The performance of PEM fuel cells (PEMFC) relies on the proper control and management of the liquid water that forms as a result of the electrochemical process, especially at high current densities. The liquid water transport and removal process in the gas flow channel is highly dynamic and many of its fundamental features are not well understood. This thesis presents an experimental and theoretical investigation of the emergence of water droplets from a single pore into a microchannel. The experiments are performed in a 250 µm × 250 µm air channel geometry with a single 50 µm pore that replicates a PEMFC cathode gas channel. A droplet manipulation platform is constructed using a microfluidics soft lithographic process to allow observation of the dynamic nature of the water droplets. Flow conditions that correspond to typical operating conditions in a PEMFC are selected. A test matrix of experiments comprised of different water injection velocities and air velocities in the gas microchannel is studied. Emergence, detachment and subsequent dynamic evolution of water droplets are analyzed, both qualitatively and quantitatively. Quantitative image analysis tools are implemented and applied to the time-resolved images to document the time evolution of the shape and location of the droplets, characteristic frequencies, dynamic contact angles, flow regime and stability maps. Three different flow regimes are identified, slug, droplet, and film flow. The effects of the air flow rate and droplet size on the critical detachment conditions are also investigated. Numerical simulations using Volume-of-Fluid method are presented to investigate the water dynamics in the droplet flow. The focus of the modeling is on methods that account for the dynamic nature of the contact line evolution. Results of different approaches of dynamic contact angle formulations derived empirically and by using the theoretically based Hoffmann function are compared with the static contact angle models used to date. The importance of the dynamic formulation as well as the necessity for high numerical resolution is highlighted. The Hoffmann function implementation is found to better capture the salient droplet motion dynamics in terms of advancing and receding contact angle and periodicity of the emergence process. To explore the possibility of using the pressure drop signal as a diagnostic tool in operational fuel cells that are not optically accessible, a flow diagnostic tool was developed based on pressure drop measurements in a custom designed two-phase flow fixture with commercial flow channel designs. Water accumulation at the channel outlet was found to be the primary cause of a low-frequency periodic oscillation of pressure drop signal. It is shown that the flow regimes can be characterized using the power spectrum density of the normalized pressure drop signal. This is used to construct a flow map correlating pressure drop signals to the flow regimes, and opens the possibility for practical flow diagnostics in operating fuel cells. / Graduate

Dans cette thèse, l'holographie numérique dans l'axe (DIH) est la principale méthode optique utilisée pour analyser des inclusions dans une gouttelette. L'holographie numérique dans l'axe est utilisée pour caractériser des inclusions du point de vue de leur taille, leur position 3D et leur trajectoire à l'intérieur de la gouttelette. Comme les particules sont situées à l'intérieur d'une gouttelette, le front d'onde incident sur l'inclusion est modifié avant qu'il l'illumine. Le défi de ce travail est double : premièrement de prendre en compte la forme de la gouttelette dans le modèle d'holographie et deuxièmement d'étendre l'analyse aux inclusions transparentes (type objet de phase). Pour décrire l'hologramme enregistré par le capteur CCD, l'intégrale d'Huygens-Fresnel et le formalisme des matrices ABCD ont été utilisés. Dans ce modèle, nous introduisons les polynômes de Zernike pour décrire la fonction de transmission d'une particule. Pour l'analyse des hologrammes, l'outil mathématique de la transformation de Fourier fractionnaire 2D (2D-FRFT) est utilisé pour restituer l'image des inclusions et dans ce cas une mesure la taille de l'inclusion et de sa position 3D sont réalisées. Les trajectoires des inclusions dans la goutte est possible avec un long temps de pose de l'obturateur du capteur CCD. Nous avons également proposé un nouveau modèle pour décrire des objets de phases quelconque et des particules opaques. Pour ce nouveau modèle, les mêmes procédés ont été utilisés. Dans le cas d'inclusions filiformes à l'intérieur d'une géométrie cylindrique comme un canal, une méthode de simulation d'imagerie interférométrique multi-coeurs est proposée. Dans ce cas, une somme de distributions de Dirac, localisées le long d'une droite, introduite dans l'intégrale de Fresnel généralisée (c'est-à-dire le formalisme des matrices ABCD et l'intégrale de Fresnel) permet d'obtenir un bon degré de similitude entre l'expérience et la simulation. / In this thesis, the digital in-line holography (DIH) is the main optical method used to analyze inclusions in a droplet. The digital in-line holography is used to characterize the inclusions in terms of of their size, their 3D position, and their trajectories inside the droplet. Since the particles are located within a droplet, the incident wavefront is changed before it illuminates the inclusions. The challenge of this work has two points : first to take into account the shape of the droplet in the holographic model and secondly to extend the analysis to the transparent inclusions (phase object). To describe the hologram recorded by the CCD sensor, the Huygens-Fresnel integral and the ABCD matrix formalism were used. In this model, we introduce the Zernike polynomials to describe the transmission function of a particle. For the analysis of holograms, the2D fractional Fourier transformation (2D-FRFT) is used to reconstruct the image of inclusions and in this case the size and their 3D position of the inclusions are performed.The trajectories of the inclusions in the drop are possible tracked with a long exposure shutter speed of the CCD. We also proposed a new simulation to describe objects of any phases and opaque particles. For this simulation, the same methods of reconstruction were used. In the case of micro-channel inclusions inside a cylindrical geometry such as a pipe, the interferometric imaging of multi-core pipe is proposed. In this case, summation of Dirac delta distribution, located along a line, introduced into the generalized Fresnel integral allows us to get a good agreement between the experiment and the simulation.

Le captage de polluants des effluents industriels, et plus particulièrement du CO2, est un défi majeur à relever. Le procédé de captage du CO2 basé sur l’absorption par des solutions aqueuses d’amines est la technique la plus maîtrisée pour le traitement des fumées en postcombustion. La substitution des colonnes à garnissage par des colonnes à pulvérisation présente un intérêt économique car la surface d’échange entre les phases gazeuse et liquide est très importante réduisant ainsi la taille de la colonne d’absorption. De plus, les pertes de charge côté gaz sont évitées et les coûts de maintenance réduits. L’objectif de ces travaux de thèse est de caractériser le transfert de matière dans un spray au cours d'une absorption du CO2 par une solution aqueuse de monoethanolamine (MEA) en utilisant une nouvelle méthode.Ainsi, l’étude s’intéresse à la caractérisation locale du transfert de matière entre un spray de MEA à 30% massique et une atmosphère de CO2. Pour cela, une technique optique non-intrusive est utilisée : la réfractométrie arc-en-ciel globale (GRT). Cette technique est une mesure de l’indice de réfraction d’un ensemble de gouttes localisé dans une partie du spray. C’est donc une mesure locale dans un volume de l’ordre de quelques millimètres cubes. L’indice de réfraction d’une solution dépend de sa température et de sa concentration. Ainsi, à l’aide d’un étalonnage préalable dans un réacteur agité, les indices de réfraction des solutions aqueuses de MEA chargées sont reliés à leurs températures et à leurs concentrations de CO2 absorbé. La mesure d’indice de réfraction permet donc de suivre l’avancement du transfert de matière à travers la concentration de CO2 absorbé à une température moyenne du volume de mesure. La GRT est donc utilisée pour la mesure d’indice de réfraction au cours de l’absorption avec réaction chimique et, la quantité de CO2 captée par unité de volume est mesurée à plusieurs hauteurs de chute. Les mesures sont ensuite comparées aux prédictions d’un modèle de transfert de matière dans une goutte résolu numériquement sous COMSOL Multiphysics. Dans un deuxième temps, l’étude s’intéresse à la caractérisation du transfert de matière côté gaz en mesurant par spectrométrie infra-rouge la quantité de CO2 présente dans la phase gaz lors de l’absorption de celui-ci par une solution aqueuse de MEA à 30 % massique. Les résultats sont présentés sous forme d’efficacité de captage et un coefficient de transfert de matière côté gaz est calculé, en fonction de paramètres opératoires tels que les débits gazeux et liquide.Ces travaux de thèse, appliqués au captage du CO2, traite principalement de la mesure de transfert de matière grâce à la GRT pour la première fois utilisée à une absorption avec réaction chimique. La méthode développée permettra son utilisation pour d’autres systèmes chimique. / Pollutant capture, especially of CO2, is still a major challenge nowadays.CO2 capture based on absorption with chemical reaction by aqueous solutions of amines is the most mature technique for post-combustion gas cleaning.The substitution of packed columns by spray columns presents an economical interest since the exchange area between both gas and liquid phases is very important, reducing the size of the absorption column. In addition, gas side pressure losses are avoided and maintenance costs are reduced.The aim of this thesis is to characterize mass transfer in a spray column during a CO2 absorption by an aqueous solution of monoethanolamine (MEA) by using a new optical technique.The study focuses on the characterization of the local mass transfer between MEA spray and a CO2 atmosphere. In order to achieve this, a non-intrusive optical technique is used: Global Rainbow Technique (GRT). This technique measures the refractive index of droplets in a local portion of the spray. Therefore, the measurement is local with a volume of few cubic millimeters.The refractive index of a solution depends on its temperature and its concentration. Thus, by using a prior calibration in a stirred reactor, the refractive indices of CO2 loaded MEA solutions are correlated with their temperatures and CO2 absorbed concentration. Therefore, measuring refractive index is a measurement of mass transfer extent.GRT is then used during CO2 absorption with chemical reaction, and the amount of CO2 captured per volume unit is measured at several column heights. The experimental results are then compared with mass transfer predictions in a droplet with a model numerically solved in COMSOL Multiphysics.In another hand, gas side mass transfer is characterized by measuring the amount of CO2 in the gas phase with infrared spectrometry during CO2 absorption in an aqueous solution of 30 % MEA. The results are presented in term of capture efficiency and a gas-side mass transfer coefficient is calculated as a function of operating parameters such as gas and liquid flow rates.This work, applied to CO2 capture, deals with mass transfer measurement with GRT through a first application to absorption with chemical reaction. The developed method in this thesis will allow its use for other chemical systems.

We demonstrate a versatile phase-change sub-micron contrast agent providing three modes of contrast enhancement: 1) photoacoustic imaging contrast, 2) ultrasound contrast with optical activation, and 3) ultrasound contrast with acoustic activation. This agent, which we name 'Cy-droplet', has the following novel features. It comprises a highly volatile perfluorocarbon for easy versatile activation, and a near-infrared optically absorbing dye chosen to absorb light at a wavelength with good tissue penetration. It is manufactured via a 'microbubble condensation' method. The phase-transition of Cy-droplets can be optically triggered by pulsed-laser illumination, inducing photoacoustic signal and forming stable gas bubbles that are visible with echo-ultrasound in situ. Alternatively, Cy-droplets can be converted to microbubble contrast agents upon acoustic activation with clinical ultrasound. Potentially all modes offer extravascular contrast enhancement because of the sub-micron initial size. Such versatility of acoustic and optical 'triggerability' can potentially improve multi-modality imaging, molecularly targeted imaging and controlled drug release. (C) 2017 The Authors. Published by Elsevier GmbH.

Hepatic lipase (HL) plays a pivotal role in the catabolism of apolipoprotein (apo)B-containing lipoproteins and high density lipoprotein (HDL) particles through its reported catalytic and non-catalytic extracellular functions. The current study tested the hypothesis that HL expression might impair formation and secretion of hepatic derived very low density lipoproteins (VLDL) and apoA-I (nascent HDL). Stable or transient expression of human HL (hHL) in McA-RH7777 cells resulted in decreased incorporation of [3H]glycerol into cell-associated and secreted (VLDL-associated) 3H-triacylglcyerol (TAG) relative to control cells. Stable expression of catalytically-inactive hHL (hHLSG) also resulted in decreased secretion of VLDL-associated 3H-TAG whereas cell-associated 3H-TAG levels were unchanged. Expression of hHL or hHLSG increased cell-associated 35S-apoB100 with relatively no change in secreted 35S-apoB100. Importantly, hHL or hHLSG expression resulted in reduced 3H-TAG associated with the microsomal lumen lipid droplets (LLD), and increased relative expression of ApoB and genes involved in lipogenesis and fatty acyl oxidation. Transient expression of hHL in HL-null primary hepatocytes, mediated by adenoviral gene transfer, resulted in decreased steady-state levels of cell-associated and secreted apoA-I and reduced rates of synthesis and secretion of 35S-apoA-I. HL-null hepatocytes exhibited increased levels of secreted 35S-apoA-I relative to wildtype hepatocytes while cell-associated 35S-apoA-I levels were normal. Transient expression of a hHL chimera (hHLmt), in which the C-terminus of hHL was replaced with mouse HL sequences, exerted an inhibitory effect on apoA-I production similar to that of hHL even though hHLmt was secreted less effectively than hHL with impaired exit from the endoplasmic reticulum (ER) as compared with hHL. In contrast, stable expression of hHL in McA-RH7777 cells resulted in a dose-dependent increase in cell-associated and secreted 35S-apoA-I levels. These studies demonstrate that hHL has an intracellular (but non-catalytic) role in reducing the content of the LLD and ultimately the buoyancy of secreted VLDL particles, and that the N-terminal sequences of ER-residing hHL directly or indirectly modulates the production and secretion of apoA-I (nascent HDL) from hepatocytes.

Cette thèse, intitulée « Emulsification en systèmes microstructurés », s’inscrit au sein de la tâche « Emulsification contrôlée » du projet européen IMPULSE. Deux micromélangeurs en acier inoxydable, un V-type et un Caterpillar, ont été testés en utilisant un pilote d’émulsification continue. Ces dispositifs conçus en acier inoxydable et fonctionnant comme des boîtes noires, des micromélangeurs transparents ont ensuite été utilisés afin de comprendre leurs mécanismes d’émulsification. Les paramètres-clés intervenant dans la formation de gouttes à un orifice à l’échelle macroscopique ont dans un premier temps été identifiés. A l’échelle microscopique, la formation des gouttelettes dans le micromélangeur V-type est issue de la mise en contact des jets des phases aqueuse et organique formés à la sortie de ce dispositif et d’un phénomène élongationnel avec des instabilités interfaciales. Dans le cas du Caterpillar, la taille des gouttelettes dépend de la géométrie interne des éléments en série de ce micromélangeur. La formation des gouttelettes est issue d’un phénomène de cisaillement au niveau de la jonction en Y. La réduction de la taille de ces gouttelettes est ensuite due à leur passage dans les éléments de mélange. L’utilisation de micromélangeurs transparents a, quant à elle, permis de caractériser davantage ces deux micromélangeurs par micro-PIV et caméra rapide. Enfin, une dépendance du diamètre des gouttelettes par rapport à l’énergie dissipée est constatée pour le Caterpillar mais par pour le V-type. L’énergie dissipée dans ces deux micromélangeurs semble être moindre et les émulsions formées de meilleure qualité par rapport aux procédés classiques d’émulsification / This thesis, entitled “Emulsification in micromixers” was carried out within the framework of the Task “Controlled Emulsification” of the European IMPULSE project. Two micromixers in stainless steel, the V-type and the Caterpillar, were tested in an experimental setup. These microdevices working as black boxes, transparent micromixers were used after to gain insight into the fundamental mechanisms for emulsification. Firstly, the key parameters enabling the drop formation at macroscopic scale were identified. At microscopic scale, the droplet formation in the V-type micromixer results from the contact of aqueous and organic phases jets at the outlet of the microdevice and from elongational phenomena with interfacial instabilities. In the case of the Caterpillar, the droplets size depends on the internal geometry of the microdevice. The droplet formation can be mainly attributed to the shearing phenomena at the Y-junction. The decrease of the droplets’ size is then due to their passage through the mixing elements in series in the outlet channel. Moreover, the use of transparent micromixers allows to characterize these two micromixers by the micro-PIV and high speed camera. A straightforward relationship between the energy dissipation and the size of droplets was established for the Caterpillar, but not for the V-type. Moreover, the energy dissipation within these two micromixers is lower and the emulsions obtained having a more satisfactory quality than in the case of the classical emulsification processes

Nous avons pour but de développer un système microfluidique en gouttes, capable, à l’échelle de la cellule/bactérie unique, de détecter et de co-localiser plusieurs marqueurs génétiques, en utilisant une version digitale et multiplexée de la réaction de polymérisation en chaîne (PCR). Les systèmes de PCR digitale actuellement commercialisés ne le permettent toujours pas. Un tel prototype garantira la présence de multiples marqueurs à l’intérieur d’un même génome, ce qui permettra l’identification du pathogène avec précision et un taux de faux-positifs proche de zéro. Comme première application, nous démontrerons la possibilité de co-localiser quatre gènes de virulence de la souche O157:H7 d’Escherichia coli, un pathogène majeur, qui est détecté dans des échantillons alimentaires ou provenant de fèces cliniques pouvant aussi contenir des E. coli non pathogènes porteuses d’une partie des gènes de virulence. Avant de procéder à des tests TaqMan multicolores en point final, E. coli sera d’abord encapsulée dans des gouttes micrométriques et lysée par la chaleur in situ. Notre objectif est de démontrer que ce test peut être appliqué avec succès à un petit ensemble d’échantillons cliniques ou alimentaires / We aim to develop a prototype of droplet-based microfluidic system capable of detecting and colocalizing multiple genetic markers at the single cell/bacteria level, using the Polymerase Chain Reaction (PCR) in a digital multiplexed version. This cannot be achieved using current commercial digital PCR systems, and should increase the sensitivity and reliability of the detection of pathogens. Importantly, the system will guarantee the presence of multiple markers within the same genome and enable accurate identification, and bring the false positive rate close to zero. As a first application, we will demonstrate the possibility to co-localize 3 virulence genes in the E.coli strain O157:H7, a major foodborne pathogen, which has to be detected in clinical feces samples or food samples, which may also contain non pathogenic E. coli carrying only a subset of these virulence genes. E. Coli will be encapsulated in micrometric droplets, lysed by heating in situ prior performing a multicolour end-point Taqman assay. Our objective is to demonstrate that this test can be successfully applied to real clinical or food samples

Lab-on-Chip, the miniaturization of the chemical and analytical lab, is an endeavor that seems to come out of science fiction yet is slowly becoming a reality. It is a multidisciplinary field that combines different areas of science and engineering. Within these areas, microfluidics is a specialized field that deals with the behavior, control and manipulation of small volumes of fluids. Agglutination assays are rapid, single-step, low-cost immunoassays that use microspheres to detect a wide variety molecules and pathogens by using a specific antigen-antibody interaction. Agglutination assays are particularly suitable for the miniaturization and automation that two-phase microfluidics can offer, a combination that can help tackle the ever pressing need of high-throughput screening for blood banks, epidemiology, food banks diagnosis of infectious diseases. In this thesis, we present a two-phase microfluidic system capable of incubating and quantifying agglutination assays. The microfluidic channel is a simple fabrication solution, using laboratory tubing. These assays are incubated by highly efficient passive mixing with a sample-to-answer time of 2.5 min, a 5-10 fold improvement over traditional agglutination assays. It has a user-friendly interface that that does not require droplet generators, in which a pipette is used to continuously insert assays on-demand, with no down-time in between experiments at 360 assays/h. System parameters are explored, using the streptavidin-biotin interaction as a model assay, with a minimum detection limit of 50 ng/mL using optical image analysis. We compare optical image analysis and light scattering as quantification methods, and demonstrate the first light scattering quantification of agglutination assays in a two-phase ow format. The application can be potentially applied to other biomarkers, which we demonstrate using C-reactive protein (CRP) assays. Using our system, we can take a commercially available CRP qualitative slide agglutination assay, and turn it into a quantitative High Sensitivity-CRP test, with a lower detection limit of 0.5 mg/L using light scattering. Agglutination assays are an incredibly versatile tool, capable of detecting an ever-growing catalog of infectious diseases, proteins and metabolites. A system such as that presented in this thesis is a step towards being able to produce high throughput microfluidic solutions with widespread adoption.

The body of literature on the impact of emulsion particle size on oxidation rates is unclear. This could be because emulsions are typically polydisperse and the oxidation rate of individual droplets is impossible to discern. Flow cytometry is a technique for studying individual cells and their subpopulations using fluorescence technologies. It is possible that individual emulsion droplets could also be characterized by flow cytometry as a novel approach for studying lipid oxidation. Typical emulsion droplets are too small to be visualized by flow cytometer, so emulsions were prepared to have droplets > 2 μm; weighting agent and xanthan gum were added to minimize creaming during storage. A radical-sensitive lipid-soluble fluorescence probe (BODIPY665/676) was added to the lipid used to prepare the emulsion so that the susceptibility of individual emulsion droplets could be determined. The results showed that in a polydisperse emulsion system, small droplets were oxidized faster than large droplets. Using mixtures of emulsions with and without prooxidants, it was possible to see the transfer of prooxidants between droplets, a process that is influenced by surfactant and salt concentrations. For example, surfactants micelles can transfer prooxidants to neighboring non-oxidized droplets and cause fluorescence loss when surfactant concentration was higher than critical micelle concentration (CMC). Transfer of prooxidants was promoted by adding NaCl and free fatty acid which could be attributed to the lower CMC. This study showed the potential for applying flow cytometry on oxidation of individual emulsion droplets.

Modern drug development is an astronomically expensive and time consuming undertaking. Because of this, studying the pharmacokinetic properties of drugs in vitro has become an integral step early in the process of drug development, with the goal of preventing costly failures late in the process, and dangerous side effects. Artificial phospholipid bilayers known as droplet interface bilayers (DIBs) have the potential to be used for these pharmacokinetics assays, combining the low cost of cell-free assays with the ability to more closely mimic structures found in life than current cell-free in vitro techniques. Combined with the reproducibility, ease of use, and low reagent consumption found with microfluidic methods, disruptive new low cost techniques for assessing pharmacokinetics in drug development may be possible using DIBs as an artificial cell membrane model. In this work, I establish the potential of DIBs to be used as a pharmacokinetics modelling platform, and advance the use of microfluidic methods for carrying out pharmacokinetics assays in drug discovery. I first developed a new microfluidic platform for the formation of DIBs, which sought to solve some of the shortcomings of current microfluidic methods for DIB formation (Chapter 2). This device is the first that can be used to form DIB networks from dissimilar droplets in parallel, without use of active controls, and with droplet contact gentle enough to enable use of biomimetic lipid mixtures. I examine for the first time the behaviour of phospholipids on microfluidic devices, and characterise the interaction that they have with a common material used to construct microfluidic devices (Chapter 3). Not only has this interaction never been studied before, but my unexpected findings indicate a new area requiring further study in order to advance the adoption of DIBs on microfluidic devices. In collaboration with my colleague Jaime Korner, I use my newly developed microfluidic platform to carry out an on-chip permeation assay for the first time using biomimetic lipid formulations and bespoke compartments modelled after the human intestine. We demonstrate that this on-chip assay has predictive accuracy greater than that of a current widely used cell-free technique (Chapter 4). Finally, I demonstrate that a DIB based microfluidic platform enables, and is critical for, characterising the effect of structural features such as membrane asymmetry on drug permeation. With this, I find measurable, previously unknown effects of membrane asymmetry on the absorption of the chemotherapy drug doxorubicin, highlighting a possible contributing factor to chemoresistance in some cancers (Chapter 5). I find, and demonstrate throughout the body of this work that microfluidic methods and DIBs can not only provide alternatives to current cell-free in vitro pharmacokinetics assays, but that they can exceed the performance of existing assays, and be used for entirely new ways of examining pharmacokinetics. Through building bespoke artificial cell membranes from the ground up, I hope to demonstrate herein the great potential of these powerful new cell-free methods. / Graduate / 2022-09-12