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Efeitos de superfície nas propriedades térmicas e dinâmicas de filmes de cristais líquidos esméticos. / Surface effects on the thermal and dynamical proprieties of smectic liquid crystal filmes.Oliveira, Italo Marcos Nunes de 03 August 2007 (has links)
The thermal and dynamical properties of free-standing films are strongly dependent
on the boundary conditions and the presence of an external field. Using distinct theoretical
models and the dynamic light scattering experimental setup, we study the surface and
external field effects on the relaxation dynamics, fluctuation-induced interaction energy,
and phase transitions of smectic films.
Using an extended McMillan model, we study as a homeotropic anchoring stabilizes
the smetic order above the bulk transition temperature of the system. In particular,
we determine as the transition temperature depends on the surface ordering and film
thickness. We identify a characteristic anchoring for which the transition temperature
does not depend on the film thickness. For strong surface ordering, we observe that the
transition temperature presents a power law scaling behavior with the film thickness, in
agreement with a series of existing experimental results in the literature.
Within a Gaussian functional approximation, we also investigate how the fluctuationinduced
interaction force depends on the nematic and smectic order parameter profiles.
Close to nematic-smectic phase transition, our results indicate that the thermal Casimir
force has a significant enhancement which reinforces the predominance of the fluctuationinduced
interaction as compared to standard van der Waals interaction in thin smectic
films. In temperatures where the smectic phase is well established, we investigate how
the interplay of the surface order and the external field induced order affect the Casimirlike
force. For asymmetrically anchored films, the fluctuation-induced interaction energy
obeys a law of corresponding states and can change its nature from attractive to repulsive
through variations of an external field. We discuss the possible relevance of this field effect
in smectic wetting transitions.
With concern to the dynamical properties, we investigate how surface operators
modify the relaxation dynamics of hexatic-B liquid crystal films. In particular, we study
how a surface ordering field modifies the damping rate of the orientational modes in the
system. In a purely diffusive regime, we demonstrate that a surface tilted order drives the
slowest relaxation mode from hydrodynamical to non-hydrodynamical character. In the
viscous regime, the hydrodynamical character of the slowest relaxation mode persists even
for a surface tilted order. However, the normal modes develop an oscillatory-exponential
relaxation.
Finally, we use the photon correlation spectroscopy technique to investigate the
dynamic properties of free-standing films close to smectic-A - crystal-B transition. We
observe that the experimental data indicate the existence of a non-hydrodynamic mode
and measure the temperature dependence of the damping rate. We considered a simplified
model that incorporates the gradient velocity field effects which reproduces qualitatively
the experimental measurements. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As propriedades térmicas e dinâmicas de filmes de cristais líquidos na fase esmética são extremamente dependentes das condições de contorno e da presença de campos externos.
Utilizando diferentes modelagens teóricas e a técnica de espectroscopia de fotocorrelação, estudamos como as condiçõoes de contorno e a presença de um campo externo afetam a dinâmica de relaxação, a energia de interação induzida por flutuações e as transições
de fase envolvendo a fase esmética.
Utilizando uma extensão para o modelo de McMillan, estudamos como o ancoramento
homeotrópico estabiliza a ordem esmética acima da temperatura de transição
do sistema. Em particular, determinamos como a temperatura de transição depende da
intensidade do ancoramento superficial e da espessura do filme. Identificamos um ancoramento
característico para o qual a temperatura de transição independe da espessura. Para
ancoramentos fortes, observamos que a depend encia da temperatura de transição com a
espessura do filme segue aproximadamente uma lei de potência, em concordância com uma
série de resultados experimentais existentes na literatura.
Baseado em uma teoria funcional Gaussiana para o funcional energia livre, investigamos
tamb´em como a força induzida por flutuações esméticas depende do perfil dos
parâmetros de ordem nemático e esmético. Nas proximidades da transição nemática esmética, nossos resultados indicam que a força de Casimir térmica cresce significativamente,
podendo ser mais relevante que a força de van der Waals usual. Em temperaturas
onde a fase esmética é bem estabelecida, investigamos como a competição entre a ordem
superficial e a ordem induzida por um campo externo se reflete nas características da
força de Casimir. Obtivemos que, para filmes com ancoramentos superficiais assimétricos,
a força de Casimir térmica obedece a uma lei de estados correspondentes e pode mudar
sua natureza de atrativa para repulsiva através de variações de um campo externo. Discutimos
como este comportamento pode influenciar as transições de umedecimento da fase
esmética.
No que diz respeito às propriedades dinâmicas, investigamos como operadores de
superfície modificam a dinâmica de relaxação de filmes na fase hexática-B. Em particular
estudamos como um campo de ordenamento superficial modifica a taxa de amortecimento
dos modos orientacionais do sistema. Num regime puramente difusivo, nós demonstramos
que uma ordem superficial com o vetor diretor não paralelo à direção normal das
camadas faz com que os modos de relaxação tornem-se não-hidrodinâmicos. No regime
viscoso, sempre existirão modos hidrodinâmicos e a dinâmica de relaxação é sempre lenta.
Entretanto, os modos normais podem apresentar um decaimento oscilatório.
Por fim, usamos a técnica de espectroscopia de fotocorrelação para investigar as
propriedades dinâmicas de filmes livremente suspensos nas proximidades da transição
esmética-A - cristal-B. Observamos que os dados experimentais indicam a existência de
um modo não-hidrodinâmico e medimos a dependência da taxa de relaxação com a temperatura.
Propusemos um modelo que incorpora a influência do gradiente do campo de
velocidades que reproduz qualitativamente as observações experimentais.
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(Endo)fullerene functionalization : from material science to biomedical applications / Fonctionnalisation d’ (endo)fullerène : de la science des matériaux aux applications biomédicalesToth, Kalman 25 September 2012 (has links)
Nous avons synthétisé différentes dyades donneurs-accepteurs (D-A) π-conjuguées à base de fullerène pour des applications photovoltaïques dans lesquelles les unités D étaient soit des oligophenylenevinylenes (OPV) soit des oligophenyleneethynylene (OPE) et les unités A étaient le C60 ou un endofullerène du type Y3N@C80. Il y avait une exigence supplémentaire pour nos matériaux, à savoir qu’ils devaient s’auto-organiser en phases liquides-cristallines. Pour ce faire, toutes les unités D contenaient un promoteur mésogène afin d'induire le mésomorphisme de la dyade D- et donc de contrôler la morphologie des couches minces nécessaires à l’élaboraiton des cellules photovoltaïques grâce à une organisation supramoléculaire. En dehors de cela, nous avons étudié l’influence de la nature chimique du donneur (par exemple lyophile ou amphiphile), de la longueur des oligomères et de la multiaddition sur les propriétés photophysiques et sur l'auto-assemblage. Nous avons synthétisé une dyade OPE-Y3N@C80 qui est le premier dérive mésomorphe et photosensible de ce type de métallofullerène endohédral. / We have synthesized different π-conjugated system-fullerene dyads for photovoltaic applications, where the donor units were either oligophenylenevinylene (OPV) or oligophenyleneethynylene (OPE) derivatives and for the acceptor, C60 or Y3N@C80 was used. There was an additional requirement for our materials: liquid crystallinity. All the donor units contained a mesogenic promoter in order to induce mesomorphism in the D-A dyad and to control the morphology of the prepared film through supramolecular organization. Apart from that, we investigated the effect of the chemical nature of the donor moiety (ie. lyophilic or amphiphilic), the oligomeric length and multiaddition on the photophysical properties and on the self-assembly. We have synthesized an OPE-Y3N@C80 dyad which is the first trimetallic nitride template endohedral metallofullerene derivative with mesomorphic and photoactive properties.
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Desenvolvimento e avaliação de cristais líquidos obtidos em emulsões O/A à base de oléo de andiroba e éster fosfórico / Development and evaluation of Liquid Crystals obtained in O/W emulsions based on andiroba oil and phosphoric ester.Fernanda Frota de Andrade 30 April 2008 (has links)
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.
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Estudo das mesofases líquido-cristalinas através da técnica de elipsometria de emissão / Study of liquid crystal mesophases by emission ellipsometry techniquePereira, Gustavo Gonçalves Dalkiranis 19 July 2013 (has links)
In present work we studied the processes of phase transition of five luminescent
liquid-crystals by using emission ellipsometry technique. The samples studied present
different mesophases liquid crystalline between the solid crystalline and liquid isotropic
phases. The samples were characterized by optical absorption, photoluminescence, and
emission ellipsometry technique (EE) in function of sample temperature. The EE
measurement allowed us obtain the Stokes parameters, the degree of polarization of emitted
light, and ellipticity and rotation angle of the polarization ellipse. In addition, we founded that
the degree polarization, the ellipticity, and the rotation angle of polarization ellipse of emitted
light change when the sample temperature increase. It was possible to correlate those changes
with the phase transition temperature for each sample in concordance with the literature data.
Finally, we propose empirical model to explain our results using the emission ellipsometry
technique to determine the phase transition temperature of luminescent liquid crystal systems. / Neste trabalho foram estudados processos de transição de fase de cinco cristais
líquidos luminescentes através da técnica de elipsometria de emissão. Os compostos
estudados possuem mais de uma mesofase líquido-cristalina entre o estado sólido-cristalino e
a fase líquido-isotrópica. As amostras foram caracterizadas opticamente pelas técnicas de
medidas de absorção óptica, fotoluminescência e elipsometria de emissão (EE) em função da
temperatura. A medida de EE nos permitiu obter os parâmetros de Stokes, o grau de
polarização, a elipsidade e o ângulo de rotação da luz emitida, sendo possível verificar as
mudanças no grau de polarização, na elipsidade da luz e no ângulo de rotação da elipse de
polarização da luz emitida pelas amostras com a variação da temperatura das amostras. Foi
possível correlacionar essas mudanças da luz emitida pelas amostras com as transições de fase
desses materiais e comprovadas por dados da literatura, com boa concordância. Finalmente,
propomos um modelo empírico para explicar nossos resultados e certificar a técnica EE para
determinação da temperatura de transição de fase em sistemas líquido-cristalinos
luminescentes. / Mestre em Física
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Desenvolvimento de nanodispersões de fase líquido-cristalina para a liberação cutânea da associação de complexo nitrosilo de rutênio e protoporfirina IX na terapia fotodinâmica do câncer de pele / Development of liquid-crystaline nanodispersions for topical delivery of the association of nitrosyl ruthenium complex and protoporphyrin IX in photodynamic therapy of skin cancerAline Regina Hellmann Carollo 21 June 2011 (has links)
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.
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Characterization of liquid crystals in porous materials by means of NMR of probe atoms and moleculesTallavaara, P. (Pekka) 15 May 2008 (has links)
Abstract
The present thesis describes a method for characterization of liquid crystals in confined spaces by means of NMR of probe atoms and molecules. 129Xe isotope enriched xenon gas and 13C isotope enriched methyl iodide and methane were used as probes. Behavior of solutes and liquid crystals confined to porous materials was investigated using 129Xe and 13C NMR spectroscopy.
Uniaxial nematic liquid crystals Phase 4 and ZLI 1115 were used as a medium. Controlled pore glass with well defined and known properties was used as a porous material. The behavior of liquid crystals and solutes in various different size pores, temperatures and magnetic fields at different solute concentrations was explained. The average pore diameter of the material varied from mesopores to macropores. The studied temperature range covered solid, nematic and isotropic phases of bulk liquid crystals, and the highest magnetic field was 2.5 times stronger than the lowest one used (4.70 T). The chemical shifts, intensities, and line shapes of the resonance signals from the solutes were observed to contain lots of information about the effect of confinement on the state of the liquid crystals. Especially the line shape of the 13C resonances of methyl iodide was observed to be very sensitive to the liquid crystal orientation distribution in the pores. By varying experimental conditions the relative contribution of field and the surface forces of pore walls to the orientation of liquid crystal molecules inside the pores was seen to change quite drastically. In addition, it was also observed that when the sample is cooled very rapidly, xenon atoms do not squeeze out from the freezing medium but they are occluded inside the solid lattice, and their chemical shift is very sensitive to crystal structure. Furthermore, because solutes experienced on average isotropic environment inside the smallest pores, isotropic value of the shielding tensor could be determined at exactly the same condition and temperature as anisotropic counterpart between the pore particles. Thus, for the first time in the solution state, shielding anisotropies could be determined as a function of temperature.
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Thermodynamics and Structure of Plate-Like Particle Dispersions / Thermodynamique et structure des dispersions de particules en forme de disqueDelhorme, Maxime 24 May 2012 (has links)
Beaucoup de personnes voient la chimie comme un sujet abstrait et difficile parce qu’elle concerne l’´étude d’éléments invisibles à l’oeil nu. Mais, en y réfléchissant, la chimie est partout ! Des processus chimiques se déroulent tout autour de nous et aussi en nous tous les jours : dans le corps humain où les protéines jouent un grand rôle, dans les bouteilles de shampoing, dans le dentifrice, dans le ciment utilisé pour bâtir les maisons... Cela ne devrait donc être une surprise pour personne qu’autant d’efforts soient employés dans l'étude des processus chimiques.Qu’elles sont ces espèces invisibles avec lesquelles la chimie fonctionne ? Je pense pouvoir affirmer avec peu de doutes que vous avez tous entendu parler des atomes et des molécules (qui sont un assemblage d’atomes). Atomes et molécules ne sont pas toujours des espèces neutres, c’est-`a-dire, elles peuvent porter une charge électrique (dans ce cas, les atomes sont appelés desions). Cette transformation d’une espèce chargée à une espèce neutre peut se dérouler lorsque la particule est plongée dans un solvant (comme l’eau).C’est le cas par exemple lorsque l’on met du sel dans l’eau et que des ions sont formés. Les exemples de particules qui deviennent chargées dans unsolvant sont nombreux: protéines, virus, polyélectrolytes ... Mais pourquoi cette charge électrique est elle si importante ? Comme pour les aimants, où lepôle positif attire le négatif, les espèces vont commencer à interagir selon leur charge. Parmi d’autres facteurs, tel que la forme de la particule, le rôle joué par les charges dans les processus chimiques est primordial. La physico-chimie se concentre sur la compréhension du comportement de telles petites particules (appelées particules colloïdales) lorsqu’elles sont immergées dans une solution. Néanmoins, à cette échelle, l’étude expérimentale des dispersions colloïdales n’est pas triviale. Dans ce contexte, les simulations informatiques se trouvent être très utile. Elles ont pour but, par l’emploi de modèles physiques et mathématiques, d’essayer de reproduire les résultats obtenus expérimentalement et d’accéder à des valeurs qu’aucunes autres techniques ne peuvent procurer. Elles sont donc complémentaires aux expériences. Cette thèse traite de simulations moléculaires, réalisées `a l’aide de l’algorithme de Metropolis, de particules minérales en forme de disques. Dans un premier projet, l’évolution du nombre de charges sur une particule en fonction de la concentration en sel est étudiée. Dans un second temps, l’influence de la charge portée par les particules sur la formation des phases de gels et de cristaux liquides est examinée. Un des résultats les plus marquant est la découverte de nouvelles phases de cristaux liquides qui pourraient permettre le développement de nouveaux matériaux. Enfin, la croissance de nanoparticules et leurs interactions sont étudiées dans des conditions similaires à celles rencontrées dans les pâtes de ciment. [résumé simplifié] / A considerable amount of mineral particles are found to have a plate-like shape. The work in this thesis concerns theoretical investigations, using a Monte Carlo method, of the properties of such particles in aqueous solutions. The objectives were first to create a model that could capture the essential physics of clay suspensions and also to understand the role of thermodynamics in certain chemical processes. For all investigations, the results are related to experimental studies. The acid-base behavior of clays have been studied, using the primitive model, and an excellent agreement between simulated and experimental results was found. The formation of gel phases as a function of the charge anisotropy have also been investigated. Liquid-gel and sol-gel transitions are found to occur for high and moderate charge anisotropy, respectively. These transitions were also found to be size and salt dependent. In absence of charge anisotropy, a liquid-glass transition is reported. The formation of smectic and columnar liquid crystals phases with plate-like particles has been found to be favored by a strong charge anisotropy, in opposition to what was observed for nematic phases. New liquid-crystal phases were also reported. The stability and growth of nanoplatelets is discussed. It was found that the internal Coulombic repulsion could be the cause of the limited growth of C-S-H platelets. The influence of thermodynamics on the agregation mode of such platelets was also investigated / De flesta ser nog kemi som ett abstrakt och komplicerat ämne mestadels föratt det behandlar byggstenar så små att de inte kan ses med blotta ögat. Menom man tänker på det så finns kemi överallt ! Kemiska processer sker runtomoch inuti oss oavbrutet : i våra kroppar där proteiners kemi spelar en stor roll,i produkter som schampo och tandkräm, i cement som används för att byggavåra hus etc. Det borde därför inte komma som någon stor överraskning attenormt mycket resurser läggs på att förstå olika kemiska processer.Så vad är då dessa osynliga beständsdelar som kemi handlar om? Jag trormig våga påstå att alla någon gång hört talas om atomer och molekyler(varav de senare utgörs av en grupp sammanlänkade atomer). Atomer ochmolekyler är inte alltid neutrala, d.v.s., dom kan bära en elektrisk laddning.Övergången från en neutral till en elektriskt laddad enhet kan exempelvis skenär atomer eller molekyler kommer i kontakt med ett lösningsmedel, vilketär fallet när ett salt löses upp i vatten och blir till fria joner. Fler exempelpå molekyler som blir laddade i vatten är proteiner, virus, polyelektrolyteretc. Liksom magneters positiva och negativa poler attraherar varandra, kommerden erhållna elektriska laddningen i molekyler spela en viktig roll förhur dessa interagerar. Bland många andra faktorer såsom tex partikelgeometrin,spelar laddningen en primär roll i kemiska processer. Fysikaliskkemi fokuserar på att förstå de processer som äger rum när så kallade kolloidalapartiklar interagerar i en lösning under olika förhållanden. Att utföraexperiment med partiklar i storleksordningen 1-1000 nanometer är inte trivialt.Här kommer beräkningskemin in som en kraftfullt komplement. Genomatt använda matematiska och fysikaliska modeller, så eftersträvar man attsimulera de experimentellt erhållna resultaten och samtidigt förstå de underliggandemekanismerna och drivkrafterna på en nivå som ej är möjlig pånågot annat sätt.Den här avhandlingen behandlar Monte Carlo-simuleringar av diskformademineralpartiklar. I första projektet undersöktes hur antalet laddningar på diskformad mineralpartikel varierar som funktion av pH i en saltlösning avolika koncentrationer. Därefter studerades hur denna laddningsfördelningpåverkar bildandet av geler och flytande kristallina faser. Genom dennastudie upptäcktes nya termodynamiskt stabila faser vilket kan leda till utvecklandetav nya material. Slutligen så studerades tillväxten av diskformadenanopartiklar och deras interaktioner under förhållande jämförbara med deförekommande i en cementblandning [populärvetenskaplig sammanfattning på svenska]
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Influence of mesoscopic structures on single molecule dynamics in thin smectic liquid crystal filmsSchulz, Benjamin, Täuber, Daniela, Schuster, Jörg, Baumgärtel, Thomas, von Borczyskowski, Christian 12 September 2013 (has links) (PDF)
Mesoscopic structures in liquids have an impact on the diffusion dynamics of the constituting molecules. Smectic 8CB liquid crystals on silicon wafers show the formation of mesoscopic structures on the μm scale at a film thickness of 200 nm. Depending on the kind of substrate (thermally grown or native SiOx), we observed the formation of focal conic domains (FCDs) and a new type of terraced holes, respectively. Dynamics are described via single perylene diimide tracer molecule tracking of translational diffusion and in the case of FCDs by a combination of translation and rotation detected via fluorescence correlation spectroscopy. Tailoring perylene diimide molecules such that the optical transition dipole moment follows the liquid crystal director allows mapping out FCDs and investigating the dynamics within a single FCD.
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Fonctionnalisation de matériaux moléculaires magnétiques : vers des systèmes soluble et cristaux liquidesSiretanu, Diana 02 December 2011 (has links)
Dans cette thèse, nous avons développé la synthèse de nouveaux matériaux magnétiques hybrides afin d’améliorer la mise en forme de ces systèmes. Une partie de notre travail a consisté à fonctionnaliser la partie organique de matériaux moléculaires possédant des propriétés magnétiques remarquables, par des groupes fonctionnels connus pour induire des phases cristal-liquide ou pour augmenter la solubilité. Nous avons réalisé la fonctionnalisation rationnelle (i) de molécules aimants (Single-Molecule Magnets, SMM), (ii) de systèmes à conversion de spin et (iii) à transfert d'électrons, induisant ainsi des matériaux plus solubles et des phases cristal liquide.Le Chapitre I présente trois classes importantes de complexes magnétiques: les molécules-aimants, les systèmes à conversion de spin et de transfert d'électrons. Afin d’illustrer les motivations de notre travail une étude bibliographique dédiée aux matériaux hybrides magnétiques est ensuit présentée. La fonctionnalisation rationnelle des SMM et des systèmes à conversion de spin, respectivement, vers des phases cristallines liquides ont été discutés dans le Chapitre II et III. De nouveaux complexes fonctionnalisés à base de Mn12, FeII/triazole et [FeII(LN2O2)(LN)2] ont été obtenus. La conservation des propriétés magnétiques après fonctionnalisation du ligand a été confirmée, mais malheureusement, ces nouveaux composés ne montrent pas de comportement mésomorphe en dessous de la température de décomposition. Le Chapitre IV porte sur la fonctionnalisation des complexes à transfert d'électrons. La fonctionnalisation du ligand alkyle confère une bonne solubilité à ces complexes, et le comportement commutable activé thermiquement à l’état solide a ainsi pu être transféré à des solutions diluées. / In this thesis, we tried to develop hybrid magnetic material chemistry in order to get soft systems that can be easy-processable. This work deals with functionalization of the organic part of interesting molecule-based magnetic materials by groups known to induce liquid crystal phase or to increase the solubility. We achieved the rational functionalization of molecule-based magnetic materials, like (i) Single-Molecule Magnets (SMM), (ii) Spin Crossover (SC), and (iii) Electron Transfer (ET) systems, towards more soluble systems and liquid crystal phases.Chapter I contains general information about three important classes of magnetic complexes: SMMs, SC and ET systems. In order to illustrate the motivation of our work, a bibliographic study about hybrid magnetic materials is then presented. Rational ligand functionalization of SMMs and SC systems towards liquid crystalline phases are discussed in Chapter II and III, respectively. New functionalized Mn12 complexes, FeII/triazole-based and [FeII(LN2O2)(LN)2] systems were obtained. The conservation of magnetic properties after ligand functionalization was confirmed, but unfortunately, these new compounds do not show mesomorphic behaviour below the decomposition temperature. The Chapter IV is focused on ligand functionalization of ET complexes. Alkyl functionalization of the ligand provides a good solubility to these complexes, and the thermally-induced switchable behaviour observed in solid state has been successfully transferred to dilute solutions.
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Spatial and temporal dependencies of the motion bridging effect: Investigations of an illusory motionStein, Maximilian 16 December 2019 (has links)
No description available.
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