Numerous engineering applications have been proposed to exploit the load-carrying and non-contact nature of noncoalescing and nonwetting systems. One such application is a lab-on-a-chip , or LOC, in which liquid samples would be delivered from point-to-point by sliding over a film of air without requiring either the large driving forces required to pump liquid through a microchannel or liquid-solid contact that could lead to sample-to-sample contamination. Due to the axisymmetry of the flow fields in both the lubricating gas and droplet associated with a stationary nonwetting droplet, such a situation has a vanishing coefficient of static friction. However, once motion is imparted, droplet deformation requires that a force be applied to sustain such motion. The program of research in this dissertation focuses on investigating the lubrication force between a drop of silicone oil and a moving unwetted substrate due to the presence of a gas lubricating film driven by a rotating disk. The frictional (or lubrication) force was measured using an optical-lever technique as a function of: (1) linear velocity of the moving solid; (2) relative displacement of the drop toward the solid; (3) drop volume; and (4) viscosity. The data reveal an increase in magnitude of the measured force with either increasing relative squeezing of the drop against the glass or increasing speed of the rotating disk. Contrary to initial expectations, no pattern could be isolated regarding drop volume or viscosity of the oil. The experimental data collected will serve to validate numerical work as further models are developed.

A droplet may be prevented from wetting a solid surface by the existence of a lubricating film of air, driven by theromcapillary convection, between liquid and solid surfaces. The noncontact nature and the load-carrying capability of a nonwetting droplet lead to potential engineering applications, e.g., low-friction bearings. The present research consists of two thrusts. The first is aimed at quantifying nonwetting-system failures (film and pinning) triggered by application of a mechanical load, gaining insights to failure mechanisms. Experimental results show that film failure occurs over a wide range of droplet volumes when the temperature difference between the droplet and the plate, the driving potential of the free-surface motion, is small. Interferometric observations reveal flow instability just prior to film failure, with the growth of a nonaxisymmetric disturbance on a free surface (m = 1). Pinning failure becomes more prevalent as the temperature difference is increased, stabilizing the film flow. As part of the present investigation, a system was devised, allowing an oscillating free-surface to be reconstructed from a series of interferograms. The dynamic responses of the free surface reveal mode coupling, with harmonics of the input frequency excited through nonlinearity. The second thrust of the research succeeded in levitating and translating a droplet using the mechanism of permanent nonwetting. In this scheme, the droplet is heated by a CO2 laser and is placed above a cooled glass surface in order to drive the lubricating film that supports the weight of the drop. Furthermore, the position of the droplet can be controlled by moving the heating location, which leads to an asymmetry of the flow fields, driving air from the cooler-end of the droplet and propelling it towards the heat source. These demonstrations suggest the techniques potential use as a liquid-delivery scheme in a Lab-On-a-Chip system. Modeling is carried out to estimate propulsive forces on the droplet and to explain oscillatory behavior observed when excessive heating is applied on the drop. The concept to sandwich a droplet between two plates, a necessary configuration for levitating smaller droplets (less than mm-scale), is also discussed.

The aim of this labor is to optimize the vortex pump. When this pump should find application on the field of health like human heart for extracorporeal circulation. We will deal with the analysis of shear stress in the pump and its size of it and consider the use nonwetting surfaces to reduce the shear stress values. All our analysis will be made by CFD calculations.

L’existence de concurrence dans l’industrie aérospatiale obligé à une évolution continue des technologies en lien avec une diminution des coûts de lancement et une fiabilité accrue. Ceci passe, entre autre, par l’amélioration des moyens de protection des charges utiles. Le but de cette thèse est de vérifier l’applicabilité des systèmes hétérogènes lyophobes (association d’un matériau nanoporeux et d’un liquide non-mouillant) dans l’amortissement des vibrations pour le confort de celles-ci. L’intrusion de liquide dans des SHL demande une énergie mécanique importante sous forme de pression. En fonction des propriétés du couple solide/liquide cette énergie peut être partiellement dissipée. Cette dissipation, de l’ordre de quelques dizaines de joules par gramme de matériau est bien supérieure à celle des systèmes conventionnels (élastomères, amortisseurs visqueux…) et montre une grande stabilité vis-à-vis de la fréquence, d’où leur intérêt dans l’amortissement des vibrations. Bien que l’eau soit déjà très largement étudié dans le cadre de la recherche sur les SHL, elle ne peut être utilisée que pour des températures comprises entre 0 et 100°C (à pression atmosphérique). Dans le but d’élargir cette gamme de températures jusqu’à -50°C, des mélanges ont été utilisés. L’ajout d’électrolytes dans l’eau permet de baisser la température de solidification du liquide. L’étude des solutions d’électrolytes a permis de mettre en évidence deux phénomènes différents menant à des augmentations de pressions d’intrusion et d’extrusion dans les SHL. Dans les matériaux microporeux (comme les ZIF-8 étudiés dans ce travail), un phénomène d’exclusion totale des ions de la matrice poreuse peut être observé. Cet effet est accompagné de l’apparition d’un terme de pression osmotique menant aux augmentations importantes de pressions d’intrusion et d’extrusion mises en évidence. Dans le cas où les ions peuvent pénétrer les pores, les variations de pressions d’intrusion et d’extrusion sont beaucoup plus faibles et ont été attribuées à des changements dans les propriétés de surface du liquide. Les matériaux mésoporeux (comme les MCM-41 étudiés au cours de ce travail) semblent se comporter de cette manière quels que soient les ions considérés. L’extension de la gamme d’application des SHL vers les hautes températures a été faite grâce à l’utilisation du Galinstan, alliage de gallium, d’indium et d’étain, non-toxique et liquide entre -20 et 1300°C environ. Ce liquide, associé à des verres mésoporeux rendus chimiquement inertes, a permis l’obtention de cycles de dissipation d’énergie reproductibles. Enfin, une étude numérique d’un amortisseur SHL simplifié dans un système mécanique a été menée. La variété des comportements a mis en évidence la complexité de ces systèmes qui nécessitent un dimensionnement très précis. Si cette condition est vérifiée, les amortisseurs SHL s’avèrent très efficaces et adaptables du fait de la grande variété des couples solide/liquide utilisables. / Competition in aerospace industry forces to follow a constant evolution of technologies linked to launching costs decreasing and reliability increasing. An improvement of payload protection systems is a way to achieve these conditions. The main issue of this PhD thesis is to verify the applicability of lyophobic heterogeneous systems (association of a nanoporous material and a non- wetting liquid) in vibrations damping for payload comfort. Intrusion of liquid in LH S requires a high mechanical energy in the form of p res sure. Depending on solid/liquid couple properties this energy can be partly dissipated. This dissipation, of the order of ten joules per gram of material, is far higher than classical systems (elastomeric ones, viscous dampers...) and shows a relative stability regarding to frequency variations. These properties explain their interest in vibrations damping applications. Although water is a very common liquid which is very studied in the research field of LHS, it can only be used in the 0 to 100˚C temperatures range (under atmospheric pressure). In order to broaden this temperatures range to -50˚C, electrolytes have been used. Adding electrolytes to water permits to decrease the liquid melting temperature. The study of electrolyte solutions has highlighted two different phenomena leading to intrusion and extrusion pressures increasing in LHS. In microporous materials (such as ZIF-8 studied here), a total exclusion phenomenon of ions from porous matrix can be observed. This effect leads to the appearance of an osmotic pressure term which explains high increasing of both intrusion and extrusion pressures. If ions can penetrate pores, intrusion and extrusion pressures increasing are smaller and have been explained by liquid surface properties changes. Mesoporous materials (such as MCM-41 studied here) seem to show this last behaviour whatever ion is. Increasing of LHS application range to high temperatures has been made using Galinstan, gallium, indium and tin alloy, which is non-toxic and stays liquid between approximately -20 and 1300˚C. This liquid, associated with chemically inert mesoporous glasses, permits to obtain reproducible energy dissipation cycles. Finally, a numerical study of a simplified LHS damper in a mechanical system has been done. The behaviours variety has brought to light the complexity of such a system which needs a very accurate design. If this condition is verified, LHS dampers can be very effective and adaptable thanks to the numerous solid/liquid couples which can be used.