Ce projet de thèse portait sur le développement d’outils microfluidiques pour la toxicologie et la recherche contre le cancer. En permettant l’analyse simultanée d’un très grand nombre de réactions biologiques ou chimiques réalisés dans des compartiments indépendants (ie. gouttelettes), la microfluidique de gouttes offre une sensibilité de détection et une précision sans précédent pour l’analyse de molécules biologiques, telles que l’ADN ou les Anticorps, en comparaison des expériences réalisées conventionnellement en tubes ou en microplaques (essais en « bulk » ou volume). Ce format permet également de réaliser des expériences à très haut débit et est particulièrement pertinent pour la toxicologie, où des analyses robustes de l’effet des médicaments sont nécessaires. De même, ces procédures sont également très adaptées à l’analyse de cellules uniques pour le séquençage ADN ou ARN et l’épigénomique. Tout cela fait de la microfluidique en goutte un outil puissant pour la toxicologie et la recherche sur le cancer. En premier temps, une méthode du comptage précise des cellules encapsulée dans des microgouttelettes, nommée « hémocytométrie microfluidique », a été développée. Un nouvel algorithme de comptage a été proposé. Des cellules bactériennes (Escherichia Coli) et des cellules de 2 lignées humaines différentes (HL60 and H1975) ont été testées. Le nombre de chaque type de cellules a été déterminé avec une haute corrélation entre la théorie (basée sur la distribution de Poisson) et les résultats expérimentaux. Avec ces résultats robustes, un protocole de microfluidique en goutte a été mis en place pour interroger la viabilité cellulaire et la prolifération des 2 lignées humaines. Ces résultats sont en concordance avec ceux de la littérature. Pour la toxicologie, 3 différents modèles, y compris des microsomes (extrait de cellules d’insectes infectées par un baculovirus exprimant le cytochrome P450 3A4 humain, CYP3A4), HepG2-CYP3A4 (modifiée génétiquement pour exprimer le gène CYP3A4 humain), et HepaRG, une lignée hépatique, ont été évaluées pour l’activité enzymatique du CYP3A4, une enzyme largement utilisée en routine pour le criblage de médicament candidat. Les microsomes ont permis de développer un essai fluorogénique permettant de mesurer l’inhibition du CYP3A4. Cependant, ni l’utilisation des microsomes ni des cellules HepG2 exprimant CYP3A4 n’a donné de résultats satisfaisants en microgouttelettes. L’utilisation des cellules HepaRG, une lignée cellulaire qui conserve la majorité de l’expression des cytochromes P450 et des récepteurs nucléaires nécessaire à leur expression, a montré des résultats encourageant à la fois sur les tests de mesure de l’activité enzymatique et d’analyse de l’induction du CYP3A4. Pour la recherche sur le cancer, 4 essais originaux de PCR digitale en gouttes ont été mis en place pour la détection et la quantification de mutations (NRAS, DNMT3A, SF3B1 and JAK2) importante pour les syndromes myélodysplasiques, un groupe hétérogène de maladies touchant les cellules souches hématopoïétiques caractérisées par une hématopoïèse inefficace et des cytopénies périphériques. Finalement, un essai de PCR sur cellule unique encapsulées au sein de billes agarose a été proposé. / This thesis project consists in developing droplet-based microfluidic tools for toxicology and cancer research. Owing to its large numbers of discretized volumes, sensitivity of detection of droplet-based microfluidics for biological molecules such as DNA and antibody is much higher than bulk assays. This high throughput format is particularly suitable for experiments where a robust dose-response curve is needed, as well as for single cell analysis with applications in genomic or sequencing and epigenetics. All above makes droplet-based microfluidics a powerful tool for toxicology and cancer research. In a first part of the work, an accurate cell counting method, named “microfluidics hemocytometry”, has been developed. A new counting algorithm was proposed to count the cells within each droplet. Escherichia Coli and two different human cell lines (HL60 and H1975) were used to validate our strategy. The number of each type of cells in droplets was determined with a high consistency between theory (Poisson distribution) and experimental results. With these robust results, a droplet-based microfluidic protocol has then been established to inquiry both cell viability and proliferation for the two human cell lines. The results are in good agreement with the one of the literature. For the toxicology, 3 different biological models, including microsomes (extracted from baculovirus-infected insect cell expressing human CYP3A4), HepG2-CYP3A4 (genetically modified to express the human CYP3A4 gene) and HepaRG liver cells lines were evaluated for enzymatic activity of cytochromes P450 (CYP3A4), a routinely used enzyme for drug candidate screening. Microsome-based assays were used to validate a fluorogenic inhibition assay. However neither microsome-based assay nor the assay using CYP3A4 expressing HepG2 gave satisfying results in droplet-based format. However, HepaRG cells, a hepatic function-conserved cell line with most cytochrome and related nuclear receptors, demonstrated high relevance both for enzymatic activity testing and CYP3A4 expression induction study. For cancer research, 4 different picoliter droplet-based PCR assays were developed for the detection and quantification of mutations (NRAS, DNMT3A, SF3B1 and JAK2) present in Myelodysplastic syndromes, a heterogeneous group of clonal bone marrow hematopoietic stem cell disorders characterized by ineffective hematopoiesis and peripheral cytopenias. Furthermore, a single cell multistep PCR assay using encapsulation of target DNA in agarose droplets was proposed.

In this thesis, a numerical method is developed for simulating non-isothermal multiphase flows, which are important in many technical applications such as crystal growth and welding. The method is based on the arbitrary Lagrangian Eulerian method of Li (2013). The interface is represented explicitly by mesh lines, and is tracked by an adaptive moving unstructured mesh. The $P2-P1d$ finite element method (FEM) is used for discretisation and the incompressible Navier-Stokes equations are solved by the uzawa method. Firstly, a thorough study is presented on the method's capability in numerically representing the force balance condition on the interface. An inaccurate representation of this condition induces the non-physical spurious currents, which degrade the simulation accuracy especially when the viscous damping is weak (small Ohnesorge number, $Oh$). For the example of a circular/spherical droplet, the interfacial tension and the associated pressure jump are exactly balanced numerically and thus the static Laplace solution exists in our method. The stability of this solution is examined numerically. The amplitude of the dimensionless spurious currents is found to be around $10^{−15}$ for $Oh \geq 10^{−3} $. Another benchmark test is the axisymmetric oscillation of a freesurface droplet/bubble. The simulation results are in good agreement with the analytical solution for $Oh = 10^{−3}$. This is by far the first successful simulation of droplet/bubble oscillation with such weak viscous damping and it demonstrates the ability of our method in simulating flows with strong capillary forces. Secondly, a numerical treatment of interface topology changes is incorporated into our method for studying problems with interface breakup. Thanks to the adaptive mesh generator, the thin region between the interface boundary and another boundary consists of one layer of elements. The interface topology change is performed once the minimum distance between the two boundaries falls below a pre-set scale $l_{breakup}$ . The numerical implementation is verified through two different examples: dripping faucet and droplet coalescence. Remarkably good agreement has been obtained with the experimental results. The simulation of the low Oh dripping problem shows both the accuracy and robustness of our method. The simulation of droplet coalescence demonstrates the great advantage of our method in solving problems with a large disparity in length scales. Finally, an FEM solver for temperature is developed and the non-isothermal effects are included in our method for the purpose of simulating non-isothermal multiphase flows. The modified method is validated to be accurate through three benchmark examples: natural convection in a cavity, thermocapillary convection of two layers, and droplet migration subject to a temperature gradient. Our method is then applied to investigate the liquid bridge breakup with thermocapillary effect. The non-isothermal liquid bridge breakup in the viscous and inertial regimes are studied. It has been found that the inertial regime breakup exhibits different pinchoff shapes as the Capillary number increases, and that the viscous regime breakup is accelerated by the thermocapillary motion.

Mitochondria play a central role in lipid metabolism and pathology in obesity and type 2 diabetes mellitus. Mitochondria have been shown to associate with lipid droplets (LDs) in multiple tissues but the functional role of these peridroplet mitochondria (PDM) is unknown. This work reveals that PDM have unique protein composition and cristae structure, and remain adherent to the LD in the tissue homogenate. We developed an approach to isolate PDM based on their adherence to LDs. Comparison of purified PDM to cytoplasmic mitochondria reveals that (1) PDM have increased pyruvate oxidation, electron transport, and ATP synthesis capacities. (2) PDM have reduced beta oxidation capacity and depart from LDs upon activation of brown adipose tissue thermogenesis and beta oxidation. (3) PDM support LD expansion as Perilipin 5-induced recruitment of mitochondria to LDs increases ATP-dependent triacylglyceride synthesis. (4) PDM maintain a distinct protein composition due to uniquely low fusion-fission dynamics. We conclude that PDM represent a segregated mitochondrial population with unique structure and function that supports triacylglyceride synthesis. We suggest that increased mitochondrial recruitment to LDs may be part of a generalized adaptive response in physiological conditions that require LD expansion, such as post-prandial lipid synthesis and storage. Furthermore, PDM-mediated LD expansion may play a role in muscle and liver injury from lipotoxicity in conditions of nutrient excess, such as obesity and hyperlipidemia. A better understanding of PDM and LD biology may therefore lead to new therapies for lipotoxic tissue injury and insulin resistance. / 2020-10-24T00:00:00Z

Orientador: Ulisses Rocha Antuniassi / Banca: Otavio Jorge Gricoli Abi Saab / Banca: Marco Antonio Gandolfo / Banca: Carlos Gilberto Raetano / Banca: Paulo Roberto Arbex Silva / Resumo: A alta demanda por agrotóxicos pelos sistemas de produção agrícola, aliada ao possível uso inadequado desses produtos, torna a deriva um dos maiores problemas potenciais da agricultura atual, e a escolha correta de adjuvantes pode ser uma das alternativas para minimizar os impactos negativos causados pela deriva nas pulverizações. Este trabalho foi desenvolvido com o objetivo de avaliar o efeito proporcionado por diferentes grupos de adjuvantes nas propriedades físicas e químicas das soluções, no espectro de gotas, bem como no potencial do risco de deriva quantificado em túnel de vento, como forma de auxiliar na escolha correta desses produtos para melhor utilização nas aplicações de agrotóxicos. Foram selecionados 18 adjuvantes comumente utilizados em misturas com agrotóxicos em pulverizações agrícolas, avaliando-se as propriedades físicas e químicas dos mesmos em soluções aquosas (viscosidade, densidade, tensão superficial e condutividade elétrica), o espectro de gotas e o potencial de deriva medido em túnel de vento. O experimento foi composto de 33 tratamentos, tendo a água como testemunha adicional, resultantes da diluição dos adjuvantes em diferentes concentrações, com três repetições. Para os ensaios em túnel de vento e análise de espectro de gotas foi utilizada uma ponta de pulverização XR8003 VK na pressão de 200 kPa, gerando um padrão de gotas médias. A deriva foi coletada no túnel de vento com fluxo de ar na velocidade de 2 m s-1. O corante Azul Brilhante a 0,6% (m v-1) foi utilizado como marcador para todas as soluções pulverizadas visando a quantificação da deriva por espectrofotometria. Os resultados mostraram que a adição de adjuvantes alterou as propriedades físicas e químicas das soluções aquosas em diferentes magnitudes, dependendo da concentração utilizada. Os surfatantes organosilicones... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Due to the high demand for pesticide by the agricultural systems and the possible inadequate use of the products, drift became one of the biggest concerns of the modern agriculture, and the correct use of adjuvants may be one of the possible alternatives to minimize the negative impact of spray operations. This study was developed to evaluate the effect of different adjuvants on physical and chemical properties of spray solutions, droplets spectra as well as drift potential measured in wind tunnel, aiming the correct choice of adjuvants to improve efficiency in pesticide application. For this purpose 18 commercially available agricultural spray adjuvants were selected including products usually mixed up with pesticides in the sprayer tank. The evaluation included physical and chemical properties of spray solutions (viscosity, density, surface tension and electric conductivity), droplets spectra and drift risk potential measured in wind tunnel. The experiment was set up with 33 treatments (solutions) obtained from 18 adjuvants used in different concentrations with 3 replications, including pure water as a standard. For wind tunnel tests and droplet spectra analysis it was used a Teejet XR8003 flat fan nozzles at 200 kPa (medium droplets) and all solutions were mixed up with a food color dye (Blue FDC) at 0,6% m v-1 for spectrophotometry analysis of drift deposits on the wind tunnel. The results showed that the addition of adjuvants changed physical and chemical properties of spray solutions in different magnitudes according to the product concentration. The organosilicon surfactants (Silwet 0.1% e 0.2% and BreakThru 0,1%) had the lowest values for surface tension, while the drift retardant based polymers (Define 0,06% e 0,12%) had the highest values for viscosity and density. There was high correlation between the Volume Median Diameter (VMD) and percentage of droplets smaller... (Completo abstract click electronic access below) / Doutor

L’évaporation du carburant injecté dans une chambre de combustion est un phénomènecrucial dans un foyer aéronautique car elle détermine la quantité de vapeur qui sera ensuite brûléepour fournir de l’énergie au moteur. Cependant, ce phénomène reste mal décrit du fait desdifficultés de mesurer expérimentalement les taux d’évaporation des gouttes appartenant à unbrouillard. D’autre part, les hypothèses des modèles théoriques ne sont toujours pas représentativesdes conditions rencontrées dans les foyers de combustion.La thèse s’inscrit dans une démarche visant à étudier l’évaporation d’un groupe de gouttesdans un écoulement turbulent au moyen de la Simulation Numérique Directe (SND). En effet, lorsde l’évaporation de groupes de gouttes, des effets collectifs peuvent influer sur le taux d’évaporationde chaque goutte ou sur le taux d’évaporation global du nuage de gouttes. L’approche SNDpermet de quantifier précisément ces effets afin d’améliorer les modèles actuels d’évaporation.Dans un premier temps, des algorithmes ont été développés et utilisés dans une configuration1D sphérique pour décrire l’évaporation d’une goutte statique isolée et sans gravité. Puisdans un second temps, l’évaporation d’une goutte a été étudiée dans un écoulement laminaire.Une analyse des échanges de chaleur entre la goutte et le milieu extérieur ainsi que de la force detraînée exercée par l’écoulement laminaire sur la goutte a été effectuée. Dans cette partie, il a étémis en évidence que l’évaporation induit une diminution des échanges thermiques et de la traînée.Il a notamment été observé que dans certains cas de forte évaporation, la traînée de la gouttepeut devenir négative. Cela implique que l’évaporation peut être à l’origine d’un phénomène depropulsion de la goutte. Une analyse théorique permet de lier ce comportement à une asymétriedu débit d’évaporation. Dans un troisième temps, l’influence de la turbulence sur l’évaporationd’une goutte a été étudiée. Pour cela, un générateur de fluctuations turbulentes a été implémentéet des techniques de calculs parallèles ont été introduites pour réduire le temps des calculs. Celaa permis d’analyser les échanges thermiques et le comportement de la traînée d’une goutte eninteraction avec un écoulement turbulent. Il a été montré que ces deux grandeurs ont tendanceà être amplifiées par la turbulence. Enfin, dans un dernier temps, l’évaporation de groupes degouttes a été étudiée. Pour trois groupes de gouttes différents, les déplacements des gouttes ontété analysés avec les échanges de chaleur lorsque ceux-ci sont placés dans un écoulement laminaireou turbulent avec ou sans changement de phase. En présence d’évaporation, il a été mis enévidence que les déplacements sont différents des cas sans évaporation et donc que le changementde phase modifie les effets collectifs. De plus, ces effets de groupes ont aussi été observés sur leséchanges thermiques. / The vaporisation of injected fuel in a combustion chamber is a crucial phenomenon inan aeronautical motor because it determines the vapour quantity which will be burned to bringenergy to the motor. Still, this phenomenon is not well understood due to the difficulties tomeasure on experiments vaporisation rates of injected sprays. Moreover, hypothesis of theoriticalmodels are not representatives of conditions encountered in combustion furnaces.The thesis take place in an effort to analyse the evaporation of droplet groups in a turbulentflow by mean of Direct Numerical Simulation (DNS). Indeed, during droplet group evaporation,collective effects can modify single droplet rates of vaporisation and the group global rate ofvaporisation. The DNS approach should allows to quantify precisely this effect and leads to animprovement of actual models of evaporation.Firstly, algorithms are developped and used in a 1D spherical configuration to describe theevaporation of a single static droplet without gravity. Secondly, the vaporistion of a droplet in alaminar flow has been studied. The analysis focus on heat exchanges between the droplet and theexternal environment as well as the force exerced on the droplet by the laminar flow. In this part,it has been highlighted that the evaporation induced a decrease in thermal exchanges and drag.In some cases of strong evaporation, the drag of the droplet has been observed to be negative.It means that the evaporation can cause a propulsion phenomenon of the droplet. A theoriticalanalysis allows to link this behaviour to an asymetry of the vaporisation rate. Thirdly, a studyof the turbulence influence on the evaporation of a droplet has been carried out. A generator ofturbulent fluctuations has been implemented and parallel approaches have been introduced toreduced computational time. It allowes to analyse thermal exchanges and drag behaviour of adroplet interacting with a turbulent flow. The analysis showed that theses two variables increasewith turbulence. Lastly, the evaporation of groups of droplets has been studied. For three differentgroups of droplets, trajectories of droplets have been analysed with heat exchanges when they areput in a laminar or a turbulent flow with or without phase change. In presence of evaporation,the analysis pointed out that trajectories were different from cases whitout evaporation and sothat phase change modifies collective effects. Moreover, these collective effects have also beenobserved on thermal exchanges.

Réussir à contrôler la morphologie et la taille de particules solides obtenues par précipitation est un enjeu industriel majeur. C’est notamment le cas dans l’industrie nucléaire pour le recyclage du combustible usé. Les caractéristiques des précipités sont liées aux conditions de mélange des phases liquides dans les procédés. Les corrélations entre les paramètres physiques des particules obtenues et les conditions hydrodynamiques n’ont pas été examinées jusqu’à présent. Dans cette étude, des systèmes expérimentaux originaux, basés sur la coalescence de deux gouttes, sont utilisés afin de mieux comprendre les liens entre hydrodynamique et réaction de précipitation. Deux configurations de gouttes aqueuses ont été investiguées, la première consiste en deux gouttes posées à fort angle de contact (>90°) dans l’huile, il s’agit d’un système modèle pour les gouttes en émulsion, la second configuration correspond à deux gouttes posées à faible angle de contact (>25°) dans l’air. Dans chaque cas, une espèce réactive est dissoute dans chaque goutte, à savoir de l’acide oxalique ou du nitrate de cérium dans la seconde. Lorsque les deux gouttes se touchent, elles peuvent éventuellement coalescer, alors les espèces chimiques se mélangent et réagissent pour produire un précipité d’oxalate de cérium. Les caractéristiques de ce précipité et ses effets sur l’hydrodynamique sont examinés en fonction du solvant utilisé. De plus, dans le cas des gouttes posées sur une surface de silice dans l’air, une différence de tension de surface entre deux gouttes crée un gradient qui génère un flux de Marangoni dirigé de la goutte de faible tension de surface au-dessus de la goutte de forte tension de surface. En jouant sur la différence de tension de surface entre les deux gouttes, et ainsi sur le flux de Marangoni, il est possible de modifier les conditions hydrodynamiques lors de la coalescence des gouttes. Des mélanges eau/diols ont été utilisés comme solvant afin de pouvoir modifier la différence de tension de surface entre les liquides des deux gouttes indépendamment de leur concentration en réactif. Les diols utilisés, le 1,2-propanediol et le 1,3-propanediol sont des isomères, ils sont la même densité, des viscosités semblables mais des tensions de surface différentes. En fixant la fraction volumique d’eau dans le solvant, et en jouant sur les fractions volumiques de chaque diols, il est possible de contrôler la tension de surface des mélanges sur une gamme de 10 mN/m pour une concentration en réactifs donnée, et en conservant la densité et viscosité des solvants. Trois régimes de précipitation ont été identifiés dans le cas de la coalescence de gouttes d’eau/diols/réactifs en fonction de l’excès oxalique. Les motifs de précipitation en découlant ont été imagés par microscopie optique et les différents précipités ont été caractérisés à l’aide de microscopie confocale, MEB, DRX et SAXS. Le régime intermédiaire présente des motifs périodiques surprenants. Ces motifs correspondent à des domaines nettement délimités d’oxalate de cérium de différentes morphologies, à savoir des aiguilles et des « microflowers ». L’obtention de tels motifs peut s’expliquer par un mécanisme de rétroaction entre convection, réaction et diffusion. / The size and morphology control of precipitated solid particles is a major economic issue for numerous industries. For instance, it is interesting for the nuclear industry, concerning the recovery of radioactive species from used nuclear fuel. The precipitates features, which are a key parameter from the post-precipitate processing, depend on the process local mixing conditions. So far, the relationship between precipitation features and hydrodynamic conditions have not been investigated. In this study, a new experimental configuration consisting of coalescing drops is set to investigate the link between reactive crystallization and hydrodynamics. Two configurations of aqueous drops are examined. The first one corresponds to high contact angle drops (>90°) in oil, as a model system for flowing drops, the second one correspond to sessile drops in air with low contact angle (<25°). In both cases, one reactive is dissolved in each drop, namely oxalic acid and cerium nitrate. When both drops get into contact, they may coalesce; the dissolved species mix and react to produce insoluble cerium oxalate. The precipitates features and effect on hydrodynamics are investigated depending on the solvent. In the case of sessile drops in air, the surface tension difference between the drops generates a gradient which induces a Marangoni flow from the low surface tension drop over the high surface tension drop. By setting the surface tension difference between the two drops and thus the Marangoni flow, the hydrodynamics conditions during the drop coalescence could be modified. Diols/water mixtures are used as solvent, in order to fix the surface tension difference between the liquids of both drops regardless from the reactant concentration. More precisely, the used diols, 1,2-propanediol and 1,3-propanediol, are isomer with identical density and close viscosity. By keeping the water volume fraction constant and playing with the 1,2-propanediol and 1,3-propanediol volume fractions of the solvents, the mixtures surface tensions differ up to 10 mN/m for identical/constant reactant concentration, density and viscosity.Three precipitation behaviors were identified for the coalescence of water/diols/recatants drops depending on the oxalic excess. The corresponding precipitates patterns are visualized by optical microscopy and the precipitates are characterized by confocal microscopy SEM, XRD and SAXS measurements. In the intermediate oxalic excess regime, formation of periodic patterns can be observed. These patterns consist in alternating cerium oxalate precipitates with distinct morphologies, namely needles and “microflowers”. Such periodic fringes can be explained by a feedback mechanism between convection, reaction and the diffusion.

La microfluidique à goutte a connu un essor remarquable ces dix dernières années. Pourtant, la dynamique de ces objets reste largement inexplorée et incomprise. En effet, une question aussi fondamentale que de prédire la vitesse d'une goutte poussée par une phase porteuse à vitesse imposée, est restée jusqu’à ce jour, sans réponse. Comprendre la dynamique d'une goutte suppose de caractériser les dissipations visqueuses (friction) au sein de la goutte et dans le film de lubrification. Ces dissipations visqueuses sont étroitement liées à la forme et aux propriétés physico-chimiques de l'interface séparant l'intérieur de la goutte de la phase externe. Ce manuscrit présente une caractérisation de la dynamique d’une goutte 2D en cellule de Hele-Shaw en exploitant la double mesure du film de lubrification par microscopie interférentielle et de la vitesse de la goutte. Dans un premier temps, nous étudions expérimentalement la forme adoptée par l'interface en fonction de la viscosité de la goutte et de la concentration en tensioactifs. La comparaison des topographies expérimentales mesurées avec des modèles théoriques déjà existants et un nouveau développé dans ce manuscrit, révèle que l'utilisation d'une approche purement hydrodynamique (sans effet Marangoni) pour déterminer la topographie théorique n'est en mesure de reproduire la topographie expérimentale que lorsque le système ne présente pas de tensioactif ou bien lorsque la viscosité de la goutte est suffisamment importante pour prendre le pas sur d'éventuels effets Marangoni à l'interface. Dans les autres cas, la forment de l'interface évolue en fonction de la contrainte de Marangoni qui peut s'exercer localement ou globalement à l'interface. Dans un deuxième temps, l’établissement d’un modèle théorique pour la vitesse de la goutte, basé sur la modélisation des topographies de films expérimentales mesurées, permet de retrouver quantitativement, et sans paramètre d'ajustement, les vitesses de goutte mesurées expérimentalement. / Droplet microfluidics is a growing field of research. However, the dynamics of these objects remain misunderstood. Indeed, a question as fundamental as predicting the droplet velocity while pushed by an external fluid at a given velocity is still not answered. Understanding the dynamics of a droplet requires to characterize the viscous dissipation mechanisms (friction) within the droplet and in the lubrication film. This dissipation is related to the shape and to the physicochemical properties of the interface separating the inner phase of the droplet from the outer phase. This thesis presents a characterization of the dynamics of 2D droplets in a Hele-Shaw cell, by taking advantage of the double measurement of the lubrication film by interference microscopy and of the droplet velocity. Firstly, we study experimentally the influence of the droplet viscosity and surfactant concentration on the shape of the interface. The comparison between the topographies measured experimentally with the theoretical models already existing and the new one developed in this thesis, reveals that the use of a purely hydrodynamical approach in order to derive the theoretical topography only allows to recover the experimental topography if the system is surfactant free or if the droplet viscosity is high enough to overcome the Marangoni effect at the interface. In the other cases, the shape of the interface depends on the Marangoni stress exerted either locally or globally at the interface of the droplet. In a second part, the derivation of a theoretical model for the droplet velocity, based on the modeling of the lubrication film topographies measured experimentally, allows to recover quantitatively, and without any fitting parameter, the experimental data on droplet velocities.

The ultimate goal of this project has been to develop a computational model for quantifying the interactions between of a body of fluid and a fibrous surface. To achieve this goal, one has to develop a model to create virtual structures that resemble the morphology of a fibrous surface (Objective-1) as well as a model that can simulate the flow of a fluid over these virtual surfaces (Objective-2). To achieve the first objective, we treated fibers as an array of beads interconnected through viscoelastic elements (springs and dampers). The uniqueness of our algorithm lies in its ability to simulate the curvature of the fibers in terms of their rigidity, fiber diameter, and fiber orientation. Moving on to Objective-2, we considered woven screens for their geometric periodicity, as a starting point. We studied how fiber diameter, fiber spacing, and contact angle can affect the skin-friction drag of a submerged hydrophobic woven screen, and how such surfaces resist against water intrusion under elevated hydro-static pressures (a requirement for providing drag reduction benefits). We also studied the impact of surface geometry and wetting properties on droplet mobility over these surfaces. Laboratory experiment was conducted at various stages throughout this investigation, and good agreement was observed between the experimental data and the results from our numerical simulation.

This study proposes a method to enhance the anti-icing capabilities of superhydrophobic surfaces by utilizing vibration to further reduce contact time of an impacting droplet in addition to keeping the droplet in the Cassie-Baxter regime, where surface adhesion is lower than the opposing Wenzel regime. We tested this with two methods: by investigating the effects of vibration normal to the plane of a superhydrophobic surface being impacted by water droplets in a room temperature environment, with the surface horizontal in a room temperature environment and tiled in a subzero degree environment. The amplitude and frequency of the vibration were varied in our experiments. Our results show that the mean contact time of a 10µL droplet consistently decreased linearly as the vibration frequency increased, though the standard deviations drastically increased. The ice accretion in the second phase of the testing also had significant variance, which obfuscated any reliable trend from the introduction of vibration.

Particle Nucleation is the forcing function in the Emulsion Polymerization processes and it plays an important role in dictating the final properties of the latex produced. Identification of the main nucleation sites and characterizing them in terms of their size and composition is important for elucidating the mechanism of particle nucleation. This research focuses on identifying the most likely nucleation locus in emulsion polymerization processes by characterizing the initial conditions of the reaction mixture. In order to achieve this objective, a methodology was devised, which used a non-reacting model emulsion system instead of the original emulsion. The model emulsion system selected has the same dispersion properties as that of the monomer emulsion system, but different optical properties. The model emulsion system enabled the study of the distribution of the emulsifier using Uv vis spectroscopy. This approach also eliminated the time constraint associated with sampling during a polymerization reaction. A quantitative deconvolution using the turbidity equation, was done on the transmission Uv vis spectra of the emulsions. This enabled the characterization of the emulsions in terms of their particle size distribution, particle number and the composition of the droplet populations comprising them. The studies conducted provide the experimental evidence for a previously unidentified nano-droplet population of size range 30 to 100nm in diameter. To further support this experimental evidence, calculations were performed to obtain the emulsifier distribution over the nano-droplet population. The calculations suggest the probability of existence of the nano-droplet population to be much higher than the probability of the existence of the swollen micelles. The results, depending upon the emulsification conditions, indicate the presence of about 15 % to 80% of the dispersed phase in the nano-droplet population. The large interfacial area offered by the nano-droplet population due to their high particle numbers and high percentage of the dispersed oil phase in them, make them the most probable particle nucleation loci in emulsion polymerization processes. Designed experiments were performed to experimentally observe the changes in the nano-droplet populations. The effects of the process variables, namely pH, surfactant concentration and temperature, on the size and compositional characteristics of the nano-droplet population were investigated. The results suggested that the surfactant to oil ratio was the dominating factor governing the size and the weight percent of the dispersed phase in the nano-droplet population.