Recently, structured surfaces, consisting of deterministic features designed to produce a particular effect, have shown promise in providing superior functional performance for a range of applications including: low friction surfaces, hydrophobic surfaces and optical effects. Methods have been developed to characterise such structured surfaces. The most widely used characterisation methods are based on segmenting the surface in feature and background regions and then determining the geometrical properties of those features. However, further work is needed to refine these characterisation techniques and provide associated uncertainties. This thesis considers the effect of various segmentation control parameters such as thresholds on the final geometric parameters. The effect of varying filter size is also considered. These considerations should help in selecting a suitable characterisation method for future projects. Additionally, uncertainty in the characterisation should be estimated in order to give an indication of the accuracy of the assessment. However, no previous work has assessed uncertainty in the dimensional properties of structured surfaces. Therefore, this thesis presents two methods to characterise the uncertainty in the geometric characteristics of structured surfaces. First, the measurement reproducibility is used, which can be determined by repeated measurement of a feature. However, measurement reproducibility cannot account for all sources of uncertainty and cannot assess any bias in the measurements. Therefore, a second method based on assessment of the metrological characteristics of the instrument is considered. The metrological characteristics estimate errors produced by the instrument in a way that can easily be measured. Monte Carlo techniques are then used to propagate the effects of the metrological characteristics and their uncertainties into the final measurement uncertainty. For the example used, it was found that the results using the metrological characteristics were in good agreement with the reproducibility results. From these results, it is concluded that the choice of segmentation method, control parameters and filtering can all significantly effect the characterisation of features on a structured surface, often in unexpected ways. Therefore, care must be taken when selecting these values for a specific application. Additionally, two methods of determining the uncertainty of the structured surfaces were considered. Both methods are valid and produce similar results. Using the measurement reproducibility is simple to perform, but requires many measurements and cannot account for some uncertainty sources such as those due to the instrument amplification factors. On the other hand, the use of metrological characteristics can account for all significant sources of uncertainty in a measurement, but is mathematically more complex, requiring Monte Carlo simulations to propagate the uncertainties into the final characteristics. Additionally, other artefacts than the sample being measured are required to determine the metrological characteristics, which may be an issue in some cases.

The effect of nano-structured surfaces on pool boiling heat transfer is explored in this study. Experiments are conducted in a cubical test chamber containing fluoroinert coolant (PF5060, Manufacturer: 3M Co.) as the working fluid. Pool boiling experiments are conducted for saturation and subcooled conditions. Three different types of ordered nano-structured surfaces are fabricated using Step and flash imprint lithography on silicon substrates followed by Reactive Ion Etching (RIE) or Deep Reactive Ion Etching (DRIE). These nano-structures consist of a square array of cylindrical nanofins with a longitudinal pitch of 1 mm, transverse pitch of 0.9 mm and fixed (uniform) heights ranging from 15 nm – 650 nm for each substrate. The contact angle of de-ionized water on the substrates is measured before and after the boiling experiments. The contact-angle is observed to increase with the height of the nano-fins. Contact angle variation is also observed before and after the pool boiling experiments. The pool boiling curves for the nano-structured silicon surfaces are compared with that of atomically smooth single-crystal silicon (bare) surfaces. Data processing is performed to estimate the heat flux through the projected area (plan area) for the nano-patterned zone as well as the heat flux through the total nano-patterned area, which includes the surface area of the fins. Maximum heat flux (MHF) is enhanced by ~120 % for the nanofin surfaces compared to bare (smooth) surfaces, under saturation condition. The pool boiling heat flux data for the three nano-structured surfaces progressively overlap with each other in the vicinity of the MHF condition. Based on the experimental data several micro/nano-scale transport mechanisms responsible for heat flux enhancements are identified, which include: “microlayer” disruption or enhancement, enhancement of active nucleation site density, enlargement of cold spots and enhancement of contact angle which affects the vapor bubble departure frequency.

The effect of nano-structured surfaces on pool boiling heat transfer is explored in this study. Experiments are conducted in a cubical test chamber containing fluoroinert coolant (PF5060, Manufacturer: 3M Co.) as the working fluid. Pool boiling experiments are conducted for saturation and subcooled conditions. Three different types of ordered nano-structured surfaces are fabricated using Step and flash imprint lithography on silicon substrates followed by Reactive Ion Etching (RIE) or Deep Reactive Ion Etching (DRIE). These nano-structures consist of a square array of cylindrical nanofins with a longitudinal pitch of 1 mm, transverse pitch of 0.9 mm and fixed (uniform) heights ranging from 15 nm - 650 nm for each substrate. The contact angle of de-ionized water on the substrates is measured before and after the boiling experiments. The contact-angle is observed to increase with the height of the nano-fins. Contact angle variation is also observed before and after the pool boiling experiments. The pool boiling curves for the nano-structured silicon surfaces are compared with that of atomically smooth single-crystal silicon (bare) surfaces. Data processing is performed to estimate the heat flux through the projected area (plan area) for the nano-patterned zone as well as the heat flux through the total nano-patterned area, which includes the surface area of the fins. Maximum heat flux (MHF) is enhanced by ~120 % for the nanofin surfaces compared to bare (smooth) surfaces, under saturation condition. The pool boiling heat flux data for the three nano-structured surfaces progressively overlap with each other in the vicinity of the MHF condition. Based on the experimental data several micro/nano-scale transport mechanisms responsible for heat flux enhancements are identified, which include: "microlayer" disruption or enhancement, enhancement of active nucleation site density, enlargement of cold spots and enhancement of contact angle which affects the vapor bubble departure frequency.

L’augmentation de la densité d’intégration de composants électroniques (CMOS, FDSOI 14 nm, mémoires flash) et le développement de nouveaux dispositifs (capteurs d’images, composants photoniques) font émerger de nouveaux problèmes de fabrication des puces dans l’industrie de la microélectronique. L’efficacité des procédés humides de gravure et de nettoyage de la surface structurée des composants peut être limitée par un mouillage incomplet des micro/nanostructures dont les dimensions chutent alors que les rapports d’aspect augmentent fortement. L’état de mouillage et les cinétiques de remplissage des micro/nanostructures constituent alors deux paramètres clés pour adapter au mieux les procédés humides. Ce travail de thèse, réalisé en collaboration avec STMicroelectronics, présente une méthode acoustique originale de réflectométrie haute fréquence appliquée à la caractérisation du mouillage de surfaces structurées industrielles aux échelles micrométriques (vias) et nanométriques (tranchées profondes d’isolation de pixels, contacts de transistors CMOS). Deux modèles acoustiques ont été développés : un modèle numérique par différences finies et un modèle analytique basé sur la diffraction. Ils nous ont permis de mieux comprendre le comportement de l’onde acoustique dans les micro/nanostructures et d’interpréter les mesures expérimentales de mouillage. Nous avons alors déterminé localement l’état de mouillage des structures (état Wenzel, Cassie, composites) et détecté l’imprégnation de surfaces initialement non-mouillantes par abaissement de la tension superficielle des liquides. La cinétique de remplissage de vias micrométriques a aussi pu être mesurée. / Large scale integration in the field of electronic components (CMOS, FDSOI 14 nm, flash memory), and the development of new devices (image sensors, photonic components) raise new issues in chip manufacturing in the microelectronics industry. Wet etching and wet cleaning efficiency of the patterned surface of the components can be limited by an incomplete wetting of the micro/nanostructures, for which dimensions shrink and aspect ratios increase highly. Wetting state and micro/nanostructures filling kinetics are then two key parameters to adapt the wet processes at best. This thesis work, conducted in partnership with STMicroelectronics, presents an original acoustic method of high frequency reflectometry for wetting characterization of industrial structured surfaces at the micrometric (vias) and nanometric scale (deep trenches for pixels insulation, CMOS transistor contacts). Two acoustic models have been developed: one numerical finite difference model and one analytical model based on diffraction. They enable us to have a better understanding of the acoustic wave behavior inside the micro/nanostructures and to interpret the experimental measurements of wetting. We determined the wetting state of the structures (Wenzel, Cassie, composite states) and imbibition of initially non-wetting surfaces has been detected by lowering the surface tension of the liquids. Micrometric vias filling kinetics has also been measured.

The rapid development of micro/nanofabrication techniques have enabled engineering of material interfacial properties. Micro/nanostructures with unique electrical, mechanical, thermal, magnetic, optical, and biological properties, have found applications in a wide range of fields such as electronics, photonics, biological/chemical sensing, tissue engineering, and diagnostics, etc. As such, numerous strategies have been developed for structuring materials into micro/nano- scale. However, the challenge still lies in the high cost, low throughput, complexity in fabrication, and difficulty in scaling up. This thesis aims to explore fabrication strategies for micro/nanostructured surfaces that are versatile, simple, and inexpensive. The thin film stencil lift-off technique with both Parylene and self-adhesive vinyl has been explored for this purpose. Further applications of the resulted micro/nanostructured surfaces are also presented in this thesis. Through improved Parylene stencil fabrication process, both spontaneously phase-segregated and arbitrary binary supported lipid bilayer patterns have been achieved. Also, the microstructured Parylene surfaces have been ddemonstrated for patterning stacked SLBs that are either homogeneous or phase-segregated. Without any lithography technique involved, vinyl stencil lift-off offers as a facile and inexpensive benchtop method for patterning thin films such as metal and glassy films. Combining the thermal shrinking of shape memory polymer, the patterned feature sizes are further decreased by 60% in both x and y dimensions, pushing the patterning resolution to down to sub-100 μm range. In addition, the shrinking process induces micro/nanostructures onto the deposited thin film, and the structure sizes are easily tunable with film thickness deposited. Further applications of such patterned micro/nanostructured surfaces has also been explored. The structured gold films have served as high-surface-area electrodes for electrochemical sensing. By introducing photoresist as a sacrificial layer, the structured gold thin films can be lifted off and transferred onto elastomeric substrate, and serve stretchable and flexible sensors. Such sensing devices exhibit great stability and reproducibility even when working under external strain. Finally, the micro/nanostructured glassy surfaces have been employed as substrate for cell growth to study topographical effect on cell morphology. It has been concluded that rougher surfaces lead to cell elongation, and finer structures promote filopodia generation. These results underscore the strength and suitability of thin film stencil lift-off as a powerful technique for creating micro- and nanostructured surfaces. These structured surfaces could find applications in many other areas, due to their great properties such as tunable structure size, high surface area, flexibility, and long-term stability. / Thesis / Doctor of Philosophy (PhD)

No description available.

Werkstoff- und Prozessgrenzen beschränken unter Beachtung ökonomischer und ökologischer Aspekte den Leichtbau gegossener Fahrwerk-Komponenten aus Al-Si-Legierungen. Zunächst werden Bauteilgewicht und Wärmebehandlungsprozess als beeinflussbare Hauptbeitragsleister für Emissionen im Herstellprozess identifiziert. Zu deren Verringerung werden abhängig von der Belastungsart mögliche Mindestwandstärken abgeleitet, die für den Kokillenguss um 35 % reduziert werden. Dies gelingt durch Einsatz neuartiger, das Formfüllverhalten verbessernder Oberflächenstrukturierungen von Gießwerkzeugen bei Einhaltung von Konstruktionsregeln. Die Gesamtprozesszeit der Wärmebehandlung kann bei gleichbleibenden mechanischen Eigenschaften um 40 % verkürzt werden. Dabei erfolgt die Charakterisierung des Werkstoff- und Bauteilverhaltens unter dynamischer Belastung bei Parametervariation, da keine Korrelation zu den statischen mechanischen Kennwerten vorliegt.

A novel surface structure comprising dendritically ordered nano-particles of copper was developed during the duration of this thesis research project. A high current density electrodeposition process, where hydrogen bubbles functioned as a dynamic mask for the materials deposition, was used as a basic fabrication method. A post processing annealing treatment was further developed to stabilize and enhance the mechanical stability of the structure. The structure was studied quite extensively in various pool boiling experiments in refrigerants; R134a and FC-72. Different parameters were investigated, such as; thickness of the porous layer, presence of vapor escape channels, annealed or non-annealed structure. Some of the tests were filmed with a high speed camera, from which visual observation were made as well as quantitative bubble data extracted. The overall heat transfer coefficient in R134a was enhanced by about an order of magnitude compared to a plain reference surface and bubble image data suggests that both single- and two-phase heat transfer mechanisms were important to the enhancement. A quantitative and semi-empirical boiling model was presented where the main two-phase heat transfer mechanism inside the porous structure was assumed to be; micro-layer evaporation formed by an oscillating vapor-liquid meniscus front with low resistance vapor transport through escape channels. Laminar liquid motion induced by the oscillating vapor front was suggested as the primary single-phase heat transfer mechanism. The structure was applied to a standard plate heat exchanger evaporator with varying hydraulic diameter in the refrigerant channel. Again, a 10 times improved heat transfer coefficient in the refrigerant channel was recorded, resulting in an improvement of the overall heat transfer coefficient with over 100%. A superposition model was used to evaluate the results and it was found that for the enhanced boiling structure, variations of the hydraulic diameter caused a change in the nucleate boiling mechanism, which accounted for the largest effect on the heat transfer performance. For the standard heat exchanger, it was mostly the convective boiling mechanism that was affected by the change in hydraulic diameter. The structure was also applied to the evaporator surface in a two-phase thermosyphon with R134a as working fluid. The nucleate boiling mechanism was found to be enhanced with about 4 times and high speed videos of the enhanced evaporator reveal an isolated bubble flow regime, similar to that of smooth channels with larger hydraulic diameters. The number and frequency of the produced bubbles were significantly higher for the enhanced surface compared to that of the plain evaporator. This enhanced turbulence and continuous boiling on the porous structure resulted in decreased oscillations in the thermosyphon for the entire range of heat fluxes. / QC 20111111

La surface d’un implant ou d’un système à libération contrôlée de médicament est la première zone en contact avec les systèmes physiologiques. Les propriétés de surface vont alors définir le devenir à court et long termes de ces biomatériaux dans l’organisme. Pour améliorer la biointégration mais aussi l’efficacité des matériaux en contact avec les fluides et tissus biologiques, un fin contrôle des phénomènes se produisant à l’interface biologique est nécessaire. Cette thèse s’intéresse à l’étude de trois types de surfaces pouvant modéliser celles de biomatériaux couramment employés. Dans un premier temps, la stabilité hydrolytique de surface amino-fonctionnalisée a été investiguée. L’amino-fonctionnalisation de surface via l’emploi de monocouche auto-assemblée rencontre un intérêt certain pour l’ancrage de diverses molécules, macromolécules, systèmes colloïdaux et cellules. Cependant, le manque de stabilité en milieu aqueux limite grandement leurs perspectives d’utilisation pour la fonctionnalisation de surface de biomatériaux. Dans ce manuscrit, une monocouche amino-fonctionnalisée à base d’aminoalkylsilane a été greffée sur des substrats de silicate (silice et mica). L’extrême stabilité hydrolytique rapportée pour cette monocouche permet une immersion prolongée en milieu aqueux et sur une large gamme de pH. Les paramètres ayant été identifiés comme impactant cette stabilité sont l’organisation de la monocouche, la densité de greffage et la longueur de la chaîne carbonée de l’aminoalkylsilane. Dans un second temps, les propriétés lubrifiantes en milieu aqueux de surfaces structurées sont rapportées. Le besoin en surface autolubrifiante couvre une large variété de biomatériaux tels que les substituts cartilagineux, les dispositifs oculaires ou bien les cathéters. Des structures dômes ont été produites sur des surfaces via l’immobilisation de particules. Des particules polymériques à base de polyélectrolytes sensibles aux variations de pH ont permis l’obtention de structures molles et déformables alors que l’immobilisation de particules de silice a permis la formation de structures dures. Deux mécanismes majeurs contrôlant les propriétés de frottement ont été mis en évidence. Les surfaces structurées à partir de polyélectrolytes présentent des propriétés de frottement directement corrélées au gonflement et donc à la teneur en eau de ces structures. Ce ii gonflement peut être contrôlé par le pH du milieu aqueux. Plus les structures sont gonflées, plus le coefficient de frottement est faible. En revanche, avec des structures dures obtenues par l’immobilisation de particules de silice, le roulement de ces particules permet d’obtenir sous certaines conditions des coefficients de frottement extrêmement faibles. Dans ce cas, la nature du lien entre la particule et le substrat importe peu et un dégreffage systématique de certaines particules est observé pour permettre le mouvement des surfaces tout en limitant les forces de frottement. Dans un troisième temps, la complexation de simples brins de siARN via différentes natures d’interactions a été étudiée à l’aide de surfaces modèles de chimie variable. Cette étude a permis de démontrer la possibilité d'adsorber des simples brins de siARN via des interactions non-électrostatiques sur des surfaces planes. Des interactions hydrophobes et les liaisons hydrogène ont par la suite pu être employées pour complexer cet acide nucléique avec des formulations micellaires et liposomales non-cationiques. Cette étude permet d'envisager la conception de nanovecteurs non-cationiques et donc moins toxiques pour la délivrance de simples brins de siARN. Les travaux présentés dans ce manuscrit contribuent à l’élargissement des connaissances en matière de propriétés physico-chimiques de surface aux interfaces biologiques. / The surface of an implant or a drug delivery system is the first area of contact with biological environment. The surface properties of these biomaterials will define the short and long term behavior in the organism. To improve biointegration and efficiency, a fine control of the biological interface is required. This thesis investigates three different kind of surfaces modelling commonly used biomaterials. First, the hydrolytic stability of amino-functionalized surfaces was investigated. The amino-functionalization using self-assembled monolayers is required for the anchorage of molecules, macromolecules, colloidal systems and cells onto biomaterials. However, the lack of stability in aqueous media limits their use. In this manuscript, an amino-functionalized self-assembled monolayer made of aminoalkylsilane was grafted onto silicate substrates (silica and mica). The extreme robustness that we reported for this monolayer allows immersion into aqueous media for a wide range of pH and over long periods of time. The most important parameters that were identified that significantly impact the hydrolytic stability are the order of the monolayers, the grafting density and the length of the alkyl chain of the aminoalkylsilane. Second, the lubricant properties in aqueous media of structured surfaces are reported. The need in self-lubricant surfaces is required in a wide variety of biomaterials such as the cartilage substitute, ocular medical device or catheters. Domed structures were produced on surfaces through immobilization of particles. Polymeric nanoparticles composed of pH-sensitive polyelectrolytes were used to prepared soft and deformable structures while the immobilization of silica particles allows hard structures to be created. Two main mechanisms controlling friction properties were identified. Friction properties of structured surfaces made of polyelectrolytes were controlled by the swelling and the water content of the particles. This swelling can be tuned by changing the pH of the aqueous media. An increase in particle swelling leads to a decrease in the friction coefficient. However, with the hard structures, the rolling of the particles in some cases can also lead to extremely low friction coefficient. In that case, the nature of the attachment of iv the particle to the surface does not matter and systematic degrafting of some particles was observed which allows surfaces to slide with small friction forces. Third, the complexation of a single-stranded siRNA through different interactions was investigated with model surfaces of various chemistry. The results show that ss-siRNA can adsorb onto hydrophilic (positively and negatively charged) as well as on hydrophobic substrates suggesting that the complexation can occur through hydrophobic interactions and hydrogen bonding in addition to electrostatic interactions. This study suggests that non-electrostatic interactions could be exploited to complement electrostatic interactions in the design of less toxic nanocarriers and that non-cationics nanovectors can be employed as a potential single-stranded siRNA delivery systems. The results presented in this thesis contribute to increase the knowledge in the field of physico-chemistry surface properties of biological interfaces.

Werkstoff- und Prozessgrenzen beschränken unter Beachtung ökonomischer und ökologischer Aspekte den Leichtbau gegossener Fahrwerk-Komponenten aus Al-Si-Legierungen. Zunächst werden Bauteilgewicht und Wärmebehandlungsprozess als beeinflussbare Hauptbeitragsleister für Emissionen im Herstellprozess identifiziert. Zu deren Verringerung werden abhängig von der Belastungsart mögliche Mindestwandstärken abgeleitet, die für den Kokillenguss um 35 % reduziert werden. Dies gelingt durch Einsatz neuartiger, das Formfüllverhalten verbessernder Oberflächenstrukturierungen von Gießwerkzeugen bei Einhaltung von Konstruktionsregeln. Die Gesamtprozesszeit der Wärmebehandlung kann bei gleichbleibenden mechanischen Eigenschaften um 40 % verkürzt werden. Dabei erfolgt die Charakterisierung des Werkstoff- und Bauteilverhaltens unter dynamischer Belastung bei Parametervariation, da keine Korrelation zu den statischen mechanischen Kennwerten vorliegt.