Lorsqu'un liquide mouillant touche un solide, on observe un ménisque de taille millimétrique. Si le solide est rugueux à une échelle submillimétrique, le liquide peut progresser le long des aspérités sur une distance qui est potentiellement illimitée si le solide est horizontal. Nous modélisons la rugosité avec des piliers cylindriques et montrons que quelques cylindres seulement suffisent à transporter et guider précisément un liquide. Nous étudions la dynamique macroscopique et microscopique de l'invasion. Nous examinons ensuite combien de liquide s'accumule dans une variété de textures et proposons un nouveau type de détergence pour extraire le liquide de la rugosité. Nous prenons aussi la gravité en compte et l'utilisons d'abord pour démontrer que plusieurs fronts liquides peuvent être observés simultanément dans des porosités multi-échelles. Nous nous intéressons enfin aux ponts capillaires millimétriques et nous dédions notre dernier chapitre à leur dynamique de croissance radiale. / When a wetting liquid contacts a solid, we observe a liquid meniscus of millimetric size. If the solid is rough at a submillimetric scale, the liquid may progress along the asperities for a potentially unlimited distance if the solid is horizontal. We model the roughness with a regular texture and show that a low number of surface features is sufficient to transport and precisely guide a liquid. We study the macroscopic and microscopic dynamics of the invasion. We examine then how much liquid accumulates in a variety of texture and propose a new kind of detergency to remove the liquid from the roughness. We also consider the influence of gravity and use it to demonstrate that multiple liquid fronts can be observed simultaneously in porosities of different scales. Then we turn our attention to millimetric capillary bridges and dedicate our last chapter to explain their dynamics of radial growth with the Cox-Voinov model.

Two-phase flow, ubiquitous to waterflood oil recovery, geological CO2 storage, and groundwater remediation, is strongly influenced by wettability, and made more complex under mixed-wet conditions. Optimum wettability for such operations is not well established due to limited experimental data and difficulties in their interpretation. This thesis investigates the impact of mixed-wettability, characterised by advancing contact angle θa on capillary pressure, relative permeability, and waterflood displacement. Using a Darcy scale simulator, relative permeability kr, capillary pressure Pc, and residual oil saturation Sor were extracted by history matching production and pressure drop data from centrifuge brine invasion and waterflood displacements completed for a range of θa. As θa increased, a larger |Pc| was required to displace oil from mixed-wet cores at high initial oil saturation. End point oil and brine permeability decreased with increasing θa. A permeability enhancement, such that kr > 1, was measured both when the flowing phase was wetting and non-wetting and was attributed to a slippage at the oil/brine interface directly correlated to θa. Residual oil saturation decreased monotonically with increasing θa while core-averaged remaining oil saturation at the end of the waterflood exhibited a non-monotonic dependence on θa. Simulations of the waterfloods revealed that both significant capillary end effects and premature termination of the waterflood in the laboratory contribute to the deviation between remaining and residual saturations. This work demonstrates that the former is not representative of the latter, as it has been assumed in a number of studies in the literature. Both corefloods and microfluidic waterfloods show the importance of combining experimental studies with simulation for correct interpretation of the measurements especially under capillary dominated flow.

L'étude de la dynamique interfaciale des liquides à l'échelle du nanomètre est cruciale pour la compréhension de nombreux phénomènes biologiques et industriels. Pour aborder cette question, nous étudions l'interaction en champ proche d'une sonde et de liquides peu visqueux. La thèse s'articule autour de deux grands axes : le premier s'intéresse à la déformation de l'interface liquide lorsqu'une pointe est approchée et à l'instabilité hydrodynamique du "jump-to-contact" qui en résulte. Le second, plus intrusif, décrit la réponse hydrodynamique d'un liquide soumis à l'oscillation d'un nanocylindre (R ~ 20-100 nm) partiellement immergé. Les mesures sont réalisées par microscope à force atomique (AFM), en mode modulation de fréquence (FM), qui permet de mesurer la force exercée sur la sonde ainsi que les composantes conservatives et dissipatives de l'interaction pointe-liquide. Une première série de mesure est réalisée sur différents liquides modèles avec un AFM couplé à une caméra rapide via un microscope optique inversé. Avant le mouillage de la sonde, les courbes de spectroscopie de force et FM mettent en évidence la déformation de l'interface liquide sur des échelles nanométriques, pour une grande gamme de tailles de sonde (de 10 nm à 30 µm). L'analyse des mesures expérimentales avec le modèle théorique récemment développé par René Ledesma-Alonso permet de déterminer la distance critique dmin en dessous de laquelle l'interface se déstabilise et mouille irréversiblement la pointe ("jump-to-contact"). Un excellent accord est trouvé entre le modèle théorique et les mesures FM. La deuxième série de mesure s'intéresse à l'immersion partielle de pointes AFM cylindriques. Les courbes de spectroscopie FM montrent qu'une certaine quantité de liquide, située dans la couche visqueuse, est entraînée par l'oscillation de la pointe. On mesure simultanément la friction exercée sur la pointe et la masse de liquide ajoutée au système, qui est directement reliée à l'extension du champ de vitesse. Un modèle analytique basé sur la résolution de l'équation de Stokes rend compte quantitativement de l'ensemble des résultats expérimentaux. La dernière série de mesure est réalisée avec des sondes cylindriques spécialement conçues pour l'étude de la dynamique de nanoménisques. Ces sondes comportent des défauts topographiques annulaires dont l'épaisseur varie entre 10 et 50 nm. Les mesures montrent une divergence du coefficient de friction aux petits angles de contact qui est bien reproduite par un modèle théorique basé sur l'approximation de lubrification. La localisation de la dissipation d'énergie au voisinage de la ligne de contact et les propriétés d'ancrage du ménisque sont également discutées. Les expériences originales développées dans cette thèse démontrent ainsi la capacité de l'AFM à étudier quantitativement les liquides à l'échelle nanométrique et ouvrent la voie à une étude systématique des processus de dissipation au sein de liquides confinés, et notamment au voisinage d'une ligne de contact en mouvement. / The study of the interfacial dynamics of liquids, down to the nanometer-scale, is of primary importance in many domains including biological and industrial phenomena. To address those questions, we study the near-field interaction between a probe and low viscous liquids. The present thesis focuses on two aspects. In the first one, we investigate the liquid interface deformation that occurs when a tip is approached and the resulting "jump-to-contact" hydrodynamic instability. The second part is more intrusive as it describes the hydrodynamic response of a liquid under the oscillation of a partly-immerse nanocylinder (R ~20-100 nm). Our measurements are performed with an Atomic Force Microscope (AFM) in the frequency modulation (FM) mode, which allows to measure the force exerted on the probe along with the conservative and dissipative components of the tip-liquid interaction. A first set of measurements is performed on several model liquids with an AFM coupled with a high-speed camera via an inverse optical microscope. Before the probe wetting, the force and FM spectroscopy curves highlight the liquid interface deformation on nanometer scales for a large range of probe size (from 10 nm to 30 µm). The fitting of our experimental measurements with the theoretical model recently developed by René Ledesma-Alonso, enables to determinate the critical distance dmin below which the interface is destabilized and irreversibly wets the tip (jump-to-contact). The theoretical model and the FM measurements were found to be in good agreement. The second set of measurements focuses on the partial immersion of cylindrical AFM tips. The FM spectroscopy curves show that a certain quantity of liquid, located in the viscous layer, is carried off with the tip oscillation. The friction exerted on the tip and the liquid mass added to the system, which is directly linked to the velocity-field extension, were measured simultaneously. An analytical model based on the Stokes equation quantitatively reproduces our experimental results. The last set of measurements is performed with cylindrical probes specially designed for the study of nanomeniscus dynamics. Those probes possess annular topographic defects, whose thickness varies between 10 nm and 50 nm. The measurements show that he measured friction coefficient surges as the contact angle is decreased. This behavior is well described by a developed theoretical model based on the lubrication approximation. Furthermore, the dissipation pattern in the vicinity of the contact line and the anchoring properties are also discussed. The original experiments developed in this thesis demonstrate thus that AFM is a relevant tool for the quantitative study of liquids at the nanoscale. This work paves the way for systematic studies of dissipation processes in confined liquids, and in particular in the vicinity of moving contact lines.

Long linear earthwork assets constructed in high-plasticity overconsolidated clay are known to be deteriorating due to long-term effects of wetting and drying stress cycles as a result of seasonal weather patterns. These stress cycles can lead to shallow first-time failures due to the mobilisation of post-peak strength and progressive failure. Design requirements of new earthworks and management of existing assets requires improved understanding of this critical mechanism; seasonal ratcheting. Incremental model development and validation to allow investigation of multiple inter-related strength deterioration mechanisms of cut slope behaviour in high-plasticity overconsolidated clay slopes has been presented. Initially, the mechanism of seasonal ratcheting has been considered independently and a numerical modelling approach considering unsaturated behaviour has been validated against physical modelling data. Using the validated model, the effects of slope geometry, design parameter selection and design life have been considered. Following this, an approach to allow undrained unloading of soil, stress relief, excess pore water pressure dissipation, seasonal ratcheting and progressive failure with wetting and drying boundary conditions has been considered. Hydrogeological property deterioration and the potential implications of climate change have been explored using the model. In both cases the serviceable life of cut slopes is shown to reduce significantly in the numerical analyses. Finally, a model capable of capturing hydrogeological behaviour of a real cut slope in London Clay has been developed and validated against long-term field monitored data. Using the validated model, a climate change impact assessment for the case study slope has been performed. The numerical analyses performed have indicated that seasonal ratcheting can explain shallow first-time failures in high-plasticity overconsolidated clay slopes and that the rate of deterioration of such assets will accelerate if current climate change projections are representative of future weather.

This research focuses on the effect of several convex and concave nose shapes on cavity formation for both hydrophilic and hydrophobic projectiles. It specifically investigates the effect of convex shape on the threshold velocity for cavity formation as well as the effect of concave shapes on cavity formation in terms of impact velocity, geometry of the concave shape and wettability of the projectile. For the convex cases, the streamlined axisymmetric shape significantly increases the threshold velocity when cavities form and is most pronounced for the ogive and cone. The study demonstrates that measuring the wetting angle and impact velocity is not enough to predict cavity behavior, rather the roughness and nose shape must also be taken into consideration for convex projectiles. For the concave cases, the cavities formed are highly influenced by impact speed and nose shape. Wetting angle did not have any visible effect on the cavity formed at higher impact speeds (7 m/s). The dynamics of the cavity formation are dominated by the pocket of trapped air formed when the concave projectiles impact the water. At low impact speeds (~0-1 m/s) the trapped air can separate the flow from the leading edge of the projectile nose when venting out and cause a large cavity to form, depending on the specific concave shape and speed. At moderate impact speeds (1-4 m/s) the trapped air will vent completely underwater forming a small ring-shaped cavity. At high impact speeds (4-10 m/s) the trapped pocket of air compresses tremendously and causes an unsteady pressure pulse, which can result in the formation of a bubble and jet in front of the cavity. The jet is formed by water passing behind the pocket of trapped air along the walls of the concave nose and converging into a jet at the top of the concave shape and entraining the trapped air as it descends.

Dans cette thèse, nous avons travaillé sur la mise au point de surfaces superhydrophobes modèles dont la mouillabilité peut être contrôlée par un stimulus externe. Composées de forêts de piliers micrométriques élastomères à forts rapports d'aspect dans lesquels sont incorporées des particules magnétiques, les surfaces présentent, via l'application d'un champ magnétique externe, une orientation modulable des piliers, donc une rugosité de surface adaptable. En faisant varier la géométrie, l'élasticité et l'aimantation de ces derniers, nous avons pu mettre en évidence les points suivants. Nous avons vu dans un premier temps qu’en accord avec la littérature, et en l’absence de champ magnétique, l’hystérèse de mouillage augmente avec la fraction de surface. Cependant, elle reste constante lorsque l’élasticité des piliers varie. Résultat déroutant, car à l’échelle du pilier, il existe bel et bien une différence de mobilité des piliers entre les piliers les plus rigides et les plus complaisants qui subissent la traction de la ligne triple.Nous avons ensuite montré que l’orientation des piliers changeait significativement l’angle de glissement via l’application d’un champ magnétique. De plus, le glissement de la goutte sur la surface est favorisé lorsque les piliers sont orientés à l’opposé de la pente. Enfin, nous avons pu contrôler la façon dont une goutte d’eau se déplace sur une surface inclinée en deçà de l’angle de glissement, puisqu’elle n’avance vers le bas de la surface que si une actuation magnétique est appliquée. Ces surfaces seront une source d’étude intéressante pour comprendre comment moduler le mouillage ou l’écoulement de liquide en état fakir. / During this thesis, we have developped superhydrophobic surfaces whose wettability can be controlled by an external magnetic stimulus. Formulating a network of elastomeric and magnetic micro-pillars with high aspect ratio allows the orientation of the pillars through magnetic forces, hence an adaptable surface roughness. Moreover, modulating the geometry, elasticity and magnetization of pillars allowed us to highlight the following conclusions.We have seen first that in agreement with the literature, without magnetic field, the wetting hysteresis increased with the surface fraction. However, it remains constant varying the elasticity of pillars. This conclusion is confusing, because at the pillar scale, there is indeed a difference of mobility between rigid and flexible pillars due to the force exerted by the triple line.We then demonstrated that the deflexion of the pillars can change significantly the sliding angle due to the applied magnetic field. Moreover, sliding of the droplet on such a surface is promoted when pillars are deflected against the slope.Finally, we managed to control the displacement of a droplet on a surface which is tilted with an angle below the sliding angle : it moves forward from the surface only if magnetic actuation is applied. This surfaces will be an attractive source of study in order to understand how to modulate wetting and liquid flow in fakir state.

Managing soil hydrophobicity caused by localized dry spots (LDS) on sand based golf greens has become one of the greatest challenges for golf course superintendents and managers, especially as water restrictions intensify. The purpose of this study was to evaluate the effectiveness of thirteen soil surfactants in eliminating LDS and in maximizing root zone soil moisture on a sand based USGA golf green located on the California Central Coast. Potential water repellency of air dried cores (measured utilizing the water droplet penetration time (WDPT) method), phytotoxicity, and climate were analyzed during two experimental trials. Phytotoxicity data was collected for Trial I using visual quality ratings and for Trial II using a chlorophyll meter. Phytotoxicity decreased during Trial I. Differences in phytotoxicity as measured using chlorophyll index were not at all significant during Trial II (p = 1). Ten of the thirteen wetting agent treatments significantly (p < 0.001) decreased soil hydrophobicity compared with the other wetting agent treated plots and the non-treated control. More frequent application of Cascade Plus resulted in a more significant reduction in soil hydrophobicity. Increasing the application rates also resulted in the reduction of soil hydrophobicity. Wetting agent treatment 6-CP(10day) maintained the highest volumetric water content (VWC) but treatment 13-2079337 maintained the highest levels for wetting agents treated monthly.

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

One of the earliest functions to express infiltration as a function of time was introduced by Green and Ampt. In this study their formula was modified to account for air compression and counterflow. Physically,infiltration, air compression, and counterflow occur simultaneously, while in this model they are decoupled within a time step. Counterflow is calculated as a mass flux and pressure is found using the perfect gas law. First, a comparison of three infiltration methods, the original Green and Ampt formulation, a modified version incorporating air compression only, and the third version including air compression and counterflow, was conducted. Then sensitivity of the model accounting for both air compression and counterflow was explored. Results showed that accounting for both air compression and counterflow improves the predicted infiltration rate. Air effect on infiltration can be significant even for environments with an impervious layer as deep as 10m; while for very deep water table environments (100m) the three models give similar results. In shallow water table environments (0.5m), air effect on infiltration rate, cumulative infiltration, ponding time, and saturation time is substantial. The model accounting for air compression and counterflow was then tested for different parameters. It provided reasonable results compared to the Green and Ampt model and the modified version accounting for air compression only. The advantages of this model are that no additional data is required other than what's needed for the original Green and Ampt formulation, and it can be applied for any environment. The assumption of uniform soil moisture content is a limitation for the model, especially for shallow water table environments where the variations in the soil moisture profile within the wetting front depth is substantial.

Les bactéries se répandent aux interfaces en formant des colonies, qui peuvent être considérées comme des suspensions denses actives. L'objet de cette thèse est le développement et l'analyse de modèles simples pour élucider le rôle des phénomènes physico-chimiques et passifs - tels que l'osmose, la tension de surface et le mouillage - dans l'expansion des colonies bactériennes aux interfaces solide/air. Les modèles sont basés sur une description hydrodynamique des couches minces de suspensions liquides, qui est complété par des processus bioactifs.Dans un premier temps, nous nous sommes intéressés à l'expansion osmotique des biofilms. Dans ce mécanisme, la bactérie sécrète une matrice polymérique qui agit comme un osmolyte et entraîne un afflux d'eau, riche en nutriments, du substrat humide vers le biofilm. Nous avons constaté que la mouillabilité du substrat est une des déterminantes principales de la vitesse d'expansion du biofilm. En-dessous d'une mouillabilité critique l'expansion s'interrompt, bien que la colonie soit biologiquement active. Cependant, une légère réduction de la tension de surface et une amélioration de la mouillabilité qui en résulte suffisent à induire un étalement continu. Les bactéries peuvent activement contrôler la tension de surface par la production de bio-surfactants.Dans un deuxième temps, nous avons étudié l'expansion de colonies bactériennes aidée par des molécules biologiques tensioactives auto-produites. Dans ce mécanisme, des flux de Marangoni résultant d'une concentration non uniforme de molécules tensioactives aux bords de la colonie peuvent favoriser l'expansion coopérative et provoquer une instabilité de la forme axi-symétrique des colonies bactériennes. Notre modèle nous a permis de reproduire quatre modes de développement différentes, à savoir l'étalement arrêté et continu des colonies circulaires, l'étalement des colonies avec des bords légèrement modulées et la formation de doigts prononcés.Dans la dernière partie, nous avons fait un premier pas vers l'incorporation de la motilité actif des bactéries dans notre modèle et présentons donc un modèle phénoménologique pour un film mince active. / Bacteria colonise interfaces by the formation of dense aggregates. In this thesis, we develop and analyse simple models to clarify the role of passive physico-chemical forces and processes - such as osmosis, surface tension effects and wettability - in the spreading of bacterial colonies at solid-air interfaces. The models are based on a hydrodynamic description for thin films of liquid suspensions that is supplemented by bioactive processes.We first focus on the osmotic spreading mechanism of bacterial colonies that relies on the generation of osmotic pressure gradients. The bacteria secrete a polymeric matrix which acts as an osmolyte and triggers the influx of nutrient-rich water from the moist substrate into the colony. We find that wettability crucially affects the spreading dynamics. At low wettability, the lateral expansion of the colony is arrested, albeit the colony is biologically active. However, a small reduction of the surface tension and the resulting improvement of the wettability suffices to induce continuous spreading. This can, e.g., result from the production of bio-surfactants by the bacteria.Next, we study passive liquid films covered by insoluble surfactants before developing a model for the surfactant-driven spreading of bacterial colonies. In this spreading mechanism, Marangoni fluxes arising due to a non-uniform surfactant concentration at the edges of the colony drive cooperative spreading and may cause an instability of the circular colony shape. We find that variations in wettability and surfactant production suffice to reproduce four different types of colony growth, namely, arrested and continuous spreading of circular colonies, slightly modulated front lines and the formation of pronounced fingers.In the final part, we take a first step towards the incorporation of active collective bacterial motion in the employed thin-film framework and present a phenomenologically derived model for active polar films.