The photophysics of highly electronically excited states of a set of d0 and d10 metallated tetrapyrroles, which have different peripheral substituents and central metal atoms, macrocycle substitution patterns and macrocycle conformations, have been investigated both theoretically and experimentally. Theoretically, the energies of ground state molecular orbitals and the energies and rank in energy of the excited states have been calculated using density functional theory and time-dependent density functional theory methods. Experimentally, the steady-state absorption and fluorescence spectra have been measured. Temporal fluorescence profiles have been measured using a time correlated single photon counting system for the S1 state and a fluorescence upconversion system for the S2 state.<p> The decay mechanisms of highly electronically excited states are governed by the nonradiative S2 S1 internal conversion. The possible existence of any excited state (such as S2' or dark state) lying close to the S2 state and its participation in the nonradiative decay processes of the S2 state has been discussed. The ultrafast nonradiative decay rates of the S2 S1 internal conversion were interpreted on the basis of the energy gap law of radiationless transition theory. For magnesium tetraphenylporphyrin (MgTPP), the radiationless rates (knr)of its S2 state follows the prediction of the energy gap law for the weak coupling statistical limit case. However, the S2 S1 electronic coupling energies of the other metalloporphyrins investigated fall within the inermediate to strong coupling range. The difference of knr relative to the weak coupling limit can be rationalized by the different magnitudes of electronic coupling energies. The magnitude of electronic coupling energies is the major factor in determining the radiationless depopulation rate constants of the S2 states in metallated tetrapyrroles which have S2 S1 electronic coupling energies exceeding the weak coupling limit. In some cases, such as ZnOEP, the magnitude of Frack-Condon factor has only minor effect.<p> The photophysics of Soret-excited metallated corroles have also been investigated in this study. Primary work has shown that two metallated corroles examined have similar S2 S1 interstate electronic coupling energies to that of CdTPP and thus the radiationless decay rates of Soret-excited S2 state are also determined by the magnitude of electronic coupling energies.

The photophysics of highly electronically excited states of a set of d0 and d10 metallated tetrapyrroles, which have different peripheral substituents and central metal atoms, macrocycle substitution patterns and macrocycle conformations, have been investigated both theoretically and experimentally. Theoretically, the energies of ground state molecular orbitals and the energies and rank in energy of the excited states have been calculated using density functional theory and time-dependent density functional theory methods. Experimentally, the steady-state absorption and fluorescence spectra have been measured. Temporal fluorescence profiles have been measured using a time correlated single photon counting system for the S1 state and a fluorescence upconversion system for the S2 state.<p> The decay mechanisms of highly electronically excited states are governed by the nonradiative S2 S1 internal conversion. The possible existence of any excited state (such as S2' or dark state) lying close to the S2 state and its participation in the nonradiative decay processes of the S2 state has been discussed. The ultrafast nonradiative decay rates of the S2 S1 internal conversion were interpreted on the basis of the energy gap law of radiationless transition theory. For magnesium tetraphenylporphyrin (MgTPP), the radiationless rates (knr)of its S2 state follows the prediction of the energy gap law for the weak coupling statistical limit case. However, the S2 S1 electronic coupling energies of the other metalloporphyrins investigated fall within the inermediate to strong coupling range. The difference of knr relative to the weak coupling limit can be rationalized by the different magnitudes of electronic coupling energies. The magnitude of electronic coupling energies is the major factor in determining the radiationless depopulation rate constants of the S2 states in metallated tetrapyrroles which have S2 S1 electronic coupling energies exceeding the weak coupling limit. In some cases, such as ZnOEP, the magnitude of Frack-Condon factor has only minor effect.<p> The photophysics of Soret-excited metallated corroles have also been investigated in this study. Primary work has shown that two metallated corroles examined have similar S2 S1 interstate electronic coupling energies to that of CdTPP and thus the radiationless decay rates of Soret-excited S2 state are also determined by the magnitude of electronic coupling energies.

Cette thèse est dédiée à l’étude analytique et numérique des instabilités d’origine thermique et thermodiffusive de fluides visco-élastiques. L’objectif recherché est de contribuer à la compréhension de la dynamique qui résulte de la compétition entre plusieurs moteurs d’instabilités. En plus du caractère visco-élastique du fluide et de la présence d’un gradient de température vertical déstabilisant, d’autres sources d’instabilités viennent s’y ajouter : Le couplage "convection/écoulement de Poiseuille" d’une part, et le couplage "convection/effet Soret" inhérent aux mélanges binaires d’autre part. Deux configurations physiques sont alors considérées. La première partie de cette thèse est consacrée aux écoulements de convection mixte de type Rayleigh-Bénard-Poiseuille de fluides visco-élastiques, alors que la deuxième partie concerne l’effet de la thermodiffusion sur les instabilités de ces fluides saturant un milieu poreux. Le choix d’un milieu poreux est essentiellement motivé par la suggestion d’un protocole industriel de séparation possible des constituants d’une solution de polymères. / This thesis is dedicated to analytical and numerical study of thermal and thermodiffusive instabilities of viscoelastic fluids. The objective is to contribute to the understanding of the dynamics that results from the competition between different origins of instabilities. In addition to the viscoelastic nature of the fluid and the presence of a destabilizing vertical temperature gradient, other sources of instabilities have to be added: the coupling "convection/Poiseuille flow" on the one hand, and the coupling "convection/Soret effect" inherent to binary mixtures on the other hand. Two physical configurations are then considered. The first part of this thesis will be devoted to the Rayleigh-Bénard-Poiseuille mixed viscoelastic fluid convection, while the second part aims to identify the effect of thermodiffusion and viscoelasticity on convective instabilities in a porous medium. The choice of a porous medium in the second part is primarily motivated by the suggestion of an industrial protocol for separating the constituents of a polymer solution.

No description available.

No description available.

Dans ce travail de thèse tant théorique que numérique, on étudie les différentes instabilités pouvant se développer dans un milieu poreux saturé par un fluide viscoélastique et chauffé par le bas. La formulation mathématique des équations de ce problème repose sur la loi phénoménologique de Darcy généralisée à un fluide viscoélastique vérifiant l’approximation de Boussinesq. Ce problème admet une solution de conduction, et on trouve que deux types de structures sont susceptibles d’apparaître lorsque l’état de conduction perd sa stabilité : des structures stationnaires et des structures oscillatoires. Les seuils d’apparition de ces structures sont étudiés en fonction des paramètres adimensionnés du problème, à savoir le nombre de Rayleigh, les temps de relaxation et de retardation associés à l’élasticité du fluide. Une étude linéaire et non linéaire est donc menée. Il est intéressant de noter qu’une compétition entre les structures stationnaires et oscillatoires peut exister au voisinage d’un point appelé point de codimension 2. Une analyse non linéaire est donc menée au voisinage de ce point et est confrontée aux résultats issus des simulations numériques. Enfin, s’appuyant sur les propriétés de mélanges binaires des fluides viscoélastiques, une étude théorique est réalisée et nous montrons qu’il y a une compétition entre deux régimes : un régime où la viscoélasticité est dominante et un autre où l’aspect mélange binaire l’emporte. Ce résultat permet d’expliquer certaines observations expérimentales. / In this theoretical and numerical work, we study differents instabilities which can develop in a porous media saturated by viscoelastic fluid and heated from below. The mathematical formulation of the equations of this problem is based on phenomenological Darcy law generalized to a viscoelastic fluid verifying Boussinesq estimate. This problem admits a solution of conduction, and we find that two types of structures may appear when the conduction state loses his stability : stationary and oscillatory structures.The apparition thresholds of these thermo-convectives structures are studied and depend on the non-dimensionnalized parameters of the problem, Rayleigh number, relaxation and retardation time associated to the fluid elasticity. A linear and non linear stability is also realized. It is interesting to note that it can have a competition between stationary and oscillatory structures near a point named codimension 2 point. A linear analysis is also realized near this point and is compared to the numerical simulation results.Finally, by taking into account binary mixtures properties of the viscoelastic fluids, a theoretical study is realized and we show that there is a competition between two states : a state in which viscoelasticity is dominant and another state in which binaries properties are also dominants. This result can explain experimental observations.

O presente trabalho investiga o fenômeno termodifusivo em dispersões coloidais de nanopartículas magnéticas de óxidos de ferro em água (ferrofluidos), com a formação de dupla camada elétrica em torno das partículas. A estabilidade da partícula em solução é controlada pela concentração de íons. Ao estabelecer uma diferença de temperatura através da amostra líquida, ocorre o efeito de termodifusão (efeito Soret) das partículas e de íons em solução. Este efeito é o movimento das partículas para o lado frio ou quente do gradiente de temperatura. O acúmulo para um dos lados do gradiente de temperatura depende das características da solução. O efeito Soret de ferrofluidos em soluções ácidas e básicas é descrito a partir da determinação experimental das grandezas físicas envolvidas na difusão das partículas. O coeficiente Soret ST e o coeficiente de difusão são determinados em experimentos ópticos de lente de matéria, utilizando o aparato experimental de Varredura-Z, e de espalhamento Rayleigh forçado para termodifusão. Para investigar a resposta dos íons ao gradiente de temperatura, são realizadas medidas do potencial termoelétrico em uma célula termoelétrica, gerado a partir da difusão das cargas dispersas no líquido. O potencial superficial das partículas também é investigado experimentalmente, para descrever a interação das partículas com o campo termoelétrico. Os experimentos são realizados em função da temperatura da amostra e usados para descrever os resultados ST(T) das partículas, a partir de equações dos principais modelos teóricos. Os resultados mostram as diferenças e semelhanças do efeito Soret das nanopartículas em soluções ácidas e básicas, e que em ambos os casos a termodifusão de nanopartículas reflete o comportamento termodifusivo dos íons dispersos em solução. / This work investigates the thermal diffusion phenomena in colloidal dispersions of iron oxide magnetic nanoparticles dispersed in water (ferrofluid). The particles are stable in water due to electrical double layer around the particles, controlled by the ionic concentration. A temperature gradient throughout the ferrofluid sample causes the thermodiffusion (Soret effect) of dispersed particles and ions. This effect is the movement of particles to the cold or hot side of the temperature gradient. The particles migration for a given side depends on the characteristics of the sample. The Soret effect of ferrofluids in acidic and basic solutions is described by the experimental measurements of the physical parameters associated to particles diffusion. The Soret coefficient ST and the mass diffusion coefficient are measured in the matter lens experiment in the Z-scan experimental setup, and by the use of Thermal Diffusion Forced Rayleigh Scattering experiments. Concerning the ionic response to the temperature gradient the thermoelectric field generated by charges diffusion is measured in a thermoelectric cell. The surface potential of the particles is also measured to describe its interactions with the thermoelectric field. These experiments are made as function of the temperature of the sample and the results are applied to describe the ST(T) of particles by the use of equations from the main theoretical models. The results show differences and resemblances of the Soret effect in acidic and basic nanoparticles solutions. In both kind of solutions the thermodiffusion of nanoparticles is mainly ruled by the thermodiffusion of ions dispersed in solution.

Esta dissertação apresenta um estudo experimental sobre o transporte de massa de nanopartículas magnéticas induzido por um gradiente de temperatura, denominado termodifusão. A técnica de Varredura-Z é utilizada para gerar o aumento de temperatura na região irradiada pelo laser Gaussiano e formar o gradiente de temperatura. A sequente migração de nanopartículas é caracterizada pelo gradiente de concentração gerado no estado estacionário do fluxo de partículas, definindo o coeficiente Soret ST. O objetivo deste trabalho é verificar a variação de ST com o tamanho médio d0 das nanopartículas de ferrofluidos eletrostaticamente carregados em solução ácida. A dependência de ST com d0 surge do coeficiente de difusão de massa, explicando a dependência linear encontrada experimentalmente. Nestes materiais, a migração de nanopartículas ocorre para a região quente da amostra. Mostramos que este comportamento ocorre pela diminuição da carga superficial da nanopartícula na parte mais quente da amostra, diminuindo a repulsão eletrostática. A influência dos íons presentes na solução é obtida através da mudança na amplitude de ST com a diminuição do pH na amostra. Uma previsão teórica, baseada na eletrostática da dupla camada elétrica, concorda com estes dados considerando alta blindagem eletrostática das nanopartículas e a diminuição da carga superficial com o aumento da temperatura. / This dissertation presents an experimental study about the mass transport of magnetic nanoparticles induced by a temperature gradient, called thermodiffusion. The Z-scan technique is used to generate the temperature increasing in the region irradiated by the Gaussian laser beam and create the temperature gradient. The following nanoparticles migration is characterized by the concentration gradient of the stationary particles flux, defining the Soret coefficient ST. The aim of this work is to obtain the variation of ST with the average size d0 of electrostatically charged ferrofluid nanoparticles in acidic solution. The ST dependence with d0 comes from the mass diffusion coefficient, in agreement with the linear dependence found experimentally. In these materials the nanoparticles migration occurs to the hot region of the sample. We show that this behavior is owing to the reduction of the nanoparticle´s surface charge in the hottest region of the sample, decreasing electrostatic repulsion. The influence of the ions from solution is obtained through the change in ST amplitude with reduction of the samples pH. A theoretical prediction, based in the electrostatic of the double layer, agrees with this data considering a high screening of the nanoparticles and decreasing of the surface charge with temperature increasing.

O presente trabalho investiga o fenômeno termodifusivo em dispersões coloidais de nanopartículas magnéticas de óxidos de ferro em água (ferrofluidos), com a formação de dupla camada elétrica em torno das partículas. A estabilidade da partícula em solução é controlada pela concentração de íons. Ao estabelecer uma diferença de temperatura através da amostra líquida, ocorre o efeito de termodifusão (efeito Soret) das partículas e de íons em solução. Este efeito é o movimento das partículas para o lado frio ou quente do gradiente de temperatura. O acúmulo para um dos lados do gradiente de temperatura depende das características da solução. O efeito Soret de ferrofluidos em soluções ácidas e básicas é descrito a partir da determinação experimental das grandezas físicas envolvidas na difusão das partículas. O coeficiente Soret ST e o coeficiente de difusão são determinados em experimentos ópticos de lente de matéria, utilizando o aparato experimental de Varredura-Z, e de espalhamento Rayleigh forçado para termodifusão. Para investigar a resposta dos íons ao gradiente de temperatura, são realizadas medidas do potencial termoelétrico em uma célula termoelétrica, gerado a partir da difusão das cargas dispersas no líquido. O potencial superficial das partículas também é investigado experimentalmente, para descrever a interação das partículas com o campo termoelétrico. Os experimentos são realizados em função da temperatura da amostra e usados para descrever os resultados ST(T) das partículas, a partir de equações dos principais modelos teóricos. Os resultados mostram as diferenças e semelhanças do efeito Soret das nanopartículas em soluções ácidas e básicas, e que em ambos os casos a termodifusão de nanopartículas reflete o comportamento termodifusivo dos íons dispersos em solução. / This work investigates the thermal diffusion phenomena in colloidal dispersions of iron oxide magnetic nanoparticles dispersed in water (ferrofluid). The particles are stable in water due to electrical double layer around the particles, controlled by the ionic concentration. A temperature gradient throughout the ferrofluid sample causes the thermodiffusion (Soret effect) of dispersed particles and ions. This effect is the movement of particles to the cold or hot side of the temperature gradient. The particles migration for a given side depends on the characteristics of the sample. The Soret effect of ferrofluids in acidic and basic solutions is described by the experimental measurements of the physical parameters associated to particles diffusion. The Soret coefficient ST and the mass diffusion coefficient are measured in the matter lens experiment in the Z-scan experimental setup, and by the use of Thermal Diffusion Forced Rayleigh Scattering experiments. Concerning the ionic response to the temperature gradient the thermoelectric field generated by charges diffusion is measured in a thermoelectric cell. The surface potential of the particles is also measured to describe its interactions with the thermoelectric field. These experiments are made as function of the temperature of the sample and the results are applied to describe the ST(T) of particles by the use of equations from the main theoretical models. The results show differences and resemblances of the Soret effect in acidic and basic nanoparticles solutions. In both kind of solutions the thermodiffusion of nanoparticles is mainly ruled by the thermodiffusion of ions dispersed in solution.

Esta dissertação apresenta um estudo experimental sobre o transporte de massa de nanopartículas magnéticas induzido por um gradiente de temperatura, denominado termodifusão. A técnica de Varredura-Z é utilizada para gerar o aumento de temperatura na região irradiada pelo laser Gaussiano e formar o gradiente de temperatura. A sequente migração de nanopartículas é caracterizada pelo gradiente de concentração gerado no estado estacionário do fluxo de partículas, definindo o coeficiente Soret ST. O objetivo deste trabalho é verificar a variação de ST com o tamanho médio d0 das nanopartículas de ferrofluidos eletrostaticamente carregados em solução ácida. A dependência de ST com d0 surge do coeficiente de difusão de massa, explicando a dependência linear encontrada experimentalmente. Nestes materiais, a migração de nanopartículas ocorre para a região quente da amostra. Mostramos que este comportamento ocorre pela diminuição da carga superficial da nanopartícula na parte mais quente da amostra, diminuindo a repulsão eletrostática. A influência dos íons presentes na solução é obtida através da mudança na amplitude de ST com a diminuição do pH na amostra. Uma previsão teórica, baseada na eletrostática da dupla camada elétrica, concorda com estes dados considerando alta blindagem eletrostática das nanopartículas e a diminuição da carga superficial com o aumento da temperatura. / This dissertation presents an experimental study about the mass transport of magnetic nanoparticles induced by a temperature gradient, called thermodiffusion. The Z-scan technique is used to generate the temperature increasing in the region irradiated by the Gaussian laser beam and create the temperature gradient. The following nanoparticles migration is characterized by the concentration gradient of the stationary particles flux, defining the Soret coefficient ST. The aim of this work is to obtain the variation of ST with the average size d0 of electrostatically charged ferrofluid nanoparticles in acidic solution. The ST dependence with d0 comes from the mass diffusion coefficient, in agreement with the linear dependence found experimentally. In these materials the nanoparticles migration occurs to the hot region of the sample. We show that this behavior is owing to the reduction of the nanoparticle´s surface charge in the hottest region of the sample, decreasing electrostatic repulsion. The influence of the ions from solution is obtained through the change in ST amplitude with reduction of the samples pH. A theoretical prediction, based in the electrostatic of the double layer, agrees with this data considering a high screening of the nanoparticles and decreasing of the surface charge with temperature increasing.