In the mammalian embryo, between 3.5 and 4.5 days after fertilisation, the cells of the inner cell mass evolve from a uniform aggregate to an ordered structure with two distinct tissue layers - the primitive endoderm and epiblast. It was originally assumed that cells differentiated to form these layers in situ, but more recent evidence suggests that both cell types arise scattered throughout the inner cell mass, and it is thus proposed that the tissue layers self-organise by physical mechanisms after the specification of the two cell types. We have developed a computational model based on the subcellular element method to combine theoretical and experimental work and elucidate the mechanisms that drive this self-organisation. The subcellular element method models each cell as a cloud of infinitesimal points that interact with their nearest neighbours by local forces. Our method is built around the introduction of a tensile cortex in each cell by identifying boundary elements and using a Delaunay triangulation to define a network of forces that act within this boundary layer. Once the cortex has been established, we allow the tension in the network to vary locally at interfaces, modelling the exclusion of myosin at cell-cell interfaces and consequent reduction in tension. The model is validated by testing the simulated interfaces in cell doublets and comparing to experimental data and previous theoretical work. Furthermore, we introduce dynamic tension to model blebbing in primitive endoderm cells. We investigate the effects of cortical tension, differential interfacial tension, and blebbing on interfaces, rearrangement, and sorting. By establishing quantitative measurements of sorting we produce phase diagrams of sorting magnitude given system parameters and find that robust sorting in a 30 cell aggregate is best achieved by a combination of differential interfacial tension and blebbing.

[pt] Os processos de formação e de dissociação de hidratos são de grande interesse nas áreas ambiental e energética. Especificamente para a indústria de petróleo e gás, o hidrato aparece como um empecilho à garantia de escoamento, alavancando ainda mais a necessidade urgente de ampliar o conhecimento sobre seus fenômenos. Neste trabalho, uma nova abordagem para observar e compreender a cinética e as propriedades mecânicas de hidratos por meio da reologia interfacial é apresentada. O conhecido anel du Nouy é empregado com uma nova célula de latão projetada para permitir o necessário gerenciamento da temperatura de teste. Ciclopentano é utilizado como formador de hidrato. Com a nova geometria interfacial, diferentes temperaturas e protocolos de contato água/ciclopentano são explorados. A importância de primeiro provocar o contato do CP com cristais de gelo a fim de iniciar a formação de hidrato é de particular interesse. Assim, time sweeps são realizados em duas etapas: uma para a formação de gelo e outra para os formação de hidrato. Foi determinado que os hidratos de ciclopentano são detectados em temperaturas Tf menor ou igual a 6 graus Celsius. Uma interessante discussão a respeito do estado de metaestabilidade dos hidratos é, então, apresentada. Depois que os hidratos preenchem completamente a interface água/ciclopentano, strain sweeps são realizados para examinar a fragilidade dos filmes de hidrato, medindo os módulos interfaciais elástico e viscoso (G e G). As propriedades mecânicas desses filmes demonstraram uma forte dependência da temperatura (Tf ): o tempo de indução (tc), medido a partir do primeiro contato do ciclopentano com gelo, bem como o módulo elástico (G) e a deformação de escoamento (γy) aumentam conforme Tf é aumentada. / [en] Hydrate formation and dissociation processes are of major interest in environmental and energy fields. Specifically for the oil and gas industry, hydrate appears as an issue regarding flow assurance, pushing even more the urgent need for expanding the knowledge on hydrate phenomena. In the current work, a new approach to observe and understand the kinetics and mechanical properties of hydrates by interfacial rheology is presented. The standard du Nouy ring is employed with a novel brass cell designed to permit the necessary temperature management. Cyclopentane is used as hydrate former. With the new interfacial geometry, different temperature and water/cyclopentane contact protocols are explored. The importance of first contacting CP against ice crystals in order to initiate hydrate formation is of particular interest. Thus, time sweeps are performed in two stages: one for ice formation and another for hydrate formation. It was determined that cyclopentane hydrates only arise at temperatures Tf less than or equal to 6 celsius degree. A worthwhile discussion regarding the hydrate metastability state is then presented. After hydrates completely populate the water/cyclopentane interface, strain sweeps of the interfacial elastic and viscous moduli (G and G) are conducted to examine the fragility of the hydrate films. The mechanical properties of hydrate films demonstrated high dependence on temperature (Tf): the induction time (tc), measured from the moment when cyclopentane first contacts ice, as well as the elastic modulus (G) and the yield strain (γy) increase as Tf is increased.

This dissertation examines the motion of colloids in a temperature gradient, a non-equilibrium phenomenon also known as thermophoresis. Chapter 1 gives an introduction to the existing applications and basic concepts of thermophoresis and outlines some of the experimental and theoretical challenges that serve as a motivation for this PhD project. In Chapter 2, a general theoretical description for thermophoresis is formulated using the theory of non-equilibrium thermodynamics. The colloidal flux is split up into an interfacial single-colloid contribution and a bulk contribution, followed by a determination of transport coefficients based on Onsager’s reciprocal relations. It is further shown how the phenomenological expression of the thermophoretic flux can be recovered when the fluid is at steady-state. The results issuing from this description are then discussed and compared to other existing approaches, some of which are shown to neglect the hydrodynamic character of colloidal thermophoresis. Chapter 3 is dedicated to the validation of the introduced theoretical framework by means of computer simulations, using a simulation technique known as multi-particle collision dynamics. More specifically, the dependence of the thermophoretic force on different system parameters is examined and deviations from the theoretical prediction are explained by an advective distortion of interfacial fluid properties at the colloidal surface. Chapter 4 presents steady-state measurements of functionalised colloids in a temperature gradient, showing how the addition of molecular surface groups increases the experimental complexity of thermophoretic motion. The relaxation process behind this steady-state is also studied, to determine how the relaxation speed depends on the applied temperature gradient. In chapter 5, a general conclusion is drawn from the presented work and its implications are briefly discussed in relation to the current state of knowledge. Finally, the discussion is closed with an outlook on remaining challenges in understanding colloidal motion that could be the subject of future research.

The technology employed by human beings for the generation, storage and usage of energy is presently undergoing the fastest and most profound change since the industrial revolution. The changes in the generation and usage of energy necessitate the development of new methods of energy storage. In these systems, electrochemical energy storage will play a crucial role and to this end new electrolytes need to be explored to complement these changes. One such class of liquids is ionic liquids, a class of salts that are molten at room temperature. These liquids have a broad applicability to batteries and supercapacitors. This thesis details work where molecular dynamics simulations have been used to explore the nanostructure of ionic liquids and their mixtures with various molecular solvents at simplistic electrodes. The thesis has two broad sections. The first is covered in Chapter 3, and explores the nanostructure of ionic liquid propylene carbonate solutions, developing a framework through which these nanostructures can be understood. The section concludes that the increasing dilution of ionic liquids decreases the surface charge at which the characteristic ionic liquid oscillatory interfacial structure gives way to a different structure featuring monotonic charge decay. The behaviour of ionic liquids at interfaces is found to be correlated to ion size and type, as well as concentration. A wide divergence in the observed behaviour is shown at positive and negative electrodes due to the asymmetry of propylene carbonate. The second section, consisting of two chapters, explores the interfacial nanostructure of solvate ionic liquids using two different boundary conditions to model the electrode. This work is the first simulation of solvate ionic liquids at electrified interfaces. This section will explore the effect of electrode model on the behaviour of these ionic liquids at the electrode. Chapter 4 uses a fixed charge electrode, whereas Chapter 5 uses one with a fixed potential. The section concludes that regardless of electrode model, the idealised portrait of a solvate ionic liquid - one where the liquid behaves exactly as an aprotic ionic liquid - is not applicable. In Chapter 4's exploration of fixed charged electrodes, the formation of 2 glyme to lithium complexes contradicts the idealised portrait of the liquid. A different change is observed in Chapter 5's exploration of fixed potential electrodes, with both lithium glyme and lithium anion clusters forming at the interface. The key difference between the two studies is that lithium does not coordinate to the electrode in the fixed charge simulations, while in the fixed potential case it does. At the end of Chapter 5 the results are compared against experimental data, with the efficacy of the two models discussed. The aim of both studies is to look at the nanostructure of ionic liquids, when the symmetry between co-ion and cation repulsion - and related effects - is broken by the presence of a non ionic constituent in the liquid.

abstract: In this work a newly fabricated organic solar cell based on a composite of fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and regioregular poly (3-hexylthiophene) (P3HT) with an added interfacial layer of AgOx in between the PEDOT:PSS layer and the ITO layer is investigated. Previous equivalent circuit models are discussed and an equivalent circuit model is proposed for the fabricated device. Incorporation of the AgOx interfacial layer shows an increase in fill factor (by 33%) and power conversion efficiency (by 28%). Moreover proper correlation has been achieved between the experimental and simulated I-V plots. The simulation shows that device characteristics can be explained with accuracy by the proposed model. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2015

Proteins can often adsorb irreversibly at fluid/fluid interfaces; the understanding of the adsorption mechanism has relevance across a variety of industrial (e.g. the creation of stable emulsions) and biological (e.g. biofilm formation) processes. I performed molecular dynamics simulations of two surfactant proteins as they interact with air/water and oil/water interfaces, describing the origin of the surface activity, the adsorption dynamics and the conformational changes that these proteins undergo at the interface. BslA is an amphiphilic protein that forms a highly hydrophobic coat around B. subtilis biofilms, shielding the bacterial community from an external aqueous solution. By investigating the behaviour of BslA variants at oil/water interfaces via coarse-grained molecular dynamics, I show that BslA represents a biological example of an ellipsoidal Janus nanoparticle, whose surface interactions are controlled by a local conformational change. All-atom molecular dynamics simulations then reveal the details of the conformational change of the protein upon adsorption, and the self-assembly into a two-dimensional interfacial crystal. Ranaspumin-2 is one of the main components of the tungara frog foam nest. Contrary to most surfactant proteins, its structure lacks any sign of amphiphilicity. All-atom simulations show that the adsorption proceeds via a two-step mechanism where firstly the protein binds to the interface through its flexible N-terminal tail and then it undergoes a large conformational change in which the hydrophobic core becomes exposed to the oil phase. I then developed a simple structure-based coarse-grained model that highlights the same adsorption mechanism observed in all-atom simulations, and I used it to compare the dynamics of adsorption and the underlying free energy landscape of several mutants. These results agree with and are used to rationalise the observations from Langmuir trough and pendant drop experiments. Colloids can often be considered simpler versions of proteins that lack conformational changes. I performed coarse-grained simulations of the compression of interfacial monolayers formed by rod-like particles. These simulations show a rich behaviour characterised by the flipping of adsorbed rods, nematic ordering and bilayer formation. I report the series of transitions that take place as the rod aspect ratio is increased from 3 to 15.

Dans ce travail, nous avons étudié certains aspects fondamentaux (i) du mouillage, (ii) de germination aux interfaces réactives et au sein de la brasure et (iii) de la cinétique de croissance de couches intermétalliques au cours de l'assemblage par brasage en électronique (système Cu/liquide Sn).Le mouillage de Cu, Ag et de leurs composés avec Sn (Cu3Sn, Cu6Sn5 et Ag3Sn) par les brasures liquide Sn-Cu a été étudié par la technique de la goutte déposée dans un four à vide et suivi d'une caméra rapide. Dans la gamme de températures 300-6000C, la première étape de mouillage a lieu en moins de 10 ms et la vitesse d'étalement est d'environ 0.25 m.s-1. Au cours de cette étape (étalement non réactif) la cinétique d'étalement est pratiquement indépendante de T et similaire à celui non réactif du Pb liquide sur Cu. L'angle de contact d'équilibre de Sn liquide sur une surface non-réagi de Cu est inférieur à 300. Les angles de contact non réactifs sur Cu3Sn, atteints en moins de 10 ms, diminuent de 23 à 100 lorsque T augmente de 300 à 5000C. Au cours du mouillage sur Cu6Sn5 à 3900C, de faibles angles de contact (200) sont atteints en moins de 10 ms. Les résultats des expériences de mouillage sur Ag et Ag3Sn ont permis de proposer un mécanisme d'étalement en deux étapes: une première étape de mouillage non réactif très rapide et une seconde de mouillage réactif lente.En mettant en œuvre un dispositif expérimental d'immersion rapide et les techniques de TEM et SEM-FEG, nous avons réussi à étudier, pour la première fois, la séquence de formation des intermétalliques à l'interface Cu/alliage liquide au début de la réaction (1 ms à 1 s) à 2500C. Ces expériences donnent, pour la première fois, la réponse à une des questions les plus ouvertes et intéressantes concernant le brasage en électronique: la première phase qui se forme à l'interface Cu/Sn liquide est Cu6Sn5. Ensuite, nous avons développé une approche théorique sur les critères de suppression de la seconde phase (Cu3Sn) en supposant que Cu6Sn5 est la première qui se développe à l'interface sous forme d'une couche continue. Par ailleurs une modélisation théorique des étapes antérieures, lorsque la germination d'un embryon isolé de Cu3Sn se développe, est proposé.La cristallisation de l'alliage eutectique Sn-Cu a été étudiée par DSC en appliquant des cycles thermiques de fusion complète et partielle. Différentes catégories de degrés de surfusion ont été obtenues. En particulier, des degrés de surfusion faibles (1-7K) ont été détectés pour la première fois dans le cas de la fusion partielle. Une approche théorique sur la nucléation hétérogène est développée et les sites responsables de la germination ont été proposés.La comparaison directe de la cinétique de croissance dans le couple standard Cu/Sn liquide et celui incrémental Cu3Sn5/Sn liquide nous a permis de proposer un mécanisme de croissance de Cu6Sn à l'interface de Cu/Sn liquide. Les résultats obtenus sont compatibles avec le modèle FDR.Des expériences spécifiques de réactions interfaciales entre Cu et l'alliage liquide métastable Sn-0.7wt.%Cu à 2220C et pour des temps de réaction aussi long que 32 h ont été effectuées pour la première fois. Ceci est réalisé par des expériences spécifiques de DSC afin de contrôler l'état physique de l'alliage et la température. La comparaison directe des cinétiques de croissance et de la morphologie des couches réactionnelles formées entre les couples Cu/liquide et Cu/solide, à la même température, a conduit à la conclusion suivante: la grande différence de cinétique de croissance est due à la diffusion à l'état liquide par l'intermédiaire des canaux liquide de largeur nanométrique formés entre les joints de grains de Cu6Sn5 et/ou par des canaux cylindriques de rayon de quelques dizaines de nm formées aux joints triples des grains de Cu6Sn5. Une évaluation théorique de la largeur de ces canaux est effectuée pour la première fois et son évaluation est cohérente avec le modèle FDR. / In this work we have studied some fundamental aspects of (i) wetting, (ii) nucleation at reactive interfaces as well as inside the solder bulk and (iii) growth kinetics of intermetallic layers during a soldering process in electronic industry (Cu/liquid Sn system).Wetting of metallic substrates Cu, Ag and their intermetallics with Sn (Cu3Sn, Cu6Sn5 and Ag3Sn) by liquid Sn-Cu solders was studied by the dispensed drop technique in a high-vacuum furnace and using a rapid camera for recording the spreading process. In temperature range 300-600C, the first stage of wetting of Cu by liquid alloy occurs in less than 10ms and the spreading rate is about 0.25 m.s-1. During this stage (non reactive spreading) the spreading kinetics is practically temperature independent and similar to that of the non-reactive liquid Pb on Cu. The equilibrium contact angle of liquid Sn on a non-reacted and clean surface of Cu is lower than 300. The non-reactive contact angles on Cu3Sn, attained in less than 10 ms, decrease from 23 to 100 when T increases from 300 to 500C. During wetting of Cu6Sn5 at 390C, low contact angle of about 20 are attained in less than 10 ms. Results of wetting experiments of Ag and Ag3Sn substrates allowed to propose a mechanism of the spreading kinetics in two stages: a very rapid non reactive wetting and a slow reactive wetting stage.By implementing a fast dipping experimental set-up and SEM-FEG and TEM techniques, we succeed to study for the first time the sequence of formation of intermetallics at the Cu/liquid alloy interface at the very beginning of reaction (1 ms to 1 s) at 250C. These experiments give, for the first time, the answer to one of the most challenging questions in soldering: the first phase that appears at Cu/liquid Sn interface is the Cu6Sn5 phase. Afterwards, we developed a theoretical approach on the suppression criteria of the second phase formation (Cu3Sn) by assuming that Cu6Sn5 is the first phase that grows at the interface in form of a continuous layer. Moreover, a theoretical modeling of even earlier stages of the isolated nucleus of Cu3Sn phase nucleation is developed.Crystallization of eutectic Sn-Cu alloy was studied by performing specific DSC experiment by applying thermal cycles of complete and partial melting of the solder. Different categories of the undercooling degrees are obtained. In particular, low undercooling degrees (1-7K) are detected for the first time in the case of partial melting. A theoretical approach on heterogeneous nucleation is developed and the responsible sites of nucleation in the case of low undercooling degrees are proposed.Direct comparison of Cu6Sn5 growth kinetics in standard Cu/liquid Sn and in incremental Cu3Sn/liquid Sn couple gave a link with the operating mechanism of the Cu6Sn5 phase growth at solid Cu/liquid Sn interface. The obtained results are also consistent with the FDR model.Specific experiments dealing with interfacial reactions between Cu substrate and metastable liquid Sn-0.7wt.%Cu alloy at 222°C for reaction times as long as 32 h were performed for the first time. This is achieved by performing specific DSC experiments in order to monitor and control the physical state of the alloy as well as to set the accurate reaction temperature. Direct comparison of Cu/liquid and Cu/solid solder growth reaction kinetics and layer morphology at the same temperature lead to the conclusion that the large difference in the growth kinetics between the two couples can be explained if the growth occurs by the liquid state diffusion via the liquid channels of nanometric width formed between grain boundaries of Cu6Sn5 phase and/or by cylindrical channels of radius of some tens of nanometers formed at the triple line junctions of Cu6Sn5 scallops. A theoretical evaluation of the liquid channel width is performed for the first time. Evaluation is consistent with the FDR model.

Made available in DSpace on 2016-06-02T19:09:58Z (GMT). No. of bitstreams: 1 TeseENI.pdf: 5287790 bytes, checksum: c30a5b5cc0b140789ff3816da6250c1e (MD5) Previous issue date: 2006-09-22 / Financiadora de Estudos e Projetos / This work was motivated by the need of a better understanding of the microrheological characteristics of polybutylene terephthalate, PBT, polymer blends, such as the matrix phase PBT and the styrene-acrylonitrile, SAN copolymer as dispersed phase. The main purpose of the microrheological studies carried out was to analyze the rheological behavior and the morphology, as well as their correlation, in the preparation of the PBT/SAN immiscible blend, with and without the use of an interfacial compatibilizer. The rheological behavior was analyzed by torque rheometry, rotational rheometry with parallelplates geometry, and capillary rheometry. The interfacial tensions were measured by the modified ellipsoidal drop retraction method, using an optical polarized light microscope coupled to a hot stage. Two complementary techniques were used in the morphological analyses: scanning electron microscopy (SEM) with tetrahydrofuran (THF) extraction of the dispersed phase, and transmission electron microscopy (TEM) with rutene tetroxide (RuO4) deposition in the dispersed phase. The interfacial tension between the PBT polymer and the SAN copolymer was found to increase as the molar mass of the PBT increased. The use of rotational rheometry with parallel plates at low shear rates allowed the increase in viscosity to be quantified as a function of the reaction of the polymeric macromolecules in the PBT/SAN blend compatibilized or not with the interfacial compatibilizer, the MMA-GMA-EA copolymer. Based on the morphological characterizations, an analysis was made of the fibril formation mechanisms, break up and coalescence of the particles of dispersed phase and their interactions with the addition of interfacial compatibilizers. The rotational rheometry at low shear rates proved to be extremely efficient in the analysis of blend compatibilization, which is usually analyzed by torque rheometry. It was checked that, at high shear rates, the viscosity ratio influenced the formation of more finely dispersed phases. / O motivo que levou à realização deste trabalho de doutorado consistiu na necessidade de um melhor entendimento das características microrreológicas de blendas poliméricas constituídas de poli(tereftalato de butileno), PBT, como fase matriz, e do copolímero estireno-acrilonitrila, SAN, como fase dispersa. Os estudos microrreológicos realizados tiveram como enfoque principal analisar o comportamento reológico e a morfologia, bem como suas correlações na preparação da blenda imiscível PBT/SAN, com e sem a utilização de um compatibilizante interfacial. Nas análises do comportamento reológico, foram utilizadas reometria de torque, reometria rotacional na geometria de placas paralelas e reometria capilar. As medidas de tensões interfaciais foram realizadas através do método de retração de gotas elipsoidais modificado, utilizando-se de um microscópio óptico com luz polarizada acoplado a um estágio a quente. Nas análises morfológicas, foram utilizadas duas técnicas complementares, através de microscopia eletrônica de varredura (MEV) com extração da fase dispersa com tetrahidrofurano (THF) e por microscopia eletrônica de transmissão (MET) com a deposição de tetróxido de rutênio (RuO4) sobre a fase dispersa. Utilizando-se do método de retração de gota modificado, verificou-se que a tensão interfacial entre o polímero PBT e o copolímero SAN aumenta com o aumento da massa molar do PBT. Utilizando-se da reometria de placas paralelas a baixas taxas de cisalhamento, foi possível quantificar o aumento de viscosidade em função da reação das macromoléculas poliméricas na blenda PBT/SAN, compatibilizada ou não com o agente de compatibilização interfacial (o terpolímero metacrilato de metilametacrilato de glicidila-acrilato de etila, MMA-GMA-EA). Por meio das caracterizações morfológicas, foi possível analisar os mecanismos de formação de fibrilas, cominuição e coalescência das partículas de fase dispersa e de suas interações com a adição de agentes de compatibilização interfacial. A técnica de reometria rotacional de placas paralelas em baixas taxas de cisalhamento mostrou-se extremamente eficiente na análise de compatibilização de blendas, que, na maioria das vezes, é feita através de reometria de torque. Verificou-se que, a altas taxas de cisalhamento, a razão de viscosidade influencia a formação de fases mais finamente dispersas em função da taxa de cisalhamento aplicada à blenda PBT/SAN.

Made available in DSpace on 2016-06-02T19:11:47Z (GMT). No. of bitstreams: 1 1263.pdf: 4842944 bytes, checksum: 847b9ce01a383be03465220269170c48 (MD5) Previous issue date: 2006-09-06 / Financiadora de Estudos e Projetos / Although the influence of interfacial adhesion on short-term mechanical performance of fiber-reinforced thermoplastic composites has been well established, very little published information is available on the influence of the composite interface/interphase characteristics on fatigue properties of these materials. Fatigue life determination is of paramount importance for engineering applications of injection moulded short glass fiber (GF) reinforced polypropylene (PP) composites. Thus, this work is related to an investigation on the influence of maleated polypropylene (PP-g-MAH) interfacial compatibilizer on the fatigue resistance properties of 30 percent GF-reinforced PP composites. The mechanical fatigue analysis was carried out using four-point bending tests under deformation controlled mode at frequencies of 1 Hz and complete reverse cycle (R = - 1). In order to obtain quick comparative data on PP-g-MAH compatibilizer performance on the fatigue life of these composites, an experimental procedure was elaborated in order to correlate the properties determined by dynamicmechanical thermal analysis (DMTA) of composite samples, both pristine or subjected to short-term cyclic loading, with the experimentally determined fatigue life of these materials. The main conclusions of this work indicate that the mechanical damping (tan d) values, related to the fiber-polymer interfacial friction, reduce with compatibilizer content; this effect being better evidenced in the fatigued samples. The decrease in tan d values with compatibilizer content clearly indicate an increase in the composite interfacial compatibility and were found to be inversely proportional to the number of cycles to failure determined by long-term fatigue testing, thus, promoting an increase in the fatigue life of the investigated PP/PP-g-MAH/30%GF composites. / Apesar de já ser conhecida a influência da adesão interfacial no desempenho mecânico de curta duração dos compósitos termoplásticos, pouco se sabe sobre a influência da natureza da interface/interfase fibra-polímero na resistência à fadiga destes materiais. Esta propriedade de longa duração é de suma importância em aplicações de engenharia, onde os compósitos moldados por injeção de polipropileno (PP) reforçado com fibra de vidro curta (FV) começam a encontrar grande relevância e atuação, em função de desempenho superior alcançado com uso de compatibilizantes interfaciais. Assim, neste trabalho, buscou-se investigar a influência da adição do compatibilizante interfacial de PP funcionalizado com anidrido maleico (PP-g-MAH) no comportamento mecânico sob fadiga cíclica em compósitos de PP reforçado com 30% em peso de FV. Os ensaios de fadiga foram realizados em flexão quatro-pontos sob deformação controlada na freqüência de 1 Hz e ciclo completo reverso com tensão média zero. Com o objetivo de obter rapidamente informações indicativas sobre a influência do teor de PP-g-MAH na durabilidade sob fadiga mecânica destes compósitos, apresenta-se neste trabalho uma metodologia experimental que busca correlacionar as propriedades obtidas por análise térmica dinâmicomecânica (DMTA) dos compósitos, sem e com envelhecimento por curto tempo sob fadiga, com o experimentalmente determinado desempenho sob fadiga mecânica destes materiais. A principal conclusão deste trabalho demonstra que a propriedade de amortecimento mecânico (tan d), associado ao atrito interfacial do compósito, diminui com aumento no teor do compatibilizante de PP-g-MAH incorporado, sendo este efeito melhor evidenciado nos compósitos pré-envelhecidos sob fadiga. Esta redução no valor de tan d do compósito indica claramente um aumento no grau de compatibilização interfacial fibrapolímero e reflete de forma coerente e inversamente proporcional ao número de ciclos até falha verificada nos ensaios de longa duração sob fadiga mecânica, proporcionando um aumento na durabilidade dos compósitos de PP em análise.

Made available in DSpace on 2016-06-02T19:12:21Z (GMT). No. of bitstreams: 1 4507.pdf: 8368845 bytes, checksum: c2fbca7be58a49b0033b38e3d5a4fc89 (MD5) Previous issue date: 2010-05-17 / Financiadora de Estudos e Projetos / Talc is a well known lamellar mineral filler much used for mechanical reinforcement of polypropylene (PP) composites. Mineral nanoclay is also a lamellar filler that is gaining much interest due to its reinforcement effect achieved at relatively much reduced filler content. So the main objectives of this work were to establish a comparative study on the mechanical fatigue properties of isotactic PP composites reinforced with both types of fillers: nanocomposites with 2 and 5 wt. % of organophilic nanoclay and microcomposites with 8 and 25 wt.% of ultrafine talc, where the influence of distinct filler particles size and different filler-matrix interfacial interactions were analyzed on the fatigue life and strength properties of these materials with potential engineering applications. All composites were subjected to short-term tensile and Izod impact tests, dynamic-mechanical thermal analysis and microstructural characterization via SEM and TEM, in order to correlate the analyzed characteristics to the fatigue behavior of the materials. The fatigue tests were carried out under stress controlled mode in tensile tension-tension, with a sinusoidal stress input at 1 Hz frequency and R = 0.1. Maleated PP contributed to the enhancement of short-term mechanical properties of talc-filled composites, whilst its influence was much reduced on the same properties of OMMT nanocomposites, due to the modest nanoclay exfoliation achieved in the non-polar PP polymer matrix. In general terms, talc-filled PP microcomposites showed better fatigue performance in comparison to the nanocomposites with O-MMT. However, their Wöhler fatigue S-N curves did not indicate fatigue endurance limits, within the fatigue span of up to 1 x 106 cycles. The main conclusion derived from this study, indicated that when both types of composites exhibited equivalent elastic modulus enhancement, the stronger filler-polymer interfacial interactions present in the talc-filled microcomposites prevailed over the reduced filler particles size of the nanocomposites of O-MMT, however with presence of nanoparticles agglomerates. / O talco é uma carga mineral lamelar conhecida e bastante usada em compósitos de polipropileno (PP), por elevar a eficiência de reforço mecânico do polímero. Por outro lado, o interesse pela nanoargila, também carga mineral lamelar, vem crescendo por esta aprimorar as propriedades do polímero, com uso do nanoreforço em teores muito mais reduzidos em comparação ao dos compósitos tradicionais. Com isso, buscou-se neste trabalho fazer uma análise comparativa do comportamento de fadiga sob ciclagem mecânica de dois tipos de compósitos de i-PP homopolímero: nanocompósitos com 2 e 5% de nanoargila organofílica (O-MMT) e microcompósitos com 8 e 25% de talco ultrafino. O objetivo foi analisar a influência do tamanho das partículas do reforço e do grau de interação interfacial matriz-reforço nas propriedades de resistência e durabilidade mecânica sob fadiga destes compósitos. Todos os compósitos empregaram o PP maleado (PP-g-MAH) como compatibilizante interfacial e foram processados numa extrusora dupla-rosca e moldados por injeção. Os ensaios de fadiga foram realizados em corpos de prova de tração no modo de tensão controlada, com uma onda senoidal na freqüência de 1 Hz e R = 0,1. Foram também realizados os ensaios estáticos de tração e resistência ao impacto, microscopia eletrônica (MEV e MET) e análise térmica dinâmico-mecânica (DMTA). De forma geral, os microcompósitos de PP com 8 e 25% de talco apresentaram desempenho sob fadiga superior em relação aos nanocompósitos de O-MMT; entretanto, sem alcançar valores de tensão limite de enduro dentro do intervalo de duração dos ensaios de até 1 x 106 ciclos. A principal conclusão neste estudo demonstrou que na definição da resistência à fadiga dos dois tipos de compósitos de PP com módulo elástico equivalentes, as fortes interações polimero-reforço presentes nos microcompósitos de PP/talco, tal como identificadas por análise DMTA, prevaleceram sobre o tamanho reduzido das nanopartículas de O-MMT, porém com presença de aglomerados.