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Polylactide homopolymers with pendent carboxylic acid functional groups have been designed and synthesized to be studied as magnetite nanoparticle dispersion stabilizers. Magnetic nanoparticles are of interest for a variety of biomedical applications including magnetic field-directed drug delivery and magnetic cell separations. Small magnetite nanoparticles are desirable due to their established biocompatibility and superparamagnetic (lack of magnetic hysteresis) behavior. For in-vivo applications, it is important that the magnetic material be coated with biocompatible organic materials to afford dispersion characteristics or to further modify the surfaces of the complexes with biospecific moieties. The acid-functionalized silane endgroup was utilized as the dispersant anchor to adsorb onto magnetite nanoparticle surfaces and allowed the polylactide to extend into various solvents to impart dispersion stability. The homopolymers were complexed with magnetite nanoparticles by electrostatic adsorption of the carboxylates onto the iron oxide surfaces, and these complexes were dispersible in dichloromethane. The polylactide tailblocks extended into the dichloromethane and provided steric repulsion between the magnetite-polymer complexes. The resultant magnetite-polymer complexes were further incorporated into controlled-size nanospheres. The complexes were blended with poly(ethylene oxide-b-D,L-lactide) diblock copolymers to introduce hydrophilicity on the surface of the nanospheres with tailored functionality. Self-assembly of the PEO block to the surface of the nanosphere was established by utilizing an amine terminus on the PEO to react with FITC and noting fluorescence. / Ph. D.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis describes the first project relating to the Control Surfaces in Confined Spaces (CoSICS) project at Stellenbosch University. The aim of CoSICS project is to reduce the size of control surface actuators, and this thesis considers the aileron system of commercial aircraft such as the Airbus A320 and A330. Specifically the project aims to reduce the aileron hinge moment, as this will result in smaller actuators. Possible methods are discussed where aerodynamic forces are used to reduce the aileron hinge moment through the use of a wing-aileron-tab configuration. In order to examine the use of the configuration, first order aerodynamic modelling is performed using two-dimensional thin-aerofoil theory, which is also extended to a basic three-dimensional approximation. To determine the maximum reduction in hinge moment several optimisations are performed where only the tab chord length is varied, both tab and aileron chord lengths are varied, and finally the tab chord length and aileron span are varied. The optimisation methods used, namely the gradient-based sequential quadratic programming (SQP) and a real-encoded genetic algorithm (REGA) are discussed in detail and include general implementations which are then applied to the problem. The optimisations performed are dual-layered where optimal deflection angles are determined as well as the optimal geometry. The results of the optimisation are tested using a roll manoeuvre in a specially developed Simulink simulation environment for this purpose. The study produces results where new hinge moment values are an order of magnitude smaller than those of the old configuration, while maintaining suitable lift and rolling moment coefficients. The optimisation and simulation infrastructure developed in this thesis provides a platform for higher-fidelity models and components being developed in future work to provide higher fidelity results. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die eerste projek in die Control Surfaces in Confined Spaces-projek1 (CoSICS-projek) uitgevoer by die Universiteit Stellenbosch. Die doel van die COSICs-projek is om die grootte van beheervlak aktueerders te minimeer en hierdie tesis handel oor die aileron stelsel van kommersiële vliegtuie soos die Airbus A320 en A330. Die doel van hierdie tesisis om die skarnier draaimoment van die aileron te minimeer deur aërodinamiese kragte in te span in ’n vlerk-aileron-hulpvlak konfigurasie. Eerste-orde aërodinamiese modelle is afgelei met behulp van twee-dimensionele dunvlerkteorie en is gebruik om die konfigurasie te analiseer. ’n Eerste orde drie-dimensionele benadering is ook ontwikkel. Om die maksimum vermindering in die skarnier draaimoment te bepaal, is verskeie optimerings uitgevoer waar eers die hulpvlak se koordlengte gevarieer word, daarna beide die aileron en hulp-vlak se koordlengtes en laastens die hulp-vlak se koordlengte en wydte. Die twee optimerings metodes wat gebruik is, nl. ’n sekwensiële kwadratiese programmerings (SKP) tegniek, en ’n reële getal-geënkodeerde genetiese algoritme (RGGA), word bespreek en ontwikkel voor hulle toegepas word op die probleem. Twee-vlak optimerings word uitgevoer waar beide die optimale defleksiehoeke en die optimale geometrie bepaal word. Die resultate van die optimering word daarna getoets deur middel van ’n rol maneuver wat uitgevoer word in ’n Simulink simulasie omgewing wat daarvoor geskep is. Hierdie studie lei tot goeie resultate met skarnier draaimoment waardes ’n ordegrootte kleiner as dié van die vorige stelsel, terwyl goeie waardes van rol-moment en verheffingskrag koëffisiënte behou word. Die optimering en simulasie infrastruktuur wat hier ontwikkel word verskaf ’n platform vir meer akkurate modelle en komponente wat ontwikkel word in toekomstige projekte om meer akkurate resultate te lewer.

The quantum confined Stark effect (QCSE) and ultrafast absorption dynamics near the bandedge have been investigated in p-i-n waveguides comprising quantum confined heterostructures grown on GaAs substrates, for emission at 1.3um. The materials are; isolated InAs/InGaAs dot-in-a-well (DWELL) quantum dots (QD), bilayer InAs quantum dots and GaInNAs multiple quantum wells (MQW). The focus was to investigate these dynamics in a planar waveguide geometry, for the purpose of large scale integration in optical systems. Initial measurements of the QCSE using photocurrent measurements showed a small shift for isolated QDs whilst a significant shift of 40nm (at 1340nm) was demonstrated for bilayer dots, comparable to that of GaInNAs MWQ (30nm at 1300nm). These are comparable to InP based quaternary multiple quantum wells used in modulator devices. With the use of a broadband continuum source the isolated quantum dots exhibit both a small QCSE (15nm at 1280nm) and minimal broadening which is desirable for saturable absorbers used in monolithic modelocked semiconductor lasers (MMSL). A robust experimental set-up was developed for characterising waveguide modulators whilst the electroabsorption and electro-refraction was calculated (dn=1.5x10⠻³) using the Kramers-Kronig dispersion relation. Pump probe measurements were performed at room temperature using 250fs pulses from an optical parametric oscillator (OPO) on the three waveguide samples. For the isolated QDs ultrafast absorption recovery was recorded from 62ps (0V) to 700fs (-10V and the shortest times shown to be due to tunneling. Additionally we have shown good agreement of the temperature dependence of these dots and the pulse width durations from a modelocked semiconductor laser using the same material. Bilayer QDs are shown to exhibit ultrafast absorption recovery from 119ps (0V) to 5ps (-10V) offering potential for applications as modelocking elements. The GaInNAs multiple quantum wells show absorption recovery of 55ps (0V), however under applied reverse bias they exhibit long lived field screening transients. These results are explained qualitatively by the spatial separation of electrons and holes at heterobarrier interfaces.

Un milieu poreux ou un matériau poreux comprend deux régions interconnectées : une perméable par un gaz ou un liquide et l’autre imperméable. Beaucoup de substances naturelles comme les roches, le sol et les tissus biologiques (par exemple, os, bio-membranes) sont poreuses ainsi que les matériaux manufacturés comme les ciments et les céramiques, etc. Les matériaux poreux ont des applications technologiques importantes et nombreuses, par exemple, comme tamis moléculaires, catalyseurs ou senseurs chimiques. Il existe un nombre très important d’études en expérience et en théorie pour comprendre la structure des matériaux poreux ainsi que les propriétés des substances confinées dans ces matériaux. Dans leur travail de pionnier, Madden et Glandt ont proposé un modèle très simple pour l’adsorption de fluide dans des milieux poreux désordonnés. Dans ce modèle, on forme la matrice en prenant une configuration figée instantanément d’un système à l’équilibre (“quench” en anglais) et puis un fluide est introduit dans une telle matrice. Récemment, T. Patsahan, M. Holovko et W. Dong ont généralisé la “scaled particle theory” (SPT) aux fluides confinés et obtenu ainsi des équations d’état analytiques pour un fluide de sphère dure dans plusieurs modèles de matrice. Dans un premier temps, j’ai développé la version de la SPT pour un mélange de sphères dures additives confiné en milieu poreux. Les expressions pour les valeurs au contact de différentes fonctions de distribution ont été obtenues également. J’ai effectué aussi des simulations de Monte Carlo. Les résultats de ces simulations sont utilisés pour valider les résultats théoriques. Ensuite, j’ai étudié aussi la séparation de phase d’un mélange binaire des sphères dures non additives confiné dans un milieu poreux. Pour obtenir l’équation d’état, nous avons utilisé une théorie de perturbation en prenant un fluide de sphères dures additive comme système de référence. Les résultats donnés par cette théorie sont en bon accord avec les résultats de simulation Monte Carlo. / A porous medium or a porous material (called as frame or matrix also) usually consists of two interconnected rejoins: one permeable by a gas or a liquid, i.e., pore or void, and the other impermeable. Many natural substances such as rocks, soils, biological tissues (e.g., bio membranes, bones), and manmade materials such as cements, foams and ceramics are porous materials. Porous materials have important technological applications such as molecular sieve, catalyst, chemical sensor, etc. In recent years, there have been considerable investigations for understanding thoroughly the structure of these materials as well as the behavior of substances confined in them. Much effort (both experimental and theoretical) has been devoted to the study of porous materials. In their pioneering work, a very simple model for the fluid adsorption in random porous media was proposed by Madden and Glandt. The matrix in Madden-Glandt model is made by quenching an equilibrium system. Then, a fluid is adsorbed in such a matrix. Recently, T. Patsahan, M. Holovko and W. Dong have extended the scaled particle theory (SPT) to confined fluids and derived analytical equations of state (EOS) for a hard sphere (HS) fluid in some matrix models. In this thesis, using SPT method, I obtained the equation of state of additive hard-sphere (AHS) fluid mixtures confined in porous media. The contact values of the fluid-fluid and fluid-matrix radial distribution functions (RDF) were derived as well. The results of the contact values of the RDFs and the chemical potentials of different species were assessed against Monte Carlo simulations. Moreover, I analyzed also the fluid-fluid phase separation of non-additive hard sphere (NAHS) fluid confined in porous media. An equation of state is derived by using a perturbation theory with a multi-component fluid reference. The results of this theory are in good agreement with those obtained from semi grand canonical ensemble Monte Carlo simulations.

The photoactive component of a polymeric organic solar cell can be produced by drying a mixture consisting of a volatile solvent and non-volatile polymers. As the solvent evaporates, the polymers demix and self-assemble into microscale structures, the morphology of which plays a pivotal role in determining the efficiency of the resulting device. Thus, a detailed understanding of the physical mechanisms that drive and influence structure formation in evaporating solvent-polymer mixtures is of high scientific and industrial value. This thesis explores several problems that aim to produce novel insights into the dynamics of evaporating solvent-polymer mixtures. First, the role of compositional Marangoni instabilities in slowly evaporating binary mixtures is studied using the framework of linear stability theory. The analysis is non-trivial because evaporative mass loss naturally leads to a time-dependent base state. In the limit of slow evaporation compared to diffusion, a separation of time scales emerges in the linear stability problem, allowing asymptotic methods to be applied. In particular, an asymptotic solution to linear stability problems that have slowly evolving base states is derived. Using this solution, regions of parameter space where an oscillatory instability occurs are identified and used to formulate appropriate conditions for observing this phenomenon in future experiments. The second topic of this thesis is the use of multiphase fluid models to study the dynamics of evaporating solvent-polymer mixtures. A two-phase model is used to assess the role of compositional buoyancy and to examine the formation of a polymer-rich skin at the free surface. Then, a three-phase model is used to conduct a preliminary investigation of the link between evaporation and phase separation. Finally, this thesis explores the dynamics of a binary mixture that is confined between two horizontal walls using a diffusive phase-field model and its sharp-interface and thin-film approximations. We first determine the conditions under which a homogeneous mixture undergoes phase separation to form a metastable bilayer. We then present a novel mechanism for generating a repeating lateral sequence of alternating A-rich and B-rich domains from this bilayer.

This dissertation is a theoretical treatment of the electric field dependence of optical properties such as Quantum Confined Stark (QCS) shifts, Photoluminescence Quenching (PLQ), and Excitonic Mixing in quantum well heterostructures. The reduced spatial dimensionality in heterostructures greatly enhances these optical properties, more than in three dimensional semiconductors. Charge presence in the quantum well from doping causes the potential to bend and deviate from the ideal square well potential. A potential bending that varies as the square of distance measured from the heterostructure interfaces is derived self-consistently. This potential is used to solve the time-independent Schrodinger equation for bound state energies and wave functions within the framework of the Wentzel, Kramers, and Brillouin (WKB) approximation. The theoretical results obtained from the WKB approximation are limited to wide gap semiconductors with large split off bands such as gallium arsenide-gallium aluminum arsenide and indium gallium arsenide—indium phosphide. Quantum wells with finite confinement heights give rise to an energy dependent WKB phase. External electric and magnetic fields are incorporated into the theory for two different geometries. For electric fields applied perpendicular to the heterostructure multilayers, QCS shifts and PLQ are found to be in excellent agreement with the WKB calculations. Orthogonality between electrons and holes gives rise to interband mixing in the presence of an external electric field. On the contrary, intraband mixing between light and heavy holes is not sufficiently accounted for in the WKB approximation.

Les contraintes résiduelles, introduites lors de la fabrication des pièces mécaniques, influent sur leur durée de vie en fatigue et doivent donc être prises en compte. Ce travail vise à développer une méthode de dimensionnement rapide en fatigue oligocyclique permettant leur prise en compte, aussi bien sous chargement de traction que de compression. L’idée principale est de calculer analytiquement le cycle stabilisé uniquement au point critique de la structure à l’aide d’une méthode simplifiée en plasticité confinée. Cette dernière est basée sur une loi de localisation, qui étend les méthodes énergétiques de type Neuber au cas général multiaxial. La loi de localisation permet de relier le chargement appliqué à la structure à celui observé localement au point critique. Elle est calibrée à l’aide d’une simulation éléments finis sous chargement monotone de la structure. Pour cela, le comportement élasto-plastique du matériau est d’abord caractérisé à partir d’un essai de traction avec charges-décharges. A l’aide de ce seul essai, la loi de comportement est identifiée de manière séquentielle, en utilisant des écrouissages cinématique et isotrope à seuil. Ce seuil permet d’améliorer la prévision de la contrainte moyenne stabilisée, utilisée dans le critère de fatigue proposé. Ce dernier a été identifié sur des essais purement alterné (Rε=-1), puis validé pour des chargements de traction alternée (Rε>-1) et de compression alternée (Rε<-1). L’application de la démarche en plasticité confinée est réalisée sur des éprouvettes à double encoche présentant initialement différents états de contraintes résiduelles. L’évolution des contraintes locales sous chargement cyclique nominal de traction répétée (Rσ=0) ou de compression répétée (Rσ=-∞) est mesurée. Cette évolution est ensuite comparée aux prévisions numériques et analytiques obtenues à l’aide de la loi de comportement et de la méthode simplifiée. L’application du critère de fatigue aux données stabilisées prévues par les modèles a permis d’obtenir des durées de vie avec un conservatisme indépendant du rapport de charge et de l’état initial. Enfin, une application de la démarche complète sur des joints soudés en T est réalisée afin d’élargir le spectre d’application de la méthode. / Residual stresses are inherent to the manufacturing processes and can have a strong effect on the fatigue life of structures. Therefore, they shall be taken into account in fatigue design. In this PhD thesis, a fast design method is developed to take residual stresses into account in low cycle fatigue, either under tensile or compressive loadings. The main idea is to calculate analytically the stabilised stress-strain curve, at the critical point, by using a simplified method for confined plasticity. This method is based on a localisation law that extends energetic methods like Neuber to general multiaxial stress states. The localization law links the applied load to the local load at the critical point. It has to be identified on a finite element analysis of the structure under monotonic load. For this purpose, the elasto-plastic behaviour of the material is characterised from one single tensile test with loadings-unloadings. The behaviour law, identified sequentially, includes isotropic and kinematic hardenings with thresholds. This improves the stabilised mean stress prediction, which is used in the proposed fatigue criterion to represent the influence of the load ratio on the fatigue life. This criterion is identified on purely alternated tests (Rε=-1), and then validated under various tensile load ratios (Rε>-1) as well as compressive load ratios (Rε<-1). The methodology is validated on plate specimens with two semi-circular notches, which initially present different residual stresses states. The experimental evolution of local stresses during cyclic compressive (Rσ=-∞) and tensile (Rσ=0) repeated applied loads have been studied experimentally and compared to the numerical and analytical predictions. The same work has been achieved on the fatigue lives predictions. It shows that a slight conservatism, independent from the load ratio and the initial state, is obtained. Finally, an application of the method on T-Joints is realised to enlarge the scope of the method.

O método Umedecimento, Compactação e Secagem (UCOS) (1, 2, 3) produz, a partir de gesso e água, um material de elevada resistência mecânica: até 90 MPa na compressão. Este trabalho apresenta o estudo do comportamento mecânico deste material e como a água, a temperatura, as impurezas e a microestrutura influenciam no seu comportamento. Durante o estudo da adesão intercristalina, foi encontrada presença de água confinada e que é responsável por grande parte da resistência mecânica. Para auxiliar o estudo, foi desenvolvido outro método: Empacotamento Direto do Dihidrato (EDD). Nesta metodologia, é produzido um material com a mesma resistência, porém com algumas diferenças no comportamento mecânico diferente. Através da elevada resistência mecânica alcançada pelos métodos UCOS e EDD, as aplicações do gesso podem ser ampliadas desde que o gesso conformado por tais métodos possuam confiabilidade e segurança. Para avaliar as propriedades mecânicas, a confiabilidade e a segurança de tal material, realizou-se o estudo dos mecanismos tenacificadores e da mecânica da fratura. Os mecanismos tenacificadores estudados neste trabalho são: controle da microestrutura (aumento da superfície de ruptura), introdução de fibras poliméricas (distribuição da tensão na ponta da trinca, ramificação da ponta da trinca e contenção da abertura da trinca) e introdução de adesivo polimérico (melhora a adesão entre cristais e distribui melhor a tensão na ponta da trinca). Os resultados mostram que os compósitos de gesso reforçados com fibras poliméricas e/ou adesivo polimérico possuem elevada resistência e comportamentos mecânicos distintos para cada tipo de compósito e método de conformação. Concluímos que, com o conhecimento adquirido, é possível intervir no processamento e na microestrutura, além de poder incorporar elementos a esse material para atender às condições de uma determinada aplicação / The humidification, compaction and drying (Umedecimento, Compactação e Secagem UCOS) (1, 2, 3) method produces a high strength material from plaster and water: up to 90 MPa in compression. This work presents the study of mechanical properties of this material and how water, temperature, impurity and microstructure influence in its behavior. During the study of the intercrystalline adhesion force, we found the presence of confined water and that it accounts for great part of the strength. In order to aid the study, another method was developed: Direct Packaging of the Dihydrate (Empacotamento Direto do Dihidrato EDD). In this methodology, it produces a material with the same resistance, but with some difference in the mechanical behavior. Through the high strength reached by the UCOS and EDD methods, the plaster applications can be extended, since the set material by these methods are reliable and safe. In order to evaluate the mechanical properties, the reliability and the safety of these pieces, we performed the study of the fracture mechanics and the fracture toughening mechanisms. In this work, the studied toughening are: microstructure control (enlargement of the fracture surface), polymeric fiber reinforcement (tension distribution on the fracture tip, fracture tip deflection, and fiber bridging), and polymer adhesive reinforcement (they enhance the adhesion between crystals and better distribute the tension on the fracture tip). The results show that the plaster composites of polymeric fibers and/or polymer adhesive have high resistance, and different mechanical behaviors for each type of composite and setting method. Based on the acquired knowledge, we conclude that it is possible to interfere on the processing and on the microstructure, as well as reinforcements in this material to satisfy the needs of a specific application

Dans cette thèse, nous utilisons des outils de simulation moléculaire pour caractériser les propriétés thermodynamiques de fluides confinés dans des matrices solides nanométriques. Alors qu'à l’échelle macroscopique, les énergies libres de fluides au contact de solides sont décrites par des pressions et des tensions de surface qui sont respectivement des énergies libres volumiques et surfaciques, à l’échelle moléculaire plusieurs paramètres additionnels doivent être considérés. Parmi eux, l'énergie libre de la ligne triple séparant trois phases, la tension de ligne. Les valeurs de la tension de ligne ainsi que les méthodologies permettant de la mesurer sont débattues.Les outils de simulation moléculaire permettent d'étudier théoriquement la thermodynamique des surfaces et des lignes. Plusieurs méthodologies statistiques peuvent être mises en œuvre pour extraire les tensions de surface et de ligne à partir d’une trajectoire moléculaire simulée. Nous nous intéressons en particulier à la méthodologie mécanique, qui consiste à mesurer les contraintes relatives à l’étalement quasi-statique d’un fluide sur un solide.Dans une première partie, nous étudions les expressions microscopiques des contraintes de mouillage à une interface solide-fluide plane. Dans le cas d’un solide latéralement homogène, l'application du théorème du viriel à un film liquide infini sans considération de la région séparant les surfaces mouillées et sèches permet de mesurer les forces relatives à l'extension du film sur un solide sec. Lorsque des hétérogénéités sont présentes à la surface du solide, cette méthodologie néglige des forces concentrées dans la région de la ligne triple. La comparaison de différentes méthodologies de mesure des tensions de surface indique que les termes ainsi négligés sont potentiellement importants dans le cas d'une forte rugosité.Dans une deuxième partie, nous nous concentrons sur des solides sans hétérogénéité tangentielle. Nous développons une méthodologie de mesure de l’énergie libre d’une interface fluide-fluide confinée et de sa tension de ligne qui s’appuie sur la considération des différentes contraintes fluides. Nous simulons des fluides de Van der Waals et de l’eau en équilibre liquide-vapeur, confinés dans des solides de différentes natures. Nous montrons que le concept de tension de ligne est robuste jusqu’à des confinements de quelques diamètres moléculaires. Les valeurs de tension de ligne mesurées sont cohérentes avec différentes approches théoriques, résolvant certains résultats paradoxaux de la littérature.Dans une troisième partie, nous appliquons la méthodologie mécanique à l’étude d’un mélange liquide-gaz confiné. Nous simulons des solvants et des solutés de Van der Waals ainsi que de l’eau avec du dioxyde de carbone. Différentes adsorptions sont observées, relatives aux surfaces mais également à la ligne triple. L’énergie libre de l’interface confinée s’en trouve fortement impactée. L'effet de l’adsorption sur la tension de ligne peut être modélisé par un équivalent linéique de l’équation d’adsorption de Gibbs surfacique. / In this thesis, we use molecular simulation tools to characterize the thermodynamic properties of fluids confined in nanometric solids. While at the macroscopic scale, the free energy of fluids in contact with a solid is described by pressures and surface tensions, respectively free energies per unit volume and per unit area, at the molecular scale, additional parameters are needed. One of them is the free energy per unit length of the triple line, the line tension. Its values and the methodologies used to measure it are controversial.The thermodynamics of interfaces and lines can be theoretically studied with molecular simulation tools. To extract the surface and line tensions from a simulated molecular trajectory, various statistical methodologies are available. In particular, we here use the mechanical methodology, which consists in measuring the stresses related to the quasistatic spreading of a fluid on a solid.In the first part, we study the microscopic expression of wetting stresses at a planar solid-fuid interface. When a laterally homogeneous solid is considered, the virial theorem applied to an infinite fluid film without consideration of the limit between wet and dry surfaces provides the forces related to the film extension on a dry solid. In the case of a laterally heterogeneous solid, this methodology neglects forces that are concentrated at the triple line. By comparing the surface tensions measured with different methodologies, we show that the neglected terms may induce important errors in the case of rough surfaces.In the second part, we focus on laterally homogeneous solids. We develop a methodology to measure the free energy and the line tension of a confined fluid-fluid interface using fluid mechanical stresses. We simulate Van der Waals fluids and water in liquid-vapor equilibrium confined in different solids. The concept of line tension appears robust down to confinements of a few molecular diameters, and its value consistent with various theoretical approaches, thus solving paradoxical results from the literature.In the last part, we apply the mechanical methodology to study the equilibrium of two fluid species in confinement, one liquid and the other gaseous. We simulate Van der Waals solvents and solutes, and water with carbon dioxide. Various adsorptions at the surfaces and the triple line are observed, strongly impacting the free energy of the confined liquid-gas interface. Finally the adsorption-induced variation of the line tension can be modelled by a unidimensional equivalent of the Gibbs isotherm.