Influence du confinement sur les mécanismes physiques régissant le trafic de gouttes au sein de réseaux micro et milli fluidiques

Dans ce travail de thèse, nous étudions la répartition d'un train périodique de gouttes monodisperses à une simple bifurcation asymétrique. Nous montrons que le trac des éléments discrets dans des réseaux microuidiques résulte de deux mécanismes physiques diérents : un mécanisme collectif de rétroaction hydrodynamique et un mécanisme local de collisions. La compétition entre ces deux mécanismes est régie par le connement des gouttes. Nous proposons des modèles phénoménologiques simples pour comprendre ce trac en fonction des paramètres pertinents du problème. Parallèlement à cette étude, nous mettons au point une méthode passive pour mesurer les pertes de charges dans des écoulements microuidiques et nous mesurons expérimentalement l'excès de résistance hydrodynamique produit par la présence d'une goutte en fonction de son connement dans des canaux de section rectangulaire et circulaire. Enn, nous montrons que la géométrie des canaux aecte notablement la mobilité des gouttes : les gouttes vont plus vite que l'écoulement moyen dans le cas de section circulaire et moins vite dans le cas de section rectangulaire. Ceci du fait de la présence de coins dans cette géométrie.In this work, we investigate repartionning of monodisperse droplets at a simple asymmetric bifurcation. We show that a trac of discrete uid in microuidic systems is regulated by two distincts mechanisms : collective hydrodynamic feedback and local colisions. The competition between these two mechanisms is controlled by the connement of the droplets. For each mechanism, we propose simple phenomenological models in terms of the various pertinent parameters of the problem. Furthermore, we develop a passive method to measure pressure drops in microuidics channels. We measure the excess hydrodynamic resistance of each droplet channel for channels having circular and rectangular cross-sections. We show that the geometry of a channel aects the mobility of droplets. Droplets travel faster (slmower) than the average ow speed for channels having circular (rectangular) cross sections.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Droplet traffic regulated by collisions in microfluidic networks

International audienceWe study droplet traffic at the inlet node of an asymmetric microfluidic loop. We observe that collisions between successive droplets may occur at the junction. We show that this phenomenon has an impact on the repartition of the droplets in the arms of the loop since it modifies the nature of the collective hydrodynamic feedback mechanism that usually regulates traffic. We present a robust indirect method to measure the excess hydrodynamic resistance added by each droplet to a microfluidic channel, and we rationalize our experimental finding using simple physical arguments

Focal Conic Stacking in Smectic A Liquid Crystals: Smectic Flower and Apollonius Tiling

We investigate two different textures of smectic A liquid crystals. These textures are particularly symmetric when they are observed at crossed polars optical microscopy. For both textures, a model has been made in order to examine the link between the defective macroscopic texture and the microscopic disposition of the layers. We present in particular in the case of some hexagonal tiling of circles (similar to the Apollonius tiling) some numeric simulation in order to visualize the smectic layers. We discuss of the nature of the smectic layers, which permit to assure their continuity from one focal conic domain to another adjacent one

Droplet motion in microfluidic networks: Hydrodynamic interactions and pressure-drop measurements

International audienceWe present experimental, numerical, and theoretical studies of droplet flows in hydrodynamic networks. Using both millifluidic and microfluidic devices, we study the partitioning of monodisperse droplets in an asymmetric loop. In both cases, we show that droplet traffic results from the hydrodynamic feedback due to the presence of droplets in the outlet channels. We develop a recently-introduced phenomenological model [W. Engl , Phys. Rev. Lett. 95, 208304 (2005)] and successfully confront its predictions to our experimental results. This approach offers a simple way to measure the excess hydrodynamic resistance of a channel filled with droplets. We discuss the traffic behavior and the variations in the corresponding hydrodynamic resistance length Ld and of the droplet mobility β , as a function of droplet interdistance and confinement for channels having circular or rectangular cross sections

Competition between local collisions and collective hydrodynamic feedback controls traffic flows in microfluidic networks.

International audienceBy studying the repartition of monodisperse droplets at a simple T junction, we show that the traffic of discrete fluid systems in microfluidic networks results from two competing mechanisms, whose significance is driven by confinement. Traffic is dominated by collisions occurring at the junction for small droplets and by collective hydrodynamic feedback for large ones. For each mechanism, we present simple models in terms of the pertinent dimensionless parameters of the problem

Design of Organic 3D microresonators with Microfluidics Coupled to Thin-Film Processes for Photonic Applications

WOSInternational audienceWe report on the design and realization of photonic integrated devices based on 3D organic microresonators (MR) shaped by an applied fluid mechanism technique. Such an interdisciplinary approach has been judiciously achieved by combining microfluidics techniques and thin-film processes, respectively, for the realizations of microfluidic and optical chips. The microfluidic framework with flow rates control allows the fabrication of microresonators with diameters ranging from 30 to 160 μm. The resonance of an isolated sphere in air has been demonstrated by way of a modified Raman spectroscopy devoted to the excitation of Whispering Gallery Modes (WGM). Then the 3D-MR have been integrated onto an organic chip and positioned either close to the extremity of a taper or alongside a rib waveguide. Both devices have proved efficient evanescent coupling mechanisms leading to the excitation of the WGM confined at the surface of the organic 3D-MR. Finally, a band-stop filter has been used to detect the resonance spectra of organic resonators once being integrated. Such spectral resonances have been observed with an integrated configuration and characterized with a Δλ = 1.4 nm free spectral range (FSR), appearing as stemming from a 78 μm-radius MR structure

Réalisation de micro-résonateurs 3D organiques par procédés micro-fluidiques et couches minces pour des applications en photonique intégrées

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Microfluidics and thin film process: a recipe for organic integrated photonics based on 3D microresonators

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