Dissertations / Theses on the topic 'Droplets'
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Umapathi, Udayan. "Droplet IO : programmable droplets for human-material interaction." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/114062.
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Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 87-93).
In this thesis, I propose aqueous droplets as a form of programmable material that can computationally transform its physical properties. Liquid matter can undergo physical transformation through interfacial forces and surface tension. I introduce a system called DropletIO to regulate interfacial forces through a programmable electric field. The system can actuate and sense macro-scale (micro-liter to milli-liter) droplets on arbitrary planar and curved surfaces. The system can precisely move, merge, split, and change shape of droplets and thus enables a range of applications with human interactivity, information displays, parallelized programmable chemistry and dynamically tunable optics. DropletIO system uses electrowetting on dielectric (EWOD) to manipulate droplets. EWOD is a physical phenomenon where a polar droplet on a dielectric surface is attracted to a charged electrode. I constructed EWOD arrays with integrated actuation and sensing on inexpensive printed circuit boards that can scale to arbitrarily large areas and different form factors. Additionally, in this thesis I discuss how semiconductor device scaling applies to electrowetting for smaller volume droplets and hence miniaturized programmable lab-on-a-chip. Droplet based microfluidics is extensively used in biology and chemistry. In this thesis I describe two novel fluid manipulation mechanism for microfluidics. First, I show an approach for splitting aqueous droplets on an open digital microfluidic platform and thus a system capable of performing a complete set of microfluidic operations on an open surface. Second, I demonstrate how electrowetting platforms can handle large volume fluids, and hence enable a new direction in programmable fluid handling called digital millifluidics.
by Udayan Umapathi.
S.M.
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Sahu, Sucharita. "Thermal state of Sn-Pb droplets in the droplet-based manufacturing process." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34081.
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Hager, Darcy B. "Investigations into exploding droplets." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22991.pdf.
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Wilms, Jochen. "Evaporation of multicomponent droplets." München Verl. Dr. Hut, 2005. http://deposit.d-nb.de/cgi-bin/dokserv?idn=979033012.
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Dunn, Gavin J. "Non-isothermal liquid droplets." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501697.
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Two problems concerning sessile liquid droplets are considered. First we report the results of physical experiments that demonstrate the strong influence of the thermal conductivity of the substrate and the nature of the atmosphere on the diffusion-dominated evaporation of a pinned sessile liquid droplet without external heating or cooling. We capture this behaviour in a mathematical model including the variation of the saturation concentration with temperature, and hence coupling the problems for the vapour concentration in the atmosphere and the temperature in the liquid and the substrate. Furthermore, we show that including two ad hoc improvements to the model gives excellent quantitative agreement with experiments. We also extend the model to include the effect of reduced atmospheric pressure and different gases, for which we again find good agreement with experiments. We then consider the special case in which both the droplet and the substrate are thin, in the extreme situation in which the substrate has a high thermal resistance relative to the droplet.
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Khare, Prashant. "Breakup of liquid droplets." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/53395.
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Liquid droplet breakup and dynamics is a phenomena of immense practical importance in a wide variety of applications in science and engineering. Albeit, researchers have been studying this problem for over six decades, the fundamental physics governing droplet deformation and fragmentation is still unknown, not to mention the formulation and development of generalized correlations to predict droplet dynamics. The presence of disparate length and time scales, along with the complex unsteady physics, makes this a formidable problem, theoretically, experimentally and computationally. One of the important applications of interest and the motivation for the current research is a liquid fueled propulsion device, such as diesel, gas turbine or rocket engine. Droplet vaporization and ensuing combustion is accelerated if the droplet size is smaller, which makes any process leading to a reduction in drop size of prime importance in the combustion system design. This thesis is an attempt to address several unanswered questions currently confronting the spray community. Unanswered questions include identification and prediction of breakup modes at varying operating conditions, quantitative description of fundamental processes underlying droplet breakup and generalized correlations for child droplet size distributions and drag coefficient associated with the deformation and fragmentation of Newtonian and non-Newtonian fluids.
The present work is aimed at answering the above questions by investigating the detailed flowfield and structure dynamics of liquid droplet breakup process and extracting essential physics governing this complex multiphase phenomena. High-fidelity direct numerical simulations are conducted using a volume-of-fluid (VOF) interface capturing methodology. To isolate the hydrodynamic mechanisms dictating droplet breakup phenomena, evaporation and compressibility are neglected, and numerical studies are performed for incompressible fluids at isothermal conditions.
For Newtonian fluids, four different mechanisms are identified- oscillatory, bag, multimode and shear breakup modes. Various events during the deformation and fragmentation process are quantitatively identified and correlations are developed to predict the breakup mechanisms and droplet size distributions for a broad range of operating conditions. It was found that for We > 300 and Oh < 0.1 for rho_l/rho_g = 8.29, the child droplet size distributions can be modeled by a log-normal distribution. A correlation to predict the sauter mean diameter, d32, is also developed, given by d32 / D = 8We^-0.72 / Cd.
Temporal evolution of momentum balance and droplet structure are also used to calculate the drag coefficient at each time step from first principles. Results show that the drag coefficient first increases to a maximum as the droplet frontal area increases and then decreases at the initiation of breakup. The drag coefficient reaches a steady value at the end of droplet lifetime, corresponding to the momentum retained by the droplet. A correlation to predict the time-mean drag coefficient given by, Cd / Cd,0 = 2We-^0.175, is developed, which indicates that the time averaged drag coefficient decreases with Weber number.
The motivation to study non-Newtonian liquid droplet breakup stems from the various advantages gelled propellants offer as compared to traditional liquid or solid propellants in combustion systems, particularly in rocket engines. It was found that the breakup behavior of pseudoplastic, non-Newtonian liquids is drastically different as compared to Newtonian droplets. Several flow features commonly exhibited by non-Newtonian fluids are observed during the breakup process. The breakup initiates with the formation of beads-in-a-string due to the non-Newtonian nature of the fluid under consideration. This is followed by rapid rotation of the droplet with the appearance of helical instability and liquid budges, which forms the sites for primary and satellite droplet shedding. Child droplet size distribution are also examined and it is found that a Gaussian curve universally characterizes the droplets produced during non-Newtonian droplet breakup process.
To put all things in perspective, the objectives of the thesis were two folds: (1) elucidate breakup physics for Newtonian and non-Newtonian liquid droplet deformation and breakup, and (2) develop correlations which can be used in an Eulerian-Lagrangian framework to study large-scale engineering problems. It is hoped that this research contributed to droplet breakup and dynamics literature by providing a more thorough and quantitative understanding of the breakup phenomena of liquid droplets and furnished models which can be used in future research endeavors.
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Cherng, Jean-Pei Jeanie. "Solidification and cooling analysis of aluminum alloy droplets with the uniform droplet spray process." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/36325.
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Marangoni, Federico. "Filter cleaning with liquid droplets." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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L’obiettivo del lavoro svolto è quello di identificare una modalità economica ed applicabile per la pulizia e rigenerazione di filtri di profondità, in particolare nella filtrazione di solidi da correnti gassose. Si ha attualmente mancanza di un tale metodo, che consentirebbe di poter rigenerare il filtro senza che debba essere necessariamente sostituito.
Il lavoro consiste in un approccio sperimentale che studia una singola fibra impolverata da particelle solide. Sono stati proposti dei modelli che descrivono le interazioni tra particella, fibra e liquido. Da questo è stato ricavato un criterio teorico per determinare la riuscita o meno della rimozione di una singola particella solida adesa ad una fibra posta verticalmente e sottoposta al passaggio di un film di liquido con un determinato spessore.
L’apparato sperimentale predisposto permette il fissaggio della fibra, sulla quale vengono fatte scorrere le gocce del liquido di pulizia. Tali gocce sono osservate nella discesa con una fotocamera ad alta frequenza. L'appartato sperimentale ha permesso di variare i principali parametri sperimentali e di testare diverse combinazioni fibra-particelle.
Il parametro chiave nella pulizia è stato individuato nella forza di adesione, dipendente dal liquido utilizzato per la pulizia. Dal punto di vista geometrico, la geometria più affine alla pulizia si è rivelata la geometria cilindrica di piccolo diametro a sfavore di una geometria planare.
L’utilizzo di gocce di liquido più grandi e l’uso di un numero elevato di gocce permette di migliorare il livello di pulizia: entrambi i fattori possono restituire un vantaggio nella pulizia ma si contrappongono al costo materiale del liquido.
Nel complesso, la metodologia di pulizia proposta si è rivelata promettente, con ampie possibilità di essere estesa a filtri industriali.
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Jalaal, Maziyar. "Controlled spreading of complex droplets." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/60120.
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The current thesis investigates the controlled spreading of droplets of complex fluids. This thesis makes four primary scientific contributions. Firstly, we provide detailed theoretical analysis on spreading of yield stress fluids. We employ lubrication theory, asymptotic solutions, and numerical simulations to explain the dynamics and final static shape of a viscoplastic droplet on a solid horizontal surface. We show that the final radius of the droplet becomes smaller with increasing the yield stress. Secondly, we provide experimental data to verify our theoretical solutions. In our experiments, we first provide a method to eliminate the apparent slip of the yield stress fluid. The method uses a chemical modification of glass surfaces to generate permanent positive charges, resulting in a no-slip boundary condition. We directly observe the slip and no-slip of the Carbopol droplets, using a visualization method based on confocal microscopy. We then perform shadowgraphy experiments to measure the final radius of the droplets under different conditions such as extruding and impacting droplets.
We compare the theoretical and experimental results and discuss the similarities and differences. Briefly, the asymptotic solutions overestimates the experimental results (most likely due to the assumption of a shallow layer), while numerical solutions are much closer to the experimental outcomes. Thirdly, we provide a comprehensive rheological characterization of a particular thermo-responsive fluid, Pluronic F127. We show that the aqueous solution of the polymer undergoes a sol(Newtonian)-gel(yield stress) transition upon heating. We further characterize the properties of the gel in detail. Finally, we show one can thermally trigger a thermo-responsive droplet to externally control the final shape of the droplet on a surface. In short, the final radius of the droplet can be controlled by heating the surface; for a given concentration, the larger the surface temperature, the smaller the final shape of a droplet. In the same part of the thesis, we introduce a novel experimental method based on optical coherence tomography to identify the solidified region inside a droplet.Applied Science, Faculty of
Graduate
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Khatchadourian, Armen. "Lipid droplets under stressful conditions." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=116901.
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Lipid droplets (LDs) are phylogenetically conserved and ubiquitous organelles with many cellular functions. In the last two decades, our understanding of LD biology and of their roles in physiological processes has increased dramatically. In addition, increasing evidence suggests that LDs are highly involved in inflammatory processes, and in metabolic disorders such as type 2 diabetes mellitus (T2DM). Despite such advancement, many aspects of LD biology and of their roles in health and disease remain unknown.The core of LDs is highly enriched with neutral lipids and these can be mobilized to provide metabolic energy. The phospholipid monolayer surrounding the LD core is associated with a wide variety of proteins, including structural and signaling proteins, as well as metabolic enzymes. While LDs may be induced by physiological stimuli such as dietary fatty acids, they can also be formed under stressful conditions, in the absence of such fatty acids. However, exactly how cellular stress leads to LD accumulation remains unclear. Our main objective is to understand the regulation of LD formation under stressful conditions, specifically oxidative stress, inflammation, and metabolic stress. We first investigated LDs in cells exposed to environmental stressors, namely cytotoxic metallic nanoparticles and reactive oxygen species. LD formation and expression of perilipin-2, a key structural LD protein, were highly increased in rodent cells exposed to these stress agents. Interestingly, supplementation with antioxidant N-acetyl cysteine or pharmacological inhibition of p38 mitogen activated protein kinase (MAPK) reduced stress-induced LD accumulation, suggesting that oxidative stress and p38 MAPK activation play a role in the induction of LD formation. Inflammatory leukocytes and macrophages contain a large number of LDs. While this phenomenon has been widely investigated in peripheral immune cells, its explanation remains elusive in immune cells of the central nervous system. We therefore investigated LD dynamics and regulation in microglia, the resident immune cells in the brain. We found that stimulation of microglia with toll-like receptor 4 (TLR4) agonist, lipopolysaccharides (LPS), increased LD formation and perilipin-2 expression in an Akt and p38 MAPK-dependent manner. Interestingly, LPS-induced LDs extensively colocalized with cytosolic phospholipase A2-α (cPLA2-α), a key enzyme involved in the synthesis of eicosanoids, which are inflammatory lipid mediators. Collectively, these findings imply that LD formation may contribute to increased eicosanoid synthesis in activated microglia and could be microglial biomarkers of inflammation in the central nervous system. To gain a better insight into the role of LDs in human pathology, we sought to examine alterations in LD metabolism in pancreatic tissue obtained from T2DM and obese individuals. Immunohistochemical studies revealed increased islet and extra-islet perilipin-2 expression in tissues from lean or obese T2DM donors, but not in non-T2DM obese donors, suggesting that the diabetic status, but not the obesity status, is a requirement for increasing perilipin-2 expression and LD formation. Gene expression analysis by RT-qPCR confirmed the increase in perilipin-2 expression and revealed significant alterations in several genes related to islet function, metabolism and antioxidant defense. These alterations seem to be consistently associated with obesity and T2DM and imply an adaptive and compensatory response to insulin resistance and metabolic stress. In summary, our studies show that LDs are an integral part of the adaptive cellular response to oxidative, inflammatory and metabolic stress. Perhaps, the most important challenge in LD research in the upcoming decade will be to determine how the subcellular lipid and protein composition of this organelle affects its function in different cells.Les gouttelettes lipidiques (GL) sont des organites phylogénétiquement conservées et impliquées dans plusieurs fonctions cellulaires. Durant les deux dernières décennies, notre compréhension des rôles biologiques et physiologiques des GL a augmenté de manière draconienne. Plusieurs observations suggèrent fortement que les GL jouent un rôle important dans l'inflammation, ainsi que dans les désordres métaboliques tels que le diabète de type 2 (DT2). Malgré cette avancée, plusieurs aspects de la biologie des GL et de leurs rôles dans des maladies demeurent méconnus.Le centre des GL est riche en lipides neutres qui peuvent se mobiliser et servir comme source d'énergie. La couche phospholipidique entourant le centre de la GL est associée à plusieurs protéines et enzymes métaboliques. Bien que les GL puissent être induites par des acides gras, elles peuvent aussi l'être dans des conditions de stress. Par contre, les mécanismes de l'accumulation de GL par des conditions de stress ne sont pas encore bien compris. Notre objectif principal est de comprendre la régulation de la formation de GL par le stress oxydatif, l'inflammation et le stress métabolique. Premièrement, nous avons investigué les GL dans des cellules exposées à des stresseurs tels que des nanocrystaux métalliques et des dérivés réactifs d'oxygène. La formation de GL et l'expression de perilipin-2, qui est une protéine structurelle des GL, ont tous deux augmenté dans les cellules stressées. De plus, une supplémentation en antioxydant (n-acétylcystéine) ou un traitement avec un inhibiteur de p38 MAPK a réduit l'accumulation de GL causée par le stress. Ces observations suggèrent que le stress oxydatif et p38 MAPK jouent un rôle dans l'accumulation de GL dans des cellules stressées. Il est bien connu que les leucocytes et macrophages qui sont engagés dans l'inflammation contiennent une grande quantité de GL. Même si ce phénomène a bien été exploré dans les cellules immunitaires périphériques, il reste inexploré dans le système nerveux central (SNC). Ce faisant, nous avons investigué la dynamique et la régulation des GL dans les microglies, les cellules résidentes immunitaires dans le cerveau. Nous avons trouvé que dans les microglies stimulées avec les lipopolysaccharides (LPS), les GL et l'expression de perilipin-2 ont augmenté d'une manière dépendante de l'activation de l'Akt et p38 MAPK. Dans ces cellules activées, la phospholipase cytosolique A2-α (PLC A2-α), une enzyme fonctionnant dans la synthèse d'éicosanoides, des médiateurs lipidiques inflammatoires, colocalisait avec les GL. Ensemble, ces résultats indiquent que la formation de GL pourrait contribuer à la synthèse d'éicosanoides dans les microglies activées et servir de biomarqueurs d'inflammation dans le SNC.Pour mieux comprendre le rôle des GL dans la pathologie humaine, nous les avons examinées dans des tissues pancréatiques provenant de patients obèses ou diabétiques T2. Nos études immunohistochimiques ont révélé une augmentation de perilipin-2 dans les îlots de Langerhans chez les patients diabétiques obèses ou maigres, mais pas dans ceux de patients non-diabétiques. Ceci suggère que le DT2, mais non l'obésité, est requis pour une augmentation de perilipin-2 dans le pancréas. L'analyse d'expression de gènes par RT-PCR a confirmé l'augmentation de perilipin-2 observé antérieurement dans les îlots et a également révélé des altérations dans des gènes reliés aux fonctions des îlots, au métabolisme, et aux défenses anti-oxydantes. Ces changements, qui sont souvent associés à l'obésité et au DT2, constituent un mécanisme d'adaptation à la résistance à l'insuline et au stress métabolique.Pour résumer, nos études démontrent que l'accumulation de GL fait partie intégrante de l'adaptation des cellules au stress. Durant la prochaine décennie, le plus grand obstacle dans la recherche sur les GL sera de déterminer comment la composition lipidique ou protéinique de ces organites affecte leurs fonctions biologiques.
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Seaton, Martin David. "Particle resuspension by liquid droplets." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614199.
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Chan, Chak Keung Seinfeld John H. Flagan Richard C. "Studies of levitated single droplets /." Diss., Pasadena, Calif. : California Institute of Technology, 1992. http://resolver.caltech.edu/CaltechETD:etd-07232007-131610.
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Guan, Jian. "Droplets on low friction surfaces." Thesis, Northumbria University, 2017. http://nrl.northumbria.ac.uk/35092/.
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Droplet mobility on surfaces is often hampered by the pinning of the droplet’s contact line. External forces would be needed if motion is to continue. The development of Slippery Liquid-Infused Porous Surfaces (SLIPS) or Lubricant-Impregnated Surfaces (LIS) has since enabled the studies of droplets in low friction situations with virtually no contact angle hysteresis. This thesis presents three separate studies of droplet mobility in the absence of contact line pinning, made possible by the use of SLIPS/LIS. Firstly, the first study of evaporation of sessile droplet under true constant contact angle mode was demonstrated. The lack of contact line pinning meant that droplet’s contact line receded smoothly with no stick-slip stepwise retreat as it evaporated. The absence of a contact angle due to the presence of the wetting ridge around the droplet led to the concept of an extrapolated apparent contact angle. The subsequent study saw the experimental realisation of both inward and outward motion of droplet having an apparent contact angle above 90° confined in a wedge geometry formed by a pair of SLIPS/LIS. Out of equilibrium, droplet was free to travel within the wedge until settling at a prescribed location, regardless to its initial position. This enabled the accurate control over the transport and localisation of the droplet by a reconfiguration of the system. The lack of pinning also suggests that the dynamics of the droplet is dictated purely by viscous dissipation. The final study showed that SLIPS/LIS can be created on macro-patterned surfaces. The macro-patterning introduced menisci features in the impregnating liquid layer which interact with the wetting ridge around a droplet. These interactions were used to induce motion to the droplet. It was also found that accurate positioning of the droplet on an otherwise completely slippery surface can be achieved using well-defined surface topography.
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De, Souza Lima Roger Williams. "Drying droplets as a template for multi-component solid particles : experimental study and modeling at the droplet scale Drying droplet as a template for solid formation: a review In situ Raman composition profiling in drying droplets." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2020. http://www.theses.fr/2020EMAC0003.
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Les gouttes liquides se sont avérées l’un des principaux vecteurs pour la génération de particules solides à propriétés contrôlées. Ce type de vecteur est utilisé dans plusieurs domaines industriels, y compris le séchage par atomisation. Le développement de ces particules structurées est poussé par la demande pour des particules à propriétés contrôlées, comme la cinétique de dissolution, le relargage contrôlé ou la réactivité. Le principal verrou scientifique est la description détaillée de la distribution des constituants au sein de la goutte pendant le séchage, en plus de la prédiction de la morphologie de la particule finale. L'objectif de cette thèse est de comprendre, par une approche couplée modélisation/expérimentation, comment les conditions de séchage et les formulations liquides impactent la structure de la poudre. L'étude expérimentale a d'abord été réalisée dans un sécheur par atomisation à l'échelle laboratoire pour la création d'une cartographie représentant les morphologies obtenues pour les deux systèmes de séchage. Un dispositif expérimental a été conçu de manière à étudier la formation d'une particule solide à partir d'une goutte suspendue par un filament, ce qui permet d'appréhender des éléments fondamentaux relatifs au séchage de la goutte ainsi que des aspects sur la modification de la structure solide. Une nouveauté explorée à l'échelle de la goutte avec un lévitateur acoustique consistait à appliquer la spectroscopie Raman in situ afin d'évaluer l'évolution de la distribution spatiale de deux composants lors du séchage de la goutte. Enfin, un modèle de séchage de goutte en 2-D avec la Dynamique des Fluides Numérique est conçu, ce qui permet de quantifier la distribution spatiale des composants de la goutte sous un séchage convectif, jusqu’à la formation de la croûte. Une analyse de sensibilité est réalisée de manière à montrer l'influence des conditions expérimentales sur la cinétique de séchage et la distribution spatiale des solutésLiquid droplets are one of the major means of generation of solid particles with controlled. These templates are encountered with a variety of industrial processes, among them, spray drying. These tailored structures would meet the demand for particles with controlled properties, like improved kinetics, sustained release or controlled reactivity. The major scientific obstacle is the detailed description of the components distribution inside the droplet during drying, besides prediction of the final particle morphology. An experimental/modeling approach is undertaken in this thesis to understand how the drying conditions and the liquid formulation impact the final structure of the powders. The drying systems studied were sucrose-dextran and lactose-whey protein isolate aqueous solutions. The experimental work was firstly carried out at the lab-scale spray-dryer giving a reference picture of the possible particle morphologies for the drying systems. An experimental set-up was designed and developed to suspend a liquid droplet by a filament, from which the droplet mass variation over time could be accurately measured, giving fundamental insight into the drying process and allowing the analysis of the modification of the solid structures. A novelty explored at the droplet scale with an acoustic levitator was to apply an in situ Raman spectroscopy to assess the evolution of the spatial distribution of two components in drying droplets. Finally, a 2-D droplet drying model using Computational Fluid Dynamics was developed for allowing the assessment of the spatial distribution of the droplet components under a convective drying, until the formation of a crust. A sensitivity analysis was performed in order to show the influence of the experimental conditions on the drying kinetics and the component spatial distribution
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Mehrotra, Rajat. "Monodispersed polygonal water droplets in microchannel." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2726.
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Jara, Javier. "Evaporation-condensation of levitated copper droplets." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ36989.pdf.
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Zhang, Yuxiang, and 张玉相. "Microfluidics: fabrication, droplets, bubblesand nanofluids synthesis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44903935.
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Stauber, J. M. "On the evaporation of sessile droplets." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25530.
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In this thesis the evolution of sessile droplets in different modes of evaporation and their lifetimes are investigated. The thesis focuses on situations in which the diffusion of vapour into the surrounding atmosphere is the rate-limiting mechanism of evaporation. First, we describe the evolution of droplets evaporating in the two extreme modes, namely the constant contact radius mode, in which the contact line of the droplet is always pinned, and the constant contact angle mode, in which the contact line of the droplet is always de-pinned. In particular, we demonstrate how these two modes converge on strongly hydrophobic substrates. Next we study the evolution of droplets evaporating in the stick-slide mode, in which the contact line is initially pinned and the contact angle decreases to the receding contact angle, but thereafter the contact line is de-pinned and the contact radius decreases to zero. The lifetimes of droplets evaporating in the stick-slide mode are investigated in two situations, namely when the initial and receding contact angles are independent and when there is a simple relationship between them based on the assumption of a constant maximum pinning force. In particular, it is shown that the lifetimes of droplets evaporating in this mode may be longer than those of initially identical droplets evaporating in the two extreme modes. Finally, we develop a model for the evolution of droplets evaporating in a stick-jump mode, in which the contact line pins, de-pins and re-pins multiple times. It is shown that the lifetimes of droplets evaporating in this mode may be longer or shorter than those of initially identical droplets evaporating in the two extreme modes. Good agreement is found between the predicted lifetimes of droplets in both the stick-slide and the stick-jump modes and the lifetimes of droplets determined from relevant experiments in the literature.
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Fradet, Etienne. "Monitoring biochemical reactions in stationary droplets." Palaiseau, Ecole polytechnique, 2013. http://pastel.archives-ouvertes.fr/docs/00/92/97/15/PDF/fradet_thesis_2013.pdf.
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La microfluidique de gouttes - i. E. L'emploi de gouttelettes comme microréacteurs - offre de nombreux avantages pour l'étude des systèmes biologiques. Dans ce travail de thèse, nous présentons une nouvelle approche pour la production et la manipulation de gouttelettes au sein de microcanaux afin de suivre l'avancement de réactions biochimiques au cours du temps. Contrairement aux approches existantes, notre dispositif utilise des gradients de confinement afin de produire et guider une unique goutte vers son lieu de stockage. Ce faisant, deux gouttes de contenus différents peuvent être appariées et fusionnées afin de déclencher une réaction chimique. Les réactifs n'étant pas activement mélangés, un front de réaction se propage alors le long de la goutte fille duquel on peut extraire la cinétique de la réaction. Nous commençons par l'étude de réactions simples ayant lieu en une étape. Un modèle 1D de réaction-diffusion permet de représenter la dynamique du front de réaction ce qui est vérifié en confrontant les solutions de ce modèle, obtenues numériquement ou analytiquement, à des mesures effectuées en gouttes. Puis, nous nous intéressons au cas des réactions enzymatiques. Nous démontrons d'abord la parallélisation de notre technique d'appariement de gouttes afin de reproduire en microcanal différents tests enzymatiques usuellement effectués en plaque multipuits. Finalement, nous étudions le cas des réactions enzymatiques rapides à l'aide de notre modèle de réaction-diffusion. Là encore, la comparaison d'expériences tenues en gouttes et de prédiction issues de notre modèle nous permet d'extraire une mesure des paramètres cinétiques de la réaction mise en jeuDroplet microfluidics - i. E. The use of droplets as microreactors - offers significant advantages for the study of biological systems. In this work, we present a new platform for the production and manipulation of microfluidic droplets in view of measuring the evolution of biochemical reactions. Contrary to existing approaches, our device uses gradients of confinement to produce a single drop on demand and guide it to a pre-determined location. In this way, two nanoliter drops containing different reagents can be placed in contact and merged together in order to trigger a chemical reaction. Then, an analysis of the observed reaction front yields the reaction rate. We start with the case of one step reactions. We derive a one dimensional reaction-diffusion model for the reaction front and compare numerical and analytical solutions of our model to experiments held in our microsystem. Then, we turn our attention to the case of enzymatic reactions. First, we show how the device operation can be parallelized in order to react an initial sample with a range of compounds or concentrations and we perform standard well-mixed enzyme assays with our parallelized chip, thereby mimicking titer plate assays in droplets. Second, we build onto our reaction-diffusion model to predict the rate of fast enzymatic reactions held in our device. Again, numerical and analytical solutions of our model are compared to experiments done in droplets which yields measurements of the kinetic parameters of the reaction at play
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Manica, Rogério. "Modelling hydrodynamic interactions between deformable droplets /." Connect to thesis, 2007. http://eprints.unimelb.edu.au/archive/00003700.
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Kotikalapudi, Sivaramakrishna. "Spreading of initially spherical viscous droplets." Link to electronic version, 2000. http://www.wpi.edu/Pubs/ETD/Available/etd-0930100-201701/restricted/kotikalapudi.pdf.
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Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: crown; splash; spreading; oscillatory; droplets; microgravity; viscosity; map; stability; solid surface; surface tension; gravity. Includes bibliographical references (p. 111-113).
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Stindt, Arne. "Probing levitated droplets with mass spectrometry." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17538.
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Ultraschalllevitation kombiniert die Vorteile von Mikrofluidik, wie beispielsweise die sehr geringe benötigte Probenmenge, mit einer wandlosen Probenhandhabung. Obwohl die Kopplung zwischen le- vitierten Tröpchen und verschiedenster analytischer Methoden wie optischer Spektroskopie und Röntgenbeugung sehr genau untersucht ist, fehlt es immer noch an einer etablierten Kopplung mit einer massenspektrometrischen Methode für die Analyse auf molekularer Ebene. Die vorliegende Arbeit beschreibt die Prinzipien, auf denen eine kontaktlose massenspektrometrische Analyse von levitierten flüssi- gen Proben beruht. Zuerst wurde der neu entworfene akustische Levitator bezüglich des Einflusses seiner Geometrie auf die Levi- tationseigenschaften experimentell und mittels numerischer Simul- tationen untersucht. Die anschließend durch geführten Experimen- te demonstrieren das Potential von Infrarot-Lasern als kombinierte Desorptions- und Ionisationsquelle für organische Substanzen aus einer Mischung aus Wasser und Glycerin als Cromophor. Um einen tieferen Einblick in die hierbei ablaufenden Ionisationsmechanismen zu erhalten, wurde als Modell ein “Sonic-Spray” Konus räumlich per Massenspektrometrie und Laser-induzierter Fluoreszenz untersucht. Levitator-Geometrie auf die Levitationseigenschaften stimmen sehr gut mit numerischen Simulationen überein. Als komplementäre Ionisationsmethode wurde eine Niedertemperatur-Plasmaquelle ein- gesetzt. Nach einer zeitaufgelösten Untersuchung der grundlegenden Ionisationsmechanismen wurde diese Quelle für die Untersuchung flüchtiger Spezies aus der levitierten Probe in deren direkten Umgebung ohne störende Interferenzen ge- nutzt.Ultrasonic levitation combines advantages of microfluidics like the required small sample volumes with a wall-less sample handling. While the coupling of analytical methods like optical spectroscopy as well as x-ray scattering are very well elaborated, an established mass spectrometric method to obtain molecular analytical information is still lacking. The herein presented work describes the fundamental processes for a contactless mass spectrometric analysis of levitated droplets. First, the influences of the specially designed levitator geometry on the levitation capabilities is described. During further experiments, the use of infrared lasers has proven useful as a combined desorption and ionization source for organic molecules from a mixture of water and glycerol as chromophore. Subsequently, sonic-spray ionization was used to gain a deeper understanding of the ionization processes occurring within the spray plume. Mass spectrometric mapping as well as laser-induced fluorescence were performed to investigate the ionization during an aerodynamic breakup of the micro droplets in the spray process. As a complementary sampling method, the ionization with a low- temperature plasma source is described. First, a time-resolved mass spectrometric investigation of the ionization process is shown. Sub- sequent to this fundamental study, the application of such a plasma source for the direct analysis of volatile compounds from within the droplets in the surrounding environment without interferences from the droplets bulk phase is described.
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Du, Xiaoli [Verfasser]. "Characterization of Lipid Droplets and Functional Analysis of Lipid Droplet-Associated Proteins in Dictyostelium discoideum / Xiaoli Du." Kassel : Universitätsbibliothek Kassel, 2013. http://d-nb.info/1038246776/34.
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Yakhshi, Tafti Ehsan. "Thermally-induced motion of droplets on a thin liquid layer and its application to droplet manipulation platforms." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4682.
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Heaters were interfaced with control electronics and driven through a computer graphical user interface. By creating appropriate spatio-temporal thermal gradient maps, transport of droplets on predetermined pathways was demonstrated with a high level of controllability and speed.; In the recent years, there has been a growing interest in droplet-based (digital) microfluidic systems due to their ability to handle multiple discrete samples in a self-contained configuration compared to continuous flow systems. Various methods for droplet manipulation are currently available based on hydrodynamic, electrostatic, chemical, photonic and thermal interactions. High speed, controlled response and minimal thermal loading with least contamination are required in practical applications, especially in chemistry and biology. Although, thermal actuation of droplets has been recognized as an attractive choice due to a wide range of thermomechanical properties that can be exploited, the previous studies yielded limited success in addressing issues such as droplet evaporation, contamination, pinning, hysteresis and irreversibility that are associated with using solid substrate platforms. In order to overcome shortcomings of traditional approaches, a novel thermally-actuated droplet manipulation platform based on using an inert liquid film was proposed and its working mechanisms were studied. Droplets at the air-liquid interface of immiscible liquids usually form partially-submerged lens shapes (e.g. water on oil). In the thermally-induced motion of droplets on the free surface of immiscible liquid films, lens-shaped droplets move from warm toward cooler regions. In addition to this structure, we showed that droplets released from critical heights above the target liquid can sustain the impact and at the end maintain a spherical ball-shape configuration above the surface, despite undergoing large deformation. It was discovered in this study that such spherical droplets migrate in the opposite direction to lens droplets when subject to a thermal gradient; i.e. direction of increasing temperatures.; The existence of this metastable spherical state above the free surface and its transition into more stable lens configuration was investigated using optical diagnostic tools and theoretical analysis. Opposite direction of motion observed for droplets at the free surface of immiscible liquids was explained based on droplet shape at the interface and the dynamics of thin liquid films subject to lateral thermal gradients: mainly 1) deformation of the free surface and 2) development of an outward moving flow (hot to cold) at the free surface due to surface tension gradients caused by thermal gradients. A lens droplet moves due to the free surface flow caused by Marangoni convection which is from hot to cold. On the other hand, the spherical droplet moves towards the maximum depression on the free surface, occurring at the hottest region as a result of the balance between gravity and drag forces from the opposing free surface flow. The proposed theoretical models predict experimental observations of droplet motion due to thermal gradients satisfactorily. Opposite responses of thermally-induced motion of lens and spherical droplets on a thin liquid layer, were characterized experimentally and compared to theory by studying droplet motion in an exponentially-decaying temperature field maintained across the length of a shallow liquid layer. The effect of droplet size and magnitude of thermal gradient (slope) on drop velocity were investigated. The down-scaling effect is prominent, which shows that the proposed concept of droplet manipulation could be used favorably in miniaturized platforms. Based on the theoretical development and measurements obtained from meso-scale experiments, a silicon-based droplet transportation platform with embedded metal film micro heaters was developed. A thin layer of a chemically-inert and thermally stable liquid was chosen as the carrier liquid.ID: 029050798; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 113-117).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
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Wilms, Jochen [Verfasser]. "Evaporation of multicomponent droplets / von Jochen Wilms." München : Verl. Dr. Hut, 2005. http://d-nb.info/979033012/34.
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Marskar, Robert. "Nonlinear Vibration-Rotation Modes Of Inviscid Droplets." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-7657.
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Barisch, Caroline [Verfasser]. "Lipid Droplets in Dictyostelium discoideum / Caroline Barisch." Kassel : Universitätsbibliothek Kassel, 2010. http://d-nb.info/1009528076/34.
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Björnander, Rahimi Klara. "Enrichment of microparticles in droplets using acoustophoresis." Thesis, Uppsala universitet, Mikrosystemteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-349376.
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Acoustophoresis is a label free method where the acoustic radiation force is used to manipulate microparticles inside microfluidic channels. The magnitude of the force is dependent of several parameters, which include the density, speed of sound and size of the microparticles, as well as the amplitude of the pressure waves. Recently, acoustophoresis has been used in microfluidics to manipulate microparticles inside moving droplets. In this Master's thesis project, two microfluidic chip designs are used to enrich droplets with polystyrene beads (10 μm in diameter) using acoustophoresis. The microchips have been fabricated with two different fabrication methods; crystalline dependent wet etching and crystalline independent dry etching. In the microchips, water droplets in oil are generated with microparticles suspended in them. By using a channel width that is half a wavelength of the incoming acoustic waves, pressure nodal lines are created in the middle of the channel in which the microparticles align. The droplets then enters a droplet splitting feature, where they are divided into three daughter droplets. Since the majority of the incoming particles are recovered in the center daughter droplet while some of the droplet volume is removed, the center droplet is enriched with the microparticles. For the wet etched design stable droplet splitting was observed when the volumetric flow was 18 μL/min and the incoming droplets had a length-to-width ratio larger than 3. The maximum recovery for this design was 81.1% ± 13.8% with an applied voltage at 10 Vpp. Stable droplet splitting was observed for the dry etched chip at 10.5 μL/min and 18 μL/min at 10 and 20 Vpp, when the incoming droplet had a length-to-width ratio of 3. In this chip the maximum recovery was 93.2% ± 8.3% at the volumetric flow of 10.5 μL/min and an applied voltage of 20 Vpp.
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Jalaal, Maziyar. "Direct numerical simulation of fragmentation of droplets." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42476.
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The work described in the present thesis is related to a series of projects that I worked on toward the better understanding of fragmentation phenomena. In the past decades, the science of fragmentation has attracted many attentions within the researchers due to its wide range of applications. However, because of the complexity of the subject, even its basic concepts need more investigations.
This thesis starts with an introduction to fragmentation of droplets using experimental or numerical approaches. It is discussed that the current mathematical and experimental tools are not able to describe all the details. Thus, high performance numerical simulations are the best alternatives to study the breakup of droplets. The introduction is followed by a discussion on the numerical method and the ranges of the non-dimensional groups. It is described that an adaptive, volume of fluid (VOF) method based on octree meshing is used, providing a notable reduction of computational cost. The rest of the thesis basically discusses the obtained results using direct numerical simulations. Two main geometries are investigated: falling droplets and droplets in a stream. For the case of falling droplets, three simulations with different Eötvös numbers are performed. For the case of droplets in a stream, two-dimensional and three-dimensional simulations are performed for a range of Weber number. The results are compared with the available mathematical theories and it is shown that the analysis presented here precisely demonstrates the mechanism of the bag breakup of falling droplets and instability growth over the droplets in an external high-speed flow. The outcomes can significantly assist the development of the secondary atomization and turbulent two-phase flows modelling.
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Zwicker, David. "Physical Description of Centrosomes as Active Droplets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-127246.
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Biological cells consist of many subunits that form distinct compartments and work together to allow for life. These compartments are clearly separated from each other and their sizes are often strongly correlated with cell size. Examples for those structures are centrosomes, which we consider in this thesis. Centrosomes are essential for many processes inside cells, most importantly for organizing cell division, and they provide an interesting example of cellular compartments without a membrane. Experiments suggest that such compartments can be described as liquid-like droplets. In this thesis, we suggest a theoretical description of the growth phase of centrosomes. We identify a possible mechanism based on phase separation by which the centrosome may be organized. Specifically, we propose that the centrosome material exists in a soluble and in a phase separating form. Chemical reactions controlling the transitions between these forms then determine the temporal evolution of the system. We investigate various possible reaction schemes and generally find that droplet sizes and nucleation properties deviate from the known equilibrium results. Additionally, the non-equilibrium effects of the chemical reactions can stabilize multiple droplets and thus counteract the destabilizing effect of surface tension. Interestingly, only a reaction scheme with autocatalytic growth can account for the experimental data of centrosomes. Here, it is important that the centrioles found at the center of all centrosomes also catalyze the production of droplet material. This catalytic activity allows the centrioles to control the onset of centrosome growth, to stabilize multiple centrosomes, and to center themselves inside the centrosome. We also investigate a stochastic version of the model, where we find that the autocatalytic growth amplifies noise. Our theory explains the growth dynamics of the centrosomes of the round worm Caenorhabditis elegans for all embryonic cells down to the eight-cell stage. It also accounts for data acquired in experiments with aberrant numbers of centrosomes and altered cell volumes. Furthermore, the model can describe unequal centrosome sizes observed in cells with disturbed centrioles. Our example thus suggests a general picture of the organization of membrane-less organellesBiologische Zellen bestehen aus vielen Unterstrukturen, die zusammen arbeiten um Leben zu ermöglichen. Die Größe dieser meist klar voneinander abgegrenzten Strukturen korreliert oft mit der Zellgröße. In der vorliegenden Arbeit werden als Beispiel für solche Strukturen Zentrosomen untersucht. Zentrosomen sind für viele Prozesse innerhalb der Zelle, insbesondere für die Zellteilung, unverzichtbar und sie besitzen keine Membran, welche ihnen eine feste Struktur verleihen könnte. Experimentelle Untersuchungen legen nahe, dass solche membranlose Strukturen als Flüssigkeitstropfen beschrieben werden können. In dieser Arbeit wird eine theoretische Beschreibung der Wachstumsphase von Zentrosomen hergeleitet, welche auf Phasenseparation beruht. Im Modell wird angenommen, dass das Zentrosomenmaterial in einer löslichen und einer phasenseparierenden Form existiert, wobei der Übergang zwischen diesen Formen durch chemische Reaktionen gesteuert wird. Die drei verschiedenen in dieser Arbeit untersuchten Reaktionen führen unter anderem zu Tropfengrößen und Nukleationseigenschaften, welche von den bekannten Ergebnissen im thermodynamischen Gleichgewicht abweichen. Insbesondere verursachen die chemischen Reaktionen ein thermisches Nichtgleichgewicht, in dem mehrere Tropfen stabil sein können und der destabilisierende Effekt der Oberflächenspannung unterdrückt wird. Konkret kann die Wachstumsdynamik der Zentrosomen nur durch eine selbstverstärkende Produktion der phasenseparierenden Form des Zentrosomenmaterials erklärt werden. Hierbei ist zusätzlich wichtig, dass die Zentriolen, die im Inneren jedes Zentrosoms vorhanden sind, ebenfalls diese Produktion katalysieren. Dadurch können die Zentriolen den Beginn des Zentrosomwachstums kontrollieren, mehrere Zentrosomen stabilisieren und sich selbst im Zentrosom zentrieren. Des Weiteren führt das selbstverstärkende Wachstum zu einer Verstärkung von Fluktuationen der Zentrosomgröße. Unsere Theorie erklärt die Wachstumsdynamik der Zentrosomen des Fadenwurms Caenorhabditis elegans für alle Embryonalzellen bis zum Achtzellstadium und deckt dabei auch Fälle mit anormaler Zentrosomenanzahl und veränderter Zellgröße ab. Das Modell kann auch Situationen mit unterschiedlich großen Zentrosomen erklären, welche auftreten, wenn die Struktur der Zentriolen verändert wird. Unser Beispiel beschreibt damit eine generelle Möglichkeit, wie membranlose Zellstrukturen organisiert sein können
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Sujith, R. I. "Behavior of droplets in axial acoustic fields." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/12487.
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Söderberg, Lovisa. "cDNA sythesis and analysis in microfluidic droplets." Thesis, KTH, Skolan för bioteknologi (BIO), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-149355.
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Duan, Hongxu. "Generation and printing of strictly monodisperse droplets." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5931.
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Highly monodisperse droplets are attracting great attention both in many research areas, such as aerosol science, combustion, and Nano-manufacturing. This thesis invents a novel aerosol generator: “Periodic Electro Hydro-dynamic Chopper” termed as “PEHD chopper”, and develops a new method to directly print micro-patterns with monodisperse droplets. The principle of the PEHD chopper is to use the fringe electric field of a capacitor to introduce controlled perturbation on a liquid jet.
We first derived the governing equations for a circular inviscid liquid jet under transverse electric fields. The electric fields were obtained through numerical simulation. Then we used a high speed camera (up to one million frames per second) to visualize the jet break-up as well as the droplets' size and shape.
The experiments show that the PEHD chopper can effectively “chop” a neutral micro-jet and generate highly monodisperse micro-droplets, which diameter range from 100 &"181;m to 500 &"181;m. To reduce the droplet size, PEHD chopper with a butterfly design is applied on a typical single electrospray. In this configuration, the jet swings at long wavelengths (?>?R), where ?R is the Rayleigh wave length, but breaks up into highly monodisperse droplets near 2?R and ?R without satellite droplets. The butterfly configuration combined with electrified jet expands the diameter range into 20 &"181;m to 100 &"181;m.
Finally, we demonstrate the electrospray printing of Polymer Derived Ceramics (PDC) for sensor applications in harsh environment. A modified single ES with an additional driving electric field is used to directly print PDC precursor without mask, we achieved 1D feature as narrow as 35 &"181;m and a micro pentagram pattern. Moreover, after pyrolysis of PDC at 1100 °C in nitrogen, amorphous alloys of silicon, carbon and nitrogen (SiCN) are obtained. The samples exhibit excellent good integrity and adhesion to the substrate.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Miniature Engineering Systems
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Pairam, Ekapop. "Toroidal droplets: instabilities, stabilizing and nematic order." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51913.
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The goal of this thesis is to study the ground or metastable state structure of nematic liquid
crystal systems confined inside handled shapes such as a torus or double torus. We begin our work
by introducing a new method to generate a toroidal droplet from a Newtonian liquid inside another,
immiscible, Newtonian liquid. In this situation, a toroidal droplet is unstable and follows one of two
routes in transforming into a spherical droplet: (i) its tube breaks in a way reminiscent to the breakup
of a cylindrical jet, or (ii) its tube grows until it finally coalesces onto itself. However, to be able to
probe the nematic structure, we need to address the issue of instabilities. This is done by replacing
the outer liquid with a yield stress material, which ultimately leads to the stabilization of the toroidal
droplet. Through the experimental investigation, we are able to establish the stabilization conditions.
Finally, we generate and stabilize toroidal droplets with a nematic liquid crystal as the inner liquid
and a yield stress material as the outer medium. Here we observe that in the ground state, the
nematic liquid crystal exhibits an intriguing twisted structure irrespective of the aspect ratio of the
torus. While there are no defects observed in a toroidal droplet case, two defects with -1 topological
charge each emerge each time we increase the number of handles.
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Sachdev, Suchanuch. "Emulsion droplets as reactors for assembling nanoparticles." Thesis, Loughborough University, 2018. https://dspace.lboro.ac.uk/2134/36206.
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Materials on the nanoscale have very interesting properties. Hence, they are commonly used for a variety of applications such as drug delivery, bio-imaging and sensing devices. Moreover, coating these particles with other materials forming core@shell or Janus particles can further enhance their properties. However, for the particles to be used in medical and electronic devices, their properties such as size, shape and composition need to be precisely controlled. In this PhD., an emulsification technique was chosen to investigate the synthesis of nanoparticles; it is a simple process, does not require any harsh chemicals or temperature and is fast. Emulsification occurs when two or more immiscible liquids and surfactants are mixed. Here, emulsion droplets were produced using a microfluidic device which allowed for the creation of uniform droplets. These were employed as templates to synthesise and assemble nanomaterials. The main aim of the Ph.D. was to develop a droplet based synthesis process to generate nanoparticles and then assemble them into core@shell particles. This Ph.D., starts by synthesising Fe3O4 nanoparticles (~ 12 nm) and assembling them into microparticles (~ 1µm 2µm) using emulsion droplets as microreactors. By tuning the surfactant, droplet size and evaporation rate of the dispersed phase, microparticles of varying shapes and sizes, such as spherical or crumbled shapes, were produced. When these particles are compared with the commercially available particles, the magnetic content of the in-house particles, or sometimes referred to as Loughborough University Enterprises Ltd. (LUEL), are much higher and more uniform, hence resulting in faster separation when used for extraction of analytes. LUEL particles were supplied as part of commercial collaboration. The use of Pickering emulsions were then explored to create core@shell particles using gold nanoparticles instead of a surfactant to produce gold shells and the addition of pre-synthesised Fe3O4 nanoparticles results in Fe3O4@Au core@shell particles. This is the first time Pickering emulsions were used to produce Fe3O4@Au core@shell particles (~ 1.5 µm) within a microfluidic device. However, the shells were not uniform in thickness. In order to improve the coverage, nanoparticles were synthesised in situ at the droplet interface. By placing the gold chloride (AuCl4-) in the continuous phase and by varying the concentration of the electron donor in hexane droplet, single crystal gold nanoparticles and platelets were formed. The reaction is spontaneous at room temperature, creating gold nanoparticles at the interface of the emulsion droplet. The size and shape of the gold nanoparticles were controlled by varying the concentration of the reactants and the size of the droplets. By adding pre-synthesised particles (Fe3O4 nanoparticles) to the droplet, Au@Fe3O4 core@shell particles were formed with an approximate size of 250 nm. The same concept of forming core@shell particles using gold nanoparticles was further expanded by using other metal ions; palladium and silver. Unlike gold, palladium and silver only formed spherical nanoparticles, no platelets were observed. The addition of preformed iron oxide nanoparticles to the palladium results in core@shell particles. However, in the case of silver, no core@shell particles were formed. The study of the rate of reaction was conducted to understand the details of the mechanism. Overall, the process developed in this Ph.D. study allows for the facile synthesis of core@shell particles in a rapid, high throughput reaction. In the future, it is believed it could be scaled up for commercial purposes.
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Lindebratt, Ludwig, and Erik Segerstéen. "Methods for active manipulation of fluid droplets." Thesis, KTH, Maskinkonstruktion (Inst.), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-182660.
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The deposition of functional materials utilising a jetting head has a large number of applications as can be seen by the growing interest in rapid prototyping. The ability to jet with precision and accuracy for high throughput application is at the core of the jetting technology. If this can be achieved at increasingly large altitudes over the substrate an increased portion of the business application space can be addressed, such as the ability to jet with smaller droplets, the ability to jet on complex PCB configurations, et cetera. A state of the art study is included in this project, which describes different potential methods that could be used for active manipulation of fluid droplets. In this project, two methods have been investigated for active manipulation of fluid droplets that could be implemented on the MY600 Jet Printer. The first method is based on using a converging air flow to focus the droplets towards the centre of a tube and thus reduce error positioning. From the simulations and analyses performed, it was concluded that this method was not suitable for implementation on the MY600 Jet Printer due to the excessively high air flow speed required to correct any misalignments. The second method investigated uses an electrostatic field to affect the positioning of charged droplets. From the performed experiments, it was concluded that the droplets can be affected by the electrostatic field, but that active charging of the droplets is necessary to achieve an adequate force required to correct any misalignments within a reasonable height.Den ständigt växande marknaden för kretskortstillverkning ställer allt högre krav på leverantörer när det kommer till tillverkningshastighet och noggrannhet. Detta är en stor utmaning för Mycronic som ständigt måste förbättra precisionen på sina produktionsrobotar för att behålla och eventuellt stärka sin position inom branschen. Genom att öka höjden från vilken skotten skjuts ifrån, och samtidigt bibehålla precisionen, skulle man kunna öppna nya dörrar för att till exempel minska volymen på skotten för att träffa allt mindre paddar eller skjuta lodpasta på komplicerade kretskort med färdigmonterade komponenter. Under projektet utfördes en undersökning om vilka metoder som idag används för att styra och manipulera droppar. Undersökningen resulterade i idéer på hur problemet kan lösas, vilka presenteras i rapporten. Två metoder har studerats och för att ta reda på om de kan bidra till en ökad precision för MY600 Jet Printer. Den första metoden baseras på ett fokuserande luftflöde där man påverkar kroppens rörelse med ett riktat luftflöde. Uträkningar och simuleringar visade att kraften, som luften verkar med, inte räcker till för de lufthastigheter som var realistiska att implementera. Den andra metoden baserades på fokuseringen av uppladdade droppar med hjälp av elektriska fält. Denna metod uppvisade positiva resultat. Efter ett flertal tester, med olika vätskor, drogs slutsatsen att det skulle vara möjligt att implementera en prototyp där dropparna laddas upp för att sedan fokuseras av ett elektriskt fält inuti en cylinder och på så sätt förbättra noggrannheten.
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Wang, Yuli. "Capillarity and wetting of non-Newtonian droplets." Doctoral thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-184146.
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Capillarity and dynamic wetting of non-Newtonian fluids are important in many natural and industrial processes, examples cover from a daily phenomenon as splashing of a cup of yogurt to advanced technologies such as additive manufacturing. The applicable non-Newtonian fluids are usually viscoelastic compounds of polymers and solvents. Previous experiments observed diverse interesting behaviors of a polymeric droplet on a wetted substrate or in a microfluidic device. However, our understanding of how viscoelasticity affects droplet dynamics remains very limited. This work intends to shed light on viscoelastic effect on two small scale processes, i.e., the motion of a wetting contact line and droplet splitting at a bifurcation tip. Numerical simulation is employed to reveal detailed information such as elastic stresses and interfacial flow field. A numerical model is built, combining the phase field method, computational rheology techniques and computational fluid dynamics. The system is capable for calculation of realistic circumstances such as a droplet made of aqueous solution of polymers with moderate relaxation time, impacting a partially wetting surface in ambient air. The work is divided into three flow cases. For the flow case of bifurcation tube, the evolution of the interface and droplet dynamics are compared between viscoelastic fluids and Newtonian fluids. The splitting or non-splitting behavior influenced by elastic stresses is analyzed. For the flow case of dynamic wetting, the flow field and rheological details such as effective viscosity and normal stress difference near a moving contact line are presented. The effects of shear-thinning and elasticity on droplet spreading and receding are analyzed, under inertial and inertialess circumstances. In the last part, droplet impact of both Newtonian and viscoelastic fluids are demonstrated. For Newtonian droplets, a phase diagram is drawn to visualize different impact regions for spreading, splashing and gas entrapment. For viscoelastic droplets, the viscoelastic effects on droplet deformation, spreading radius and contact line motion are revealed and discussed.QC 20160329
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Black, James Aaron. "Compound droplets for lab-on-a-chip." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54947.
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The development of a novel method of droplet levitation to be employed in lab-on-a-chip (LOC) applications relies upon the mechanism of thermocapillary convection (due to the temperature dependence of surface tension) to drive a layer of lubricating gas between droplet and substrate. The fact that most droplets of interest in LOC applications are aqueous in nature, coupled with the fact that success in effecting thermocapillary transport in aqueous solutions has been limited, has led to the development of a technique for the controlled encapsulation of water droplets within a shell of inert silicone oil. These droplets can then be transported, virtually frictionlessly, resulting in ease of transport due to the lack of friction as well as improvements in sample cross-contamination prevention for multiple-use chips. Previous reports suggest that levitation of spherical O(nL)-volume droplets requires squeezing to increase the apparent contact area over which the pressure in the lubricating layer can act allowing sufficient opposition to gravity. This research explores thermocapillary levitation and translation of O(nL)-volume single-phase oil droplets; generation, capture, levitation, and translation of O(nL)-volume oil-encapsulated water droplets to demonstrate the benefits and applicability to LOC operations.
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Lau, Gabriel. "Droplets : from molecular nanoclusters to atmospheric aerosols." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/45358.
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Atmospheric aerosols play a key role in affecting climate, pollution and human health by in- fluencing the properties and lifetimes of clouds and precipitation. Despite this, the molecular mechanisms involved in the nucleation of nanoscale liquid droplets are not yet fully under- stood. In this thesis, we attempt to gain a better understanding of the surface properties and small-scale thermodynamics of nanoscopic clusters of water using molecular dynam- ics simulation to complement the recent surge of scientific interest in atmospheric aerosol nucleation. Existing literature is reviewed on simulation techniques to obtain the surface tension of planar and curved interfaces, as well as studies on vapour-liquid nucleation. This is followed by several in-depth computational investigations into the surface properties of water. In the first, we apply a free-energy perturbation technique, namely the test-area (TA) method, to compute the surface tension of planar, cylindrical and spherical geometries of water. In addition, a mathematical analysis of the TA method is carried out, revealing further insight into the underlying features of perturbation methods as well as their limi- tations. The results are compared to previous literature and the differences discussed. In the second and third, the excess free energy is obtained for small clusters of water using an extension of a non-equilibrium disassembly method originally developed for studies on argon clusters. The results are used to construct free-energy curves that are subsequently fed into classical rate expressions and compared to experimental values. In the final part of the thesis, the formalism generalising the cluster disassembly method to multi-component systems is presented.
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Gao, Fan. "The Impact Dynamics of Weakly Charged Droplets." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/92888.
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Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces Through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing.Doctor of Philosophy
Electric charges are often found in naturally or artificially formed droplets, such as raindrops, waterfall, and inkjet printer. Neutral droplets impact on flat surfaces will usually trap a bubble inside because of the viscosity of air. The air bubble entrapped can be ignored if the droplet is water because the air bubble will eventually pinch-off. However, if the droplet is metal or some other viscous liquid, the air bubble will stay inside the liquid. This entrapped air bubble is undesired under some circumstances. For example, the existence of air bubble during metal 3D printing can influence the physical property. I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the maximum charges a droplet can carry for representative impact conditions, the electric stress will dominate the deformation of droplet. A conical liquid tip forms at the droplet bottom, avoiding the entrapment of air bubble. The critical charge level is experimentally proved to be only dependent on the gas viscosity and impact velocity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing.
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Mirheydari, Mona Sadat. "INVESTIGATION OF THE BIOPHYSICS OF LIPID DROPLETS." Kent State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=kent1498862985023767.
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Ali, Hassan H. "The mechanisms of drying of single droplets." Thesis, Aston University, 1985. http://publications.aston.ac.uk/10180/.
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Sen, Prosenjit. "Driving liquid-metal droplets for RF microswitching." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1495961571&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Wilking, Connie Chang. "Viral encapsulation of emulsion and nanoemulsion droplets." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1692370451&sid=4&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Al, Qubeissi Mansour. "Heating and evaporation of automotive fuel droplets." Thesis, University of Brighton, 2015. https://research.brighton.ac.uk/en/studentTheses/540596d9-e14f-4007-9533-acd625e14b8e.
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The previously introduced fuel droplet heating and evaporation models, taking into account temperature gradients, recirculations, and species diffusion within droplets, are further developed and generalised for the application to a broad range of automotive fuel droplets. The research has been conducted in three directions: modelling of biodiesel fuel droplets, modelling of Diesel fuel droplets, and modelling of gasoline fuel droplets.
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Rydblom, Staffan. "Measuring Water Droplets to Detect Atmospheric Icing." Licentiate thesis, Mittuniversitetet, Avdelningen för elektronikkonstruktion, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-31827.
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This thesis describes the exploration of a method to measurethe droplet size and the concentration of atmospheric liquid water. The purpose is to find a cost effective technique to detect the conditions for icing on structures. Icing caused by freezing atmospheric water can be a signifi- cant problem for infrastructure such as power lines, roads and air traffic. About one third of the global installed wind power capacity is located in cold climates, where icing of rotor blades is one of the major challenges. The icing process is complex and the result depends on a combination of the aerodynamic shape of the structure or airfoil, the velocity of the air and its contained water, the temperature, the mixing of snow and water, the concentration of liquid water and the Droplet Size Distribution (DSD). The measurement method is based on a shadowgraph imag- ing system using light emitting diode (LED) light as background illumination and digital image processing. A prototype instru- ment has been constructed. The components were selected keeping the possibility of low-cost volume production in mind. The applications of a commercial instrument based on this tech- nique are e.g. real-time in-situ icing condition measurements and assimilation and verification of data in numerical weather models. The work presented shows that measurements of the size and concentration of water droplets using shadowgraph images can be used for the comparison and validation of Numerical Weather Prediction (NWP) models and other instruments. The accuracy of the particle size measurement is high. The accuracy of the concentration measurement has the potential to become high due to the single-particle measurement range calibraiton. The precision of the instrument depends mainly on the number of images that is used to find each measurement value. The real-time performance of the instrument is limited by the image retrieval and processing speed and depends on the precisionrequired.Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 3 inskickat.
At the time of the defence the following papers were unpublished: paper 3 submitted.
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
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Bryant, Benjamin. "Modeling Moving Droplets: A Precursor Film Approach." Scholarship @ Claremont, 2003. https://scholarship.claremont.edu/hmc_theses/142.
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We investigate the behavior of moving droplets and rivulets, driven by a combination of gravity and surface shear (wind). The problem is motivated by a desire to model the behavior of raindrops on aircraft wings. We begin with the Stokes equations and use the approximations of lubrication theory to derive the specific thin film equation relevant to our situation. This fourth-order partial differential equation describing the height of the fluid is then solved numerically from varying initial conditions, using a fully implicit discretization for time stepping, and a precursor film to avoid singularities at the drop contact line. Results describing general features of droplet deformation, limited parameter studies, and the applicability of our implementation to the long-term goal of modeling wings in rain are discussed.
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Sabourin, Shaun. "Auto-Ignition of Liquid n-Paraffin Fuels Mixtures as Single Droplets Using Continuous Thermodynamics." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20135.
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This thesis reports a model to predict the auto-ignition time of single droplets of n-paraffin fuel mixtures using the method of continuous thermodynamics. The model uses experimental data for pure fuels to fit rate parameters for a single-step global chemical reaction equation; from this, correlations for rate parameters as a function of species molecular mass are derived, which are integrated to produce a continuous thermodynamics expression for mixture reaction rate. Experiments were carried out using the suspended droplet-moving furnace technique. The model was then tested and compared to experimental data for three continuous mixtures with known compositions: one ranging from ¬n-octane to n-hexadecane, the second ranging from n-dodecane to n-eicosane, and the third being a combination of the first two mixtures to produce a “dumbbell” mixture. Discrete and continuous mixture models of the ASTM standard distillation test were compared to design the experimental mixtures and provide the distribution parameters of the continuous mixtures intended to simulate them. The results of calculations were found to agree very well with measured ignition times for the mixtures.
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Caën, Ouriel. "Droplet microfluidics for cancer cell evolution Parallelized ultra-high throughput microfluidic emulsifier for multiplex kinetic assays Counting single cells in droplets Multiplexed droplet sorting." Thesis, Sorbonne Paris Cité, 2016. https://wo.app.u-paris.fr/cgi-bin/WebObjects/TheseWeb.woa/wa/show?t=1888&f=11697.
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Cette thèse porte sur une problématique moderne: la prise en charge de patients cancéreux par thérapie ciblée. De tels traitements sont efficaces et représentent une récente avancée thérapeutique majeure pour des patients multi-traités en cas d'échec thérapeutique. Cependant, les réponses des patients sont souvent transitoires puisqu'ils rechutent plusieurs mois après le traitement. Il a été récemment démontré que pour les cancers du poumon, ces rechutes sont associées à l'émergence de nouvelles altérations génétiques au sein des tumeurs. Il est donc important de discriminer avant traitement le processus de résistance qui pourrait se produire et proposer ainsi la combinaison de traitements qui empêcheraient l'apparition d'une résistance. Une telle évaluation précoce pourrait être facilitée grâce à l'utilisation de la microfluidique de goutte qui permet un criblage à haut débit à l’échelle de la cellule unique. Cette technologie pourrait ainsi devenir un outil générique pour identifier la résistance à un traitement à un stade précoce de son développement. Dans le cadre de cette thèse, nous avons utilisé comme modèle in vitro des lignées cellulaires NSCLC (Non-Small Cell Lung Cancer) respectivement sensibles et résistantes au traitement. Nous avons développé de nouveaux outils de microfluidique de goutte qui ont permis de discriminer entre le phénotype et le génotype de cellules uniques sensibles au traitement et résistantes au traitement. Une telle preuve de principe constitue une première étape vers la compréhension de l'hétérogénéité de populations de cellules tumorales, dont il a été montré qu’elle est corrélée avec la résistance aux thérapiesThis thesis deals with a modern problematic: the management of cancer patients using targeted therapy. Such treatments are efficient and represent a recent major therapeutic advance for multi-treated patients in therapeutic failure. However patients responses are often transitory as they relapse several months following the treatment. It has been recently demonstrated that for lung cancers these escapes are associated with the emergence of new genetic alterations within tumors. It is thus important to discriminate before treatment the resistance process that could occur and thus propose the therapeutic combination of treatments that would prevent the appearing of a resistance. Such early assessment could be eased-up thanks to the use of droplet microfluidics which allows high-throughput screening at a single-cell level resolution. This technology could hence become a generic tool to identify resistance to a treatment in an early stage of its development. In the framework of this thesis we used as an in vitro model treatment-sensitive and treatment-resistant NSCLC (Non-Small Cell Lung Cancer) cell lines. We developed novel droplet microfluidics tools which allowed to discriminate between the phenotype and genotype of single treatment-sensitive and treatment-resistant single cells. Such a proof of principle constitutes a first step towards the understanding of tumor cell population heterogeneity, which has been shown to be correlated with resistance to therapies
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Bradshaw, Joel. "Mathematical modelling of droplets climbing an oscillating plane." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33768/.
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Recent experiments [P. Brunet, J. Eggers, and R. Deegan, Phys. Rev. Lett. 99, 114501 (2007)] have shown that a liquid droplet on an inclined plane can be made to move uphill by sufficiently strong, vertical oscillations. In order to investigate this counterintuitive phenomenon we will derive three different models that qualitatively reproduce the main features of the experiment. For the first model the liquid's inertia and viscosity are assumed negligible, so that the motion of the droplet is dominated by the applied acceleration due to the oscillation of the plate, gravity and surface tension and that the droplet is thin. We explain how the leading order motion of the droplet can be separated into a spreading mode and a swaying mode. For a linear contact line law, the maximum rise velocity occurs when the frequencies of oscillation of the two modes are in phase. We show that, both with and without contact angle hysteresis, the droplet can climb uphill and also that, for certain contact line laws, the motion of the droplet can produce footprints similar to experimental results. We show that if the two modes are out of phase when there is no contact angle hysteresis, the inclusion of hysteresis can force them into phase. This in turn increases the rise velocity of the droplet and can, in some cases, cause a sliding droplet to climb. For the second model we use a two-dimensional flow where the Reynolds number is assumed large enough for viscosity to be neglected. We show that the leading order motion of the droplet can be separated into the same two modes and the net motion of the droplet is an oscillatory function of the frequency. For increasingly non-wetting droplets we discover that the rise velocity begins to oscillate very rapidly as a function of the static contact angle. What we also discover is that the change in the free surface of the droplet is actually a wave travelling travelling across the droplet, and the amount of modes present coincide with the rapid change in the rise velocity. Using a cubic contact line law and contact angle hysteresis we observe a droplet that can climb uphill for parameter values similar to that of the experiment. With the addition of a time dependent term within the contact line law we show that it is possible to obtain a multi-valued relationship between the velocity of the contact line and the respective contact angles, reproducing experimental observations seen for unsteady, moving contact lines. For the third model we again assume that the liquid's viscosity is negligible, similar to model 2, only now for a three-dimensional, thin droplet. For very small amplitudes the motion of the droplet is a combination of a swaying mode and a spreading mode that interact causing a net motion of the droplet. This motion is found to be an oscillatory function of the driving frequency and the magnitude of the peak rise velocity is proportional to one over the frequency squared. By examining the velocity of the centre of the droplet and the displacement of the contact line we see that the absolute maximums of both of these, over one period of oscillation, contain natural frequencies, which are evenly spaced with respect to the square root of the frequency of the oscillation.