Dès sa découverte, le graphène oxydé (GO), le plus accessible des précurseurs du graphène, a été largement utilisé pour des applications en science et technologie. La motivation de ce travail est d'étudier, d'un point de vue fondamental, le couplage entre des bicouches amphiphiles auto-associées (lesquelles peuvent être vues comme une matrice anisotrope formée d'objets bidimensionnels) et un objet lui-même bidimensionnel, en l'occurrence le feuillet de graphène oxydé, quand ils sont dispersés dans un solvant commun. La compétition entre les élasticités intrinsèques des bicouches et des feuillets de GO, ainsi que les interactions directes bicouche-bicouche, bicouche-GO et GO-GO, permet d'envisager un riche polymorphisme en fonction de la composition du système. Après avoir développé une procédure destinée à contrôler, dans une gamme étendue de teneur en GO, le système binaire GO-eau, le domaine confiné des dispersions aqueuses de GO a été exploré et, par la suite, le diagramme de phases ternaire a été construit. Les systèmes obtenus ont été caractérisés par des techniques comme la microscopie optique et la diffusion du rayonnement (diffusion dynamique de la lumière et diffusion des rayons-X aux petits angles). Les propriétés élastiques et thermodynamiques ont été décrites par l'application de modèles initialement conçus pour les phases lamellaires à deux constituants et adaptés dans le cadre de cette étude. / Since the discovery of graphene oxide (GO), the most accessible of the precursors of graphene, this material has been widely studied for applications in science and technology. The motivation of this work is to study with a fundamental perspective the coupling between amphiphilic bilayers, which can be seen as an anisotropic matrix formed of two-dimensional objects, and another two-dimensional object, namely the graphene oxide sheet when they are dispersed in a common solvent. The competition between the intrinsic elasticities of the bilayers and GO sheets, as well as between direct bilayer-bilayer, bilayer-GO and GO-GO interactions allows us to envisage a rich polymorphism, depending on the composition of the system. Following the development of a dedicated procedure for controlling in an extended range of GO content the binary GO-water system, the confined domain of aqueous GO dispersions was first investigated, and the ternary phase diagram then constructed. The obtained systems have been characterised, using techniques such as optical microscopy, light and x-ray scattering. Elastic and thermodynamic properties have been described by applying, and adapting to the scope of this study, models for two-component lamellar stacks. / Desde sua descoberta, o grafeno oxidado (GO), o mais acessível dos precursores do grafeno,tem sido amplamente utilizado para aplicações na ciéncia e tecnologia. A motivação destetrabalho é de estudar, de um ponto de vista fundamental, o acoplamento entre bicamadas anfifílicas auto-organizadas (que podem ser vistas como uma matriz anisotrópica formada por objetos bidimensionais) e um objeto ele mesmo bidimensional, neste caso a folha de óxido de grafeno, quando estão dispersados em um solvente comum.A competição entre as elasticidades intrínsecas das bicamas e das folhas de GO, assimcomo as interaçãoes diretas bicamada-bicamada, bicamada-GO e GO-GO, permitem esperar um rico polimorfismo em função da composição do sistema. Seguindo o desenvolvimento de um procedimento destinado ao controle, em um intervalo extendido da quantidade de GO, o sistema binário GO-água, o domínio confinado de dispersões aquosas de GO foi explorado e, em seguida, o diagrama de fases ternário contruído.Os sistemas obtidos foram caracterizados por t_ecnicas como microscopia ótica, espalhamento dinâmico de luz e espalhamento de raios-x à baixos ângulos. As propriedadeselásticas e termodinâmicas foram descritas pela aplicação de modelos inicialmente concebidos para fases lamelares à dois constituintes e adaptados ao escopo deste estudo.

Cette thèse concerne la production et le contrôle d'hologrammes de haute qualité par un modulateur de phase à cristaux liquides (SLM) et l'utilisation de ces hologrammes pour la manipulation d'atomes froids. Ces hologrammes utilisés pour mettre en forme des faisceaux lasers et créer des potentiels dipolaires doivent être de bonne qualité. Or le SLM a des défauts qui peuvent les dégrader. Pour mesurer ces défauts nous avons développé une méthode reposant sur la mesure par polarimétrie de la biréfringence du SLM. La cartographie de biréfringence permet de mesurer l'hologramme en temps réel sans perturber l'expérience en cours. C'est donc une mesure in-situ. Une fois mesurés les défauts sont corrigés par une rétroaction sur la consigne donnée au SLM. Pour le démontrer nous avons créé un défaut artificiel avec un pointeur laser et nous l'avons réduit à λ/7 soit une amélioration de 42 %. Ensuite avec l'objectif d'appliquer des potentiels produit par un SLM aux atomes froids, j'ai dessiné, conçu puis réalisé en partie une expérience basée sur un jet d'atomes froids de rubidium issu d'un MOT-2D. Dans le chapitre correspondant je présente une étude de la faisabilité d'une expérience de guidage du jet d'atomes froids par un mode de Laguerre Gauss désaccordé vers le bleu de la transition. Nous avons montré que dans un tel guide le chauffage par émission spontanée est plus faible que dans un guide gaussien usuel désaccordé vers le rouge de la transition. De plus en réduisant la divergence naturelle du jet issu du MOT-2D nous devrions augmenter le flux d'atomes et améliorer l'efficacité de chargement d'un MOT-3D par un MOT-2D. / This thesis reports on the production and monitoring of high quality holograms generated by a liquid crystal spatial light modulator (SLM), and the application of these holograms to cold atoms manipulation. In order to produce accurate optical potentials by shaping a laser beam we need high quality holograms. Nevertheless SLMs suffer from defects which limit the quality. To measure defects we have developed a method based on polarimetry to get the birefringence map of the SLM. Birefringence mapping is suitable to monitor the hologram without disturbing the on-going experiment. It's an in-situ measurement. After the measurement, defects are corrected by a feedback on the input hologram. As a proof we created an artificial defect with a laser pointer and reduced it to λ/7 which corresponds to a 42% improvement. Our second goal is to apply SLM-shaped potentials to cold atoms, so I designed and did part of an experiment based on a cold atom beam provided by a rubidium 2D-MOT. In the corresponding chapter I've studied the feasibility of guiding the cold atom beam with a blue-detuned Laguerre-Gaussian beam. We showed that in such a guide the spontaneous emission is lower than in the usual red detuned gaussian guide case. Furthermore by reducing the cold atom beam divergence we expect to enhance the atomic flux and improve the loading efficiency of a 3D-MOT from a 2D-MOT.

Dans ce travail nous avons élaboré des matériaux ferroélectriques Ba0,9Sr0,1TiO3 (BST) de tailles de plus en plus réduites : céramiques, couches minces et nanoparticules pour des applications en microélectronique. Des matériaux composites constitués de nanoparticules de BST dispersées dans un cristal liquide ont également été réalisés. Le caractère ferroélectrique des films BST a été mis en évidence par des mesures des cycles d'hystérésis électriques. Les meilleures propriétés électriques ont été obtenues avec un recuit à 950 °C pendant 15 mn. Les analyses physico-chimiques sur les nanopoudres BST indiquent que la température optimale de calcination est de 900 °C. La taille des grains obtenue, entre 30 et 100 nm. Les caractérisations par diffraction de rayons X des nanopoudres montrent une structure quadratique à l'ambiante donc la possibilité d'un caractère ferroélectrique de celles-ci. La synthèse de céramiques BST par voie sol-gel et frittées à différentes températures a montré que la taille des grains dépend directement de la température de frittage et s'avère être un paramètre clé influençant la réponse diélectrique du matériau. Les céramiques BST élaborées par la méthode solide-solide permettent d'obtenir une taille de grains supérieure et en conséquence des valeurs de permittivité diélectrique plus élevées. L'étude comparative des propriétés diélectriques du cristal liquide seul et du mélange nanoparticules BST-cristal liquide a confirmé l'influence des nanoparticules BST sur l'orientation des molécules du cristal liquide. La confrontation des résultats expérimentaux aux lois de mélanges a permis l'estimation de la permittivité diélectrique des nanoparticules de BST. / In this work a ferroelectrics Ba0,9Sr0,1TiO3 (BST) ceramics, thin layers and nanoparticles were elaborated in order to obtain suitable materials for microelectronics. A mixture of BST nanoparticles dispersed in a liquid crystal was also performed. The ferrolectric nature of BST films has been demonstrated by measurements of the electrical hysteresis cycles. The best electrical properties were obtained with annealing at 950 °C for 15 min. The physico-chemical analyzes of BST nanapowders indicate that the optimum calcination temperature is at 900 °C. The grain size obtained is between 30 and 100 nm. The characterizations of nanapowders with X-Ray Diffraction show a tetragonal structure at room temperature therefore the possibility of a ferroelectric character. The ceramics synthesized by sol-gel method and sintered at different temperatures showed that the grain size depends directly on the sintering temperature and proves to be a key parameter influencing the dielectric response of the material. The BST ceramics prepared by solid-solid method used to get a size larger grain and consequently a higher value of dielectric permittivity. The comparative study of the dielectric properties of the liquid crystal single and the mixture "BST nanoparticles- liquid crystal" confirmed the influence of nanoparticles on the orientation of liquid crystal molecules. The comparison of experimental results with the mixtures laws allowed the estimation of the dielcectric permittivity of BST nanoparticles.

Développer des méthodes efficaces pour mettre en forme les matériaux moléculaires magnétiques demeure un enjeu majeur et représente une étape essentielle en vue de possible applications. A cet égard, l’élaboration d’hybrides magnétiques présentant des propriétés de cristaux-liquides ou des systèmes solubles apparait comme une approche prometteuse. Ce travail de thèse a été axé sur la conception, la synthèse et la caractérisation de nouveaux hybrides basé sur des molécule-aimants (SMMs), des complexes à conversion de spin (SCO) et systèmes à transfert d'électrons (ET). Le chapitre I contient des informations générales et concepts théoriques sur ces trois classes de complexes magnétiques (SMM, SCO et ET) ainsi qu’un aperçu bibliographique sur les hybrides magnétiques connus. Le chapitre II est axé sur nos travaux de fonctionnalisation de molécules-aimants basés sur le complexe Mn12, en vue d’obtenir des phases cristaux-liquides. Dans le chapitre III, l’étude d’une série de complexes à conversion de spin de type Fe(II)-pyridylbenzohydrazone au sein de phases cristallines ou de phases molles est décrite. Le chapitre IV est dédié à l’étude de complexes tetra nucléaire a pont cyanure de type {Fe2M2} (M = Co2+, Ni2+),qui sont connus pour présenter des propriétés de transfert de charge ou SMM avec l’ion Co(II) etNi(II), respectivement. Dans ces trois chapitres expérimentaux, l’influence de la fonctionnalisation des ligands sur l’auto-organisation et les propriétés thermiques et magnétiques des matériaux résultants est discutée en détail. / Developing efficient methods to process molecular magnetic materials remains a considerable challenge and constitutes one of the critical steps toward possible applications. In this scope, the development magnetic hybrids featuring liquid crystal properties or improved solubility appears as a promising approach. This thesis work aimed to design, synthetize and characterize new hybridmaterials based on the single-molecule magnets (SMMs), spin crossover (SCO) and electrontransfer (ET) complexes. Chapter I contains general information and theoretical concepts on these three classes of magnetic complexes (SMMs, SCO and ET complexes), followed by a bibliographicsurvey on hybrid magnetic materials. Chapter II, rational is focused on the functionalization ofMn12-based SMM towards liquid crystalline phases. In Chapter III, a series of pyridylbenzohydrazone-based Fe(II) SCO complexes is investigated in both crystalline and soft matter phase. Chapter IV is dedicated to the study of cyanido-bridged {Fe2M2} molecular squares(M = Co(II), Ni(II)), which are known to exhibit SMM and thermally- or photo induced ET,respectively with Co(II) and Ni(II). In these three experimental chapters, the influence of ligand functionalization on self-organization, thermal and magnetic properties of the resulting materials is discussed in detail.

O óxido nítrico (NO) é um versátil agente biológico, atuando em diversas partes do organismo, tais como cérebro, artérias, sistema imunológico, fígado e pulmões. Sua natureza radicalar lhe confere grande reatividade e versatilidade, tornando o entendimento de sua bioquímica um desafio. A molécula de NO tende a reagir rapidamente com alguns metais de transição, formando compostos estáveis denominados complexos nitrosilos, os quais podem ser utilizados como fonte geradora de óxido nítrico. A liberação de NO a partir de complexos nitrosilos pode ocorrer por redução química, eletroquímica e fotoquímica. No presente trabalho foi estudada a obtenção, caracterização e permeação cutânea de um complexo nitrosilo de rutênio, o trans-[RuC(cyclam)(NO)]C2 (cyclam-NO), que associado ao fotossensibilizador protoporfirina IX, possui a peculiaridade de absorver na região do visível, podendo então ser aplicados na terapia fotodinâmica (TFD) para tratamento de câncer de pele. A mistura dos compostos foi incorporada em nanodispersões de cristais líquidos, de fase cúbica (DFC) e de fase hexagonal (DFH), e sua penetração/permeação in vitro em pele de modelo animal foi avaliada, assim como o comportamento fotoquímico do sistema, no que se refere à liberação de NO, visando uma futura aplicação em TFD. A atividade citotóxica dos compostos isolados e em mistura foi avaliada frente às linhagens B16F10 e Melan-A, na ausência e presença de luz, mostrando maior atividade da mistura dos compostos quando irradiados em 630 nm. Foram construídos diagramas de fase binário e ternário e, a partir destes, foram escolhidas as formulações a serem estudadas. Estas formulações foram caracterizadas por microscopia de luz polarizada e difração de raios-X e foram avaliados o tamanho médio de partícula e o índice de polidispersividade das nanodispersões obtidas e sua estabilidade por turbidimetria. Também foi analisada a liberação de oxigênio singlete e de NO a partir dos compostos em solução e destes incorporados nas formulações. Foi desenvolvido e validado um método analítico por cromatografia líquida de alta eficiência para a quantificação simultânea dos compostos nos experimentos. A liberação dos compostos a partir das formulações usando membrana de acetato de celulose também foi avaliada, sendo possível detectar apenas o cyclam-NO. O estudo da eficiência de encapsulação mostrou que cerca de 70% da quantidade adicionada dos compostos foi incorporado na DFC e cerca de 80% na DFH. Os experimentos in vitro de permeação e retenção dos compostos em pele de orelha de porco mostraram aumento significativo da concentração dos compostos, comparado a controles contendo os mesmos em PEG. A DFH promoveu um aumento na concentração de PpIX no estrato córneo (EC) de 2,6 vezes e na epiderme+derme se EC ([E+D]) de 3,4 vezes, e para o cyclam-NO de 2,7 vezes no EC e 2,4 vezes na [E+D]. Já a DFC aumentou em 1,6 vezes a quantidade de PpIX no EC e 1,9 vezes na [E+D] e em 4,6 vezes a quantidade de cyclam-NO no EC e em 2,0 vezes na [E+D]. Os resultados obtidos permitem sugerir que estes sistemas são adequados para utilização como potenciais carreadores para a associação cyclam-NO e PpIX na TFD do câncer de pele e que esta associação apresentou efeito sinérgico, sendo mais eficiente que a utilização de apenas um dos compostos. / Nitric oxide (NO) is a versatile biological agent, acting in several parts of the body such as brain, arteries, immune system, liver and lungs. Its radical nature gives great versatility and reactivity, making the understanding of its biochemical a challenge. The NO molecule tends to react quickly with some transition metals, forming stable compounds called nitrosyl complexes, which can be used as a source of nitric oxide. NO release from nitrosyl complexes can occur by chemical, electrochemical or photochemical reduction. In this work, the acquisition, characterization and permeation of a nitrosyl ruthenium complex, trans-[RuC(cyclam)(NO)]C2 (cyclam-NO), which associated with the photosensitizer protoporphyrin IX, has the peculiarity of absorbing in the visible region, and could then be applied in photodynamic therapy (PDT) for treatment of skin cancer, were studied. The mixture of compounds was incorporated into liquid crystal nanodispersions, cubic (DFC) and hexagonal (DFH) phases, and its penetration/permeation in vitro in an animal model skin was evaluated, as well as the photochemical behavior of the system, with regard to NO release, seeking a future application in PDT. The cytotoxic activity of the compounds alone and in combination was evaluated against the B16F10 and Melan-A cell lines, in the absence and in the presence of light. Binary and ternary phase diagrams were constructed, and from these, the formulations to be studied were chosen. These formulations were characterized by polarized light microscopy and X-ray diffraction and were evaluated for particle size and polydispersity index of nanodispersions obtained and their stability by turbidimetry. Also, the release of singlet oxygen and NO from the compounds in solution and incorporated in the formulations was discussed. An analytical method using high efficiency liquid chromatography was developed and validated for simultaneous quantification of compounds in the experiments. The release of compounds from formulations using cellulose acetate membrane was evaluated, and only the cyclam-NO could be detect. The study of the encapsulation efficiency showed that about 70% of the added amount of the compounds was incorporated in the DFC and approximately 80% in DFH. In vitro permeation and retention experiments of the compounds in pig ear skin were performed, showing a significant increase in the concentration of the compounds in the skin layers, compared to controls containing compounds in polyethylene glycol. The DFH promoted an increase in the concentration of PpIX in the stratum corneum (EC) of 2.6 times and in the epidermis + dermis without EC ([E + D]) of 3.4 times, and the cyclam-NO by 2.7 times for EC and 2.4 times in the [E + D]. DFC already increased by 1.6 times the amount of PpIX in EC and 1.9 times at the [E+D] and 4.6 times the amount of cyclam-NO in EC and 2.0 times in the [E + D]. The results may suggest that these systems are suitable for use as potential carriers for the association of cyclam-NO and PpIX for use in skin cancer PDT and that this association showed a synergistic effect, being more efficient than the use of only one of the compounds.

Dans cette thèse, l'interaction entre les grains colloïdaux avec une ligne de disclinaison dans un cristal liquide nématique est explorée. Deux types de colloïdes ont été utilisés; sphérique (billes de silice) et allongé (nanotubes de carbone). En plus, différents types d'ancrage sur leur surface sont obtenus; planaire, homéotrope, et Janus (moitié planaire - moitié homéotrope). Ces paramètres ont été modifiés dans le but d'examiner et d'évaluer la force nématique agissant entre les grains colloïdaux et la ligne de disclinaison, qui est le résultat de l'interaction élastique entre les deux. Cette force est de l'ordre du pico-Newton et capable d'attirer et de fixer les colloïdes dispersés dans le cristal liquide nématique sur la ligne de disclinaison. Une fois que les colloïdes sont fixés sur la ligne de disclinaison, ils peuvent être collés ensemble par électropolymérisation de pyrrole. Ce qui donne lieu à un nanofil conducteur en 3 dimensions, qui est auto-assemblé et auto-connecté à des électrodes prédéfinies à l'intérieur du cristal liquide nématique. / Throughout this thesis, the interaction between the colloidal grains with a disclination line in a nematic liquid crystal is explored. Two types of colloids were used; spherical (silica beads) and elongated (carbon nanotubes). In addition different types of anchoring conditions on their surface is obtained; planar, homeotropic, and Janus (half planar – half homeotropic). These parameters were varied in the aim to examine and evaluate the nematic force acting between the colloidal grains and the disclination line, which is a result of the elastic interaction between the two respectively. This force is in the order of pico-newton, and capable of attracting and fixing the dispersed colloids, in the nematic liquid crystal, on the disclination line. Once the colloids are fixed on the disclination line, they can be glued together by means of electropolymerization of pyrrole. This gives rise to a 3 dimensional conductive nanowires, which are auto-assembled, and auto-connected to predesigned electrodes inside the nematic liquid crystal.

Nesta pesquisa emulsões O/A contendo cristais líquidos (CL) foram desenvolvidas a partir da técnica do diagrama ternário, utilizando óleo de andiroba e uma base auto-emulsionante aniônica constituída de éster fosfórico (Crodafos CES®), como sistema tensoativo. Foram obtidas dispersões com diferentes aspectos, classificadas como instáveis, cerosa e emulsões estáveis. A formulação constituída de 10,0 % óleo de andiroba, 10,0 % Crodafos CES® e 80,0 % de água foi selecionada para dar seqüência a pesquisa, devido a estabilidade e viscosidade aparente adequadas. Devido a aeração, foi adicionado à formulação o silicone PEG- 12 Dimethicone e para analisar a influência desse silicone na formação de cristais líquidos das emulsões, desenvolvemos um diagrama ternário contendo PEG-12 Dimethicone, Crodafos CES® e água onde as emulsões apresentaram melhor fluidez. À formulação com óleo de andiroba selecionada foi adicionada concentrações crescentes de silicone para avaliação da interação deste com o produto obtido. Foram utilizados como parâmetros para a avaliação os testes preliminares de estabilidade, teste de estabilidade acelerada (TEA), comportamento reológico e valores de potencial zeta. Em seguida, estudou-se o comportamento das emulsões durante a evaporação utilizando-se diagrama de fases e testes de evaporação. Três formulações foram submetidas ao estudo de avaliação da atividade cosmética in vivo. Para isto foram empregadas as formulações com CL, e avaliadas a influência sobre os parâmetros de hidratação, oleosidade e pH cutâneos, e também avaliação sensorial. Os resultados sugeriram uma correlação entre ambos os diagramas, onde a taxa de componentes das formulações que apresentaram CL foi similar especialmente associado à concentração de Crodafos CES® sugerindo que o silicone foi efetivo na diminuição da viscosidade das emulsões. Todas as emulsões apresentaram-se estáveis nos testes de estabilidade e foram classificadas como fluido pseudo-plástico e tixotrópicos, características estas relacionadas a formação de CL do tipo lamelar. Durante a evaporação das emulsões houve a manutenção dos CL, porém seu tipo variou em função da diminuição de água no sistema demonstrando a transição de fases dependente da concentração do solvente. Através dos testes in vivo, as emulsões de óleo de andiroba contendo CL promoveram a hidratação da pele independente da adição do silicone, de acordo com o teste de hidratação em curto prazo; não alteraram estatisticamente a oleosidade cutânea, não deixando assim a pele com aspecto gorduroso; alteraram os valores de pH cutâneo devido ao baixo valor encontrado nas emulsões, porém sem provocar nenhum tipo de irritação à pele; e na avaliação sensorial, a formulação sem silicone foi a melhor aceita. / In this researche, O/W emulsions containing liquid crystals were developed using the phase diagram technique, employing andiroba oil and a cripto-anionic selfemulsifying base constituted of phosphoric ester (Crodafos CES®), as surfactant system. Dispersions were obtained with different aspects, being classified as unstable, with wax aspect and stable emulsions. The formulation constituted of 10% andiroba oil, 10% Crodafos CES® and 80% water was selected due stability and appropriated apparent viscosity, to give sequence this research. Trying to improve the macroscopic characteristics, reducing the aeration and viscosity, the silicon PEG- 12 Dimethicone was added to the formulation. To analyze the influence of that silicon in the formation of liquid crystals on emulsions, a ternary phase diagram was developed containing PEG-12 Dimethicone, Crodafos CES® and water. The results were similar with that obtained with the andiroba oil; however the emulsion with silicon presented better fluidity. In selected formulation was an added growing concentrations of silicon in order to evaluate their interaction in the final product. Preliminary and accelerate stability tests, rheological behavior, values of zeta potential were used as evaluation parameters. Afterwards, it was studied the behavior of the emulsions during evaporation, being used phase diagrams and evaporation test. Three formulations were submitted to the study of cosmetic activity in vivo. For this evaluation the formulations with liquid crystal, with or without silicon, parameters, such as hydration, oiliness and cutaneous pH values, and also sensorial evaluation, were used. Results suggested a correlation between both diagrams, where the rate of components of the formulations that presented lamellar liquid crystalline phases was similar, especially associated with Crodafos CES® concentration. It suggests that silicon used in the study was effective in decreasing the viscosity of the emulsions, also maintaining the formation of lamellar phases when compared to formulations of the diagram containing andiroba oil. All the emulsions were stable in the stability tests and they were classified as pseudoplastic fluid and tixotropic, characteristic these related the formation of liquid crystalline phases of the type lamellar. During evaporation of the emulsions, liquid crystals were maintained, however their type varied in function of the decreasing of water rate in system, demonstrating that phase transition is dependent to solvent concentration. Through the in vivo test, emulsions with andiroba oil containing liquid crystal promoted skin hydration independently of the silicon addition, according to hydration test in a short period (kinetic test); the emulsions did not changed cutaneous oiliness, not leaving skin with greasy aspect; they altered cutaneous pH values due low value found in emulsions, however any irritation was showed in the skin; and in the sensorial evaluation, the formulation without addition of the silicon was better accepted by the volunteers.

Made available in DSpace on 2017-07-21T19:25:48Z (GMT). No. of bitstreams: 1 Vinicius Mariani.pdf: 12327357 bytes, checksum: 1e83d3e17afc9ea8500a2b6e3adf5a5f (MD5) Previous issue date: 2015-03-05 / The optical properties as well as thermal transport nanoparticles attract great attention due to the possibilities of applications and research in basic physics. Among the most studied systems are gold nanoparticles by presenting a plasmon resonance frequency in the visible wavelength. However, the manner in which generate heat when excited optically and how the surface plasmon can be used as a probe medium in which the particles are dispersed have been little explored. In this work we present an experimental study of the thermal lens effect of lyotropic liquid crystals doped with gold nanoparticles, under cw 532 nm optical excitation, and a study of how the surface plasmon resonance of colloidal gold can probe the local ordering of a anisotropic media. Spherical gold nanoparticles of approximately 12 nm were synthesized by the Turkevich’s method and the two lyotropic liquid crystals were prepared with a ternary mixture of sodium dodecyl sulfate (SDS) and potassium laurate (KL) with 1-decanol (1-DeOH ) and water. The lyotropic matrix with SDS induced the formation of nanoparticle aggregates, leading to a broad and a red shift of the plasmon resonance band. The nonlinear refraction index of thermal origin increases as a power law with respect to particle density, being possible to adress this behavior with the presence of nanopaticles clusters. In the case of liquid crystal composed of KL, we studied the reentrant isotropic - nematic calamitic - isotropic phase transitions, monitoring the plasmon resonance of the nanoparticles. For transitions at low temperatures, isotropic reentrant to nematic, the resonance band has a red-shift of 7 nm which can be assigned mainly with the increase of the dielectric constant due to a change in the shape anisotropy of the micelles. On the other hand, in the high temperature transition, the maximum absorption wavelength suffer a slight extra red-shift which may be due to a small change in the correlation length. / As propriedades ópticas, assim como as de transporte térmico em nanopartículas atraem grande atenção devido as possibilidades de aplicações e pesquisa em Física básica. Entre os sistemas mais estudados estão as nanopartículas de ouro por apresentar uma frequência de ressonância de plasmon no comprimento de onda do visível. No entanto a forma com que geram calor quando excitadas opticamente e como a superfície de plasmon pode ser utilizada como sonda do meio em que as partículas estão dispersas têm sido pouco exploradas. Neste trabalho apresentamos um estudo experimental do efeito de lente térmica de cristais líquidos liotrópicos dopados com nanopartículas de ouro, sobre a excitação óptica de 532 nm, e um estudo de como a ressonância de plasmon de superfície do ouro coloidal pode sondar o ordenamento local de um meio anisotrópico. Nanopartículas esféricas de ouro em torno de 12 nm foram sintetizadas pelo método de Turkevich e dois cristais líquidos liotrópicos foram preparados com uma mistura ternária de dodecil sulfato de sódio (SDS) ou laurato de potássio (KL) com 1-decanol (1-DeOH) e água. A matriz liotrópica com SDS induziu a formação de agregados de nanopartículas, levando a um alargamento e deslocamento da banda de ressonância de plasmon para o vermelho. O índice de refração não linear de origem térmica aumenta como uma lei de potência em relação à densidade de partículas, sendo possível relacionar seu comportamento com a presença de agregados. No caso do cristal líquido composto por KL, estudamos as transições de fase isotrópica reentrante - nemática calamítica e posteriormente para a fase isotrópica em alta temperatura, monitorando a ressonância de plasmon das nanopartículas. Para transições em baixas temperaturas, isotrópica reentrante para nemática, a banda de ressonância tem um deslocamento de 7 nm para o vermelho que pode ser associado principalmente com o aumento da constante dielétrica devido a uma alteração na anisotropia de forma das micelas. Por outro lado, para transição em alta temperatura, o comprimento de onda do máximo de absorção sofre um sutil deslocamento extra para o vermelho o qual pode ser devido à uma pequena mudança no comprimento de correlação.

The delivery of tunable millimetre-wave components at 60GHz is of research and development interests with the advent of 5G era. Among applications such as high-data-rate wireless communications, high-precision automotive radars and hand-gesture sensing, variable phase shifters are vital components for antenna arrays to steer an electromagnetic beam without mechanical movement. However, present microwave technology has limited scope in meeting more and more stringent requirements in wavefront phase control and device performance for those cutting-edge applications in the millimetre-wavelength range. Although some existing microwave switchable techniques (such as RF MEMS and solid-state p-i-n diodes) can offer ultra-fast speed for phase modulation, their binary beam-steering nature is resolution-limited and thereby degrades the beam-scanning performance. In response to this, continuously-tunable phase shifting can be realised by using tunable dielectric materials such as ferroelectric BST and liquid crystals (LCs). BST thin films can offer relatively fast switching and modest tunability. However, the increased dielectric loss beyond 10GHz impedes their implementation for higher frequency applications. By comparison, liquid crystals (LCs) have drawn attention in recent years because of their continuous tunability as well as low losses especially at millimetre-wavebands. The principle of shifting the phase continuously is based on the shape anisotropy of LC molecules for variable polarizabilities and hence tunable dielectric constants, which allows wave speed to be controlled with ease by a low-frequency field of only up to 10V. However, LC-based tunable delay lines are not well established in the frequency regime of 60GHz-90GHz because of the limited status of LC microwave technology in which most of the LC based devices have been designed for below 40GHz. It is the aim of this PhD research to bridge the gap and address future societal needs based on our group's focus and experience in developing cutting-edge LC-based agile microwave components. In this work, a liquid crystal (LC) based 0-180˚continuously-variable phase shifter is developed with insertion loss less than -4.4dB and return loss below -15dB across a wide spectrum from 54GHz to 67GHz. The device is driven by a 0-10V AC bias and structured in a novel enclosed coplanar waveguide (ECPW) including an enclosed ground plate in the design, which significantly reduces the instability due to floating effects of the transmission line. This structure screens out interference and stray modes, allowing resonance-free quasi-TEM wave propagation up to 90GHz. The tunable ECPW is optimised by competing spatial volume distribution of the millimetre-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics and minimising the total of dielectric volumetric loss and metal surface loss for a fixed phase-tuning range. A variety of influences affecting the actual device performance are studied, experimented and optimised. Fabricated prototypes exhibit wideband low-loss performance and 0-π continuous tuning with low power consumptions and high linearity compared with the state-of-the-arts. Potentially, the ECPW-fed phased antenna array will be incorporated with advanced beam-forming algorithms to develop compact beam-steering systems of improved performances and targeted for ultra-high-data-rate wireless communications, inter-satellite communications, current road safety improvement, futuristic autonomous driving, and other smart devices such as the hand-gesture recognition.

Progress in biomedicine requires the design of functional biomaterials, in particular, 3-dimensional (3D) scaffolds. Shear thinning, β-sheet based peptide hydrogels have attracted wide interest due to their potential use in tissue engineering and biomedical applications as 3D functional scaffolds. The emergence of carbon nanomaterials has also opened the door for the construction of increasingly functional hybrid hydrogels built from nanofibres and graphene-based materials using non-covalent physical interactions. The relationship between peptide molecular structure and the formed hydrogel is important for understanding the material response to shear. In particular, the physicochemical properties of peptide based biomaterials will affect the feasibility of injecting them during medical procedures. In the first part of this work, four peptides: FEFKFEFK (F8), FKFEFKFK (FK), KFEFKFEFK (KF8) and KFEFKFEFKK (KF8K) (F - phenylalanine, E - glutamic acid, K - lysine) were designed and used at identical charge to explore the effect of lysine rich β-sheet self-assembling sequences on the shear thinning behaviour and final properties of bulk hydrogels. By varying the peptide sequence design and concentration of the peptide, the tendency of the nanofibres formed to aggregate and the balance of nanofibre junction strength versus fibre cohesive strength could be explored. This allowed the existing theory of the shear thinning behaviour of this class of materials to be extended. The relationship between molecular structures of nanofibres forming the 3D network and the nano-filler is critical to understand in order to design tuneable and functional materials. In the next part of the work, three rationally designed β-sheet peptides, which form hydrogels: VEVKVEVK (V8), FEFKFEFK (F8) and FEFEFKFE (FE) (V - valine) and five graphene-based materials: graphene oxide (GO), reduced graphene oxide (rGO), three graphene-polymer hybrid flakes: GO with polydiallyldimethylammonium chloride (GO/PDADMAC), rGO with PDADMAC (rGO/PDADMAC) and rGO with polyvinylpyrrolidone (rGO/PVP) were used to form a selection of hybrid hydrogels. Graphene derivatives of the lateral flake sizes of 16.8 ± 10.1 µm were used. Various interactions between the graphene flakes and the peptides were observed that affected the overall mechanical properties of the hydrogels. Electrostatic interactions and pie-pie stacking, when phenylalanine residues are present, were shown to play a key role in determining the dispersion of graphene materials in the peptide hydrogels and stiffness of the hybrid materials. In particular, FE with reduced graphene oxide (rGO) and FE with rGO covered with polydiallyldimethylammonium chloride (PDADMAC) thin film formed double network-like hybrid hydrogels due to strong formation of peptide nanofibrillar bridges between adjacent rGO flakes. This corresponded to the 3- and 4-fold increase in the storage modulus (Gꞌ) of these hydrogels in comparison to controls. FE hydrogels with homogeneus dispersions of graphene oxide (GO) and reduced graphene oxide (rGO) are further shown to be suitable for 3D culture of human mesenchymal stem cells (hMSCs) with no cytotoxicity. These results focus attention on the importance of understanding interactions between the nano-filler and the nanofibrillar network in forming hybrid hydrogels with tuneable mechanical and biological properties, and demonstrates the possibility of using these materials as 3D cell culture scaffolds for biomedical purposes. Furthermore, graphene oxide (GO) itself is currently used in a number of processes of technological relevance such as wet spinning, injection moulding or inkjet printing to form graphene fibres, composites and printed conductors. Typically, such processes utilise well-aligned layered GO liquid crystal (LC) structures in aqueous dispersions. Flow and confinement encountered during processing affects the alignment and stability of this phase. In the final part of this work, the alignment of GOLCs of two lateral flake sizes (42.1 ± 29.4 µm and 15.5 ± 7.5 µm) were probed under a wide range of rotational shear flow conditions that overlap with the manufacturing processes defined by angular speeds from 0.08 to 8 rad.s-1 (and corresponding maximum shear rates from 0.1 s-1 to 100 s-1), in real-time, using shear induced polarized light imaging and small angle X-ray scattering, both coupled with an in-situ rheometer (Rheo-SIPLI and Rheo-SAXS, respectively). Under certain conditions, a unique pattern in Rheo-SIPLI: a Maltese cross combined with shear banding was observed. This phenomenon is unique to GO flakes of sufficiently large lateral size. The structure formed is attributed to a helical flow arising from a combination of shear flow and Taylor-vortex type flow, which is reinforced by a mathematical model. The orientations prescribed by this model are consistent with anomalous rheopecty oberved in Rheo-SIPLI and an anomolous scattering pattern in Rheo-SAXS. With the current trend towards producing ultra-large GO flakes, evidence that the flow behaviour changes from a Couette flow to a Taylor vortex flow was provided, which would lead to undesired, or alternatively, controllable alignment of GO flakes for a variety of applications, including aligned structures for biomedical purposes.