This thesis presents work on the DNA directed assembly of colloids at liquid and solid interfaces under specifically sculpted attractive interactions via depletion forces and/or magnetic fields. The highly specific and thermally reversible nature of binding between two complementary single strands of DNA allows us to encode binding rules among various (solid or liquid) components of the system. The thesis begins by presenting a new approach for introducing mobile DNA linkers on oil droplets, enabling a reversible adsorption of colloids at the oil/water interface. In comparison to previous cumbersome approaches involving expensive biotinylated lipids, this simple method provides a relatively higher grafting density of DNA anchors at the interface. Further, it is possible to kinetically control the surface coverage of oil droplets with colloidal particles while preserving fully ergodic colloidal dynamics on the droplets. The equilibrium nature of the absorbed colloids is illustrated by exploring the quasi-two-dimensional (2d) phase behaviour under the influence of depletion interactions. Colloids bound to the oil water interface are found to be significantly less diffusive compared to their bulk counterparts. Simulation studies from collaboration reaffirm the experimentally observed phase behaviour and the nature of compositional arrest. Further, some preliminary results on the phase behaviour of binary colloidal mixtures at the oil/water interface are also presented. The last section of this thesis demonstrates an approach for creating novel superstructures of DNA coated colloids (DNAcc) directed via an externally applied magnetic field. Raspberry-like and long coaxial skeletons of smaller colloids around larger superparamagnetic colloidal cores in a two component system are shown. The rigidity of these mesoscopic superstructures is enhanced by adding a suitably functionalized third component. Finally, the thesis concludes by presenting various dimensions that have emerged out of this work and are being currently pursued.

O intumescimento é um dos fatores decisivos que influenciam o comportamento de desintegração de formas farmac6uticas compactadas e, consequentemente, o perfil biofarmacêutico de substancias ativas. Entre os diversos adjuvantes empregados para promover a desagregação daquelas formas farmac6uticas nas suas partículas primarias originais, são utilizadas varias substancias, abrangidas pelo conceito de desintegrantes intumescedores. A escolha do adjuvante mais adequado nestes casos pode ser vista como uma atividade que exige o gasto considerável de tempo e de custos elevados. Além disto deve ser levada em consideração a existência de vários produtos similares no mercado. A questão da equival6ncia representa portanto um desafio importante na fase de formulação. Com o objetivo de aumentar os conhecimentos nesta área, foi desenvolvido equipamento para a avaliação dinâmica do intumescimento de pês. Inicialmente foram considerados fatores de construção do aparelho, tais como a porosidade, espessura e área do filtro de vidro sintetizado. Foram tamb6m avaliadas variações metodológicas, entre as quais a temperatura de realização do teste e o meio liquido empregado. Croscarmelose, um superdesintegrante, foi utilizada como adjuvante-modelo no teste do equipamento. A alteração do meio liquido de ensaio foi o fator que causou a maior influ6ncia sobre os resultados, embora a espessura dos filtros de vidro sintetizado tenha causado alguma alteração quer no tempo como no volume final de intumescimento. intumescimento. Já a mudança de temperatura não provocou diferenças significativas nas observações. Numa segunda fase foi investigada a influência deste desintegrante sobre as características de intumescimento de quatro celuloses microcristalinas (CMCr) isoladas ou adicionadas com um lubrificante. Para tanto elaborou-se um planejamento fatorial 4 X 2 X 2. A presença do desintegrante, como esperado, provocou aumento do volume final de intumescimento das CMCr, que apresentaram, no entanto, comportamentos diferenciados frente ao adjuvante. Já a presença do lubrificante conduziu a resultados totalmente dependentes do tipo de CMCr testada. A análise comparativa entre estes produtos demonstrou que somente num caso houve simitaridade de comportamento. / Swelling is one of the decisive factors influencing the disintegrant behavior of compacted pharmaceutical dosage forms and consequently the biopharmaceutical profile of drug substances. Among the various excipients used to promote the disintegration of such dosage forms in its originally primary particles, several substances, classified as swelling disintegrants, are employed. The choice of the most appropriate excipient in this case can be a time and cost consuming enterprise. Additionally it must be considered that the same substance can be delivered in the market by different producers. The question of equivalence represents also an important challenge in the formulation phase. In order to provide more knowledge in this area an apparatus to analyze the dynamic swelling of powder admixtures was developed. Construction factors such as filter porosity, thickness and area were considered. Methodological variants including essay temperature and liquid medium were also evaluated. Croscarmelose, a superdisintegrant, was used as model excipient to test the self built equipment. The change of the test fluid was the determinant factor on the results, although the thickness of the sintered glass filter showed some influence on both swelling volume and swelling time of this adjuvant. As a second step, the influence of this disintegrant on the swelling behavior of four microcrystalline celluloses (MCC) alone or added with a lubricant were investigated by using a 4 X 2 X 2 factorial design. The presence of the disintegrant was able to increase the swelling volume. Both final swelling volume and time were dependent of the MCC type. The lubricant showed different influences on the four tested MCC. A comparative study demonstrated that only in one case these products presented similarly swelling behavior.

L’étude et la réalisation de métamatériaux auto-assemblés possédant une réponse magnétique aux fréquences optiques font l’objet d’un champ de recherche très actif depuis plusieurs années. De nombreux calculs théoriques ont prédit qu’un arrangement dense de briques élémentaires plasmoniques, « les méta-atomes », conduirait à des matériaux à indice négatif actifs dans le domaine du visible. Il a été démontré qu’un nano-objet ayant un coeur de silice décoré de 12 nanoparticules d’or sphériques permettrait d’optimiser le phénomène de magnétisme optique. Ma thèse repose sur l’élaboration de ces objets à partir de particules colloïdales, parfaitement symétriques, constituées d’un coeur de silice et 12 nodules de polystyrène. Ces nodules de PS pouvant être éliminés ultérieurement par dissolution. Ces objets ont permis de fabriquer des particules de silices décorées d’un nombre précis de « patchs » ou de « fossettes ». Ces objets ont été formés en grande quantité. Nous sommes parvenus à rendre les cavités de surface des particules à fossettes collantes pour des germes d’or de 2-3 nm de diamètre et initier leur croissance. Les mesures de propriétés optiques de ces dodécapodes dorés ont reflété le couplage intense existant entre les nanoparticules plasmoniques autour du coeur diélectrique. La possibilité de faire croitre de l’argent à la surface des germes d’or permet de générer des nanorésonateurs avec des modes magnétiques optiques encore plus intenses que ceux observés pour les systèmes à base d’or. / Over the last decade, the field of self-assembled metamaterials exhibiting unusual properties such as a magnetic response in the visible range represents a challenging and attracting area. Many simulations reported that a dense arrangement of specific plasmonic sub-units called “meta-atoms”, may lead to a material with a negative refractive index. It was reported by computational modelling that a dodecapod clusters made of a central dielectric core and surrounded by a controlled number of satellites (12 satellites, here) with a specific size can exhibited some interesting properties. Here, the purpose was to fabricate such clusters from colloidal particles, which are perfectly symmetrical, made of a silica core and 12 polystyrene nodules. Subsequently, those polystyrene nodules can be dissolved to get silica particles with a specific number of “patches” or “dimples”. Those objects were synthesized in a large quantity. We were able to make those dimples sticky to tiny gold seed of 2-3 nm size and to grow then for a specific size. Optical measurements reported the strong magnetic coupling in-between the plasmonic nanoparticles around the dielectric core. We also reported that growing silver on tiny gold seeds generates stronger magnetic responses than those observed from gold clusters.

Nous avons cherché à comprendre le comportement sous écoulement de suspensions colloïdales d'argiles naturelles. Les particules constitutives de ces argiles ont comme particularité d'être extrêmement anisotropes puisqu'elles se présentent (en moyenne) sous la forme de disques de 200 nm de diamètre pour une épaisseur de 1 nm. Ces matériaux présentent des propriétés mécaniques remarquables parmi lesquelles une forte rhéofluidification ainsi que l'apparition de seuils d'écoulement et ce, pour de très faibles fractions volumiques en particules (environ 1%). Afin de comprendre l'origine de ces propriétés mécaniques, nous avons mis en place un dispositif expérimental permettant d'effectuer simultanément des mesures de viscosité (en cellule de Couette cylindrique) et des mesures de diffusion de rayons-X aux petits angles. Le champ orientationnel de particules 2D très anisotropes en écoulement cisaillé a ainsi été mesuré. En l'absence de cisaillement, et dans la phase de liquide isotrope, les particules s'orientent librement et occupent statistiquement un volume équivalent à celui de la sphère de volume exclu englobant la particule. En appliquant un cisaillement croissant on confine les particules discoïdales, faisant passer progressivement le volume de fluide piégé dans le mouvement moyen des particules de la sphère de volume exclu à un ellipsoïde à double anisotropie. Connaissant le champ orientationnel des particules on peut alors, par le biais d'une relation viscosité - fraction volumique de type Quemada, reconstruire la rhéofluidification de ces suspensions en prenant en compte, non pas la fraction volumique en disques mais celle en ellipsoïdes de confinement / We focussed our interest on the flow behaviour of colloidal suspensions of natural swelling clays. Such systems are strongly anisotropic since the disk-shaped particles in suspensions display an average diameter around 200 nm with a thickness close to 1 nm. Under flow, and for very low volume fractions (around 1%), these materials display remarkable mechanical properties going from quasi-Newtonian liquid to yield stress gel. In order to understand the mechanisms leading to such macroscopic behaviour, we have set up an experimental device that enables us to perform simultaneously viscosity (in a cylindrical Couette cell) and small angles x-ray scattering measurements. Thanks to this Rheo-SAXS device, we measured the orientational field of strongly anisotropic bi-dimensional particles in shear flow. When no shear is applied (and in the isotropic liquid phase), the particles are randomly oriented and occupy statistically a volume equivalent to that of the sphere of excluded volume encompassing the particle. The stronger is the applied shear stress, the more confined are the disk-like particles and consequently the small amount of fluid trapped in the statistical motion of the particles decreases from that of the sphere of excluded volume to that of an oblate ellipsoid with double anisotropy. Thus, knowing the orientational field of the particles (measured by SAXS) and applying an effective approach as the one suggested by Quemada for hard spheres, we tried to rebuild the shear-thinning behaviour of these suspensions by taking the volume fraction in statistical ellipsoid instead of that of disk-shaped particles

A ítria vem sendo muito utilizada como material luminescente e estrutural resistente a altas temperaturas, devido às suas excelentes características ópticas e refratárias. No processamento coloidal da ítria, o controle da estabilidade da suspensão consiste em uma importante etapa quando se objetiva produzir componentes reprodutivos, com densidade controlada, microestrutura homogênea e estabilidade estrutural. Desta maneira, os estudos envolvendo o comportamento de superfície, as condições de estabilidade das suspensões e o comportamento frente às condições de conformação (fluxo), fornecem importantes subsídios para controle dos processos na fabricação de componentes cerâmicos para queimadores de gás. Neste sentido, realizaram-se estudos sobre o comportamento de superfície, de estabilidade e reológico de suspensões aquosas de ítria e do concentrado de terras raras contendo ítria a fim de adequá-las para o processo de conformação por impregnação, onde foram testados diferentes materiais orgânicos como matrizes de réplica, para a confecção de membranas porosas para queimadores de gás. Neste estudo foram avaliados os parâmetros como: pH do meio, concentrações de dispersante, sólidos e ligante na estabilidade e no comportamento ao fluxo das suspensões cerâmicas, e também os aspectos dos distintos materiais orgânicos selecionados como matrizes de réplica para impregnação com as suspensões cerâmicas otimizadas. Os resultados obtidos indicam que se pode confeccionar membranas cerâmicas porosas pelo método de réplica a partir das suspensões aquosas de ítria e do concentrado de terras raras contendo ítria, utilizando-se pH alcalino, polieletrólito aniônico e uma tela mista de nylon-algodão como matriz de réplica. / Yttria has been used very much as luminescent and high temperature material due to its excellent optical and refractory characteristics. In yttria colloidal processing, the control of the stability of suspension is an important step in the fabrication of reproducible products with controlled density, homogeneous microstructure and structural stability. So, the studies concerning surface behavior, stability conditions of the suspensions and the behavior under conformation conditions (flow), give important information for the control of fabrication process of ceramic components for gas burners. In this way, studies concerning surface behavior, stability and rheology of aqueous suspensions of yttria and rare earth concentrate containing yttria were carried out, in order to adequate them for impregnation method, where different organic materials were tested as replica matrix to fabricate porous membranes for gas burners. In this study, the effect of some parameters as pH and concentrations of dispersant, solids and binder on stability and flow behavior of ceramic suspensions were evaluated, and also, different kinds of organic materials selected as replica matrix for impregnation method using optimized ceramic suspensions. The results show that porous ceramics membranes can be produced by replica using yttria and rare earth concentrate containing yttria, using alkaline pH, anionic polyelectrolyte and a nylon-cotton cloth as replica matrix.

Este trabalho investigou a técnica de solução coloidal(gelcasting) em meio polimérico para a obtenção de partículas de óxido de cério, visando seu emprego como catalisadores na combustão do metano. A formulação do sistema coloidal foi baseada na hidrólise de sais, como acetilacetonato de cério e nitrato de cério em presença de aditivos tais como polivinilbutiral (PVB), polivinilpirrolidona (PVP) e polivinilacetato (PVA), nas concentrações de 5, 10 e 15%, em meio alcoólico ou aquoso. Essas soluções, contendo os íons de interesse, foram submetidas a um tratamento térmico a 650°C, por 30 minutos, com taxa de aquecimento de 2°C/min. Após o tratamento térmico, os produtos obtidos foram caracterizados quanto a sua morfologia, área superficial, cristalinidade, perda de massa e atividade catalítica. As amostras obtidas a partir de acetilacetonato de cério mostraram-se mais reativas do que as obtidas a partir de nitrato de cério na catálise da combustão do metano, pois apresentaram maiores conversões e atingiram maiores temperaturas durante o processo, o que é de extrema importância uma vez que a combustão catalítica do metano é utilizada para a geração de energia térmica. Durante o processo de combustão, utilizando-se as partículas obtidas a partir de acetilacetonato de cério, observou-se a liberação de grandes quantidades de compostos nitrogenados quando comparado aos resultados dos ensaios com as partículas obtidas com nitrato de cério. Após a combustão do metano, as amostras sofreram significativa alteração na área superficial, provavelmente devido à intensidade do calor liberado, o que deu origem a maior aglomeração dos particulados. / This study investigatedto obtainparticles ofcerium oxide, for use as catalysts for thecombustion of methaneusing the techniqueofthroughpolymericcolloidal solution (gelcasting).Obtaining thecolloidal systemisbased onhydrolysis ofsalts such asceriumacetylacetonate,cerium nitratein the presence ofadditives such aspolyvinylbutyral(PVB),polyvinylpyrrolidone (PVP) and polyvinyl acetate(PVA),at concentrations of 5, 10 and 15% inaqueousoralcoholic medium. Thesesolutions containingionsof interestwere subjected to aheat treatment at 650°C for30 minutes, with heating rate of2°C/min.After heat treatment, the fibers were characterized accordingto their morphology, surface area, crystallinity, weight loss andcatalytic activity. Samplesobtained fromceriumacetylacetonatewere morereactivethan theceriumnitrateto thecombustion of methane, as showed greaterconversions andhigher temperaturesreachedduring the process, which is of utmost importancesince thecombustioncatalyticmethaneis usedfor generatingthermal energy.Duringthe combustion processusing theobtained fromparticlesof ceriumacetylacetonate, there was the release of largequantities ofnitrogencomparedto the results ofassays withthe particles obtainedwithcerium nitrate.Afterthe reactionwith methane, the samples underwentsignificantchange insurface area, probably dueto the intensity of heat of this reaction, which helps to agglomerate the particles.

Les suspensions colloïdales se trouvent un peu partout autour de nous, dans les matériauxde constructions, en cosmétique, dans l'alimentation, en biologie. Elles sont composésde particules nanométriques ou micrométriques dispersés dans un gaz, un liquide ou unsolide.Cette thèse porte sur les suspensions colloïdales dans des solutions ioniques,où les colloïdes portent une charge électriques, par exemple des particules de silicedans une solution aqueuse de chlorure de sodium, à un pH basique. Les colloïdes,ici approximés par des sphères, peuvent varier significativement en taille,ce qui peut avoir un effet important sur le comportement de ces systèmes.Cette étude vise à améliorer la compréhension de ces suspensions colloïdales chargéespar des modèles théoriques résolus par des simulations numériques.Un des défis de ces simulations est le grand nombre de degrés de libertés. Pour chaque(micro-)ion il y a des centaines de molécules de solvant, et pour chaque colloïdedes centaines voire des milliers d'ions. Pour s'en sortir, nous avons calculéles interactions effectives à l'échelle colloïdale. Nous avons repris et développéplusieurs approches, présentant chacune un compromis en terme de temps de calcul etprécision.La variation en taille des colloïdes peut introduire des effets intéressants,observés expérimentalement, notamment le fractionnement des suspensions en plusieursphases cristallines quand on augmente la concentration en colloïdes.Des techniques de simulations Monte-Carlo simples associées aux interactions inter-colloïdescalculées précédemment ont permis d'obtenir des résultats en bon accord avec l'expérience. / Colloidal suspensions are found a bit everywhere around us, in construction materials,in cosmetics, in food, in biology. They are composed of nanometric or micrometric particlesdispersed in a gas, a liquid or sometimes a solid.This thesis is about colloidal suspensions in ionic solutions, where colloids bear anelectric charge, for example silica particles in an aqueous solution of sodium chloride,at a basic pH. The colloids, here approximated by spheres, can vary significantly in size,which can have an important effect on the behavior of these systems.This study aims at improving the understanding of these charged colloidal suspensionsby theoretical models solved by numerical simulations.of these charged colloidal suspensionsby theoretical models solved by numerical simulations.One of the challenge of theses simulations is the huge number of degrees of freedom.For each (micro-)ion there is hundreds of solvent molecules, and for each colloidthere is hundreds if not thousands of ions. To get away with it, we calculated theeffective interactions at the colloidal scale. We took and developed several approaches,each showing a trade-off in terms of computational time and accuracy.The size variation of colloids may introduce interesting effects, experimentallyobserved, notably the fractionation of suspensions in several crystalline phaseswhen the colloidal concentration is increased. Some simple Monte-Carlo simulationtechniques in combination with the inter-colloid interactions computed previouslyallowed us to obtain results in good agreement with experiments.

Nanoparticulas magnéticas (NPMs) de óxido de ferro tem sido amplamente utilizadas em diversas áreas da biotecnologia e biomedicina, tais como no tratamento de câncer, na entrega controlada de fármacos e como agentes de contraste em imagem por ressonância magnética. O intuito deste trabalho foi sintetizar nanopartículas magnéticas com magnetização de saturação intensificadas via processo do poliol modificado e modificar sua superfície afim de promover a biocompatibilização dos sistemas. Além da funcionalização de nanopartículas previamente biocompatibilizadas utilizando dois métodos: via ligação amida com moléculas de ácido fólico (AF) e com a encapsulação das nanopartículas com quitosana. A modificação de superfície deu-se via procedimentos de lavagem de superfícies, adição e/ou troca de ligantes utilizando moléculas de ácido ?- aminocapróico (EACA), aminopropiltrimetoxisilano (APTMS) e ácido dimercaptosuccínico (DMSA). Através da microscopia eletrônica de transmissão (TEM), foi obtido que as nanopartículas magnéticas de magnetita obtiveram um diâmetro médio de 8 nm, em uma estreita distribuição de tamanho. A difração de raios-X (DRX) indicou a formação de magnetita em todos os sistemas em que o método do poliol modificado foi utilizado. As medidas de espectroscopia vibracional na região do infravermelho (FTIR) evidenciaram a presença de modos de vibração relacionados às macromoléculas e compostos inorgânicos utilizados na modificação de superfície das nanopartículas magnéticas e/ou funcionalização. A TEM das diferentes modificações de superfície mostram a formação de aglomerados dependendo da molécula utilizada. Os estudos de estabilidade coloidal foram necessários para que o meio biológico fosse simulado para uma possível aplicação destes sistemas como carreadores para tratamento via magnetohipertermia ou entrega controlada de NPMs para tratamento de câncer. A nanopartícula recoberta com DMSA apresentou melhores resultados de estabilidade coloidal. Com os sistemas funcionalizados com ácido fólico, o procedimento via ligação com carbodiimida na presença de NHS demonstrou ser eficaz na formação de ligação amida, confirmada por FTIR e quantificação de ligantes. A funcionalização com quitosana necessita de alguns ajustes, visto ser um novo procedimento, porém alguns sistemas em que foi utilizado o método da gelificação iônica possuíram bons resultados de nanocápsulas de quitosana formadas com nanopartículas biocompatibilizadas em seu interior. / Magnetite, iron oxide, is a type of magnetic nanoparticles (NPMs) that is a widely adopted in several areas of biotechnology and biomedicine, such as in the treatment of cancer, controlled delivery of drugs and as contrast agents in magnetic resonance imaging. The purpose of this work is to synthesize magnetic nanoparticles with enhanced saturation magnetization via modified polyol process and modify its surface to promote a biocompatibilization in these systems. In addition, there was the aim to functionalize nanoparticles with modificate surfaces, using two methods: via amide bonding with folic acid molecules (AF) and encapsulation of nanoparticles with chitosan. Surface modification was done via surface washing, addition and / or exchange ligands using ?-aminocaproic acid (EACA), aminopropyltrimethoxysilane (APTMS) and dimercaptosuccinic acid (DMSA) molecules. By transmission electron microscopy (TEM), it was obtained that the magnetite nanoparticles had an average diameter of 8 nm, in a narrow size distribution. X-ray diffraction (XRD) indicated formation of magnetite in all systems where modified polyol method was used. Infrared spectroscopy (FTIR) showed the presence of vibration modes related to macromolecules and inorganic compounds used in the surface modification of magnetic nanoparticles and / or functionalization. The TEM of different surface modifications showed the formation of agglomerates, depending on the molecule used. Colloidal stability studies were necessary to simulate a biological medium for a possible application of these systems as carriers for treatment via magnetohyperthermia or controlled delivery of NPMs for cancer treatment. Nanoparticles coated with DMSA showed better colloidal stability results. With folic acid functionalized systems, the procedure via carbodiimide linkage in the presence of NHS had been shown to be effective in FTIR-confirmed amide bond formation and ligand quantification. The functionalization with chitosan requires some adjustments, since it was a new procedure, however some systems using the ionic gelation method had good results of chitosan nanocapsules formed with biocompatibilized nanoparticles in structure.

Dans cette étude nous avons étudié la polymérisation de l’aniline en milieu aqueux micellaire eau-acide décylphosphonique (DcPA) ainsi qu’en milieu micellaire inverse acide décylphosphonique/eau/n-heptane : chloroforme (2 :1 v/v). Contrairement au système aqueux micellaire, la vitesse de polymérisation dans le système micellaire inverse augmente lorsque la concentration en DcPA dans le milieu réactionnel diminue. Ce résultat a été attribué à des différences de compacité de la couronne hydrophobe des micelles inverse, qui impactent la diffusion de l’aniline au cœur des gouttelettes d’eau, le lieu préférentiel de la polymérisation.La conductivité électrique maximale obtenue est de 3.6 S.cm-1. Cette valeur de conductivité est plus élevée de 4 ordres de grandeur comparée à la conductivité électrique de PANI dopée DcPA préparée par post-traitement de la PANI EB avec une solution de DcPA (2.3x10-4 S cm-1). Les analyses de diffraction des rayons X (DRX) ont révélé une structure lamellaire de la polyaniline préparée en milieu micellaire eau-DcPA dans laquelle les chaînes de polyaniline sont séparées par les longues chaînes alkyle du DcPA. Cette organisation diminue les interactions interchaînes de la polyaniline et contribue à l’augmentation de la solubilité en milieu organique de la polyaniline.La polyaniline dopée DcPA a été incorporée comme pigment dans un liant polymère polyvinyl butyral (PVB), puis appliqué sur un acier à faible teneur en carbone. Dans le cas de la polyaniline préparée dans le milieu aqueux micellaire de DcPA, la dispersion de polyanilinea été également appliquée après dialyse sur acier en couche mince, puis revêtue d’une couche de finition PVB. Les films PVB-PANI ont été exposés à des environnements neutres chlorurés (brouillard salin et milieu NaCl 3.5%). A partir de mesures de spectrométrie d’impédance électrochimique, nous avons montré que l’efficacité de la protection anticorrosion de la polyaniline dopée DcPA augmentait avec le taux de dopant DcPA du polymère. Ces résultats suggèrent un rôle actif du DcPA dans le mécanisme de protection. Ce rôle actif du DcPA a été confirmé par analyse de la surface métallique après exposition qui a révélé la présence de sels de phosphonates de fer insoluble. La protection anticorrosion apportée par polyaniline dopée DcPA apparaît supérieure à la polyaniline non dopée ainsi qu’à la polyaniline dopée HCl. / In this thesis, the polymerization of aniline in micellar solutions of decylphosphonic acid (DPA) as well as reversed micellar solutions of decylphosphonic acid / water / n-heptane : chroloform (2 : 1 vol/vol) was investigated. Unlike micellar solution, the polymerizations rate in the reversed micellar solution increases as the DPA concentration in the reaction medium decreases. This result was attributed to the packing density of DPA molecules in the surfactant shell of inverse micelles, which affects the diffusion of aniline into the inner of the water droplets in which the polymerization is preferred. The maximum electrical conductivity obtained is 3.6 S.cm-1. This value is four orders in magnitude greater than the value of DPA doped PANI prepared by postsynthesis treatment of the PANI-base with the solution of DPA (2.3 x 10-4 S.cm-1). The results of the X-ray diffraction analysis suggested the formation of layered structure of PANI backbone separated by long alkyl side chains of DPA. This organization reduces interchain interactions of the polyaniline and contributes to the increase in solubility of PANI in an organic solvent.The DPA doped PANI was incorporated as a pigment in the polymer binder polyvinyl butyral (PVB), and then applied to a steel material with a low content of carbon. In the case of the polyaniline prepared in the micellar solution of DPA, the dispersion of PANI was also applied to steel with thin layer after dialysis, and then coated with a top coat PVB. The PVB-PANI coatings applied on steel substrates are exposed in neutral saline corrosive media such as salt-spray or 3.5% NaCl solution. Based on the electrochemical impedance spectroscopy measurements, it is found that the corrosion protection efficiency of the DPA doped PANI increases with the amount of dopant of DPA. These results show an active role of DPA in the mechanism of protection. The active role of DPA was also confirmed by the analysis of the exposed metallic surface with the presence of insoluble phosphonate of iron. The corrosion protection provided by the DPA doped PANI appears better than the undoped polyaniline and the one doped with HCl.

"Hydrophobic hydration of non polar molecules is the principal driving force that dictates several interfacial phenomena in nature such as self assembly of surfactant molecules, fate of environmental pollutants, wetting of surfaces, solution behavior of polymers and folding of biological molecules such as proteins. However, the physics associated with hydrophobic interactions on a molecular length scale, which is central to self assembly and protein folding, is different from the macroscopic phenomena of de-mixing of oil and water or wetting of surfaces. This dissertation seeks to understand the implication of hydrophobic interactions to energy and environmental applications using different approaches. The first approach is to examine the behavior of water molecules with hydrophobic moieties at a molecular level using molecular dynamics simulations and evaluate macroscopic thermodynamic properties. The first problem addressed in this dissertation is the enclathration of gas molecules by water molecules in the presence of quaternary ammonium ions. Small polar organic molecules such as quaternary ammonium salts form crystalline inclusion compounds called semi-clathrate hydrates, where these polar molecules occupy a lattice position of the hydrogen bond network of water molecules. These crystalline structures of water are formed at ambient temperature and pressure conditions and can store as much 3%(w/w) of methane, making them potential materials for gas storage. The stability and structure of semi-clathrate hydrates of tetrabutylammonium bromide (TBAB) and methane were investigated using molecular dynamics (MD) simulations. MD simulations were done at varying conditions of temperature and pressure for methane-TBAB ratios of 0, 0.5, 1, 1.5 and 2. Thermo-mechanical properties evaluated using MD simulations were in agreement with experimental data available. Our investigation of this system shows that enclathration of methane in these semi-clathrate hydrates is thermodynamically favorable even at higher temperatures and shows signatures of hydrophobic hydration. Our estimation of free energies associated with successive inclusion of methane molecules in these cavities suggests a Langmuir-type adsorption of methane in these cages. Another problem investigated in this dissertation is the effect of chemical heterogeneity of crystalline cellulose (110) and (100) surfaces on their respective wetting behavior. Understanding the interaction of water with cellulose is important in the view of its role in consumer textiles made from cotton cellulose and potential applications of cellulose as biomaterials and as an energy source. The difference in the wetting behavior of (110) and (100) crystal surfaces is due to the asymmetry in the exposure of the hydroxyl groups by these surfaces. MD simulations were used to evaluate the contact angles of hemi-cylindrical water nanodroplets on crystalline (110) and (100) surfaces of the cellulose Iβ allomorph. While the native crystalline surfaces were completely wetted by water nanodroplets, substituting the primary hydroxyl groups with methyl and methoxy groups results in dewetting. The contact angle of a hemicylidrical water nanodroplet on the hydrophobically-modified (110) surface is greater than on the (100) surface suggesting that the (110) surface has a greater exposure of the primary hydroxyl groups. The solubility of cellulose in aliphatic N-oxides has been of particular interest because of its application in industrial processes such as Lyocell process. However, the mechanisms that dictate the dissolution of cellulose in these selective solvents are not clearly understood. Attempt is made to understand the solvation of cellulose in N-Methylmorpholine oxide (NMMO) and water from a molecular perspective. MD simulations of a model cellohexaose crystallite solvated respectively in pure water, NMMO and in an equimolar mixture suggest that while NMMO molecules preferentially cluster around the primary hydroxyl groups in cellohexaose chains, the role of water is critical in its ability to access the glycosidic oxygen. The second approach is to study the implication of introducing hydrophobicity at molecular level and experimental determination of its implication to addressing interfacial aspects of environmental remediation. Sub-micron size carbon particles derived from hydrothermal decomposition of sucrose are effective in stabilizing water-in-trichloroethylene (TCE) emulsions. Irreversible adsorption of carbon particles at the TCE-water interface resulting in the formation of a monolayer around the water droplet in the emulsion phase is identified as the key reason for emulsion stability. Cryogenic Scanning Electron Microscopy was used to clearly image the assembly of carbon particles at the TCE-water interface and the formation of bilayers at regions of droplet-droplet contact. The results from this study have broad implications to the subsurface injection of carbon submicron particles containing zerovalent iron nanoparticles to treat pools of chlorinated hydrocarbons that are sequestered in fractured bedrock. Interfacial aspects of hydrophobically modified biopolymer and its ability to enhance the stability of crude-oil droplets formed were investigated. Turbidimetric analyses show that emulsions of crude oil in saline water prepared using a combination of the biopolymer and the well-studied chemical dispersant (Corexit 9500A) remain stable for extended periods in comparison to emulsions stabilized by the dispersant alone. The hydrophobic residues attached to the polymer preferentially anchor at the oil-water interface and form a protective layer of the polymer around the droplets. The enhanced stability of the droplets is due to the polymer layer providing an increase in electrostatic and steric repulsions and thereby a large barrier to droplet coalescence. The implication of this study to current remediation methods is significant since the addition of hydrophobically modified chitosan following the application of chemical dispersant to an oil spill can potentially reduce the use of chemical dispersants. Increasing the molecular weight of the biopolymer changes the rheological properties of the oil-in-water emulsion. Emulsions stabilized by using a combination of Corexit 9500A and high molecular weight hydrophobically modified chitosan show characteristics of a weak gel. The ability of the biopolymer to tether the oil droplets in a gel-like matrix has potential applications in the immobilization of surface oil spills for enhanced removal. Carbon microspheres containing magnetite nanoparticles, synthesized using inexpensive precursors such as sucrose and iron chloride, are ferromagnetic and have affinity to the oil phase. We demonstrate that a thin layer of crude oil can be corralled and thickened by the application of nonionic surfactant. Following the application of magnetite-carbon particles, hydrophobically modified chitosan was applied to form a gel-like phase. This gel-like phase of crude oil containing magnetic carbon spheres can be removed as an aggregate using a magnet resulting in enhanced recovery of crude oil. The results from the current study point to developing potential applications for confinement, magnetic tracking and removal of surface oil. " / acase@tulane.edu