomposites with a high dielectric constant and low dielectric loss have received broad interest for use in the field of the electrostatic capacitor and they are usually composed of dielectric polymers as matrix and inorganic or organic nanofillers as the reinforcement. Generally, the improved dielectric performance of nanocomposites is decided by the type and nature of selected polymers and nanofillers as well as interfacial coupling effect between matrices and nanofillers. Among these factors, the physical properties, geometries, component structures of nanofillers play a critical role in deciding the dielectric performance of nanocomposites. According to the conductivities of nanofillers, the dielectric polymer nanocomposites can be classified into two types: conductive-dielectric polymer nanocomposites (CDPNs) and dielectric-dielectric polymer nanocomposites (DDPNs). However, the accompanied high dielectric loss in the vicinity of the percolation threshold for CDPNs and high loading of ceramic nanofillers hinders the development of high performance dielectric polymer nanocomposites.Firstly, ternary BNNSs/CNTs/PVDF nanocomposites were fabricated. The incorporation of BNNSs into the binary CNTs/PVDF nanocomposites improved the dispersion of CNTs and optimized the conductive network, which contributed to the enhanced dielectric constant. The direct connection between CNTs could be hindered by increasing the content of BNNS.Secondly, core-shell structured CNTs@AC hybrids were prepared by CVD method. The amorphous carbon layer not only hindered the direct contact of CNTs but also improved the dispersibility of CNTs in the PVDF matrix. The percolation threshold increased with the prolongation of carbon deposition time. More importantly, the dielectric loss underwent a sharp decrease after the coating process, which was attributed to the decrease in leakage current. The results suggested that the influence of AC interlayer on the final dielectric performance after percolation was much more obvious than that before percolation.Thirdly, BNNSs@C hybrids with different carbon contents were synthesized by the CVD method. The carbon fraction in the BNNSs@C hybrids could be accurately adjusted through controlling the carbon deposition time. The dielectric properties of BNNSs@C/PVDF nanocomposites could be accurately tuned by adjusting the carbon content. The improved interfacial polarizations of BNNSs/C and C/PVDF interfaces endowed the nanocomposites with enhanced dielectric performance.Fourthly, core-shell structured TiO2@C NW hybrids were synthesized by a combination of a hydrothermal reaction and the CVD method. The carbon shell thickness in the obtained TiO2@C NW hybrids could be precisely tuned by controlling the carbon deposition time. The TiO2@C NWs/PVDF nanocomposites exhibited a percolative dielectric behavior. Moreover, the dielectric properties of the TiO2@C NWs/PVDF nanocomposites could be accurately adjusted by tuning the carbon shell thickness. The enhanced interfacial polarizations of the TiO2/C and C/PVDF interfaces endowed the nanocomposites with excellent dielectric performance.Lastly, core@double-shells structured TiO2@C@SiO2 nanowires were synthesized by a combination of modified hydrothermal reaction, CVD, and sol-gel reaction. The introducing of carbon as an inner shell between the TiO2 core and SiO2 outer shell induced two additional types of interfacial polarization. The obtained PVDF nanocomposites with TiO2@C@SiO2 NWs exhibited simultaneously enhanced dielectric constant and suppressed dielectric loss characteristics. The dielectric constant and loss of nanocomposites increased with the increase of carbon inner shell thickness and decreased with the increasing of SiO2 outer shell thickness. The relationship between the dielectric loss and SiO2 outer shell thickness was further demonstrated by the finite simulation results.
202

Síntese e caracterização de polímero híbrido acrílico-alquídico produzido por polimerização em miniemulsão. / Synthesis and characterization of alkyd-acrylic hybrid polymer produced by miniemulsion polymerization.

Badin, Caroline 06 February 2015 (has links)
Polímeros híbridos são caracterizados por conter numa mesma partícula dois tipos diferentes de polímero, normalmente incompatíveis e ligados por ligações covalentes. Neste trabalho, a síntese de um polímero híbrido acrílico-alquídico pelo processo de miniemulsão foi investigada. Com o objetivo de compreender como diferentes variáveis na fórmula afetam as características físico-químicas finais do látex, um planejamento experimental foi desenhado com o auxílio do software DX9 e os resultados analisados por modelos empíricos de superfície de resposta. Os fatores variados (variáveis independentes) foram: quantidade de co-estabilizante, surfactante e iniciador. Cada um dos fatores contribuiu para a alteração de pelo menos uma característica avaliada, e a sinergia entre eles afeta diretamente o teor de RDG, resposta indicativa do grau de grafitização entre as espécies. O coestabilizante contribuiu para o aumento do diâmetro médio de gotas e da polidispersidade de tamanho de partículas, enquanto reduziu a dureza do filme. A concentração de surfactante alterou o número de partículas por litro, reduzindo o diâmetro médio de partículas e aumentando a polidispersidade. O iniciador aumentou a conversão monomérica. Todas as dispersões de polímero híbrido produzidas apresentaram redução do tamanho médio de gotas para partículas, indicando evidência de nucleação secundária. As avaliações por microscopia eletrônica de transmissão (TEM) e microscopia de força atômica (AFM) mostraram que a morfologia obtida é do tipo núcleo-casca. / Hybrid polymers are defined by the presence of two or more different kinds of polymers in the same particle, typically incompatible and linked by covalent bonds. In this work, the synthesis of an alkyd-acrylic hybrid polymer produced by miniemulsion polymerization has been investigated. With the goal of understanding how different variables in the recipe affect the final characteristics of the latex, a design of experiment was planned using DX9 software and the results were analyzed by response surface methodology. The factors studied (independent variables) were: amount of co-stabilizer, surfactant and initiator. Each of these factors contributed to change at least one of the evaluated characteristics, and the synergy between them directly affects the RDG content, response of the polymer degree of grafting. Costabilizer contributed to increase the average droplets diameter and polydispersity of particle size, while reducing the film hardness. The amount of surfactant changed the number of particles, reducing the average particle size and increasing polydispersity. Initiator increased the monomer conversion. All hybrids dispersions presented a decrease in the droplet size to particle size, indicating evidence of secondary nucleation. Core-shell morphology was observed through transmission electron microscopy (TEM) and atomic force microscopy (AFM).
203

Desenvolvimento e avaliação de métodos de extração e separação cromatográfica em colunas monolíticas e superficialmente porosas para determinação de herbicidas triazínicos em solos e águas / Development and evaluation of extraction and chromatographic methods in monolithic and core-shell columns for determination of triazine herbicides in soils and waters

Urio, Ricardo De Prá 10 December 2015 (has links)
O uso de pesticidas levou ao aumento da produtividade e qualidade dos produtos agrícolas, porém o seu uso acarreta na intoxicação dos seres vivos pela ingestão gradativa de seus resíduos que contaminam o solo, a água e os alimentos. Dessa forma, há a necessidade do monitoramento constante de suas concentrações nos compartimentos ambientais. Para isto, busca-se o desenvolvimento de métodos de extração e enriquecimento de forma rápida, com baixo custo, gerando um baixo volume de resíduos, contribuindo com a química verde. Dentre estes métodos destacam-se a extração por banho de ultrassom e a extração por ponto nuvem. Após o procedimento de extração, o extrato obtido pode ser analisado por técnicas de Cromatografia a Líquido de Alta Eficiência (HPLC) e a Cromatografia por Injeção Sequencial (SIC), empregando fases estacionárias modernas, tais como as monolíticas e as partículas superficialmente porosas. O emprego de SIC com coluna monolítica (C18, 50 x 4,6 mm) e empacotada com partículas superficialmente porosas (C18, 30 x 4,6 mm, tamanho de partícula 2,7 µm) foi estudado para separação de simazina (SIM) e atrazina (ATR), e seus metabólitos, desetilatrazina (DEA), desisopropilatrazina (DIA) e hidroxiatrazina (HAT). A separação foi obtida por eluição passo-a-passo, com fases móveis compostas de acetonitrila (ACN) e tampão Acetato de Amônio/Ácido acético (NH4Ac/HAc) 2,5 mM pH 4,2. A separação na coluna monolítica foi realizada com duas fases móveis: MP1= 15:85 (v v-1) ACN:NH4Ac/HAc e MP2= 35:65 (v v-1) ACN:NH4Ac/HAc a uma vazão de 35 µL s-1. A separação na coluna com partículas superficialmente porosas foi efetivada com as fases móveis MP1= 13:87 (v v-1) ACN: NH4Ac/HAc e MP2= 35:65 (v v-1) ACN:NH4Ac/HAc à vazão de 8 µL s-1. A extração por banho de ultrassom em solo fortificado com os herbicidas (100 e 1000 µg kg-1) resultou em recuperações entre 42 e 160%. A separação de DEA, DIA, HAT, SIM e ATR empregando HPLC foi obtida por um gradiente linear de 13 a 35% para a coluna monolítica e de 10 a 35% ACN na coluna com partículas superficialmente porosas, sendo a fase aquosa constituída por tampão NH4Ac/HAc 2,5 mM pH 4,2. Em ambas as colunas a vazão foi de 1,5 mL min-1 e o tempo de análise 15 min. A extração por banho de ultrassom das amostras de solo com presença de ATR, fortificadas com concentrações de 250 a 1000 µg kg-1, proporcionou recuperações entre 40 e 86%. A presença de ATR foi confirmada por espectrometria de massas. Foram realizados estudos de fortificação com ATR e SIM em amostras de água empregando a extração por ponto nuvem com o surfactante Triton-X114. A separação empregando HPLC foi obtida por um gradiente linear de 13 a 90% de ACN para a coluna monolítica e de 10 a 90% de ACN para a coluna empacotada, sempre em tampão NH4Ac/HAc 2,5 mM pH 4,2. Em ambas as colunas a vazão foi de 1,5 mL min-1 e o tempo de análise 16 min. Fortificações entre 1 e 50 µg L-1 resultaram em recuperações entre 65 e 132%. / The use of pesticides has led to increased productivity and quality of agricultural products, but its use brings the intoxication of living beings by the gradual intake of their residues that contaminate soil, water and food. Thus, there is the need for constant monitoring of their concentrations in environmental compartments. For this, there is a quest for development of fast extraction and enrichment methods, at low cost, generating a low volume of waste, contributing to green chemistry. These methods include the extraction assisted by ultrasound bath and the cloud point extraction. After the extraction, the extract obtained can be analyzed by techniques such as High Performance Liquid Chromatography (HPLC) and Sequential Injection Chromatography (SIC) employing modern stationary phases, such as monolithic and superficially porous particles. The use of SIC with either monolithic column (C18, 50 x 4.6 mm) or column packed with superficially porous particles (C18, 30 x 4.6 mm, 2.7 µM particle size) was studied for separating simazine (SIM) and atrazine (ATR), and metabolites, deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (HAT). Separation was obtained by stepwise elution, with a mobile phase consisting of acetonitrile (ACN) and 2.5 mM ammonium acetate / acetic acid (NH4Ac / HAc) pH 4.2 buffer. The separation was performed with two mobile phases: MP1 = 15:85 (v v -1) ACN: NH4Ac / HAc and MP2 = 35:65 (v v-1) ACN: NH4Ac / HAc at a flow rate of 35 µL s-1. The separation in the column with superficially porous particles was carried out with the mobile phases MP1 = 13:87 (v v-1) ACN: NH4Ac / HAc and MP2 = 35:65 (v v-1) ACN: NH4Ac / HAc at 8 µL s-1. The ultrasound bath extraction from a soil fortified with herbicides (100 and 1000 µg kg-1) resulted in recoveries between 42 and 160 %. Separation of DEA, DIA, HAT SIM and ATR was obtained by HPLC employing a linear gradient from 13 to 35% for the monolithic column and from 10 to 35% ACN in the column packed with superficially porous particles, with the aqueous phases consisting of 2.5 mM NH4Ac / HAc buffer pH 4.2. In both columns the flow rate was 1.5 mL min-1 and the analysis time was15 min. Ultrasonic extraction from a soil sample containing ATR, fortified with concentrations from 250 to 1000 µg kg-1, provided recoveries between 40 and 86%. The presence of ATR was confirmed by mass spectrometry. Fortification studies with ATR and SIM were carried out in water samples employing cloud point extraction using Triton-X114 surfactant. The separation was accomplished by HPLC using a linear gradient from 13 to 90 % of ACN for the monolithic column and from 10 to 90 % ACN for the packed column, always in 2.5 mM NH4Ac / HAc pH 4.2 buffer. In both columns the flow rate was 1.5 mL min -1 and the analysis time 16 min. Fortifications between 1 and 50 µg L-1 resulted in recoveries between 65 and 132%.
204

Synthèse et caractérisation de nanomatériaux hybrides de type Au@SiO2 : potentialités dans le domaine de la nanomédecine / Synthesis and characterization of hybrid Au@SiO2 nanomaterials with potentialities in nanomedicine

Soulé, Samantha 10 December 2015 (has links)
Depuis une décennie, dans le domaine de la nanomédecine, les recherches s’orientent de plus en plus vers l’élaboration de nanomatériaux multifonctionnels avec l’espoir d’améliorer la précision des diagnostics ou encore l’efficacité des traitements à mettre en place. Dans ce contexte, notre travail visait à mettre en œuvre des nanoparticules hybrides Au@SiO2 de type cœur-coquille associant les propriétés photothermiques de la phase métallique à la fonction délivrance de médicaments du réseau inorganique poreux. Avec le greffage d’obturateurs organiques à l’entrée des pores de la silice, ces assemblages deviennent dès lors de véritables nanosystèmes « mécanisés ». La première partie du travail a donc concerné la synthèse du cœur du nanomatériau (nanoparticules d’or creuses appelées « nanoshells ») réalisée par un procédé de remplacement galvanique. L’influence des paramètres de synthèse sur la morphologie et la structure, sur l’état de surface ainsi que sur les propriétés optiques des nanoparticules a été largement discutée ici. Après la coupe transverse des nanoshells ainsi élaborées, les techniques d’analyse de surface (XPS, AES) ont permis de préciser la formation d’un alliage Ag-Au de composition hétérogène. L’élaboration d’une coquille de silice mésoporeuse autour des cœurs métalliques a ensuite été réalisée. Après avoir démontré le potentiel de ces nanoparticules pour le confinement moléculaire, les nano-objets Au@SiO2 ont finalement été fonctionnalisés par des assemblages supramoléculaires constitués d’un diaminoalcoxysilane (greffé à la surface) en interaction avec un macrocycle. Le couplage spécifique des techniques XPS et RMN a permis de caractériser précisément la fonctionnalisation. Une ouverture à ce travail a été initiée vers des systèmes davantage biocompatibles avec l’élaboration cette fois-ci d’une coquille hybride polymère/silice. Une première série de tests in vitro a permis d’explorer l’impact et l’interaction des nanoparticules avec des cellules de type HaCaT et a montré tout le potentiel de la poly-L-lysine dans cette approche. Cette étude originale propose de nouvelles informations dans l’étude des systèmes nanostructurés avec une caractérisation physico-chimique appropriée qui signale l’importance des phénomènes aux interfaces au sein de l’architecture hybride. Les perspectives visent maintenant à une optimisation fonctionnelle de ces nano-objets pour des applications en nanomédecine. / Nowadays, in the field of nanomedecine, the major challenge is to design multifunctional nanomaterials in order to improve diagnosis and treatment efficiency. In this context, our work has concerned the conception of hybrid Au@SiO2 core-shell nanoparticles combining the photothermal properties of the gold core and the drug delivery function associated with the inorganic porous network. The entrance pore functionalization with gatekeepers leads finally to mecanized nanosystems. The first part of the work has concerned the core material synthesis (hollow gold nanoparticles called « nanoshells ») which has been achieved by a galvanic replacement reaction. The influence of synthesis parameters on the structure, the morphology and on the optical properties has been studied. Moreover, the analysis of a nanoparticle cross-section by XPS and AES has evidenced the formation of a heterogeneous Ag-Au alloy. Then, the growth of a mesoporous silica shell on the metal cores has been conducted leading to Au@SiO2 nanomaterials. After demonstrating the potential of these core-shell nanoparticles for hosting molecules, the nano-objects have been functionalized with supramolecular nanovalves based on a diaminoalkoxysilane (grafted on the silica surface) interacting with a macrocycle. The combination of XPS and NMR allowed us to characterize precisely the functionalization. In a last section, we have been interested in the design of biocompatible systems with the elaboration of a hybrid polymer/silica shell. The in vitro effect and interaction of nanoparticles with HaCaT cells have been studied; the first results have demonstrated a real interest for using poly-L-lysine in these systems. This original study offers new details about the physico-chemical characterization of nanostructured systems which highlights the important role of interfaces in hybrid materials. The perspectives will concern the optimization of the synthesized nanosystems for direct nanomedicine applications.
205

Synthèse de catalyseurs de type coeur@coquille pour le procédé d’hydrodésulfuration en phase gazeuse / Synthesis of core shell catalysts for hydrodesulfurization process

Wery, Madeleine 26 September 2018 (has links)
Afin de réduire la teneur en soufre des essences, l’hydrodésulfuration transforme les molécules soufrées en hydrocarbures en présence d’un catalyseur supporté (métaux de transition sulfurés : MoS2) et dopé (Co, Ni). Cette phase active, déposée sur des nanoparticules, présente un nombre plus important de défauts, sites actifs essentiels à la catalyse. Les nanoparticules ont un ratio S/V élevé, une grande réactivité de surface avec une juste utilisation des quantités de métaux. L’objectif de ce projet de thèse est de synthétiser des catalyseurs nanométriques de type coeur@coquille possédant une meilleure activité catalytique qu’un simple mélange mécanique de deux métaux sulfurés. Le coeur est composé de Fe3O4 ou de nanodiamants et la coquille de MoS2, NiMoS, CoMoS ou NiCoMoS, supporté sur du TiO2 ou de la γ-Al2O3. Une réaction modèle (HDS du thiophène) a été utilisée afin d’évaluer l’activité catalytique et d’optimiser la structure du catalyseur. L’étude portera sur les paramètres de synthèse et l’effet de la taille du coeur, la synthèse utilisée, les interactions entre le coeur et la coquille, le support, la (co)– promotion (Ni/Co) et l’activation par la température. / In hydrodesulfurization of fossil fuels, the sulfur levels are reduced by sulfur extraction from hydrocarbons by using supported catalysts (MoS2), doped (Co, Ni). Ultra-deep hydrodesulfurization will be achieved by improving new catalysts. Nanoparticles are a promising candidate with their high S/V ratio and permit to use the precise amount of metallic sulphide. The aim of this thesis is the synthesis of core@shell nanometric catalyst with improved activities. Core composed of Fe3O4 or nanodiamonds will be surrounded by a shell formed of MoS2, NiMoS, CoMoS or NiCoMoS, supported on TiO2, γ-Al2O3. Model reaction (thiophene) has allowed to compare conversion rates between each catalyst. Additionally, characterizations have provided a better understanding of the HDS catalyst structure and performances. Some factors have been investigated such as the size of the core, theinteractions between the core and the shell, the type of synthesis, the support chosen, the synergetic effect with doping ions and also the activation of the catalyst at low temperature.
206

Preparação de nanopartículas funcionalizadas do tipo casca-núcleo à base de poliestireno e poli(acrilato de butila) para processamento baroplástico / Functionalized poly(butyacrylate-co-styrene) core-shell nanoparticles for baroplastic processing

Fernanda Furtado de Melo Albino 09 September 2009 (has links)
Copolímeros casca-núcleo de poli(acrilato de butila) (núcleo) e poliestireno (casca) foram sintetizados por meio de polimerização em emulsão, conduzida em duas etapas. A adição de ácido itacônico como monômero funcional na polimerização do núcleo foi realizada para verificar seu efeito sobre suas propriedades mecânicas e de processamento. Os copolímeros foram caracterizados por espalhamento dinâmico de luz (DLS), microscopia eletrônica de transmissão (MET), cromatografia de exclusão por tamanho (SEC), espectrometria na região do infravermelho (FTIR) e calorimetria diferencial por varredura (DSC). A incorporação do monômero funcional foi confirmada por DSC e quantificada por titulação. A proporção de poli(acrilato de butila) e poliestireno influenciou diretamente o processamento e as propriedades mecânicas do polímero. Os copolímeros com teores de poliestireno acima de 50% foram processados por compressão e extrusão a temperatura ambiente, apresentando comportamento baroplástico. A presença do monômero funcional não alterou o processamento do polímero e melhorou significativamente sua resistência à tração, aumentando sua tenacidade / Core shell copolymers of poly(butyl acrylate) cores and polystyrene shells were synthesized in a two-stage emulsion polymerization. The addition of itaconic acid as functional monomer in the core polymerization was carried out in order to study its influence on polymer processing and mechanical properties. The copolymers were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The functional monomer incorporation was confirmed by DSC and quantified by titration. The poly(butyl acrylate) and polystyrene proportions had a direct influence on the polymer processing and mechanical properties. Copolymers with polystyrene contents higher than 50% presented baroplastic behavior and they could be processed at room temperature by compression molding and extrusion. The presence of itaconic acid did not affect polymer processing and significantly improved tensile resistance, increasing its toughness
207

Formulation de bitumes aux propriétés rhéologiques modulables / Bitumen with tunable rheological properties

Merce, Manuel 14 December 2015 (has links)
La construction des routes avec des techniques d'enrobage à chaud (T=160 °C) implique une consommation d'énergie fossile et des rejets de gaz à effet de serre importants. Une production plus écologique du bitume nécessite de diminuer les températures d'enrobage en conservant les propriétés mécaniques des enrobés ainsi obtenus. Le développement de techniques permettant de réduire les températures est donc un enjeu majeur de l'industrie routière. Dans ce travail, nous avons joué à la fois sur la composition et le procédé pour moduler les propriétés du bitume et atteindre l’objectif fixé.Nous avons décomposé le bitume en ses différentes fractions en utilisant des techniques de séparation asphaltènes/maltènes à l'aide d'un alcane (pentane et heptane). Nous avons formulé des bitumes à différentes proportions et natures d'asphaltènes en introduisant des protocoles de préparation originaux. A l’aide de techniques de caractérisation variées telles que la rhéologie, la diffusion des rayons X ou encore des techniques de microscopies et d'analyses thermiques, nous avons déterminéles rôles des différentes fractions du bitume. Nous avons ainsi montré l'impact important des asphaltènes, mais également des fractions que nous avons qualifiées « d'intermédiaires », sur les comportements rhéologiques. Enfin, nous avons élaboré des objets coeur-écorce, composés d’une écorce rigide, non collante, riche en asphaltènes et d’un coeur mou, riche en maltènes. Ces objets sont particulièrement intéressants pour le transport du bitume à température ambiante. / The classic manufacture of hot mix asphalt for road construction is associated with a high consumption of fossil fuels and a high level of emissions of greenhouse gases into the atmosphere. A cleaner production of bitumen requires lowering the manufacturing temperature of these products without impoverishing their level of mechanical performances. The development of technologies that enable temperature reduction had thus become a major objective in the field of road engineering. In this work, we are playing on both composition and process in order to control the final properties of the material and propose an interesting way to reduce temperature during transportation. We have been interested in the different fractions composing the bitumen. We have there by employed a separation technique with alkane (heptane and pentane) to segregate the maltenes and asphaltenes. We could therefore realize diverse reconstituted bitumen using original protocols. Using various characterization techniques (such as rheology, X-ray scattering, optic, electronic and atomic force microscopy, infrared spectroscopy, thermal analysis...), we get insight into the effect of asphaltenes content and nature on bitumen properties. Our results show the huge impact of asphaltenes and other fractions called "intermediate fractions" on bitumen rheological properties. Finally, we propose an innovative processing of bitumen via the elaboration of core/shell objects composed of a rigid, nonsticky and asphaltenes-rich corona and a soft maltenes-rich core. These objects are very interesting for transporting bitumen at ambient temperature.
208

Germania-based Sol-gel Coatings and Core-shell Particles in Chromatographic Separations

Jiang, Chengliang 23 July 2018 (has links)
Chapter one reviewed the development of sol-gel stationary phase for gas chromatograph (GC). Inorganic sol-gel precursor creates the substrate support for stationary phase bind to silica surface through the condensation of silanol groups, the rough surface with enhanced surface area enlarger the capacity of the sol-gel stationary phase, the porosity of sol-gel structure decreases the mass transferring coefficient, the term C in Van Deemter equation, which makes sol-gel stationary phase thicker coating up to 1 um but keeps the high resolution for gas chromatography. Chemical bound stationary phase significantly improve GC column with better thermal stability and solvent stability. Partial derivatizations of known polymers have not increased the column performance but remained at the same level of 3200 plates per meter. The sol-gel chemistry with essential structure rebuilding will make sol-gel stationary phase to a new level. The chapter two reported the non-silica-based metal alkoxide oxide as the new building block, cooperated with known polymer poly(dimethyldiphenylsilanoxan), developed the original nonpolar feature of the stationary phase to broad the polarity from the nonpolar to extreme polar, overcome the thermal stability for other types of polar column. The theoretical plate number reached the 3200 plates per meter, and the optimized plate number arrived at the top level at 3800 plates per meter. The basic recipe and preparation of sol-gel process were verified by tungsten alkoxide incorporated with poly(dimethyldiphenylsilanoxan) as the stationary phase which arrived the same plate number level at 3800 per meter. Chapter three demonstrated the preparation of core-shell particle for HPLC. Conventional silica core particles were prepared with stÖbe methods. The extended layer of germanium oxide coating was made with acid and alkaline as a catalyst. EDS characterize the extended layers of germanium oxide has been coated at ratio 12/1(Ge/Si). Then the carbon loading with C 18 for surface derivatization were also confirmed with EDS testing. 2 um core-shell particles were successfully prepared from the external composition (1.7 um core, 0.3 um shell). The function of the core-shell particles was slurry packed with 5cm regular steel column and the capillary column with sol-gel frit. The preliminary HPLC testing showed the core-shell particles had more retention ability compare with 4 um commercial core particles. The backpressure of the short steel column and capillary both were beyond the pressure limit of conventional HPLC pump. Chapter three demonstrates the new ideal of the surface sol-gel process for GC stationary phase. Without the catalyst, the sol solution has constant viscosity and gelation time is much longer, the sol-gel reaction was taking on the silica surface only, to accomplish the thinner coating for sol-gel stationary phase. From the retention time of the grob mixture, the surface sol-gel coated 2 meters of column acquired the half retention time, grob mixture analytes were eluted within 7 minutes, compared with conventional sol-gel coated column eluted within 14 minutes. Without the TFA as the catalyst, the sol-gel matrix may not form effective surface area and porosity to support the functional polymer for separation, the column performances were two third of the protocol column, at 1500-2500 plate number per meter. The coating results proved the sol-gel stationary phase could be fulfilled with diluted sol solution by static coating. Basic parameters for dynamic coating and static coating with conventional coating and surface sol-gel were acquired for further development. The germania and niobium precursor is highly active, the water amount in the solvents used as received without drying process can meet the surface sol-gel coating without precipitates and gelation formed before finishing coat. For germania -PDMDPS column, thermal stability is very important because of the temperature for remaining the low residual OH- group in silica and germania film at 350 °C.
209

Dendritic functionalization of core-shell magnetic nanoparticles for biotechnology / Fonctionnalisation dendritique de nanoparticules magnétiques coeur-écorce pour la biotechnologie

Artiomenco Mitcova, Liubov 17 April 2014 (has links)
Le but de ce travail a été d’élaborer des nanoparticules magnétiques (MNPs) fonctionnalisées avec un groupement maléimide, stables, dispersibles dans l’eau et qui assureront une immobilisation covalente,sélective et efficace de biomolécules. Bien qu’un large choix de MNPs soit disponible dans le commerce, lamodification chimique de surface des MNPs reste une étape indispensable pour l’élaboration de matériauxspécifiques. Un contrôle précis de la fonctionnalisation de surface des MNPs est crucial, car en découlentleurs propriétés physico-chimiques, leur stabilité colloïdale, et la préservation de l’activité biologique de labiomolécule immobilisée. Dans ce travail, nous proposons d’augmenter le nombre de groupes fonctionnels(maléimide) accessibles à la surface de MNPs, en la modifiant par des agents de couplage dendritiques. Deuxtypes de MNPs coeur-écorce de 300 nm (avec un noyau de γ-Fe2O3 et une écorce de polymère ou de silice)ont été utilisés. Afin d’étudier l’effet «dendritique» sur la fonctionnalisation de surface, trois types d’agentsde couplage ont été conçus: des agents de couplage linéaires (contenant un groupe maléimide), des agents decouplage dendritiques à deux branches (contenant deux groupes maléimide) et des agents de couplagedendritiques à quatre branches (contenant quatre groupes maléimide). L’efficacité de ces MNPsfonctionnalisées pour immobiliser des biomolécules ou des modèles de biomolécules a été étudiée. Cetteétude a démontré l’intérêt de la fonctionnalisation de la surface des MNPs coeur-écorce par des structuresdendritiques pour une immobilisation efficace et spécifique de biomolécules. / The purpose of this work is to design stable, water-dispersible, maleimide functionalized magneticnanoparticles (MNPs) that will ensure selective covalent immobilization of biomolecules. While, a largechoice of MNPs is now commercially available, the surface modification of MNPs remains an indispensablestep in the elaboration of such MNPs. A precise control over the surface functionalization of MNPs iscrucial, because it governs their physicochemical properties, their colloidal stability, and their biologicalbehaviour. In this work with the aim to increase the number of functional groups on MNPs’ surfaces, it wasproposed to functionalize MNPs with dendritic coupling agents and to compare their efficiency with thosefunctionalized with a linear analogue. Moreover, it was decided to investigate the “dendritic effect” of thesurface functionalization on two types of core-shell MNPs (300 nm) that consist of a maghemite (γ-Fe2O3)ferrofluid core coated with: (I) polymer shell or (II) silica shell. Therefore, three types of coupling agents(that possess an amino or silane anchoring site) were synthesized: linear coupling agents (containing onemaleimide functional group); two-branched coupling agents (containing two maleimide functional groups)and four-branched dendritic coupling agents (containing four maleimide functional groups). Then, thecapacity of MNPs functionalized with dendritic or linear coupling agents to immobilize biomolecules ormodels of biomolecules was investigated. This study proved the efficiency of the surface functionalizationwith dendritic structures for the immobilization of biomolecules.
210

Die Entwicklung superparamagnetischer Kern-Schale-Nanopartikel und deren Einsatz als Trägermaterial in der festphasengebundenen Synthese von Peptiden, Peptid- Polymerkonjugaten und Oligonucleotiden

Stutz, Christian 20 October 2015 (has links)
Die im Jahre 1963 von Robert Bruce Merrifield vorgestellte festphasengebundene Peptidsynthese beeinflusste in hohem Maße verschiedene Bereiche der Naturwissenschaften. Doch trotz zahlreicher neuer Entwicklungen hat sich in der das Prinzip der eingesetzten Trägermaterialien nicht grundlegend geändert. Geringfügig quervernetzte Polystyrol-Harze sind immer noch die meist verwendeten Trägermaterialien in der standardisierten Peptidsynthese. In dieser Arbeit wurden superparamagnetische Kern-Schale-Nanopartikel entwickelt und erstmals deren Einsatz als neues Trägermaterial für die Synthese von Peptiden, Peptid-Polymer-Konjugaten und Oligonucleotiden demonstriert. Unter Verwendung einer mikrowellenunterstützten Syntheseroute gelang es zunächst superparamagnetische Magnetitpartikel mit einem Durchmesser von durchschnittlich 6 nm darzustellen. Anschließend wurde ein neu entwickelter mikrowellenunterstützter Stöber-Prozess zur Herstellung von Magnetit-Silica-Kern-Schale-Nanopartikel angewendet, welche im dritten Schritt mit Aminopropyltrimethoxysilan funktionalisiert wurden. Es wurden hochpräzise, monodisperse Kern-Schale-Nanopartikel mit einem Durchmesser von durchschnittlich 69 nm und einem Beladungswert von 0.11 mmol/g erhalten, welche in durchgeführten Stabilitätstests hervorragende Ergebnisse zeigten und als neue Trägermaterialien für festphasengebundenen Synthesen getestet wurden. Die erforderliche Produktaufreinigung erfolgte durch ein externes Magnetfeld, durch welches die Partikel reversibel sedimentierbar sind. Erste Studien der Synthese einer 4-mer-Peptidsequenz zeigten Ausbeuten von über 70% und mit herausragender Reinheit von über 95%. Besonders eindrucksvolle Ergebnisse erzielten die Partikel bei der Synthese von Peptid-Polymer-Konjugaten, bei denen die Ligationsreaktionen mit vorher nicht dokumentierten Umsatzraten verliefen. Außerdem konnte die Anwendbarkeit bei der Synthese eines Trinucleotids nachgewiesen werden. / In 1963 Merrifield introduced the method of solid-phase supported synthesis and thus revolutionized peptide synthesis. In spite of several new developments, the main principle of established solid supports has not changed much. Still lightly cross linked poly(styrene) resins dominate the used supports. This work reports on surface amino functionalized, superparamagnetic nanoparticles with a protective silica shell to be applicable as colloidal supports for organic synthesis of peptides, peptide polymer conjugates and oligonucleotides. A microwave supported synthesis route lead to superparamagnetic magnetite particles with an average particle diameter of 6 nm. Subsequently a new developed microwave assisted Stöber process was used to build up magnetite-silica-core-shell-nanoparticles, which were functionalized in a third step with aminopropyltrimethoxysilane. Defined monodisperse core-shell nanoparticles were obtained with an average diameter of 69 nm and a concentration of free amino groups of 0.11 mmol/g, which showed excellent results in conducted stability tests and were used as new support materials for solid-supported syntheses. Convenient magnetic sedimentation proved to ensure ease of purification after each reaction step. Initial studies of a synthesis of a tetramer peptide sequence showed yields of more than 70% and an outstanding purity of more than 95%. The particles also showed impressive results in the synthesis of peptide-polymer conjugates, in which the ligation reactions proceeded conversion rates, which had not been published before. In addition, the applicability of the particles was demonstrated in the synthesis of a trinucleotide.

Page generated in 0.0491 seconds