La tendance à la miniaturisation des produits n'est pas sans influence sur l'évolution de leurs moyens de production et d'assemblage. En effet, dû à la réduction d'échelle, l'assemblage de petits composants (appelé microassemblage) est perturbé par les forces de surface comme les forces de capillarité. Ces forces, exercées par le pont liquide reliant manipulateur et composant, sont habituellement négligeables (et négligées) dans l'assemblage conventionnel dominé par les forces de gravité. L'approche originale suivie dans ce travail consiste à tirer parti de ces effets et à les utiliser pour la manipulation de microcomposants, c'est-à-dire de composants dont la taille va de quelques dizaines de microns à quelques millimètres. Ce travail tente donc d'apporter quelques réponses aux problèmes de conception posés par un tel choix: quels sont les avantages d'une telle approche? Comment ces forces `fonctionnent-elles'? Sont-elles suffisamment grandes pour manipuler des microcomposants? Comment, dans ce cas, relâcher le composant? Quel rôle la tension de surface joue-t-elle? En quoi le choix des matériaux est-il important? Comment optimiser la conception du manipulateur? Tout au long de ce travail, le lecteur trouvera un inventaire des principes de manipulation existants, les éléments nécessaires à la modélisation des forces de capillarité, ainsi que la description de la simulation et du banc d'essai développés par l'auteur dans le but d'étudier ces paramètres de conception. Les résultats présentés dans cette thèse recouvrent essentiellement deux thèmes: quelles sont les règles de conception à suivre pour maximiser les forces de capillarité (problème de la préhension) et comment choisir une stratégie de relâche adéquate (problème de la relâche)?

This doctoral research was realized within the frame of the SMARTNET Project which aimed at developing coatings to improve the cleanability of stainless steel, targeting open surface applications. Throughout this thesis, the radial-flow cell was selected to study the removal of different soils due to its ability to generate well-controlled wall shear stress distributions on the investigated surfaces. Model surfaces were selected for their different physico-chemical and mechanical properties to study the interactions between the soils and the surfaces in detail. A thin layer chromatography sprayer giving a narrower and more reproducible droplet sizes distribution was preferred to mimic splashing and produce controlled spatters. The first experimental campaign involving oil droplets showed that the analytical models available to relate the detachment radius with the critical wall shear stress (minimal wall shear stress required for soil detachment) and the soil adhesion strength in the radial flow cell could only be applied for weakly adherent soils for which removal occurs below 3 Pa, due to the complex hydrodynamics near the inlet. Consequently, the flow inside the radial-flow cell has been characterized using computational fluid dynamics over the whole inlet laminar regime and validated experimentally. Studying the adherence of starch granule aggregates in the radial-flow cell revealed that the conversion of critical radius into critical wall shear stress may be biased when the adhering aggregate height is not negligible with respect to the channel height and when the adherence is such that flow rates above creeping flow conditions are required for soil detachment. The influence of several environmental factors and substrate properties was then examined to improve the understanding of the mechanisms affecting soiling and cleanability. By influencing droplet spreading and competition between capillary forces at the granule-substrate and granule-granule interfaces, substrate wettability affects the shape and compactness of the adhering aggregates, the efficiency of shear forces upon cleaning, and finally the adherence of soiling particles. Macromolecules originating from the starch granules suspension are adsorbed on the substrate from the liquid phase or carried by the retracting film and accumulated at the granule-substrate interface. They influence granule adherence by acting as an adhesive joint, the properties of which seem to be influenced by the detailed history of drying and exposure to humidity. On compliant substrates, the aggregate-substrate interactions induce stresses at the granule-substrate interface which may lead to substrate deformation and promote a more intimate contact between the granules and their substrate, thereby appreciably increasing adherence.

No description available.

Self-Assembly in the context of micro-scale integration refers to a developing set of techniques which exploit phenomena resulting in the spontaneous integration of micro-scale components into designed systems. Self-Assembly may be leveraged most effectively in parallel assembly processes. This thesis studies the modeling of micro-scale self-assembly processes as stochastic processes. The researchers propose that self-assembly processes may be modeled as Markov chains. In order to develop these models a Self-Assembly test system was created and trials were conducted using this system. Initial tests into the hypothesis that variables contributing to the transition probabilities include the kinetic energy of the assembly interaction, the energy minimized during assembly, and the area fraction of bonding sites on the assembly surface are tested.

Mechanical assembly of systems and structures on the micro-scale can be inefficient as pthesiss of sub-millimeter dimensions are difficult to manipulate. Cutting edge manufacturing methods implement self-assembly as an approach to ordering micro and nano-sized parts into a desired arrangement. This thesis studies a technique utilizing surface tension as a method of actuating microparts on a liquid-liquid interface via lateral capillary interactions. Preliminary experimentation is conducted to investigate the feasibility of developing a new method for self-alignment of microparts by observing the influence of interfacial geometry on the movement of silicon tiles along a hexadecane-water interface. Different surface geometries are created by implementing vertical rods of different wetting properties that alter the curvature of the interface. Results demonstrate that the microparts attain an equilibrium separation distance from the vertical rods. It is indicated that this equilibrium distance is determined by the dimensions of the micropart and the curvature of the interface. With further investigation, these results may be used to cultivate a method for self-alignment of microparts into rings of a desired radius.

Micro-assembly processes suffer from some breaches due to the continuing trend towards an increase in the production capabilities as well as in the size reduction of the components manipulated. Usual manipulating schemes have reached their limit and capillary forces constitute a valuable alternative strategy. The goal of this work is to describe the dynamics of liquid bridges in the application of micro-assembly processes. The description is obtained using the Kelvin-Voigt model, with a spring, a damper, and a mass connected in parallel, supported by numerical simulations, analytical approximations and experiments. The works is divided into three parts. First we present important aspects of microfluidics, as well as the constitutive equations and an overview of numerical approaches used to describe fluid flow problems with moving interfaces. The second part is devoted to the capillary rise case, intended to validate and to compare the numerical approaches to analytical laws and experimental results. The implementation of the slipping and the dynamic contact angles is discussed. The last part focuses on the dynamics of the liquid bridge. The liquid bridge is confined between two circular and parallel plates and presents an axial symmetry. The description reveals that the stiffness depends on the surface tension and on the shape of the air/liquid interface, the damping coefficient depends on the viscosity and the volume of liquid and the equivalent mass depends on the density and the volume.

The use of hydrophobic surfaces is important for many processes both in nature and industry. Interactions between hydrophobic species play a key role in industrial applications such as water-cleaning procedures and pitch control during papermaking but they also give information on how to design surfaces like hydrophobic mineral pigments. In this thesis, the influence of surface properties on wetting and interaction forces has been studied. Surfaces with close-packed particles, pore arrays, randomly deposited nanoparticles as well as reference surfaces were prepared. The atomic force microscope (AFM) was utilized for force and friction measurements while contact angles and confocal Raman microscopy experiments were mainly used for wetting studies. The deposition of silica particles in the size range of nano- to micrometers using the Langmuir-Blodgett (LB) technique resulted in particle coated surfaces exhibiting hexagonal close-packing and close to Wenzel state wetting after hydrophobization. Force measurements displayed long-range interaction forces assigned to be a consequence of air cavitation. Smaller roughness features provided larger forces and interaction distances interpreted as being due to fewer restrictions of capillary growth. Friction measurements proved both the surface structure and chemistry to be important for the observed forces. On hydrophobic pore array surfaces, the three-phase contact line of water droplets avoided the pores which created a jagged interface. The influence of the pores was evident in the force curves, both in terms of the shape, in which the three-phase contact line movements around the pores could be detected, as well as the depth of the pores providing different access and amount of air. When water/ethanol mixtures were used, the interactions were concluded to be due to ethanol condensation. Confocal Raman microscopy experiments with water and water/ethanol mixtures on superhydrophobic surfaces gave evidence for water depletion and ethanol/air accumulation close to the surface. Force measurements using superhydrophobic surfaces showed extremely long-range interaction distances. This work has provided evidence for air cavitation between hydrophobic surfaces in aqueous solution. It was also shown that the range and magnitude of interaction forces could, to some extent, be predicted by looking at certain surface features like structure,roughness and the overall length scales. / <p>QC 20121011</p>

Micro-assembly processes suffer from some breaches due to the continuing trend towards an increase in the production capabilities as well as in the size reduction of the components manipulated. Usual manipulating schemes have reached their limit and capillary forces constitute a valuable alternative strategy.<p><p>The goal of this work is to describe the dynamics of liquid bridges in the application of micro-assembly processes. The description is obtained using the Kelvin-Voigt model, with a spring, a damper, and a mass connected in parallel, supported by numerical simulations, analytical approximations and experiments.<p><p>The works is divided into three parts. First we present important aspects of microfluidics, as well as the constitutive equations and an overview of numerical approaches used to describe fluid flow problems with moving interfaces.<p><p>The second part is devoted to the capillary rise case, intended to validate and to compare the numerical approaches to analytical laws and experimental results. The implementation of the slipping and the dynamic contact angles is discussed.<p><p>The last part focuses on the dynamics of the liquid bridge. The liquid bridge is confined between two circular and parallel plates and presents an axial symmetry. The description reveals that the stiffness depends on the surface tension and on the shape of the air/liquid interface, the damping coefficient depends on the viscosity and the volume of liquid and the equivalent mass depends on the density and the volume.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

This thesis deals with the surface of a gecko in relation to its adhesion ability. Understanding the mechanism of movement and adhesion principle is important for the design and manufacture of nanostructured material. Likewise, knowledge of the origin of the self-cleaning ability allows the description of the influence of surface structure on movement and forces acting at the contact. The work describes the process of making nanostructured surface, which was modified in order to obtain maximum adhesion forces. The material properties were determined by the values of wettability and by force spectrum measurement. Their results were compared with the theoretical assumption of capillary forces and other possibilities to increase adhesion.

La tendance à la miniaturisation des produits n'est pas sans influence sur l'évolution de leurs moyens de production et d'assemblage. En effet, dû à la réduction d'échelle, l'assemblage de petits composants (appelé microassemblage) est perturbé par les forces de surface comme les forces de capillarité. Ces forces, exercées par le pont liquide reliant manipulateur et composant, sont habituellement négligeables (et négligées) dans l'assemblage conventionnel dominé par les forces de gravité. L'approche originale suivie dans ce travail consiste à tirer parti de ces effets et à les utiliser pour la manipulation de microcomposants, c'est-à-dire de composants dont la taille va de quelques dizaines de microns à quelques millimètres. Ce travail tente donc d'apporter quelques réponses aux problèmes de conception posés par un tel choix: quels sont les avantages d'une telle approche? Comment ces forces `fonctionnent-elles'? Sont-elles suffisamment grandes pour manipuler des microcomposants? Comment, dans ce cas, relâcher le composant? Quel rôle la tension de surface joue-t-elle? En quoi le choix des matériaux est-il important? Comment optimiser la conception du manipulateur? Tout au long de ce travail, le lecteur trouvera un inventaire des principes de manipulation existants, les éléments nécessaires à la modélisation des forces de capillarité, ainsi que la description de la simulation et du banc d'essai développés par l'auteur dans le but d'étudier ces paramètres de conception. Les résultats présentés dans cette thèse recouvrent essentiellement deux thèmes: quelles sont les règles de conception à suivre pour maximiser les forces de capillarité (problème de la préhension) et comment choisir une stratégie de relâche adéquate (problème de la relâche)? / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished