Current advanced engineering composites suffer from high-cost of manufacturing as well as design and processing weaknesses. On the other hand, nature produces high-performance composites under benign conditions using simple constituents. Hence, it seems that imitating nature constitutes the future of material science. This thesis attempts to answer some of the basic questions concerning the formation of biological fibrous composites. Microstructural studies of these materials have revealed that they exhibit a common architecture known as twisted plywood. This architecture results from the passage of the matrix into a cholesteric liquid crystalline phase during the development of the composite. The main objectives of this work are: to develop a mathematical model based on the well-established liquid crystalline theory of Landau-de Gennes, to describe the formation process of the twisted plywood architecture; to solve the set of governing partial differential equations, to use the theoretical and computational results obtained to provide a picture of the structure evolution and its kinetics.

This thesis reports results on the investigation of the thermodynamics and kinetics of adsorption of bovine serum albumin (BSA) on a platinum electrode at pH 7.4 in a wide temperature range using the electrochemical techniques of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential capacitance (DC). / The adsorption of BSA at anodic potentials has been found to be a competitive process occurring in parallel with platinum oxide formation. It has been found that the adsorption charge is directly proportional to the amount of protein adsorbed. With the increase in temperature, the maximum amount of adsorbed BSA (saturated surface concentration) also increases. This dependence has been found to be linear. It has also been shown that the adsorption process is dependent on the electrode surface charge.

Two nearly monodisperse polybutadienes (PBd) having different molecular weights were used to study nonlinear viscoelastic behavior using a sliding plate rheometer incorporating shear and normal stress transducers. / Comparison of data for the shear stress growth function at the start-up of steady simple shear with predictions of the Wagner model was used to estimate the time-dependency of wall slip. Both the time-dependent slip velocity and the steady-state values were found to depend on molecular weight, thus supporting the hypothesis that "slip" actually involves a shear-induced disentanglement between molecules strongly adsorbed at the wall and those in the bulk. The critical shear stress for the onset of slip was about 230kPa for both PBds, suggesting that the critical stress is independent of molecular weight and related to the plateau modulus. Slip behavior on steel and glass substrates was quite similar. Rubber-like high-molecular-weight polybutadiene exhibited well-defined, steady, normal stresses at moderate shear rates, while molten polystyrene exhibited a steady normal stress up to much higher shear rates. / Step strain data were used to determine the time and strain dependency of the nonlinear relaxation modulus. Time-strain factorability was observed, and the damping function was determined. For the moderately entangled PBd2 the experimentally determined damping function agreed with the predictions of the Doi-Edwards constitutive model and thus the Lodge-Meissner relationship. The higher molecular weight PBd3 exhibited strong wall slip.

The processability of a resin in film blowing is strongly influenced by its flow behavior in extension. In this study, the suitability of the Sentmanat Extensional Rheometer (SER) and of a novel tester for polyethylene film resins was evaluated. The SER, which subjects the resin to simple extension, is simple and fast to use, requires a small quantity of sample and gives reliable data that can be used to detect differences in molecular weight, molecular weight distribution and levels of long-chain branching. The data are also related to the stability of the bubble in film blowing. The tester, on the other hand, is a simple device that generates biaxial extension by inflating a sheet into a bubble. The resulting pressure traces from this empirical test were found capable of differentiating resins on the basis of their flow in biaxial extension.

A new methodology is proposed to solve the runner balancing problem. The proposed methodology avoids problems associated with the traditional approach. The issues associated with runner balancing and the effects of design variables and processing conditions are evaluated. A general methodology for the robust optimization of a practical industrial problem is also developed. The runner balancing problem is optimized employing deterministic and robust schemes and the results were compared and analyzed. This provided insight into robust runner system design. Finally, an existing constrained genetic algorithm, the superiority of feasible points method is modified to include infeasible solutions in the search, based on their distance from the current best feasible point. The revised and standard algorithms are tested on a series of constrained optimization problems, including the runner balancing problem and results are analyzed and interpreted.

Lower members of the glyme family CH3-(-O-CH2-CH2-)n O-CH3 are refractory to the usual biological and physicochemical treatments, do not get retained on biofilters and are hardly sorbed to activated sludge or carbon. An alternate form of elimination is hence to be devised. TiO 2 particles have been utilized in the photocatalytic degradation of organic compounds often found in contaminated waste streams. When they are exposed to UV light, an electron is excited from the TiO2 valence band into the conduction band. The photogenerated electron vacancy ("hole") can initiate the oxidation of the organic, while the photogenerated electron must be removed from the particle by transfer to a suitable electron acceptor (scavenger). / The photocatalytic oxidation of triglyme in an aqueous suspension of TiO2 has been studied, proving the concept to be feasible. Characterization of the light distribution in the reactor has been carried out and related to the influence of catalyst load. The rate of the reaction was considerably enhanced by introducing Cu2+ as co-catalyst and by controlling the pH, with the existence of an optimum co-catalyst concentration ([triglyme]/[Cu 2+] = 2) and an optimum pH at 3.5. The influence of both parameters is explained and the pathway of the interfacial charge-transfer reaction is proven to be of the Fenton type (indirect oxidation through activation of water) and not of the Photo-Kolbe type (direct attack of the holes).

Supercritical carbon dioxide (SC-CO2) is used as a physical blowing agent in the manufacture of plastic foam and as a plasticizer to reduce melt viscosity during processing. Pressure is also an important variable for processing, and the combined effects of dissolved SC-CO 2 and pressure on rheological properties must be known to achieve optimum processing conditions. However, until recently there was no method to measure these effects accurately. A high-pressure sliding plate rheometer in which the shear rate, temperature, pressure, and CO2 concentration are uniform, was used in the present study. The effects of CO2 and pressure on the viscosity, stress growth function, and creep compliance of a high density polyethylene (HDPE) were determined. To separate the effects of pressure and CO2, samples were first pressurized without CO 2, and then pressurized and saturated with CO2. It was possible to use shift factors for pressure and CO2 concentration to obtain a master curve. For the purpose of comparison, the effect of nitrogen on the viscosity is also determine. Another important concern in plastics processing is molecular structure, which has a strong effect on melt flow properties. The effects of long- and short-chain branching and side groups on the pressure sensitivity of viscosity were also determined in this project.

This thesis is focused on the study of material transformations from the disordered state to the lamellar-ordered/smectic-A liquid crystalline state via multi-scale multi-transport modeling and simulation. This approach utilizes a high-order Landau-de Gennes phenomenological model able to bridge the gap between experimentally observed macro-scale phenomena and the nano-scale growth and structure inherent to liquid crystalline ordering. A unique feature of this simulation-based thesis is the direct verification of predictions with past experimental observations. In this context, the main contributions of this thesis work focuses on three experimental systems: free growth of an isolated domain, defect/texture formation, and the evolution of texture/defect interactions as the system approaches equilibrium. / Simulation studies of free growth were first performed under conditions of deep undercooling, where non-isothermal effects can be neglected. The growth/shape kinetic evolution of initially textured and homogeneous spherulites growing into an unstable isotropic matrix phase was found, elucidating nano-scale morphology/texture processes and growth instabilities inaccessible experimentally. Undulation instabilities in growing smectic-A spherulites discovered in this work shed light on a possible mechanism for the formation of experimentally observed anisotropic "batonnet" morphologies and two-dimension focal conic defect structures. Recent experimental observations of growth kinetic phenomena of meta-stable nematic pre-ordering was studied, showing that the high-order model both predicts this phenomenon and explains the underlying mechanisms for experimentally determined morphological trends. A non-isothermal extension to the high-order model is derived and applied to study free growth under shallow undercooling conditions, where latent heat and anisotropic thermal diffusion are non-negligible. Growth laws, agreeing with experimental observations, are determined and novel diffusional/diffusionless growth kinetics found. / The effects of surfaces, focusing on the experimentally/industrially prevalent thin-film geometry, were studied using a de Gennes surface model allowing for energetic self-selection. Layer transitions and defect-mediated surface-enhanced growth phenomena were studied and used to simulate equilibrium defect core structure (of the smectic-A elementary edge dislocation), inaccessible via previous theory and experiment. / Finally, the last stages of phase transformation, texture formation and coarsening, are studied. The obtained simulation results are compared directly to relevant experimental data of a system with the same symmetries, self-assembled cylindrical block copolymer films. Multi-body defect interactions are studied and both compared to experimental macro-scale results and analyzed at the nano-scale, as is resolved by the simulations. The formation, structure, and complex interactions of "giant" split-core edge dislocations, composite structures composed of both orientational and translational defects, are presented and validated by experimental observations of this phenomena. / The models, computational techniques, and predictions developed in this thesis work provide a substantial basis on which to further develop the computational material science of anisotropic soft matter. / Cette thèse se concentre sur l'étude de la transformation des matériaux d'un état isotrope à une phase cristalline liquide ordonnée lamellaire de type smectique A par l'entremise de modélisations et de simulations de multi-échelles. Cette approche s'appuie sur le modèle phénoménologique de Landau-de Gennes qui est capable de faire le lien entre les observations expérimentales de phénomènes macroscopiques et la croissance nanoscopique associé à la structure inhérente d'un cristal liquide. L'un des attraits principaux de cette thèse basée sur les simulations provient du fait qu'elle vérifie directement des données expérimentales observées par le passé. Dans la même optique, les apports majeurs de ce travail de thèse se répartissent en trois principaux systèmes expérimentaux: la croissance libre d'un domaine isolé, la formation de texture/défauts, l'évolution de l'interaction entre les textures/défauts à mesure que le système atteint l'équilibre . fr / Les études de la croissance libre réalisé au moyen de simulations ont tout d'abord été effectuées dans des conditions où l'ordre liquide cristallin est très prononcé et dans laquelle les effets non-isothermaux peuvent être négligés. L'étude de la cinétique de croissance durant laquelle se forme des sphérulites texturés et homogènes se développant dans une matrice de isotrope instable a pu être mettre en évidence les processus de changement morphologie à une échelle nanoscopique ainsi que les instabilités de croissances, phénomènes inaccessibles sur le plan expérimental. Les ondulations instables des sphérulites de phase smectique A découvertes dans ce travail ont permis de mettre en évidence un possible mécanisme responsable des morphologies anisotropiques de type bâtonnets et des défauts de structure en deux-dimensions de type coniques focaux observés expérimentalement. Un phénomène de cinétique de croissance pré-ordonné en nématique metastable, phénomène qui a été récemment observé expérimentalement, a ensuite été étudié, démontrant qu'un modèle d'ordre supérieur à la fois prédit ce phénomène et les mécanismes sous-jacents régissant aux tendances morphologiques déterminées expérimentalement. Une extension non-isothermale au modèle d'ordre supérieur a été dérivée et employée pour l'étude de la croissance libre dans des conditions de faible congélation, où la chaleur latente et la diffusion thermique anisotropique sont non-négligeables. Les lois de croissance, en accord avec les observations expérimentales, sont déterminées et une nouvelle cinétique de croissance de diffusion et de non-diffusion est développée. fr / Les effets de surfaces, et plus particulièrement la géométrie expérimentale/industrielle prédominante des films fins, ont été étudiès à l'aide d'un modèle de surface de de-Gennes permettant une auto-sélection énergétique. Les phénomènes de transition de couches et de croissance de surface augmentée gérés par les dèfauts ont été étudiés et utilisés afin de simuler un équilibre dans la structure des défauts (les dislocations des bordures du smectique A), non-accessible via les anciennes théories et expériences. Finalement, les dernières étapes de transformation de phase, de formation de texture et d'alignement de texture ont été étudiées. Les résultats obtenus de la simulation ont été directement comparés aux données expérimentales issues d'études similaires, démontrant les mêmes symétries que des blocs cylindriques de co-polymères auto-assemblés. Les interactions entre les défauts de différents corps sont à la fois comparés aux résultats expérimentaux obtenus à une échelle macroscopique et analysés à une échelle nanoscopique, tel qu'obtenu par les simulations. La formation, la structure, et les interactions complexes entre les dislocations de bordures à noyaux divisés, structure composite formée à la fois de défauts orientationnels et translationnels, sont présents et validés par des observations expérimentales de ce phénomène. fr

Crystallization that occurs during or after a strong shear is important in polymer processing due to its strong effect on product properties and production rate. This study addresses several major gaps in our knowledge of this phenomenon by investigating shear-induced crystallization of nucleated isotactic polypropylenes by simultaneous measurement of light intensity and rheology using a sliding plate rheometer at high, uniform shear rates. An optical fiber probe was devised for the light intensity measurement. For the conditions studied, both measurements were found equally able to detect nascent crystalline structures, but light intensity is more suitable for monitoring changes during the early stages, whereas rheology is more useful for tracking the late kinetics. The relative influence of a melt-insensitive nucleating agent, molecular weight, shear rate, and strain were studied under isothermal, low-supercooling conditions following brief shearing. In contrast to that in quiescent crystallization, the nucleation pathway of nucleated polymers after strong shear was found to be governed not by the nucleating agent but by the molecular weight. The primary effect of shear was confirmed to be in inducing nucleation and is much weaker in changing growth kinetics. Shear and nucleating agent both shorten the induction time, but the effects were found not to be additive. With increasing shear rate or strain, crystallization was found to first accelerate as a result of the increase in the number of point-like nuclei, then saturate due to either slip or consumption of high-molecular weight components for the creation of nuclei, and finally accelerate again at the onset of the transition from spherulitic to highly oriented morphology. Both a critical shear rate and a critical strain are necessary to initiate this morphological transition. The product of shear rate and strain was found useful for describing the acceleration in crystallization associated with the increase / La cristallisation sous ou après un cisaillement fort est importante dans les procédés de mise en forme des polymères dus à ses effets significatifs sur les propriétés du produit et sur le taux de production. Cette étude traite de plusieurs importantes lacunes dans notre connaissance de ce phénomène en étudiant la cristallisation induite par cisaillement des polypropylènes isotactiques contenant un agent nucléant par une mesure simultanée de l'intensité lumineuse et de la rhéologie en utilisant un rhéomètre à plaques parallèles à des taux de cisaillement élevés et homogènes. Une sonde à fibres optiques a été conçue pour mesurer l'intensité lumineuse. Pour les conditions étudiées, ces deux mesures se sont avérées être aussi bien en mesure de détecter des structures cristallines naissantes, mais l'intensité lumineuse est mieux adaptée pour surveiller les changements au cours des premiers stades de la cristallisation, considérant que la rhéologie est plus utile pour en suivre les derniers stades. L'influence relative d'un agent nucléant ne réagissant pas à la fusion, le poids moléculaire, le taux et la déformation du cisaillement ont été étudiés en conditions isothermes avec faible surfusion après un cisaillement bref. Si on la compare à une cristallisation en condition statique, la voie de la germination des polymères nucléés suite à un fort cisaillement est apparue être régie non pas par l'agent nucléant, mais par le poids moléculaire. Le principal effet du cisaillement a été confirmé être présent durant la germination induite et est beaucoup plus faible en changeant la cinétique de croissance. Le cisaillement et l'agent nucléant ont à la fois réduit le temps d'induction, mais les effets se sont révélés ne pas être cumulatifs. Avec l'augmentation du taux de cisaillement ou de la déformation, la cristallisation s'est avérée tout d'abord accélérée comme une conséquence de l'augmentation du

Enantiomers are chiral molecules (i.e. they are mirror-images of each other). They have identical physical properties except for the rotation of polarized light. However their chemical properties are different when reacting with other chiral molecules. The majority of biological processes involve the reaction of two or more chiral molecules. There is therefore a strong interest coming from the pharmaceutical, food and agricultural industry for the separation of enantiomers. / Separation methods such as chromatography exist but are generally expensive and limited in scale. Stereosynthesis often has prohibitive development and operating costs. / For 10 to 15% of known enantiomeric systems, a conglomerate is formed upon crystallization (each individual crystal contains only one type of enantiomer). / Crystallization is widely used as an inexpensive separation process which takes advantage of the difference in solubility of the compounds to be separated and yields very high purities in one separation stage. There is no difference in solubility between two enantiomers but in the special case of conglomerates, a difference in crystallization rate can be used as the driving force for the separation of the enantiomers. / In this project, the effects of the important parameters governing the crystallization of asparagine (ASN) were studied in order to develop a separation method based on crystallization. ASN is an amino acid having two enantiomers (L-ASN and D-ASN) and forming a conglomerate. The effects of mixing speed, crystallization temperature, initial supersaturation and seeds (amount, type and time of addition) on the crystallization rates were studied. The crystallization temperature was shown to have a negligible effect over the range studied. Increasing initial supersaturations had a strong accelerating effect on the crystallization. The addition of L-ASN seeds increased the crystallization rate of L-ASN without affecting that of D-ASN. The corresponding statement was true for D-ASN. Larger amounts of seeds and faster mixing increased crystallization rates. Separation methods were developed and 95.8-97.7% pure enantiomers with yields of 73.1% were obtained in a cyclic process. The growth and desupersaturation rates were also modeled.