Condensation of water vapor is an everyday phenomenon which plays an important role in power generation schemes, desalination applications and high-heat flux cooling of power electronic devices. Continuous dropwise condensation is a desirable mode of condensation in which small, highly-spherical droplets regularly form and shed off the surface before a thick liquid is formed, thereby minimizing the thermal resistance to heat transfer across the condensate layer. While difficult to induce and sustain, dropwise condensation has been shown to achieve heat and mass transfer coefficients over an order of magnitude higher than its filmwise counterpart. Superhydrophobic surfaces have been extensively studied to promote dropwise condensation with mixed results; often surfaces that are superhydrophobic to deposited droplets formed in the gas phase above the surface do not retain this behavior with condensed droplets nucleated and grown on the surface. Recently, nanostructured superhydrophobic surfaces have been developed that are robust to vapor condensation; however, these surfaces still are not ideal for condensation heat transfer due to the high thermal resistance of the vapor layer trapped underneath the droplets and the reduced footprint of direct contact between the highly-spherical droplets and the underlying substrate. This work has two main objectives. First, a comprehensive free energy based thermodynamic model is developed to better understand why traditional superhydrophobic surfaces often lose their properties when exposed to condensed droplets. The model is first validated using data from the existing literature and then extended to analyze the suitability of amphiphilic (e.g. part hydrophobic and part hydrophilic) nanostructured surfaces for condensation applications. Secondly, one of the promising amphiphilic surfaces identified by the thermodynamic model is fabricated and tested to observe condensation dynamic behavior. Two complementary visualization techniques, environmental scanning electron microscopy (ESEM) and optical (light) microscopy, are used to probe the condensation behavior and compare the performance to that of a traditional superhydrophobic surface. Observations from the condensation experiments are used to propose a new mechanism of coalescence that governs the temporal droplet size distribution on the amphiphilic nanostructured surface and continually generates fresh sites for the droplet nucleation and growth cycle that is most efficient at heat transfer.

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In our study, the superhydrophobic surface based on biomimetic lotus leave is explored to maintain the desired properties for self-cleaning. In controlling bead-up and roll-off characteristics of water droplets the contact angle and contact angle hysteresis were very important and we investigated the determining conditions on different model surfaces with micro- and nanostructures. Two governing equations were proposed, one for contact angle based on Laplace pressure and one for contact angle hysteresis based on Young-Dupré equation. Based on these understanding on superhydrophobicity, possible applications of the superhydrophobicity for self-cleaning and water repellency were explored and application related technical issues were addressed. Based on our understanding of the roughness effect on superhydrophobicity (both contact angle and hysteresis), structured surfaces from polybutadiene, polyurethane, silica, and Si etc were successfully prepared. For engineering applications of superhydrophobic surfaces, stability issues regarding UV, mechanical robustness and humid environment need to be investigated. Among these factors, UV stability is the first one to be studied. Silica surfaces with excellent UV stability were prepared. UV stability on the surface currently is 5,500 h according the standard test method of ASTM D 4329. No degradation on surface superhydrophobicity was observed. New methods for preparing superhydrophobic and transparent silica surfaces were investigated using urea-choline chloride eutectic liquid to generate fine roughness and reduce the cost for preparation of surface structures. Another possible application for self-cleaning in photovoltaic panels was investigated on Si surfaces by construction of the two-scale rough structures followed by fluoroalkyl silane treatment. Regarding the mechanical robustness, epoxy-silica superhydrophobic surfaces were prepared by O2 plasma etching to generate enough surface roughness of silica spheres followed by fluoroalkyl silane treatment. A robustness test method was proposed and the test results showed that the surface is among the most robust surfaces for the superhydrophobic surfaces we prepared and currently reported in literature.

Les nanotechnologies représentent un potentiel de développements et d’applications considérables dans le domaine des matériaux ouvrant la voie à d’innombrables développements pour l’énergie, le transport, la santé, l’industrie, etc. Le biomimétisme a ainsi trouvé un nouveau moteur d'étude et de développement. La feuille de lotus est capable de faire perler l’eau avec une efficacité remarquable transformant n’importe quelle goutte d’eau en une bille répondant aux lois de la physique des solides. Cette propriété extraordinaire est due à l’association d’une composition chimique intrinsèquement hydrophobe avec une texturation hiérarchique de sa surface.Cette thèse s’intéresse à la compréhension des principes physiques qui régissent l'interaction des gouttes d'eau avec les surfaces de films polymères structurées de FEP, PMMA et PET. Deux technologies ont été mises en oeuvre pour la fabrication de surfaces superhydrophobes hiérarchiques : la nanoimpression (NIL) thermique et la gravure plasma. Nous avons mesuré les angles de contact et hystérésis de ces surfaces structurées afin d’identifier leur état de mouillage de Wenzel ou de Cassie-Baxter. Nous avons attaché une importance particulière au développement de solutions de fabrication et de caractérisations sur de grandes surfaces.Les propriétés antigivre ont été caractérisées, ainsi le rôle de la condensation dans la propagation du givre a été corrélé à la structuration de surface. De plus, nous avons mis en évidence le rôle du potentiel électrostatique de surface sur les retards de gel. Enfin, au vue du potentiel applicatif de ces surfaces, nous avons ajouté une dimension dynamique à l’étude en considérant les vitesses d’impact des gouttes. Un modèle de prédiction de la littérature a été comparé avec succès aux résultats expérimentaux. / Nanotechnologies represent a considerable potential of development and application in the field of material science opening the way to innumerable developments for energy, transport, health, industry, and so on. Thus, biomimicry found a new driving force for study and development. The lotus leaf is able to repulse water with a remarkable efficiency transforming any drop of water into a ball following the laws of solid physics. This extraordinary property is due to the association of a hydrophobic chemical composition with a hierarchical texturing of its surface.This thesis focuses on the understanding of the physical principles governing the interaction of water drops on the surfaces of structured polymer films of FEP, PMMA and PET. Two technologies have been implemented for the production of hierarchical superhydrophobic surfaces: thermal nanoimprint lithography (NIL) and plasma etching. We have measured the contact angles and hysteresis of these structured surfaces in order to identify their Wenzel or Cassie-Baxter wetting state. We have attached particular importance to the development of manufacturing and characterization solutions on large surfaces.The anti-icing properties have been characterized and the role of condensation in the propagation of frost has been correlated with the surface texturing. In addition, we have highlighted the role of the electrostatic surface potential on frost delays. Finally, in view of the applicative potential of these surfaces, we added a dynamic dimension in the study considering the velocity of drops impact. A model of prediction from the literature was successfully compared to our experimental results.

The wetting of a rough material is controlled by surface chemistry and morphology, the liquid phase, solutes, and surfactants that affect the surface tension with the gas phase, and environmental conditions such as temperature and pressure. Materials with high (>150˚) apparent contact angles are known as superhydrophobic and are very resistant to wetting. However, in complex biological mixtures eventually protein adsorbs, fouling the surface and facilitating wetting on time scales from seconds to months. The work here uses the partially-wetted (Cassie-Baxter) to fully-wetted (Wenzel) state transition to control drug delivery and to perform surfactant detection via surface tension using hydrophobic and superhydrophobic materials. First there is an overview of the physics of the non-wetting state and the transition to wetting. Then there is a review of how wetting can be controlled by outside stimuli and applications of these materials. Next there is work presented on controlling drug release using superhydrophobic materials with controlled wetting rates, with both in vitro and in vivo results. Then there is work on developing a sensor based on this wetting state transition and its applications toward detecting solute levels in biological fluids for point-of-care diagnosis. Finally, there is work presented on using these sensors for detecting the alcohol content in wine and spirits.

Neste trabalho, exploramos o uso de técnicas de microestruturação de materiais poliméricos a laser, visando a obtenção de superfícies superhidrofóbicas. Primeiramente, empregamos o fenômeno de transporte de massa em larga escala, obtido quando polímeros azoaromáticos são expostos a um padrão de interferência, para microestruturar a superfície dos filmes. Com esse método, produzimos uma morfologia superficial com formato semelhante ao de uma caixa de ovos, com espaçamento entre picos variando de 1,0 a 3,5 µm. Essa microestruturação permitiu a obtenção de amostras com distintas características hidrofóbicas; um ângulo de contato com água de 117º foi observado para a estrutura com período de 2 µm, o que corresponde a um aumento de 9º em relação à superfície não estruturada. Visando obter superfícies com características ainda mais hidrofóbicas, desenvolvemos uma técnica de microestruturação que utiliza pulsos laser para produzir micro-ranhuras por ablação na superfície polimérica. Neste caso, a morfologia da superfície produzida era composta por pilares, de seção reta quadrada, dispostos lado a lado, com distintos espaçamentos. Com esse tipo de microestruturação, e utilizando pulsos de 100 ps e 532 nm, observamos ângulos de contato com água acima de 150º, ou seja, o regime superhidrofóbico foi atingido Quando pulsos de femtossegundos foram utilizados, ranhuras com alta resolução lateral são obtidas, porém com pouca profundidade, o que não possibilitou a obtenção de um aumento significativo na hidrofobicidade. De maneira geral, nossos resultados mostram a viabilidade do uso de técnicas de microestruturação a laser para criar superfícies com propriedades de molhamento controlável, que podem ser exploradas para aplicações tecnológicas. / In this work, we investigate the use of laser microstructuring techniques to obtain superhydrophobic surfaces in polymeric materials. Initially, we employed the large-scale mass transport mechanism, obtained when azoaromatic polymers are exposed to an interference pattern, to structure the film surface. With this method, we produce an egg-crate-like surface morphology, with periods from 1.0 to 3.5 m that present distinct wetting properties. This method allowed obtaining samples with different hydrophobic characteristics; a contact angle with water of 117° was observed for the structure with period of 2 m, which corresponds to an increase of 9° with respect to the unstructured surface. Aiming at surfaces with higher hydrophobicities, we developed an ultrashort pulse micromachining technique to produce grooves, by ablation, on the polymer surface. In this case, square-shape pillar morphologies, with distinct periods, were fabricated. With this microstructuring method, and using 100 ps at 532 nm pulses, we observed contact angles with water above 150°, ie superhydrophobicity was achieved. When femtosecond pulses were used, although grooves with high lateral resolution are obtained, they are too shallow to produce a significant increase in hydrophobicity. Overall, our results indicate the use of laser microstructuring for the fabrication of surfaces with controllable hydrophobicity, which can be exploited for technological applications.

Les surfaces texturées sont devenues, ces dernières années, des substrats de choix pour de nombreuses applications. Dans le domaine de l'application superhydrophe, elles ont permis de fabriquer des surfaces autonettoyantes. Nous nous intéressons à la préparation de surfaces texturées par électrodépôt en utilisant des électrodes modifiées par des auto assemblages de nanoparticules métalliques fonctionnalisées. Notre stratégie de texturation a montré sa puissance vis-à-vis du contrôle de l'électrodépôt de métaux (Ag, Cu et Co). Des électrodes structurées avec une résolution de 2 nm entre les motifs électrodéposés, ont pu être préparées avec succès par notre méthode. Parallèlement, nous avons montré qu'il est possible de contrôler la morphologie des films électrodéposés et directement leurs propriétés de mouillage. Le rôle des molécules fonctionnalisant les nanoparticules a été montré déterminant dans ce contrôle. Par ailleurs le rôle électrocatalytique des nanoparticules métalliques sur la surface d'HOPG a été mis en évidence. L'application superhydrophobe des textures préparées a été évaluée pour les différents métaux électrodéposés. / In recent years, textured surfaces become desired substrates for different nanotechnology applications. In the field of superhydrophobic applications, structured surfaces are used as self-cleaning surfaces. In the present PhD work, we are interested in the fabrication of textured surfaces using electrodeposition process and self assembled functionalized Au NPs modified electrodes. Our strategy shows interesting possibilities to control metal electrodeposition (Ag, Cu and Co). Structured surfaces with 2 nanometer resolution have been prepared successfully using our approach. In the other hand, it is demonstrated that for convenient molecules which functionalized Au NPs, it is possible to control the morphology of electrodeposited materials and in turn their wetting properties. Furthermore, it is found that Au NPs behave as electronanocatalysts on HOPG surface. Superhydrophobic application was evaluated for different textured surfaces with different materials

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Understanding the hemodynamics of the cardiovascular system and associated diseases is important for mitigating health risks. We applied flow diagnostic techniques to investigate pulsatile flow characteristics past sidewall cavities, which have implications to two biomedical problems in the cardiovascular system: sidewall aneurysms and the left atrial appendage. Superhydrophobically-coated mesh diverters and synthetic slippery surfaces were studied for their effects on flow diversion and cavity flow enhancements. The study of pulsatile flow over a coated mesh diverter showed that the formation of the primary vortex was prevented which prevents flow stagnation and downwash flow in the cavity. The second study indicates that the healthy heart cycle is essential to reducing flow stasis inside the left atrial appendage. After applying a synthetic slippery surface to the interior of a side wall cavity model, this surface reduced the wall shear stress and allowed vortical flow to reach deeper into the cavity.

<blockquote><div><div>Methods and techniques for tailoring the surface morphology of metallic surfaces are determined in part by the complex behavior of elemental interactions in conjunction with electrochemical reactions. In this work, we show how the surface morphology can be predicted based on experimental data resulting from polarization curves and compositional differences of Fe- and Ni-based superalloys. Electrochemical treatments utilizing NaCl as the electrolyte were adapted using parameters such as the pitting resistance equivalent (PRE) number and polarization curves to obtain both rough and smooth surfaces. Utilizing these metrics, we electrochemically etched Inconel 600, SS304, Inconel 718 and Inconel 625 obtaining average surface roughness values that ranged from 0.05 to 57.4 μm indicating the success of tailoring the technique to obtaining rough and smooth surfaces. The effect of current density, current pulsing, and temperature were varied to elucidate roughness and pitting behavior, and strong correlations to the PRE number and polarization curve properties of the alloy were observed. Heat treatments and subsequent evolution to the microstructure in the form of grain growth and precipitation altered the etching behavior. These techniques can be used in preventing corrosion failure and enhancing electrochemical machining</div></div></blockquote>