Techn. Hochsch., Diss., 2000--Aachen.

Techn. Universiẗat, Diss., 2003--Darmstadt.

Techn. Hochsch., Diss., 2002--Aachen.

University, Diss., 2001--Frankfurt (Main). / Zsfassung in dt. und engl. Sprache.

University, Diss., 2003--Kassel.

The use of the radioisotope 14C in polymer chemistry has been reviewed, showing how it has been used to investigate the mechanistic aspects of free radical polymerizations, and the use of polymers in other scientific disciplines such as environmental, physical, chemical and medical sciences. An overview of the application of fluorescent spectroscopy to polymer chemistry is also reported. It covers the fundamentals of fluorescence chemistry, its application and the potential problems of the use of fluorescent labels in polymer chemistry. The application of radioisotopes to atom transfer radical polymerisation (ATRP) to investigate the fate of initiators used in the ATRP of 2-hydroxypropyl methacrylate (2- HPMA) is also reported. By using 14C radiolabelled initiators, radio thin layer chromatography (Radio TLC) and the liquid scintillation counting of fractions, collected from gel permeation chromatography (GPC), the fate of the initiating species where monitored during the polymerization of samples of 14C poly(2-HPMA), with degrees of polymerization of 10, 25 and 50 was assessed. GPC and Radio TLC, data showed that there was an under-utilisation of the initiator, 16% clearly observable at high monomer conversion (>97%), which could result in the initiation of new chains at monomer conversions of >90% and as late as 300 minutes after the polymerisation had started. These results contradict ATRP theory which states all initiator is consumed immediately at the commencement of the polymerization. 14C poly(2-HPMA) was also used to determine the efficiencies of the polymer purification methods, flash chromatography and precipitation. Although repeated precipitation increased fractionation, it was shown to be superior to flash chromatography in removing residual unreacted or terminated initiator. Finally, the possible effects of fluorescent labels on adsorption of low molecular weight 14C poly(DEAEMA) onto real surfaces (filter paper, photo graphic paper and hair) from aqueous solutions at pH=2 were investigated. Three low molecular weight samples of 14C poly(DEAEMA) were prepared by ATRP using 14C labelled initiators synthesized from alcohols of increasing hydrophobicity i.e. methyl, benzyl and 9-hydroxyfluorene (fluorescent label). The levels of adsorption were determined using phosphor imaging, oxidation of organic samples and liquid scintillation counting. Results indicated that differences in the chemistry of the polymer end groups can affect adsorption of the 14C poly(DEAEMA) and polymer assembly at the air/water interface. There was greater adsorption of polymers with a fluorescent end group. The increasing deposition was attributed to the increasing hydrophobicity of the polymer end group. Moreover, the controlled placement of one fluorescent label per polymer chain can influence the polymer’s properties, prompting the question, is the use of fluorescent groups to assess polymer behaviour and properties viable?

Les alliages Al-Cu-Li sont particulièrement attractifs pour les applications aéronautiques du fait de leur faible densité, haute limite d'élasticité et bonne ténacité. Ils reçoivent une attention particulièrement importante actuellement, depuis le développement de la troisième génération qui contient des concentrations relativement élevées pour le cuivre et relativement basses pour le Li. Ces nouveaux alliages sont caractérisés par une dureté élevée, une bonne résistance à la fatigue et une bonne stabilité thermique. La phase principale de durcissement est la phase T1 – Al2CuLi qui se présente sous la forme de plaquettes d'environ 1 nm d'épaisseur et 50 nm de diamètre, situées sur les plans {111} de la matrice avec une structure hexagonale. La germination efficace de cette phase durcissante entre en compétition avec d'autres précipités des sous-systèmes constituant ces alliages (comme Al-Cu et Al-Li), et nécessite des conditions particulières, en particulier la présence de dislocations (introduites par pré-déformation) et d'éléments d'alliage mineurs (Mg, Ag, Zn). Bien qu'il soit connu depuis longtemps que l'addition de ces éléments favorise la cinétique de précipitation dans ces alliages et le durcissement associé, leurs mécanismes d'action sont encore très mal compris.Dans ce contexte, l'objectif de la thèse est d'évaluer systématiquement l'effet des additions mineures de Mg, Ag et Zn sur la germination, la cinétique de précipitation et le durcissement correspondant. La caractérisation détaillée de la microstructure est utilisée pour comprendre les mécanismes de modification de la microstructure par les éléments mineurs. Les mesures de la diffusion des rayons X à petits angles et la DSC fournissent respectivement la cinétique de précipitation et la séquence de formation des phases. La microscopie électronique en transmission, utilisée en mode conventionnel, en résolution atomique et en mode de cartographie chimique met en évidence la structure et la distribution spatiale des phases. La dureté donne accès au durcissement. Des matériaux à gradient de concentration ont été élaborés et caractérisés pour évaluer l'effet de la concentration des alliages sur la précipitation et le durcissement.Les résultats mettent en évidence que le Mg est l'élément le plus efficace pour accélérer la cinétique de précipitation et de durcissement. L'addition d'Ag et de Zn augmente également la cinétique de précipitation mais dans une moindre mesure. L'addition de Mg change la séquence de précipitation tout au long de la séquence de vieillissement. La différence principale liée à la présence de Mg pour les premiers stades de traitement thermique est observée par rapport à la précipitation sur les dislocations. Dans les alliages qui contiennent du Mg, les dislocations sont décorées par des phases précurseur contenant de Cu et Mg. Par contre dans les alliages sans Mg celles-ci sont associés à des zones GP qui évoluent ensuite en précipités θ'. Cette différence est attribuée à la germination favorable de T1 sur les phases précurseur de Cu/Mg dans les alliages contenant du Mg, et par la saturation des sites de germination hétérogène par θ' dans les alliages sans Mg.L'augmentation de dureté associée à l'addition d'Ag et Zn est attribuée à une fraction volumique plus élevé de la phase T1. Ag est ségrège à l'interface entre T1 et la matrice et Zn est incorporé dans la structure de T1. Ces résultats suggèrent que les additions de Zn et Ag stimulent la formation de T1.L'influence de la concentration en éléments d'addition mineurs a été caractérisée par une approche résolue en temps et en espace, sur les matériaux contenant un gradient en composition. Cela révèle que l'effet de l'addition de Mg sur la précipitation se produit à une valeur seuil de ~0.1% en poids, suggérant que cela est la concentration nécessaire pour germer des phases précurseur sur les dislocations dans les premiers stades de la précipitation. / Al-Cu-Li alloys are very attractive for aerospace applications alloys due to their low density, high modulus and high strength. They are experiencing a strong interest since the so-called 3rd generation alloys, with relatively high Cu and low Li content, have been developed with high toughness, fatigue resistance and thermal stability. The main precipitating phase in these alloys is the T1-phase which precipitates on {111}Al-planes with a hexagonal structure. It is known that obtaining a fine dispersion of T1, and hence a high strength requires the presence of dislocations as nucleation sites. In addition, commercial Al-Cu-Li alloys contain several minor alloying elements such as Mg, Ag and Zn, which help reaching the desired properties. Although the effect of these minor additions on precipitation of T1 has been characterized, it has not been understood yet.In this context the aim of this thesis is to systematically investigate the effect of minor additions of Mg, Ag and Zn on precipitation nucleation, precipitation kinetics and related strengthening, and to use a detailed characterization of the microstructure to understand the mechanisms by which the modifications induced by these minor additions take place. In-situ Small-Angle X-ray Scattering and Differential Scanning Calorimetry provide the precipitation kinetics and sequence, respectively. Transmission Electron Microscopy, both in conventional mode, atomically-resolved and in chemical mapping mode, reveals the structure and distribution of phases. Hardness gives access to the strengthening. Compositionally gradient materials are fabricated and characterized to evaluate the effect of alloy composition on precipitation and strengthening.The results reveal that Mg is most effective in order to enhance precipitation kinetics and hardening. Additional Ag and Zn further enhance precipitation kinetics but to a lower extent. The addition of Mg changes the precipitation sequence at all times of ageing. The main differences in early aging conditions are observed with respect to precipitation on dislocations. In Mg-containing alloys, dislocations are decorated by Cu-Mg precursor phases, whereas dislocations in Mg-free alloys are mainly associated to GP-zones which evolve subsequently into θ'-phase. In fully precipitated conditions the microstructure of Mg-containing alloys is dominated by the T1 phase, whereas that of Mg-free alloys is dominated by the θ'-phase. This difference is attributed to the favourable nucleation of T1 on Mg-Cu precursor phases in the Mg-containing alloys, and to the consumption of T1-heterogeneous nucleation sites by the θ'-phase in the Mg-free alloys.The increase of hardness associated to the addition of Ag and Zn is associated to a higher volume fraction of the T1-phase. Ag was found to segregate at the T1/matrix interface and Zn was incorporated into the T1-phase, so that it is assumed that their additions stimulate the formation of T1.The influence of the concentration of the minor solute additions has been characterised by combined space and time-resolved experiments on compositionally gradient materials. It reveals that the effect of an Mg addition on precipitation occurs at a threshold level of ~0.1wt%, suggesting that this concentration is that necessary to form the precursor phase at the dislocations during early ageing.

Esta pesquisa analisa a história dos modelos atômicos no início do século XX a partir das contribuições de Joseph John Thomson, Hantaro Nagaoka, Ernest Rutherford, John William Nicholson e Niels Bohr e seus contemporâneos, enfatizando as explicações desde a Física Clássica até a introdução da Teoria Quântica. A tese apresenta uma introdução e oito capítulos. O primeiro capítulo procura dar conta do “estado da arte” antes da proposição dos modelos discutidos. Neste capítulo enfatizamos questões que se localizam no campo da ciência clássica, sem mergulhar no campo da teoria quântica nascente. Na continuidade, apresentamos seis capítulos, cronologicamente organizados com uma breve biografia de cada um dos cientistas mencionados e o detalhamento das idéias e dos episódios científicos que levaram às publicações que apresentaram seus modelos pela primeira vez. A publicação dos modelos de átomo quantizados teve grande impacto e suscitou muitos debates, o que nos levou a produzir o capítulo sete tratando especificamente desses embates. Para concluir no capítulo oito apresentamos algumas considerações sobre a integração das diversas trilhas investigativas que levam à publicação dos modelos atômicos discutidos; ao trabalho nas fronteiras de campos investigativos diversos; à intrincada dinâmica de poder entre campos, cientistas e publicações; e à afirmação de novos campos. / The present research examines the history of atomic models in the early twentieth century dealing with the contributions of Joseph John Thomson, Hantaro Nagaoka, Ernest Rutherford, John William Nicholson and Niels Bohr and his contemporaries. It emphasizes the explanations from the classical physics till the introduction of the Quantum Theory. This thesis presents an introduction and eight chapters. Chapter 1 presents the investigations which took place before the proposition of the models pointed out in the first paragraph. This chapter emphasizes the classical science, without diving into the quantum explanations. The next six chapters present a chronological sequence of biographies, ideas and publications and discuss the atomic models proposed by the quoted scientists. The publication of the papers on the quantized atom models had great impact and caused many debates, which led us to produce a specific chapter dealing with such subject. . In conclusion, the chapter eight presents some considerations about the integration of the investigative trails that led to the publication of the atomic models discussed, the work on investigative borders fields, the intricate dynamics of power between fields, scientists and publications, and the assertion of new fields.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A possibilidade da existência de átomos de hidrogênio estáveis em dimensões superiores a três é abordada. O problema da dimensionalidade é visto como um problema de Física, no qual relacionam-se algumas leis físicas com a dimensão espacial. A base da análise deste trabalho faz uso das equações de Schrödinger (não relativística) e de Dirac (relativística). Nos dois casos, utiliza-se a generalização tanto do setor cinemático bem como o setor de interação coulombiana para variar o parâmetro topológico dimensão. Para o caso não relativístico, os auto-valores de energia e as auto-funções são obtidas através do método numérico de Numerov. Embora existam soluções em espaços com dimensões superiores, os resultados obtidos no presente trabalho indicam que a natureza deve, de alguma maneira, se manifestar em um espaço tridimensional. / The question of whether hydrogen atoms can exist or not in at spaces with a number of dimensions D greater than 3 is revisited. The dimensionality problem is taken as physical one, which physics laws are related to the space dimension. The main framework of the analysis through out this tesis are the Schrödinger Equation (non relativistic) and the Dirac Equation (relativistic). Both cases use the kinematic and Coulombian interaction sectors generalized in order to vary the topological paramenter dimension. For the non relativistic case, eigenvalues of energy and eigenfunctions are evaluated using the Numerov numerical method. Although there are solutions in higher dimensions, the results obtained in this tesis indicate that nature should somehow prefer a tridimensional space.

No description available.