É apresentado um estudo sobre a influência da escolha dos parâmetros constitutivos no comportamento de misturas asfálticas, estudando o comportamento do material tanto no regime linear como o regime não-linear de deformações. Foram utilizados os dados experimentais da dissertação de Brito (2006), no qual realizou ensaios de compressão diametral medindo simultaneamente deslocamentos horizontais e verticais, além de que seus ensaios contemplavam corpos-de-prova variando o índice de vazios, crucial para as análises da presente tese. Comparou-se o comportamento das misturas de Brito extraindo-se delas as compliancias de cisalhamento J(t), de compressibilidade B(t) e a curva de fluência D(t) com coeficiente de Poisson assumido como constante. Os resultados das análises no regime linear mostraram que a consideração do coeficiente de Poisson implica alteração do comportamento do material em função do índice de vazios, resultando curvas de fluência diferentes na horizontal e vertical, não condizendo com a lógica de aumento da rigidez com a queda do índice de vazios. Provou-se também que o coeficiente de Poisson é totalmente incorreto para materiais viscoelásticos e assumi-lo como constante negligencia grau de viscoelasticidade do mesmo. Na análise não- linear, as principais conclusões foram que o uso do coeficiente de Poisson pode superestimar a rigidez do material quando este está em fluência não-linear, além de que independentemente do coeficiente de Poisson, o uso da Teoria de Potencial de Trabalho de Schapery não deve ser aplicado se considerada a fase de condicionamento nos dados do ensaio de fadiga, onde foi proposto um modelo para tal consideração que apresentou resultados de previsão satisfatórios frente aos resultados experimentais. Por fim, concluiu-se que o uso do coeficiente de Poisson em misturas asfálticas deve ser abandonado, recomendando-se o uso das compliancias J(t) e B(t), pois são parâmetros constitutivos fundamentais e sem as limitações impostas pelo coeficiente de Poisson. Além disto, recomenda-se cuidado no uso da Teoria do Potencial de Trabalho, não adaptada para a fase de condicionamento do material, recomendando-se uso de modelo auxiliar para, sugerindo-se assim o modelo deduzido nesta tese para uso conjunto com a Teoria do Potencial de Trabalho. / A study on the influence of the choice of constitutive parameters on the behavior of asphalt mixtures, studying the behavior of the material both in the linear and non-linear level of strains. The experimental data from the dissertation of Brito (2006) has been used, which performed indirect tensile tests measuring both horizontal and vertical displacements. The material tested by Brito has taken into account a reasonable range of air voids, which was crucial for the analysis of this thesis. The behavior of the mixes has been compared extracting from them the shear compliances J(t), compressibility B (t) and creep compliance D (t) with Poisson's ratio assumed as constant. The analysis results in the linear level of strains has shown that the consideration of Poisson's ratio implies change in material behavior in function of the air voids, resulting different creep compliances in the horizontal and vertical, not matching the logic increasing of stiffness with the decreasing of the air voids. It was also proved that the Poisson ratio is totally incorrect for viscoelastic materials and assume it as constant neglect of degree of viscoelasticity. In nonlinear analysis, the main conclusions were that the use of Poisson's ratio may overestimate the stiffness of the material when it is in nonlinear creep, despite the use of Poisson's ratio, the Schapery’s Work Potential Theory should not be applied if considered in the conditioning phase of the fatigue test data, where a model was proposed for such consideration and the results were satisfactory prediction compared to experimental results. Finally, it was concluded that the use of Poisson's ratio in asphalt mixtures must be abandoned, recommending the use of compliances J (t) and B (t), which are fundamental constitutive parameters without the constraints imposed by the Poisson’s ratio. Moreover, caution is advised in the use of the Schapery’s Work Potential Theory, not adapted to the conditioning phase of the material, recommending the use of auxiliary model, thus suggesting the model deduced in this thesis for use in conjunction with the Schapery’s Work Potential Theory.

Em túneis, a deformação do maciço e a pressão do solo no revestimento dependem das tensões e características do maciço, das tensões do maciço, da geometria, da rigidez, do instante da colocação do revestimento. A variação das tensões no revestimento e as deformações são causadas pelo avanço da escavação e as propriedades dependentes do tempo do maciço rochoso e revestimento. O objetivo desta dissertação é apresentar um modelo numérico para a análise tridimensional de túneis em maciços rochosos no programa ANSYS. Ele constitui uma ferramenta para calcular um túnel, revestido de concreto em diferentes situações de rigidez do revestimento, processo construtivo e características do maciço. O processo de escavação e colocação do revestimento é simulado pelo método da ativação/desativação de elementos em etapas sequenciais. O maciço apresenta comportamento elástico na primeira parte, e posteriormente uma lei viscoplástica. O concreto projetado e o concreto pré-moldado do revestimento são modelados como elásticos na primeira parte, e posteriormente, como materiais viscoelásticos utilizando o modelo da cadeia de Maxwell e de Kelvin, propostos por Bazant. Ambos os modelos foram calibrados por comparação com o Código Modelo fib 2010. A simulação do túnel é realizada através da incorporação de sub-rotinas para o concreto viscoelástico no programa ANSYS. Para validar o modelo são feitas comparações dos resultados obtidos no programa ANSYS com a solução analítica, com o programa GEOMEC91 e com o Novo Método Implícito, dependendo do caso. Um estudo paramétrico em elasticidade é realizado com o código ANSYS variando alguns parâmetros relevantes. Na segunda parte, o mesmo túnel revestido é modelado com dois diferentes tipos de revestimento e os dois modelos de cadeia citados. Finalmente, é comparado o comportamento com o túnel experimental Kielder, do qual se tem dados disponíveis da instrumentação. A comparação destes dados com os resultados do programa ANSYS mostra uma aproximação muito boa. / Stabilizing underground openings such as tunnels excavated in rock mass remain a major concern of geotechnical engineers dealing with this kind of structures. In tunnels, the rock mass strain and the ground pressure on lining depend on the stress and characteristics of the rock mass as well as of the geometry, the stiffness and the moment of the lining installation. Pressure variation on lining and strain are caused by the advance of excavation and the time-dependent properties of the rock mass and lining. This dissertation describes the numerical implementation of constitutive laws in the numerical code ANSYS. It is performed a numerical simulation with 3D finite elements of a tunnel. The rock mass presents elastic behavior in the first part and then a viscoplastic law. The shotcrete and precast concrete are modeled as elastic in the first part and then viscoelastic material with the constitutive laws of the Maxwell and the Kelvin chain model, proposed by Bazant. So the characteristics of the viscoelastic concrete changes with time until the stabilization. Both chain models had to be calibrated by comparing with de fib Model Code 2010. The finite elements simulation is performed by incorporating subroutines for the viscoelastic concrete model in the ANSYS code. The method to simulate the tunnel excavations is by activating and deactivating elements in sequential steps. In the first part of the dissertation two validations are performed. The analytical solution and the deformation achieved on the stabilization in the ANSYS code are compared for the validation of an unlined tunnel. For a lined tunnel, with an elastic and viscoplastic rock mass and elastic lining, validation is performed by comparing the results of the GEOMEC91 code with the ANSYS code. The results show a very good approximation in viscoplasticity and agree perfectly in elasticity. Also a parametric study is undertaken with the ANSYS code varying some relevant parameters. In the second part, it is compared the same tunnel with the two different concrete lining and the two chain models. Finally, it is compared with the Kielder experimental tunnel, which in situ measured data is available. The comparison of this data with the results from the ANSYS code shows a very good approximation.

Les élastomères présentent une diversité d’utilisation et des caractéristiques mécaniques spécifiques (grandes déformations, comportement dissipatif, ...) qui en font une famille de matériaux très utilisés dans l’industrie. Lors de leur fonctionnement, les pièces réelles subissent des sollicitations complexes. Comprendre les phénomènes induits par la fatigue multiaxiale constitue ainsi un enjeu important dans la phase de conception industrielle. Le matériau utilisé au cours de cette étude est un polychloroprène (CR), fourni par la société Hutchinson et présent dans les poulies découpleuses. Celui-ci possède une réponse dissipative en grandes déformations. Son comportement est modélisé à partir de lois de comportements viscohyperélastiques suivant deux approches : une méthode analytique impliquant un calcul simple en un point d’un cylindre et l’autre utilisant un calcul éléments finis implémenté dans ANSYS. Une campagne expérimentale en fatigue multiaxiale est alors réalisée, en traction-torsion afin de tester l’énergie dissipée comme critère de fatigue multiaxial. Celui-ci présente des résultats intéressants. Des diagramme de Haigh ont été établis afin de mettre en évidence le phénomène de cristallisation. Des analyses post-mortem ont été menés avec un microscope électronique à balayage et expose des spécificités morphologiques liées à la sollicitation vue par le matériau. / Due to their interesting mechanical behavior (large strain, dissipative behavior ...) and their diversity, elastomers are more and more used in industry. In service conditions, rubber components are subjected to complex loadings. Therefore, understanding phenomena induced by multiaxial fatigue constitutes an important issue in the industrial conception’s step. The material used in this work is a polychloroprene rubber, provided by Huchinson society and dedicated to silent-block’s applications. This elastomer possess a dissipative component at large strains. This behavior is determined following two approaches : an analytic method, implying a simple calculation at a local point of a cylinder and a finite elements analysis implemented with ANSYS software. An experimental investigation in multiaxial fatigue is then realized to test the dissipated energy density as a multiaxial fatigue criterion. This parameter obtained interesting results. Haigh diagrams has been built to point out crystallization phenomenon. Post-mortem analyses has been carried out with a scanning electronic microscope and exposes morphological specificities related to the material’s sollicitation.

xii, 89 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Lipid membranes are a basic structural element of all cells. They provide a framework for the physical organization of the cell, act as a scaffold for numerous proteins, and serve as the host site for countless chemical reactions integral to cell function. Several key problems in membrane biophysics hinge on reliable methods for measuring membrane material properties. Properties such as rigidity, fluidity, charge density, etc., are important factors that govern membrane structure and function. As such, we need controllable, reliable, and quantitative methods of probing membrane material properties. In pursuit of such methods, we completed two related projects that, while distinct, aimed to create and apply quantitative measures of membrane material properties to current problems in biophysics. The first of these two lines of inquiry centered on the pervasive, pathogenic family of mycobacteria that is known to not only cause several diseases but also to survive prolonged periods of dehydration. We developed an experimental model system that mimics the structure of the mycobacterial envelope consisting of an immobile hydrophobic layer supporting a two-dimensionally fluid, glycolipid-rich outer monolayer. With this system, we show that glycolipid containing monolayers, in great contrast to phospholipid monolayers, survive desiccation with no loss of integrity, as assessed by both fluidity and protein binding, revealing a possible cause of mycobacterial persistence. In the second line of inquiry, we developed another general platform for probing membrane material properties that has produced the first reported observations of viscoelasticity in lipid membranes. We utilized recently developed microrheological techniques on freestanding lipid bilayer systems using high speed video particle tracking. The complex shear modulus of the bilayers was extracted at a variety of temperatures that span the liquid-ordered to disordered phase transition of the membranes. At many temperatures measured, the membranes displayed viscoelastic behavior reminiscent of a Maxwell material, namely elastic at high frequencies and viscous at low frequencies. Moreover, the viscoelastic behavior was suppressed at the critical phase transition temperature where the membranes behave as a purely viscous fluid. Surprisingly, the viscoelastic behavior was found in all of several distinct membrane compositions that were examined. / Committee in charge: Dr. Daniel Steck, Chair; Dr. Raghuveer Parthasarathy, Research Advisor; Dr. Darren Johnson; Dr. Heiner Linke; Dr. John Toner

As vigas mistas de aço e concreto têm sido muito empregadas em obras civis de pequeno e grande porte. O emprego em conjunto de vigas de aço e lajes de concreto armado visa explorar as melhores características de cada um dos elementos, gerando uma solução estrutural econômica e eficiente. Os conectores de cisalhamento, que são os dispositivos de união desses elementos, permitem a transferência do esforço cortante ao longo da estrutura. O presente trabalho trata-se de uma continuação do estudo realizado por Tamayo (2011), o qual desenvolveu um código computacional em linguagem Fortran 90, utilizando o método dos elementos finitos, que é capaz de representar estruturas de vigas mistas em análises de curta duração. A teoria da plasticidade associada com um algoritmo de retorno explícito para o concreto e aço foi empregada em um procedimento incremental iterativo. O presente trabalho visa incluir a análise de serviço no código elasto-plástico, ou seja, a consideração dos efeitos de longa duração que interferem na distribuição de tensões e deformações da estrutura. A teoria da solidificação proposta por Bazant e Prasannan (1988) foi empregada para analisar os efeitos devido à fluência do concreto. Para o cálculo da fluência empregou-se um modelo reológico baseado na cadeia de Kelvin em série. Usando conceitos da série de Dirichlet, os parâmetros desta cadeia foram obtidos através de uma aproximação por mínimos quadrados. Em conjunto com a teoria da solidificação, os modelos de fluência e retração, propostos pelo Comité Euro-International du Béton (1990), foram utilizados. O amolecimento do concreto foi adicionado ao modelo computacional. Para os conectores de cisalhamento foi testada uma nova formulação empregando uma rigidez secante. As tarefas de pré e pós processamento foram realizadas através do software GiD que auxiliou nas etapas de geração da geometria e malha de elementos finitos, confecção de arquivo de entrada, e visualização dos resultados. Exemplos testados experimentalmente foram empregados para validação do modelo numérico proposto. / Steel-concrete composite beams have been widely applied to both small and large civil works. The combined use of steel beams and reinforced concrete slabs aims to explore the best features of each one, creating an efficient structural solution with low cost. The shear connectors are the device joining the steel beam and concrete slab, allowing the transfer of shear along the structure. This work follows the research of Tamayo (2011) who developed a program in Fortran 90 language, using the finite element method, capable of representing composite beam structures in short time analyzes. The associated theory of plasticity with an explicit return algorithm for concrete and steel was used in an incremental iterative procedure. This study aims to include the service analysis into the code, which means to account for long-term effects that influence the stress and strain distribution in the structure. The solidification theory proposed by Bazant and Prasannan (1988) was used to examine the creep effects of concrete. For the creep calculation, a rheological model based on the Kelvin chain in series was employed. Using concepts of Dirichlet series, the chain parameters were obtained through a least squares approximation. Together with the solidification theory, the creep and shrinkage models proposed by the Comité Euro-International du Béton (1990) were used. The concrete softening was added to the computational model. A new formulation using secant stiffness was tested for the shear connectors modeling. The pre and post processing tasks were performed using the GiD software, which was used for geometry and finite element mesh generation, input file writing, and results viewing. Specimens tested experimentally were used for the validation of the proposed numerical model.

A caracterização das propriedades visco-elástico-plásticas dos materiais asfálticos são importantes para uma melhor compreensão do comportamento mecânico e performance de pavimentos. O módulo complexo visa caracterizar as propriedades viscoelásticas lineares do material presente no campo das pequenas deformações. O ensaio para obtenção do módulo dinâmico pode ser realizado a partir de um carregamento senoidal uniaxial de compressão com frequências que podem variar de 0,1Hz a 25Hz e com temperaturas de -10°C a 54°C. O valor absoluto do módulo complexo é conhecido como módulo dinâmico |E*|, que pode ser definido como uma relação entre a amplitude de tensão e a amplitude de deformação. Já, a defasagem entre a tensão e a deformação é conhecida como ângulo de fase, que é um indicador das propriedades viscosas do material. Esta dissertação possuiu como objetivo caracterizar as propriedades viscoelásticas das misturas asfálticas quentes e mornas comumente utilizadas no Rio Grande do Sul, utilizando um aditivo surfactante para as misturas mornas. Para tanto foram dosadas 4 misturas asfálticas com agregados basálticos e os ligantes CAP 50/70, AMP 60/85, AB8 e CAP TLA e obtidos os parâmetros de adesividade e resistência dessas misturas quentes e mornas. Para a realização do ensaio de módulo dinâmico foi realizado uma revisão bibliográfica sobre os procedimentos de ensaio e análise de dados, posteriormente, foi adotada a metodologia adequada para os ensaios. Os mesmos foram realizados utilizando uma prensa universal MTS e a análise dos dados foi realizada com o auxílio das ferramentas do Microsoft Excel. Através do estudo foi possível concluir que as misturas com ligante convencional possuem um comportamento similar entre a mistura convencional e a morna. O mesmo não ocorre nas misturas com ligante modificado, onde ocorre uma alteração tanto da fase viscosa como da elástica, sendo esse efeito mais predominante nas misturas modificadas por polímero. / The characterization of the viscoelastic-plastic properties of asphaltic materials are important for a better understanding of the pavements’ mechanical behavior and performance. The complex module aims to characterize as linear viscoelastic properties of the material present in the field of small deformations. The assay for obtaining the dynamic modulus can be performed from a compression uniaxial sinusoidal loading with frequencies ranging from 0.1Hz to 25Hz and temperatures from -10 °C to 54 °C. The absolute value of the complex modulus is known as dynamic module | E * |, which is defined as a relation between a stress amplitude and a strain amplitude. Already, a discrepancy between stress and strain is known as phase angle, which is an indicator of the viscous properties of the material. This dissertation aimed to characterize as viscoelastic properties of hot and warm asphalt mixtures commonly used in Rio Grande do Sul, using a surfactant additive for warm mixtures. In order to do so, four asphalt concrete mixes - composed with the basalt aggregates and binders CAP 50/70, AMP 60/85, AB 8 and CAP TLA – were designed. In addition, the parameters of adhesiveness and resistance to hot and warm mixtures were obtained. For a dynamic modulus test, a literature review was performed about the data analysis and test procedure, and a suitable methodology for testing was subsequently adopted. The tests were realized with an universal testing machine of MTS and the data analysis were performed by means of the Microsoft Excel tools. Through the study it was possible to conclude that mixtures with conventional binder presented similar behavior between a conventional and a warm mixture. The same does not occur in mixtures with modified binder, where a change in both the viscous and the elastic phases occurs, and this effect is more predominant in the polymer modified mixtures.

Le présent travail porte sur l’étude expérimentale, analytique et numérique du comportement mécanosorptif et viscoélastique couplé du bois. Le comportement mécanosorptif intègre notamment le phénomène hygroverrou qui se caractérise par un blocage des déformations en phase de séchage sous contrainte. Afin d’aborder cette étude, la structure, la microstructure ainsi que le comportement hydromécanique du bois sont rappelés. Parallèlement, la théorie de la viscoélasticité linéaire ainsi que les méthodes analytiques propres à la résolution de tels problèmes sont présentées. Ensuite, des essais mécanosorptifs préliminaires de caractérisation des propriétés mécaniques sont effectués sur du Sapin Blanc (Abies alba Mill.) du Massif central grâce à un dispositif expérimental approprié. La description du dispositif expérimental, du protocole utilisé ainsi que les dimensions des échantillons testés sont présentées. Des essais mécanosorptifs en relaxation et en fluage sous chargement et humidité relative variables sont également effectués. En particulier, deux essais en relaxation sous déformation imposée constante et humidité relative variable et un essai de fluage sous contrainte et humidité relative variables de façon cyclique, sont exposés. Sur la base des données issues des essais préliminaires et viscoélastiques, la déformation hygroverrou est isolée via la partition de la déformation selon des parts élastique, visqueuse et hydrique. Par la suite, un modèle analytique est proposé pour la modélisation de la déformation hygroverrou. Un modèle pseudo élastique, basé sur les lois de Hooke (en humidification) et de Hooke restreint (en séchage), est formulé en rigidité et en complaisance. Dans ce cas, plusieurs modèles rhéologiques viscoélastiques mécanosorptifs sont proposés. Ces modèles sont classés en fonction du couplage de leurs effets et du principe de partition formulés en contrainte ou en déformation. Des lois de comportement basées sur ces modèles et formulées sous forme d’équations intégrales et incrémentales adaptées à la mise en oeuvre numérique sont finalement développées. Enfin, des exemples illustratifs montrent l’équivalence des deux expressions pseudo élastiques formulées en rigidité et en complaisance ; parallèlement, une validation des modèles viscoélastiques mécanosorptifs proposés, en relaxation et en fluage, par comparaison aux résultats expérimentaux est effectuée. Ces résultats montrent l’efficacité des modèles établis ainsi que la pertinence des essais expérimentaux réalisés pour la mise en évidence et la prise en compte des comportements mécanosorptif et viscoélastique couplés. / This work focuses on experimental, analytical and numerical study of the coupled viscoelastic mechanosorptive behavior of wood under complex mechanical loading. The mechanosorptive behavior incorporates hygroverrou phenomenon, it is the deformation locking that expresses a distortion in the drying phase under stress. For this study, the structure, microstructure and hydromechanical behavior of wood are recalled. Meanwhile, the viscoelasticity linear theory’s and the analytical resolution methods of such problem are presented. Then, mechanosorptive tests are performed on white fir (Abies Alba Mill.) with appropriate experimental device. The description of the experimental device, the protocol used and the dimensions of the samples tested are shown. Moreover, mechanosorptive tests in relaxation and creep under variables load and in relative humidity are carried out. Two relaxation tests under constant imposed deformation and variable relative humidity and a test under variables stress and relative humidity cyclically are exposed. Based on data from preliminary viscoelastic and tests, the hygrolock strain is isolated according to the partition of the deformation to elastic, viscous and hydric parts. Subsequently, an analytical model is proposed for modeling the hygrolock strain. Finally, a pseudo-elastic model, based on the Hooke (humidification) and Hooke restricted laws (in drying), is formulated in rigidity and compliance. Subsequently, several viscoelastic mechanosorptive rheological models are proposed. The models are classified according to the coupling effects as well as the partition stress or strain principle. The behavior laws based on these models are formulated as integrals and incremental equations suitable for numerical implementation. Thereafter, illustrative examples have shown the equivalence of the two formulations and followed by validation of viscoelastic models mechanosorptive proposed in relaxation and creep compared with experimental results. Finally, these results demonstrate the effectiveness of established models and the quality of the proposed models on consideration of viscoelastic mechanosorptive behavior and experimental tests coupled.

abstract: Finite element simulations modeling the hydrodynamic impact loads subjected to an elastomeric coating were performed to develop an understanding of the performance and failure mechanisms of protective coatings for cavitating environments. In this work, two major accomplishments were achieved: 1) scaling laws were developed from hydrodynamic principles and numerical simulations to allow conversion of measured distributions of pressure peaks in a cavitating flow to distributions of microscopic impact loadings modeling individual bubble collapse events, and 2) a finite strain, thermo-mechanical material model for polyurea-based elastomers was developed using a logarithmic rate formulation and implemented into an explicit finite element code. Combining the distribution of microscopic impact loads and finite element modeling, a semi-quantitative predictive framework is created to calculate the energy dissipation within the coating which can further the understanding of temperature induced coating failures. The influence of coating thickness and elastomer rheology on the dissipation of impact energies experienced in cavitating flows has also been explored. The logarithmic formulation has many desired features for the polyurea constitutive model, such as objectivity, integrability, and additive decomposition compatibility. A review and discussion on the kinematics in large deformation, including a comparison between Lagrangian and Eulerian descriptions, are presented to explain the issues in building rate-dependent constitutive models in finite strains. When comparing the logarithmic rate with other conventional rates in test examples, the logarithmic rate shows a better conservation of objectivity and integrability. The modeling framework was validated by comparing predictions against temperatures measured within coatings subjected to a cavitating jet. Both the experiments and models show that the temperatures generated, even under mild flow conditions, raise the coating temperature by a significant amount, suggesting that the failure of these coatings under more aggressive flows is thermally induced. The models show that thin polyurea coatings synthesized with shorter molecular weight soft segments dissipate significantly less energy per impact and conduct heat more efficiently. This work represents an important step toward understanding thermally induced failure in elastomers subjected to cavitating flows, which provides a foundation for design and optimization of coatings with enhanced erosion resistance. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2016

Electrospinning or electrostatic fibre spinning employs electrostatic force to draw fibres from a liquid, either a polymeric solution or a polymer melt in the form of a charged jet. The jet solidifies and is deposited on a collector in the form of a non-woven fibrous mat. Electrospun fibres have diameters between several nanometres to a few microns, which is one of the main advantages of the process, as materials at the nanoscale have shown great potential in a wide range of healthcare and energy applications. The initial selection of solvents to dissolve the polymer for production of electrospun defect-free nanofibres has generally been based on experience from similar polymer-solvent systems. The selection of a solvent is important to control the fibre surface morphology that would eventually determine the field of application for the electrospun nanofibrous structures. However, little attempt has been made to study the correlation between the solubility behaviour of the polymer in different solvents and the electrospinnability of the polymer solutions. From this perspective, the first part of this thesis focused on the selection of different solvents for the production of poly (lactic acid) (PLA) nanofibres. Solution properties were measured and the electrospun nanofibrous structures were analysed in terms of morphology and nanofibre diameter. Understanding the molecular interactions between polymer and solvents enables the correct solvent selection to ensure the desired nanofibrous structure. Solubility is not the only criterion for nanofibre formation from a polymer solution. Polymer concentration is one of the main factors affecting electrospinning. For this reason, a relationship between PLA concentration and nanofibre morphology was determined by solution property measurements. A three step systematic methodology has been proposed in this thesis in order to select appropriate solvent and polymer concentration for the production of homogeneous electrospun mats made of defect-free nanofibres. This methodology was validated for PLA nanofibres, but it can be used for a wide range of polymers. It simplifies the solvent selection process and can significantly improve the trial and error approaches used at present. Despite several models for electrospinning having been proposed to predict the behaviour of the electrospun jet, there are no simple methods for a priori prediction of the final morphology of the electrospun mat from the knowledge of solution properties and electrospinning process parameters. Moreover the prediction of nanofibre diameter is still a difficulty and little research has been done on this. For these reasons, the second part of this thesis is dedicated to understanding the effect of some process parameters on the jet electric current and hence on the morphology of PLA nanofibres. The values of current measured were used to verify an equation proposed in the literature for the prediction of the final diameter. The experimental diameter of the PLA nanofibres was compared with the predicted value. In the last chapter coaxial electrospinning was employed to produce PLA nanofibres with a core shell structure for the incorporation of a model hydrophilic drug in the nanofibre core. The large surface area to volume ratio of nanofibres offers the great advantage of higher efficiency of encapsulation and better control of the release profile compared with other drug delivery systems. Even though successful encapsulation of drug and proteins have been reported, it is not clear how to verify the continuous drug distribution in the core throughout the whole length of the fibre. The solution properties of both core and shell strongly affect the outcome of the electrospinning process. For this reason, several techniques have been used to verify the formation of a core shell structure and proper encapsulation of the drug. In addition, the efficiency of drug encapsulation was evaluated and drug release studies were performed.

Le sang est un fluide complexe mis en écoulement par la pompe très peu puissante qu'est le cœur (environ 1 W), dans un réseau branché de plusieurs milliers de kilomètres de vaisseaux. Pour que cela soit réalisable, il se peut que les propriétés mécaniques du sang contribuent à l'entretien de l'écoulement. Malgré le nombre important d'études sur la rhéologie du sang, sa viscoélasticité n'a jamais été caractérisée en cisaillement simple. Le rôle physiologique du caillot est, lui, d'éviter un épanchement excessif de sang en présence d'une brèche vasculaire. Une de ses fonctions principales est donc de résister aux contraintes générées par l'écoulement sanguin, c'est-à-dire d'avoir une résistance mécanique appropriée. Que ce soit pour la caractérisation mécanique du sang ou du caillot, le principal verrou est l'absence de méthode de mesure adaptée à un matériau peu consistant, et dont les propriétés mécaniques sont en évolution rapide. Il est donc nécessaire de produire une méthode de mesure adéquate, couplée à un système de mesure assez sensible. Dans ce travail, nous présentons la méthode de rhéométrie que nous avons développée dans ce but, baptisée Optimal Fourier Rheometry (OFR). Cette technique a été validée avec succès sur différents matériaux modèles de plus en plus complexes : une huile newtonienne, une gomme viscoélastique (PDMS), une suspension de micelles vermiformes (CpCl Nasal) et enfin un alginate dentaire tout au long de sa gélification. Nous montrons ainsi que l'OFR est une technique de mesure fonctionnelle, fiable et optimale temporellement. Elle permet le suivi de grandeurs mécaniques dont le temps caractéristique de mutation est très inférieur à la minute. En raison de la sédimentation des globules rouges, le sang est un fluide évoluant dans le temps. Par conséquent l'OFR est bien adaptée pour la mesure de ses propriétés viscoélastiques. Pour nous affranchir de la variabilité très importante du sang de témoins, nous avons balayé de façon systématique la concentration en les composants sanguins les plus abondants sur des suspensions de globules rouges lavés. De façon a priori surprenante, nous montrons qu'en présence de fibrinogène, le sang présente une élasticité importante, du même ordre de grandeur, voire plus grande que sa viscosité. Cette élasticité augmente avec la concentration en fibrinogène et l'hématocrite et provient du réseau percolé de globules rouges agrégés de dimension fractale 2.08 qui existe dans la suspension lorsqu'elle est peu cisaillée. L'OFR a également été appliquée au suivi de la coagulation activée par voie intrinsèque et extrinsèque. Cela a permis de montrer que le procédé d'activation n'avait d'effet que sur la cinétique de la réaction, mais que cela ne changeait pas les étapes mécaniques observées. L'OFR permet grâce à sa résolution fréquentielle élevée et son temps de mesure minimal, d'affirmer que le processus de coagulation du sang n'est pas une transition sol-gel. / Blood is a complex fluid set into flow by the heart, which is a very low power pump (approximately 1 W), in a connected network consisting of several thousand kilometers of vessels. To do so, it seems reasonable that the mechanical properties of blood contribute to the maintenance of the flow. In spite of the important number of studies on blood rheology, the viscoelasticity of blood has never been characterized in simple shear. The physiological role of the blood clot is to avoid an excessive effusion of blood in the presence of a vascular breach. Thus, it has to resist to the stress induced by the blood flow. So, one of its essential functions is this mechanical resistance. Whether it is for the mechanical characterization of the blood or the clot, the main obstacle is the absence of viscoelasticity measurement techniques adapted to a low viscosity material evolving rapidly in time. So, it is necessary to provide an adapted measurement method, coupled with a sensitive enough measurement. In this work, we present the new rheometry method we developed, named Optimal Fourier Rheometry (OFR) as it is optimal both in duration and signal to noise ratio This method was successfully validated on materials of increasing complexity: a Newtonian oil, a viscoelastic gum (PDMS), a suspension of wormlike micelles (CpCl Nasal) and a dental alginate during its gelation. Because of the sedimentation of red blood cells, the mechanical properties of blood are evolving in time. Consequently the use of the OFR is well suited for the measurement of its viscoelastic properties. A systematic scanning of the concentrations in the most abundant blood components added to washed blood allowed to highlight the most important parameters. Our results show that blood has a surprisingly large elasticity, which is of the same order of magnitude as the viscosity of the material. This elasticity increases with fibrinogen concentration and hematocrit. When these two parameters are in the physiological range, a percolated network of aggregated red blood cells exists in the suspension of fractal dimension 2.08. The, OFR was applied to the monitoring of blood clot formation. The activation by intrinsic and extrinsic pathway was used on whole blood. It showed that the process of activation affects only the kinetics of the reaction, but does not change the observed mechanical s. Due to its high frequency resolution and minimal measurement time, OFR shows that coagulation is not a gelation process.