Ce travail de thèse s'articule autour de plusieurs variations sur le thème du rebond d'une goutte d'eau sur une surface non-mouillante. Nous engendrons des rebonds spéciaux que nous caractérisons expérimentalement. Notre analyse de ces rebonds se concentre sur la mise en évidence des paramètres et des phénomènes physiques contrôlant leur extension spatiale et temporelle, deux quantités qu'il est important de comprendre tant d'un point de vue fondamental qu'appliqué. Nous étudions, dans un premier temps, les effets de la géométrie du substrat sur le rebond d'une goutte d'eau. Nous montrons qu'une modification locale, l'ajout d'une macrotexture ponctuelle, crée un mécanisme de rebond nouveau que nous associons à une réduction du temps de contact d'un facteur 2. Nous réalisons également des impacts sur des substrats coniques et sphériques en mettant en avant les différences et les similitudes avec les impacts sur une surface plane. Dans un second temps, nous nous intéressons aux effets créés par un substrat mobile. Nous étudions l'impact de gouttes sur des surfaces déformables et comprenons comment l'échelle de temps du rebond est influencée par une interaction entre celle de la goutte et celle du substrat. Nous discutons aussi l'influence de la déformation du substrat sur le splash. Notre étude de l'influence du mouvement s'est poursuivie en utilisant des surfaces rigides auxquelles nous pouvons imposer un déplacement vertical. En soumettant des gouttes initialement au repos à un mouvement impulsionnel, nous engendrons de surprenantes cavités coniques dont nous modélisons la dynamique. Cette expérience permet de faire un constat étonnant, la faible adhésion des surfaces superhydrophobes est nécessaire à l'obtention des cavités. Nous réalisons des impacts sur une surface dont le déplacement peut-être déclenché au moment du contact entre le liquide et le solide à l’aide du signal provenant d’un capteur de force de type MEMS. Nous atteignons des temps de contact extrêmement réduits, de l’ordre de 20% de celui observé sur le même substrat sans mouvement. Enfin, nous modifions le liquide et non le substrat. Nous montrons que des gouttes jusqu'à 200 fois plus visqueuses que l'eau peuvent rebondir sur des matériaux superhydrophobes. / This thesis revolves around the ability of liquid drops to bounce off superhydrophobic materials. We generate special rebounds and characterize them experimentally.We focus on finding the relevant physical phenomena to describe the temporal and spatial extension of such events, both quantities being of importance from the fundamental and applied point of vue. First, we study the influence of the susbtrate geometry. We modify the surface locally, by introducing a singular macrotexture, and show that it leads to a new bouncing mechanism that shortens the contact time by a factor typically 2. We also modify the substrate at the size of the drop. We perform impacts on non wetting cones and spheres and compare them to what is observed on a flat surface. Then, we study the effect of substrate motion. We make impacts on soft materials that can be deformed by the drop. We show that this situation can lead to fast bouncing and interpret the contact time as the result of an interplay between the timescale of the drop and that of the substrate. We also discuss the influence of substrate deformation on splashing. We go deeper into the effect of substrate motion by using rigid materials which movement we can trigger. We evidence new liquid shapes, conical cavities, by submitting a drop, initially at rest, to a vertical impulse.Surprisingly, the low, but present, adhesion of superhydrophobic materials is the key ingredient needed to observe such shapes. We also work on the effect of motion at the onset of impact, by trigerring the substrate movement using the signal from a MEMS force sensor intregrated in the surface. This setup allow us to reach contact times that represent 20% of the contact time on an immobile substrate. Finally, we change perspective and modify the liquid instead of the solid. We show that viscous drops can bounce as long as their viscosity does not exceed 200 times that of water.

This thesis studies multi-phase flows within two different types of porous nature-inspired material systems: multi-layered feathers and synthetic trees. (1) How multilayered feathers enhance underwater superhydrophobicity. Inspired by ducks, here we demonstrate that air pockets can withstand up to five times more hydrostatic pressure when using stacked layers of synthetic feathers instead of a single layer. The mechanism for the multi-layered enhancement is the more tortuous pathway required for water impalement, which serves to pressurize the air pockets enclosed in the pores. We study this air compression effect using a probabilistic model, in which we quantify the tortuous pathway in stacked feather layers in terms of filled volume fraction of the pores. Our findings suggest that multi-layered coatings could enable robust underwater superhydrophobicity. (2) Oil-Water separation using synthetic trees. In the world's tallest trees, water evaporating from leaves generates enough suction to lift water over 100 m high. Transpiration can similarly be attained in synthetic trees by coupling nanoporous leaves" with conduits mimicking xylem capillaries. Here, we demonstrate that by adding filters to the free ends of the xylem conduits, the hydraulic load generated by transpiration can be used for oil-water separation. The working principle is illustrated using the pressure balance equation for the synthetic tree. / Master of Science / Nature abounds in complex systems and fascinating phenomena that have inspired us, from the way we live to the things we create. The engineering profession is no exception to being inspired by nature. In fact, engineers have created revolutinary robots inspired by animals. The work in this theis draws inspiration from the water-repellant property (superhydrophobicity) of duck feathers and the transpiration process in plants. In the first study, we created 'synthetic feathers' to study how layers of duck feathers are able to sustain superhydrophobicity under water. We discovered the 'layer-effect' that explains enhanced underwater superhydrophobicity. Surfaces covered in such multi-layered feather-like porous structures are potentially useful for reducing drag in underwater applications. In the second study, we develop a 'synthetic tree' that captures the main attributes of the transpiration mechanism in plants. We show that the 'pull' generated by transpiration can be used for oil-water separation. This macroscopic synthetic tree can be useful in cleaning oil spills.

Si l’eau d’une rivière coule sous l’influence d’une petite pente, une goutte de pluie millimétrique s’accroche généralement à son substrat. Cette thèse considère les problèmes engendrés par cette adhésion liquide-solide à l’aune de l’application culinaire. Nous nous intéressons aux surfaces superhydrophobes dont la chimie et la rugosité rendent ces solides non-adhérents. Par ailleurs, le comportement de ces matériaux en température rend compte de différents domaines d’adhésion. Ces surfaces voient leur adhésion augmenter avec la température lorsque la vapeur se recondense au sein des textures du solide. Mais, à mesure que la température s’élève, des bulles de vapeur se forment et réduisent l’adhésion, jusqu’à l’annuler lorsque le liquide lévite sur un coussin continu de vapeur. Nous décrivons cet état, dit de caléfaction, et notamment l’origine de la température critique pour laquelle ce phénomène apparaît. La superhydrophobie permet de réduire considérablement cette température, dite de Leidenfrost, et de rendre accessible la caléfaction pour des températures typiques de cuisson. Enfin, nous comparons ces résultats aux stratégies de non-adhésion culinaire : à savoir les revêtements hydrophobes et l’utilisation d’huile. Des surfaces mixtes piégeant une fine couche d’huile dans des textures hydrophobes sont ainsi discutées. / Water flows inside a river due to extremely low slopes whereas a millimetric raindrop generally sticks on its substrate. This thesis investigates problematics induced by liquid-solid adhesion as regards the cooking device application. We study superhydrophobic substrate whose both chemistry and roughness promote anti-adhesion. We describe the anti-adhesive behaviour in temperature. First, because of condensation through the porous media, the adhesion rises with temperature before vapour bubbles nucleate below the drop. Then, the production of vapour generates a lack of contact. Thus, adhesion decreases until the liquid levitates on its own vapour. We describe this phenomenon known as the Leidenfrost effect. We especially discuss the critical Leidenfrost temperature and its origin. Superhydrophobic coatings promote Leidenfrost effect at remarkably low temperature close to cooking typical one. Finally, those results are compared to two strategies used in cooking: hydrophobic anti-adhesive coatings and lubrication by oil. Some lubricant-infused substrates are investigated.

<p>The interaction between liquid drops and textured surfaces not only offers fundamental challenges in capillarity and wetting, but also enables new applications ranging from self-cleaning materials to self-sustaining condensers. The first part of this dissertation deals with the fundamental wetting and dewetting dynamics of drops on textured surfaces, and the self-propelled jumping of dropwise condensate on superhydrophobic surfaces. The second part builds upon these findings in dynamical superhydrophobicity to develop a jumping-drop thermal diode that rectifies heat flow between textured superhydrophilic and superhydrophobic surfaces. </p><p>On the fundamental side, anti-dew is an essential property of robust superhydrophobic surfaces, particularly those deployed in ambient environments or phase-change systems. A superhydrophobic lotus leaf retains water repellency after repeated condensation in nature but becomes sticky to water drops after condensation on a fixed cold plate. To solve this mystery, we first study the possible wetting states of superhydrophobic surfaces possessing two-tier surface roughness mimicking that on the lotus leaf. By incrementally increasing the ethanol concentration of water/ethanol drops, two distinct wetting transitions are observed on two-tier surfaces. Drops in the intermediate wetting state uniformly wet the microscale roughness but not the nanoscale roughness. Dew drops exhibited a similar intermediate wetting state. Our experiments show that mechanical vibration can be used to overcome the energy barrier for transition from the intermediate wetting (Partial Wenzel) state to the fully dewetted (Cassie) state, and the threshold for the dewetting transition follows a scaling law comparing the kinetic energy imparted to the drop with the work of adhesion. </p><p>Although vibration-induced dewetting is effective for removing millimetric condensate from the surface, micrometric condensate cannot be removed as surface energy dominates at small scales. We report a new discovery in which the micrometric condensate can spontaneously dewet and jump off the superhydrophobic surface. The spontaneous jumping results from the surface energy released upon drop coalescence, which leads to the rapid out-of-plane jumping motion of the coalesced drops. The jumping drops follow an inertial-capillary scaling and give rise to self-sustained dropwise condensation with a micrometric average diameter. Using two approaching Leidenfrost drops suspended on a vapor layer to simulate superhydrophobicity, we show that the out-of-plane directionality results from the impingement of the expanding liquid bridge against the heated Leidenfrost surface, which is initially formed between coalescing drops above the substrate.</p><p>On the practical side, textured surfaces offer new possibilities for phase-change heat transfer. Taking advantage of the self-propelled jumping condensate, we developed a planar phase-change thermal diode that transports heat in a preferential direction. The jumping-drop diode is composed of parallel superhydrophobic and superhydrophilic plates, and the thermal rectification is enabled by spontaneously jumping dropwise condensate which only occurs when the superhydrophobic surface is colder. The superhydrophobic surface has nanoscale surface roughness that is anti-dew, while the superhydrophilic surface consists of porous copper wick borrowed from heat pipes. Our planar thermal diode with asymmetric wettability is scalable to large areas with an orientation-independent diodicity of over a hundred. </p><p>More broadly speaking, the self-propelled jumping offers an alternative means to return liquid condensate in phase-change systems. We systematically investigate the heat transfer performance of a vapor chamber enabled by the jumping condensate. When the non-condensable gases are removed, the effective heat transfer coefficient is mainly governed by the interfacial resistance of the phase-change processes and the conduction resistance across the superhydrophilic wick. Potential routes for improving the heat transfer performance are discussed, including the optimization of the superhydrophilic wick and its separation with the opposing superhydrophobic surface. The new jumping return mechanism is unique in that it neither relies on external forces nor requires wick structures along the return path, and is expected to be applicable to a variety of phase-change heat transfer systems.</p> / Dissertation

Superhydrophobic coatings attract significant attention regarding a variety of applications, such as in friction drag reduction, anti-contamination surfaces, and recently metals corrosion protection. Superhydrophobic surfaces are known to protect metals and their alloys from natural degradation by limiting water access and its surface interaction. Non-wetting properties of superhydrophobic surfaces are attributed to their low-surface energy, in combination with their surface microtexture. Several approaches based on tailoring a microtextured surface followed by surface modification with a low-surface-energy material have been employed for developing non-wetting metallic surfaces. However, developing a durable superhydrophobic coating, in terms of mechanical abrasion, thermal and chemical stability, which could serve in harsh environments, is still an outstanding challenge. In this research work two different approaches have been employed to create durable superhydrophobic aluminium alloy surfaces. In the first approach a practical and cost-effective method, which is based on direct surface acid/base etching is used to promote desired rough microstructure on aluminium alloy. Then, a facile surface modification with chlorosilanes as a low-surface-energy compound is utilized to generate surface superhydrophobicity. The superhydrophobic aluminium alloy has a water contact angle of about 165 ± 2˚ and rolling angle of less than 3 ± 0.2˚. The developed superhydrophobic aluminium alloy surfaces shows remarkable thermal stability up to 375 ˚C for 20 min. In the second approach, a controlled hydrothermal deposition process is utilized to develop cerium oxide based coatings with well-defined microtextured surface on aluminium alloy substrates. The superhydrophobicity of the cerium oxide coatings is acquired by further treatment with trichloro(octyl)silane surface. The impacts of various hydrothermal processing conditions on surface microstructure of coatings, wettability, and ultimate corrosion protection have been also investigated. The fabricated cerium oxide based coating exhibit high level of water repellency with a water contact angle of about 170 ± 2˚ and rolling angle of about 2.4 ± 0.2˚. The superhydrophobic coatings show outstanding wear-resistance by maintaining their non-wetting properties after abrasion by #800 abrasive paper for 1.0 m under applied pressures up to 4 kPa pressure. The coatings also show remarkable chemical stability under acidic and alkaline condition and during immersion in corrosive 3.5 wt % NaCl solution for more than 2 days. They also provide excellent corrosion protection for T6-6061 aluminium alloy substrate by decreasing its corrosion rate for about three orders of magnitude. / Graduate

Il a été montré que l’addition de fluor en petite quantité sur la surface de nanotubes de carbone mono et multiparois engendre des radicaux à long temps de vie, caractérisés ici par RPE. Ce phénomène a pu être mis à profit pour initier la polymérisation du styrène, de l’acide acrylique ou encore de l’aniline. Les chaînes polymères formées apparaissent alors greffées à la surface des tubes. Il a été observé qu’un tel greffage facilite grandement la mise en suspension des nanotubes dans des solvants organiques. Ce travail s’est également attaché à exalter la complémentarité entre nouveaux matériaux fluorés et techniques avancées de mise en œuvre. Pour la première fois, l’incorporation de nanocarbones fluorés de différentes dimensionnalités (noirs de carbone, nanotubes, nanofibres, nanodisques) dans une matrice polymère électrofilée de polyvinylpyrrolidone a été réalisée. Les tissus nanocomposites microfibreux ainsi obtenus ont ensuite fait l’objet de traitements de re-fluoration en conditions douces, afin d’augmenter leur taux de fluor final et d’en modifier la texture. Les caractérisations par microscopie à balayage, RMN du solide et XPS ont permis d’établir que l’enrichissement en fluor de la matrice polymère et la structure multi échelle spectaculaire résultant du traitement de post-fluoration réalisé permettent d’induire la propriété de superhydrophobicité, mise en évidence par la mesure d’angles de contact avec l’eau supérieurs à 150°. / It has been shown that the addition of a small amount of fluorine to the surface of single and multi-walled carbon nanotubes generates long life-time radicals, here studied by EPR. The latter phenomenon can be usefully harnessed to initiate the polymerization of styrene, acrylic acid or still aniline. The polymeric chains thus formed appear to be grafted to the tubes surface. It has been observed that such a grafting process highly increases the dispersibility of tubes in some organic solvents. This work also focused on illustrating how advanced processing techniques may complement the assets of novel fluorinated materials. Hence, the inclusion of fluorinated nanocarbons with varied dimensionalities (carbon black, nanotubes, nanofibers, nanodisks) into an electrospun polyvinylpyrrolidone polymer matrix has been achieved for the first time. The nanocomposite-based microfibrous membranes thus obtained have been reacted with gaseous fluorine in mild conditions, in order to increase their final fluorine content and modify their texture. Characterizations performed using scanning electron microscopy, solid state NMR and XPS have shown that both the fluorination of the polymer matrix and quite spectacular multiscale structure resulting from etching by fluorine induce superhydrophobicity, evidenced through contact angles of the membranes with water exceeding 150°.

In order to study inlight ice adhesion at the droplet-scale, a strategy is presented to simulate the impact and solidification of a supercooled water droplet on a cooled substrate. Upon impact, nucleation is assumed to occur instantaneously, and properties of the droplet are chosen to account for the nucleation process. Simulations are performed in ANSYS Fluent using a coupled Volume of Fluid and Level-Set method to capture the air-water interface and an Enthalpy-Porosity method to capture the liquid-solid interface. Calibration of a simulation parameter, Amush, is performed in order to match experimental data for different surface types and surface temperatures. The calibrated simulation strategy is applied to low-speed, inlight icing conditions. The effects of surface variation and droplet diameter variation are investigated, providing insight into the icephobicity of superhydrophobic surfaces. Numerical results suggest that large droplets (approximately 200 micron-diameter) will freeze and adhere to a superhydrophobic surface.

​ Nombreuses stratégies de contrôle ont été récemment proposées par la communauté scientifique afin depouvoir réduire la traînée dans les écoulements pariétaux. Entre autres, les Surfaces Superhydrophobes (SHS) ontmontré leurs capacités de pouvoir réduire considérablement le frottement pariétal d’un écoulement liquide grâce à laprésence de microbulles de gaz piégées dans les nano-rugosités de la surface. Dans des conditions géométrique etthermodynamique données pour lesquelles la transition de mouillage est évitée (condition pour laquelle normalementla taille des rugosités qui caractérise la SHS est de plusieurs ordres de grandeur plus petite que l'échellecaractéristique de l'écoulement principal), on peut atteindre ce qu’on appelle ‘l'effet Lotus’, pour lequel l'écoulementglisse à la paroi, avec une vitesse différente de zéro.. Dans ce cadre, nous nous sommes proposés d’étudier, à l’aidede simulations numériques l’influence des SHS sur la transition laminaire-turbulent dans un écoulement de canal.Pour cela, nous avons réalisé une série de simulations numériques directes (DNS), allant de l'état laminaire au casturbulent pleinement développé, en traitant la plupart de scénarios de transition connu en littérature. Des analyses destabilité locale et globale ont aussi été réalisées afin de déterminer l’influence de ces surfaces sur la première phasedu processus de transition. Bien que la procédure de déclenchement de la transition contrôlée (type K, H, C,...) soitbien décrite dans la littérature, cela n’est pas le cas pour les transitions naturelles. À cette fin, une nouvelle méthode aété développée pour déclencher puis étudier la transition naturelle dans des écoulements de type canal. Cette méthodeest basée sur des mécanismes de réceptivité de l'écoulement (resolvent global) permettant de construire un forçagevolumique spécifique. Plusieurs approches pour modéliser les SHS ont été utilisées, de complexités croissantes, touten tenant en compte des caractéristiques physiques de ces surfaces. Dans un premier temps, une condition deglissement homogène a été utilisée et son influence analysée. Chaque rugosité a été ensuite discrétisée spatialement,d’abord avec une alternance de condition limite sur une surface plate, ensuite en tenant compte de la dynamique del’interface gaz-liquide par une méthode Lagrangienne-Eulerienne Arbitraire (ALE). Nous avons montré que les SHSpermettent d’efficacement retarder les transitions contrôlées mais qu’en revanche elles ont peu d’influence sur lestransitions naturelles (développant des stries de vitesse). En effet, ce comportement dérive de l'équilibre entre deuxeffets contradictoires. D’un côté, le glissement pariétal nuit au développement des structures cohérentes de typehairpin ​ , en altérant le processus de ​ vortex stretching-tilting ​ . D’autre part, le mouvement de l’interface gaz-liquideinteragit avec les structures cohérentes de l'écoulement, en produisant des vitesses normales à la paroi favorisantdavantage le processus de ​ sweep-ejection et entraînant le développement de structures en forme d’arche. Nous avonsmontré que les interfaces gaz-liquide statiques retardent la transition de façon analogue à une condition aux limiteshomogène (si l’hétérogénéité pariétale est petite). En revanche la prise en compte de leur dynamique limite le retardde la transition, montrant l’importance du modèle de SHS dans les écoulements transitionnels. / Many passive control strategies have been recently proposed for reducing drag in wall-bounded shearflows. Among them, underwater SuperHydrophobic Surfaces (SHS) have proven to be capable of dramaticallyreducing the skin friction of a liquid flowing on top of them, due to the presence of gas bubbles trapped within thesurface nano-sculptures. In specific geometrical and thermodynamical conditions for which wetting transition isavoided (in particular, when the roughness elements characterizing the SHS are several orders of magnitude smallerthan the overlying flow), the so-called ’Lotus effect’ is achieved, for which the flow appears to slip on the surfacewith a non zero velocity. In this framework, we propose to study, by means of numerical simulations, the influence ofSHS on laminar-turbulent transition in a channel flow. To do so we have performed a series of direct numericalsimulations (DNS), from the laminar to the fully turbulent state, covering the majority of transition scenarios knownin the literature, as well as local and global stability analysis so to determine the influence of SHS onto the initialstages of the process. While the conditions for observing controlled K-type transition in a temporal channel flow arewell defined, this is not the case for uncontrolled ones. To this end, a novel theoretical numerical framework has beendeveloped so to enable the observation of natural transition in wall-bounded flows. This method, similarly to theFree-Stream-Turbulence framework available for the boundary layer flow, is capable of triggering uncontrolledtransition t​ hrough flow receptivity to a purpose-built forcing. Different surface modellings for the superhydrophobicsurfaces are tested. First, homogeneous slip conditions are used. Then, the spatial heterogeneity of the SHS has beenconsidered by modelling it as a flat surface with alternating slip no-slip boundary conditions. Finally, the dynamics ofeach microscopic liquid-gas free-surface has been taken into account by means of a fully coupled fluid-structuresolver, using an Arbitrary Lagrangian Eulerian formulation. We show that while SHS are ineffective in controllingtransition in noisy environment​ , they can strongly delay transition to turbulence for the K-type scenario​ . Thisbehaviour results from the balance of two opposing effects. On one hand slippery surfaces inhibit the development ofcharacteristic hairpin vortices by altering the vortex stretching-tilting process. On the other hand, the movement ofthe gas-liquid free-surfaces interacts with the overlying coherent structures, producing wall-normal velocities thatenhance the sweep-ejection process, leading to a rapid formation of hairpin-like head vortices. Thus, whenconsidering flat interfaces transition time is strongly increased, while taking into account the interface dynamicsinduces smaller changes with respect to the no-slip case, indicating the need for an appropriate modelling of SHS fortransition delay purposes.

Une surface est dite superhydrophobe si l’angle de contact d’une goutte d’eau avec cette surface est supérieur à 150°. Les domaines d’application de telles surfaces anti-adhérentes sont variées : du bâtiment avec l’élaboration de vitres anti-salissures au biomédical pour empêcher ou limiter l’adhésion bactérienne en passant par l’aéronautique. La superhydrophobie provient de la combinaison de deux paramètres : la structuration de la surface et la faible énergie de surface du matériau. Dans la plupart des références de la littérature, l’élaboration de telles surfaces s’effectue en plusieurs étapes. La polymérisation électrochimique de monomères conducteurs est une technique simple, rapide et reproductible pour obtenir des surfaces superhydrophobes. En effet, en une seule étape, le film de polymère se dépose et se structure. Cette méthode permet de contrôler les propriétés de mouillage en jouant sur les paramètres électrochimiques (charge de dépôt, substrat, sel électrolyte) ou sur la structure chimique du monomère. Ce travail porte sur l’élaboration et la caractérisation de films de polymères conducteurs obtenus par électrodéposition de dérivés du 3,4-éthylènedioxythiophene (EDOT), du 3,4-ethylènethiathiophene (EOTT) et du 3,4-propylenedioxythiophene (ProDOT) portant une chaîne hydrocarbonée de longueur variable. Des surfaces aux propriétés de mouillage polyvalentes (hydrophiles à superhydrophobes) ont été obtenues. De plus, l’influence de la part chimie et de la part physique sur l’angle de contact à l’eau a été déterminée pour les EDOT hydrocarbonés. Ce travail contribue à trouver une alternative aux composés fluorés. dans la domaine de la superhydrophobie. / Controlling wettability of a solid surface is important in many practical applications. This property, resulting from the combination a low surface energy material with a surface structuration, is commonly expressed by the contact angle of a water droplet on the surface. Surfaces with a water contact angle (θwater) larger than 150° are usually called superhydrophobic surfaces. Such surfaces are very interesting because of their expected self-cleaning or anti-contamination properties, which could be applied in various applications such as in biomedical devices, paint or in aeronautics for example. Among all the techniques to prepare superhydrophobic surfaces, electrochemical polymerization is a fast and versatile technique. In current literature on this field, the general approach is the use of highly fluorinated tails to reach the water-repellency. However, as observed in nature, fluorine is not necessary and can present environmental impacts. In this work, we focused on the synthesis of original monomers with hydrocarbon chain as hydrophobic part in order to find alternative to fluorine chemistry to prepare electropolymerized superhydrophobic surfaces. We succeeded to reach high water repellency (θwater > 150°) with hydrocarbon conducting polymers and we determined the influence of chemical and physical parts onto the water contact angle. We also found similar dewetting properties than the fluorinated series meaning the hydrocarbon conducting polymers could be a real alternative to fluorine chemistry.

Microbial colonization on the surface of silicone rubber high voltage outdoor insulators often results in the formation of highly hydrated biofilm that influence the surface properties, such as surface hydrophobicity. The loss of hydrophobicity might lead to dry band formation, and, in the worst cases, flashover and failure of the insulator. In this work, the biocidal effects of various antimicrobial compounds in silicone rubber materials were determined. These materials were evaluated according to an ISO standard for the antimicrobial activity against the growth of aggressive fungal strains, and microorganisms that have been found colonizing the surfaces of outdoor insulators in several areas in the world. Several compounds suppressed microbial growth on the surfaces of the materials without compromising the material properties of the silicone rubber. A commercial biocide and thymol were very effective against fungal growth, and sodium benzoate could suppress the fungal growth to some extent. Thymol could also inhibit algal growth. However, methods for preservation of the antimicrobial agents in the bulk of the material need to be further developed to prevent the loss of the compounds during manufacturing. Biofilm formation affected the surface hydrophobicity and complete removal of the biofilm was not achieved through cleaning. Surface analysis confirmed that traces of microorganisms were still present after cleaning. Further, surface modification of the silicone rubber was carried out to study how the texture and roughness of the surface affect biofilm formation. Silicone rubber surfaces with regular geometrical patterns were evaluated to determine the influence of the surface texture on the extent of microbial growth in comparison with plane silicone rubber surfaces. Silicone rubber nanocomposite surfaces, prepared using a spray-deposition method that applied hydrophilic and hydrophobic nanoparticles to obtain hierarchical structures, were studied to determine the effects of the surface roughness and improved hydrophobicity on the microbial attachment. Microenvironment chambers were used for the determination of microbial growth on different modified surfaces under conditions that mimic those of the insulators in their outdoor environments. Different parts of the insulators were represented by placing the samples vertically and inclined. The microbial growth on the surfaces of the textured samples was evenly distributed throughout the surfaces because of the uniform distribution of the water between the gaps of the regular structures on the surfaces. Microbial growth was not observed on the inclined and vertical nanocomposite surfaces due to the higher surface roughness and improved surface hydrophobicity, whereas non-coated samples were colonized by microorganisms. / <p>QC 20151002</p>