Une surface superhydrophobe est caractérisée par un angle de contact apparent supérieur à 150° et un angle de contact dynamique faible. Ce phénomène, découvert dans la nature, suscite une grande attention de la part de la communauté scientifique. En effet, le contrôle de la mouillabilité d’une surface solide est important dans de nombreuses applications. De nombreuses techniques d’élaboration de surfaces superhydrophobes ont été décrites, dont la polymérisation par voie électrochimique qui permet d’obtenir des surfaces avec une mouillabilité variée, de façon contrôlée et en utilisant des polymères conducteurs. Le développement de matériaux à mouillabilité réversible, sensibles aux stimuli extérieurs revêt un grand intérêt pour leurs diverses applications potentielles. Le but de ce travail de thèse est d’élaborer des matériaux superhydrophobes réversibles par l’utilisation de polymères conducteurs électrodéposés. Nous avons obtenu des surfaces superhydrophobes par introduction de monomères hydrophiles ammoniums. Des changements de la mouillabilité ont été obtenus en utilisant la réduction par voltage et l’échange d’ions. Des propriétés réversibles hydrophobes / hydrophiles ont aussi été atteintes par post-fonctionnalisation de surface par différents acides boroniques. / Superhydrophobic surface is characterized by an apparent contact angle higher than 150° and a low dynamic contact angle. This phenomenon, found in nature, arouses great attention from the scientific community. Indeed, controlling the wettability of a solid surface is important in many applications. Many techniques to prepare superhydrophobic surfaces have been described, including the electrochemical polymerization which allows to obtain surfaces with various wettability by a controlled way and using conductive polymers. The development of materials with switchable wettability, sensitive to external stimuli is of great interest for their potential applications. The aim of this thesis is the development of reversible superhydrophobic materials by using conducting polymers. We obtained superhydrophobic surfaces by using hydrophilic ammonium monomers. Changes in wettability were obtained by dedoping and ion exchange. Reversible hydrophobic / hydrophilic properties were achieved by surface post-functionnalization using differents boronic acids.

Superhydrophobicity refers to surfaces with extremely large water droplet contact angles (usually greater than 150°). This phenomenon requires a hydrophobic material with micro or nano-scale roughness. Superhydrophobic surfaces exist in nature (e.g. the lotus leaf) and can be produced synthetically. This project focuses on the development and characterization of superhydrophobic materials with tunable wettability (i.e. smart superhydrophobic materials). In this study, surfaces were prepared by electrospinning thin, aligned polystyrene fibers onto a piezoelectric unimorph substrate. Results showed electric field induced changes in substrate curvature, which produced corresponding changes in surface wettability. From experiments, an average change in water contact angle of 7.2° ± 1.2° with 90% confidence was observed in ~2μm diameter fiber coatings electrospun for 5 minutes with applied electric field. In addition, fiber coatings electrospun with equivalent deposition showed average electric field induced changes in WCA of 2.5° ± 0.92° for lower diameter fibers (~1μm) and 3.5° ± 1.37° for higher diameter fibers (~2μm) with 90% confidence.

Superhydrophobic surfaces are able to entrap gas pockets in-between surface roughness elements when submerged in water. These entrapped gas pockets give these surfaces the potential to reduce drag due to the overlying flow being able to locally slip over the gas pockets, resulting in a mean slip at the surface. This thesis investigates the different effects that slip and the texturing of the surface have on turbulence over superhydrophobic surfaces. It is shown that, after filtering out the texture-induced flow, the background, overlying turbulence experiences the surface as a homogeneous slip boundary condition. For texture sizes, expressed in wall units, up to $L^+ \lesssim 20$ the only effect of the surface texture on the overlying flow is through this surface slip. The direct effect of slip does not modify the dynamics of the overlying turbulence, which remains canonical and smooth-wall-like. In these cases the flow is governed by the difference between two virtual origins, the virtual origin of the mean flow and the virtual origin experienced by the overlying turbulence. Streamwise slip deepens the virtual origin of the mean flow, while spanwise slip acts to deepen the virtual origin perceived by the overlying turbulence. The drag reduction is then proportional to the difference between the two virtual origins, reminiscent of drag reduction using riblets. The validity of slip-length models to represent textured superhydrophobic surfaces can resultantly be extended up to $L^+ \lesssim 20$. However, for $L^+ \gtrsim 25$ a non-linear interaction with the texture-coherent flow alters the dynamics of the background turbulence, with a reduction in coherence of large streamwise lengthscales. This non-linear interaction causes an increase in Reynolds stress up to $y^+ \lesssim 25$, and decreases the obtained drag reduction compared to that predicted from homogeneous slip-length models.

Diamond is a material with many exceptional properties. In this thesis methods for fabrication of microstructures as well as several applications of such structures in optics, microfluidics and electrochemistry are presented. A method for etching deep and highly precise gratings is described. This method was used to fabricate circularly symmetric half wave plates for use in vector vortex coronagraphs. Such coronagraphs are a very promising approach to the direct imaging of extrasolar planets. By varying the lateral etch rate of the aluminum mask during diamond etching in an inductively coupled plasma, the sidewall angle of the etched structures could be controlled. This method was used to make smooth sloped sides on a waveguide for coupling light into it. Antireflective structures that drastically reduced the surface reflection in a wavelength band between 10 and 50 µm were also fabricated. An array of boron doped diamond microelectrodes for electrochemical measurements in a microchannel was fabricated and tested, showing very good stability and reusability. Several hundred hours of use did not adversely affect their performance and no damage to them could be detected by atomic force microscopy or scanning electron microscopy. Superhydrophobic surfaces in diamond were demonstrated, using both hydrogen and fluorine termination. Hydrogen termination on a flat surface gives contact angles below 90°. To achieve a superhydrophobic surface with this low intrinsic hydrophobicity, structures looking like microscopic nail heads were fabricated. The effect of water pressure on immersed superhydrophobic surfaces was also studied and it was found that the collapse of the superhydrophobic state due to pressure was sometimes reversible as the pressure was lowered. Finally, a method was tested for functionalizing diamond surfaces using block copolymers of polyethylene oxide and polypropylene oxide to both passivate the surface and to attach synthetic binder molecules. This method was found to give very high signal to noise ratios when detecting C-reactive protein.

In this research, a low-cost template-based process has been developed to structure the surfaces of polymeric materials rendering them superhydrophobic. This biology-inspired approach was developed using results from the first part of this thesis: the first known detailed study of superhydrophobic aspen leaf surfaces. Aspen leaves, similar to lotus leaves, possess a dual-scale hierarchical surface structure consisting of micro-scale papillae covered by nano-scale wax crystals, and this surface structure was used as a blueprint in the structuring of templates. These distinctive surface features coupled with a hydrophobic surface chemistry is responsible for these leaves’ extreme non-wetting property. Non-wetting is further augmented by the unique high aspect ratio aspen leafstalk geometry. The slender leafstalks offer very little resistance to twisting and bending, which results in significant leaf movement in the slightest breeze, facilitating water droplet roll-off. The structured template surfaces, produced by sand blasting and chemical etching of electrodeposited nanocrystalline nickel sheets, resemble the negative of the superhydrophobic aspen leaf surfaces. Re-usable templates were subsequently employed in a hot embossing technique where they were pressed against softened polymers (polyethylene, polypropylene and polytetrafluoroethylene) thereby transferring their surface structures. The resulting pressed polymer surfaces exhibited features very similar to aspen leaf surfaces. This process increased the water contact angle for all pressed polymers to values above 150 degrees. Additionally, after pressing the water roll-off angle for all polymer surfaces dropped below 5 degrees. The effects of water surfactant concentration, water drop size and temperature on the wetting characteristics of the structured polymers were studied to indicate in which applications these functional surfaces could be most beneficial. Coupling this attractive superhydrophobic surface property with mechanical motion (shaking, bending, or vibrating) could result in superhydrophobic surfaces with superior non-wetting properties suitable for a wide range of applications.

In this research, a low-cost template-based process has been developed to structure the surfaces of polymeric materials rendering them superhydrophobic. This biology-inspired approach was developed using results from the first part of this thesis: the first known detailed study of superhydrophobic aspen leaf surfaces. Aspen leaves, similar to lotus leaves, possess a dual-scale hierarchical surface structure consisting of micro-scale papillae covered by nano-scale wax crystals, and this surface structure was used as a blueprint in the structuring of templates. These distinctive surface features coupled with a hydrophobic surface chemistry is responsible for these leaves’ extreme non-wetting property. Non-wetting is further augmented by the unique high aspect ratio aspen leafstalk geometry. The slender leafstalks offer very little resistance to twisting and bending, which results in significant leaf movement in the slightest breeze, facilitating water droplet roll-off. The structured template surfaces, produced by sand blasting and chemical etching of electrodeposited nanocrystalline nickel sheets, resemble the negative of the superhydrophobic aspen leaf surfaces. Re-usable templates were subsequently employed in a hot embossing technique where they were pressed against softened polymers (polyethylene, polypropylene and polytetrafluoroethylene) thereby transferring their surface structures. The resulting pressed polymer surfaces exhibited features very similar to aspen leaf surfaces. This process increased the water contact angle for all pressed polymers to values above 150 degrees. Additionally, after pressing the water roll-off angle for all polymer surfaces dropped below 5 degrees. The effects of water surfactant concentration, water drop size and temperature on the wetting characteristics of the structured polymers were studied to indicate in which applications these functional surfaces could be most beneficial. Coupling this attractive superhydrophobic surface property with mechanical motion (shaking, bending, or vibrating) could result in superhydrophobic surfaces with superior non-wetting properties suitable for a wide range of applications.

Superhydrophobic surfaces, which display water contact angles of larger than 150°, have attracted more and more attention due to their importance in both fundamental research and practical applications. This dissertation is mainly focused on the fundamental understanding and exploring applications of superhydrophobic surfaces. First, some specific examples of superhydrophobic surface fabrication were given, which include superoleophobic Si surface, robust superhydrophobic SiC surface, and reversible wettability nanocomposite films. Based on the study of superhydrophobic surfaces, the application of superhydrophobic surfaces in electronic packaging were explored. Superhydrophobic silica/epoxy nanocomposite coating serves as an encapsulant to improve the electronic device reliability. Such superhydrophobic coating showed good stability under humidity at elevated temperatures and was applied on the triple track resistors test coupons. In addition, the applications of superhydrophobic surfaces in solar cells were studied. Two multi-functional hierarchical structure solar cells with self-cleaning, low reflection and high efficiency properties were built up by coating or etching methods.

Highly fluid repellent have application in many industries ranging from marine to biomedical due to their self-cleaning antifouling properties. The development and implementation of these superhydrophobic (water contact angle >150 degrees ) and superoleophobic (oil contact angle > 150 degrees ) surfaces were studied in this thesis. We focused our studies on paper as a substrate for these superhydrophobic and superoleophobic surfaces. Cellulose based paper is a biodegradable, inexpensive material that is ideal for disposable use applications. Applying an oxygen plasma etching technique combined with the deposition of a fluoropolymer from a pentafluoroethane precursor, superhydrophobic paper can be attained. This superhydrophobic paper is functionalized by printing wax islands onto the surface, thereby creating areas of high fluid adhesion. These wax functionalized sheets are used to sample droplets from bulk droplets, with the sampled volume being controlled by the hysteresis of the wax island. Disposable biomedical devices can be envisioned from these wax designs. While these superhydrophobic surface excel at repelling water, they continue to readily absorb water. Formation of paper that is both superhydrophobic and superoleophobic, or superamphiphobic, is accomplished through a combination of steps: mechanical fiber refining, solvent exchange processing and plasma treatment. The fiber refining creates nano-scale fibrils that are separated in the solvent processing. Subsequent plasma treatment of oxygen etching and fluoropolymer deposition creates superamphiphobic paper, exhibiting contact angles of > 150 degrees for water, ethylene glycol, motor oil and n-hexadecane. Further studies were conducted to increase the strength of these superamphiphobic sheets by using layered paper. Development of superhydrophobic paper from a hydrophilic diamond-like carbon surface coating was also demonstrated. When combined with oxygen plasma etching, diamond-like carbon coated paper sheets attain superhydrophobic properties similar to fluoropolymer coated sheets. Based on the knowledge gained from the studies on paper, superhydrophobic surfaces are created on 304 and 316 stainless steels. Samples are etched in hydrofluoric acid and then passivated in nitric acid to create the necessary surface structure. Deposition of fluoropolymer onto the etched samples yields superhydrophobic properties.

L’eau sur une feuille de Lotus est connue pour être étonnamment mobile, cette propriété émergeant de la présence sur la feuille de rugosités hydrophobes micrométriques. À l’image d’un fakir qui ne touche que les pointes des clous de son tapis, une goutte sur une telle surface ne repose que sur les sommets des rugosités. Le liquide est ainsi sur coussin d’air d’où sa grande mobilité. Cette propriété est appelée superhydrophobie et permet de repousser efficacement l’eau. Cependant en situations humides, comme au contact d’un liquide chaud, la buée qui se condense dans les textures micrométriques de la surface altère ces propriétés anti-eau. D’autres surfaces naturelles sont superhydrophobes, parmi elles, les ailes des cigales, qui sont pourvues de cônes de l’ordre de 100 nm. Sur ces ailes, et contrairement au lotus, l’eau sous forme de buée semble garder sa mobilité : des gouttes qui coalescent sur cette surface peuvent s’éjecter de la surface par transfert d’énergie de surface en énergie cinétique.Dans cette thèse, nous avons étudié avec des surfaces modèles l’effet de la taille et de la forme de nano-rugosités sur les propriétés antibuée de surfaces superhydrophobes. Cette thèse se divise en deux parties.Dans une première partie, nous avons étudié la résistance des surfaces nanostructurées aux figures de souffle. Nous avons mis en évidence avec des surfaces modèles que la forme des rugosités jouait un rôle clé dans l’antibuée. Des piliers coniques permettent d’obtenir une éjection des gouttes de buée pour la quasi-totalité (95%) des coalescences, alors que des piliers cylindriques de même échelle ont une efficacité proche de zéro. Nous nous sommes alors naturellement intéressés au mécanisme d’éjection de la buée et avons d’abord montré que la vitesse de saut des gouttes est gouvernée par un transfert de quantité de mouvement de l’horizontale à la verticale. Nous avons ensuite observé que la dissipation visqueuse limitait la vitesse de saut des gouttes de rayon inférieur à 5 µm.Dans la seconde partie de cette thèse, nous avons testé l’adhésion de gouttes d’eau chaudes sur des surfaces dont la rugosité va de la cinquantaine de nanomètres au micromètre. Nous avons montré que plus une structure est compacte, plus elle apporte une résistance aux liquides chauds. C’est du compartimentage de la buée par les piliers qu’émerge cette propriété : si les rugosités sont trop espacées, la buée qui se condense sous la goutte remplace l’air à l’origine de la mobilité; à l’inverse, des piliers suffisamment rapprochés permettent de bloquer le liquide et ainsi de conserver air et mobilité. Ces résultats fondés sur une étude statique ne prennent pas en compte, par définition, la dynamique de la formation de buée. Nous avons donc pour compléter cette étude, à la situation dynamique des impacts de gouttes chaudes. Contrairement à toutes les conclusions précédentes, dans ce cas anti-pluie, des surfaces de rugosité micrométrique peuvent avoir un meilleur comportement antibuée que celles de rugosité sub-micrométrique. Cela est dû au temps nécessaire pour que les gouttes de condensation remplissent les textures sous la goutte : il augmente avec la hauteur des piliers, si bien que la buée n’a pas d’effet quand le temps de rebond est inférieur au temps de remplissage.Au total, cette thèse a permis de mettre en évidence la grande diversité des propriétés antibuée que l’on peut obtenir en fonction de l’échelle des rugosités. / Water on a lotus leaf is known to be surprisingly mobile. This surprising property arises from the hydrophobic micrometric roughness of the leaf. Like a fakir that sits only on the nails’ tip, water drop on such surface contacts only the tops of the surface features. Water is then, as a hovercraft, on an air cushion that makes it extremely mobile. This property water repelling property is called superhydrophobicity. However, in humid atmospheres or when in contact with hot water, water condensate in the roughness, which may destroy the repellence. Other natural surfaces are superhydrophobic: cicada wings are covered with hydrophobic conical features of typical size 100 nm. On those wings, water condensing seems to stay really mobile: merging drops can be ejected from the surface.In this thesis, we study with model superhydrophobic surfaces the shape and size effect of roughness on the antifogging properties. In particular, we focus on the decrease of size to the nanometric scale. This work has two main parts.In the first part, we studied the resistance of nanostructured materials to breath figures. We demonstrate, with model surfaces, the key role played by the shape of the features on antifogging property. Conical pillars are close to a full efficiency for jumping droplets: 95% of the coalescing drops jump of the substrate, with cylindrical pillars this rate falls below 0.5%. Naturally, we then studied this jumping mechanism. We found out that a momentum transfer from horizontal to vertical governs the jumping velocity of merging drops. We then observed that viscosity dissipation limits the jumping velocity of droplets with a radius lower than 5 µm.In the second part of this work, we probed hot water repellency. To do so, we studied adhesion of hot water drops on model nanotextures of size ranging from 50 nm to 1 µm. Our study shows that the denser the textures are, the more the surface resists to hot water. This property comes from the subdivision of condensation: close pillars limit the propagation of liquid in the air layer under the drop responsible for water mobility. On the contrary, if pillars are more spaced than condensation nucleii, water will invade all the roughness and the solid will behave as a hydrophilic surface and sticks the drop. This study does not take into account the dynamic effect of condensation. To investigate this, we probed antifogging ability in hot water drops bouncing experiments. Surprisingly, in this case taller features (typically a few micrometers) are more efficient than their nanometric counterparts. The time needed for condensation to fill the gap between the surface and pillars top can be greater than the bouncing time of water drops. In that case condensation has no effect on adhesion.In this thesis, we probed the different kind of antifogging abilities that appear when varying the textures’ scale.

The general objective of this thesis is to conduct experiments on sphere free-falling in liquid that advance our understanding of the drag reduction on solids moving in liquid by means of lubricating gas layers and attached streamlined air cavities. Part I of the thesis investigates the effect of thin air layers, naturally sustained on superhydrophobic surfaces, on the terminal velocity and drag force of metallic spheres free- falling in water. The surface of 20 mm to 60 mm steel or tungsten-carbide spheres is rendered superhydrophobic by a simple coating process that uses a commercially available hydrophobic agent. By comparing the free-fall of unmodified spheres and superhydrophobic spheres, in a 2.5 meters tall water tank, it is demonstrated that even a very thin air layer (~ 1 – 2 μm) that covers the freshly dipped superhydrophobic sphere, can reduce the drag force on the spheres by up to 80 %, at Reynolds numbers 105 to 3×105, owing to an early drag crisis transition. Part II of the thesis investigates the drag reduction by means of the dynamic Leidenfrost vapor-layer sustained on the surface of heated metallic spheres free-falling in a fluorocarbon liquid, FC-72 (perfluorohexane). In these experiments we employed two tall liquid tanks: a 3 meter tall 14 cm wide tank and a 2 meter tall 20 × 20 cm cross-section tank with a heater device. These tanks are significantly larger than the tanks used in prior studies and allow us to track the extended fall trajectories and to compare the drag on room-temperature no-vapor-layer spheres to that of heated Leidenfrost vapor-layer spheres. Analysis of the extended free-fall trajectories and acceleration, based on the sphere dynamic equation of motion, enables the accurate evaluation of the vapor-layer-induced drag reduction, without the need for extrapolation. We demonstrate that the drag on the Leidenfrost sphere in FC-72, can be as low as CD = 0.04 ± 0.01, or an order of magnitude lower than the values for the no-vapor-layer spheres in the subcritical Reynolds number range. This drag reduction extends into the supercritical Reynolds number range. The analysis method developed herein, to describe the sphere trajectories, can be applied in other related studies. Part III of the thesis examines a recently demonstrated phenomenon of the formation of stable-streamlined gas cavity following the impact of a heated Leidenfrost sphere on a liquid surface or a superhydrophobic sphere on water. The sphere encapsulated in a teardrop-shaped gas cavity was found to have near-zero hydrodynamic drag due to the self-adjusting streamlined shape and the free-slip boundary condition on the cavity interface. Here it is shown that such cavities can be formed following the water impact from a sufficient height of non-superhydrophobic spheres with water contact angles between 30° and 120°. In this case the streamlined cavity is attached just above the sphere’s equator, instead of entirely wrapping the sphere. Nevertheless, this sphere with attached cavity has near-zero drag and predetermined free-fall velocity in compliance with the Bernoulli law of potential flow. Last, the effect of surfactant addition to the water solution is investigated. The shape and fall velocity of the sphere with streamlined cavity formation were unaffected by the addition of low-surface-modulus synthetic surfactants, but was destabilised when a solution containing high-surface-modulus surfactants, such as soaps were used.