Beim Stoffübergang einer grenzflächenaktiven Substanz in einem flüssigen Zweiphasensystem kann solutale Marangoni-Instabilität einsetzen. Die weitere nichtlineare Entwicklung der Marangoni-Instabilität geht mit einer enormen Vielfalt von Strömungsmustern einher. In der Literatur wird dieser Aspekt häufig unter dem unscharfen Ausdruck „Grenzflächenturbulenz“ zusammengefasst. Diese Arbeit stellt heraus, dass drei grundlegende Strukturformen existieren: Rollzellen, Relaxationsoszillationen und Relaxationsoszillationswellen. Ein großer Teil der Komplexität der Strömungsmuster ist dadurch begründet, dass die Grundstrukturen unterschiedliche Hierarchieebenen aufweisen. Es werden die zugrunde liegenden Bedingungen für das Auftreten der jeweiligen Strukturtypen, ihre transiente Natur und die Bildung der hierarchischen Strömungsmuster untersucht. Des Weiteren betrachtet diese Arbeit die Wechselwirkungen mit Dichteeffekten, die sowohl die Charakteristik der Strukturen als auch ihre zeitliche Entwicklung beeinflussen.

Ce travail de thèse est consacré à l’étude des écoulements thermogravitaires et thermocapillaires induits par chauffage laser dans des couches liquides. Le chauffage d’un système à deux liquides donne naissance à deux effets thermiques. Le premier est dû à la variation de la masse volumique avec la température et le second à la variation de la tension interfaciale avec la température. Nous avons dans un premier temps étudié ces deux contributions séparément. En confrontant expériences, théorie et simulations numériques nous avons démontré que la morphologie des écoulements thermogravitaires dépend de l’épaisseur de la couche liquide ainsi que de la largeur du champ de température. Ensuite nous nous sommes intéressés à l’étude théorique et numérique de l’effet thermocapillaire. Cette étude a révélé qu’il est possible d’étudier les écoulements à partir des déformations d’interface induites par ces mêmes écoulements. Nous avons montré qu’il existe deux régimes de déformations en fonction du rapport de hauteurs et du signe de la variation de la tension interfaciale avec la température. Enfin, nous nous sommes intéressés à la compétition entre ces deux mécanismes. L’analyse des déformations d’interface et la comparaison avec un modèle à une dimension a montré qu’en fonction du rapport de hauteurs des couches liquides nous avons une transition d’un régime d’écoulements thermocapillaires vers une régime d’écoulements thermogravitaires. De plus, nous avons montré expérimentalement et numériquement qu’il est possible d’induire une instabilité d’origine thermogravitaire conduisant à la formation d’un pont liquide. / This thesis work is dedicated to thermocapillary and thermogravitary flows induced bylaser-heating in liquid layers. The laser-heating of a two fluids system induces two thermaleffects. The first effect come from the variation of the density with temperature andthe second one is due to the variation of the interfacial tension with the temperature.In a first part, we study separately these two mechanism. With a comparison betweenexperiments, theory and numerical simulations we demonstrated that the morphology ofthe flows depends on the thickness of the layer and the width of the temperature field.Then, we studied numerically and theoretically the thermocapillary effect. That revealedit is possible to understand the flows from the interface deformations. We highligth theseare two deformation regimes depending the thickness ratio and the sign of the interfacialtension gradient. Finally, we studied the competition between the two mechanism and theexperiments revealed a transition between two flow regimes. The comparison of these resultsand a theoritical model showed there is a transition from a thermocapillary regime to athermogravitary regime. In addition, we showed the possibility to induce an instibility bythermogravitary effect which can lead to the formation of a liquid bridge.

The interfacial structuring of three non-halogenated ionic liquids was examined at the air-liquid interface for both dry and humid condition by analysis of X-ray reflectometry data using a slab model approach. The aim was to investigate the effect of humidity on the air-liquid interface. Pure ionic liquids as well as solutions of 5% w/w and 20% w/w in propylene carbonate were examined. Three different cations were used, a phosphonium cation ([P6,6,6,14]+) and two dialkylimidazolium cations ([C6C1Im]+ and [C10C1Im]+). The anion was bis(mandelato)borate ([BMB]-), which is a non-commercial anion that has been shown to exhibit excellent tribological properties. The results reveal that the presence of ambient water has an impact on the interfacial structure and the layering of all pure ionic liquids, as well as most cases of ionic liquid solutions. Exposure to humidity had the largest response in the case of all pure and diluted solutions of [C6C1Im][BMB], for which a more pronounced layering was observed. The [P6,6,6,14][BMB] solutions did not exhibit any significant changes when exposed to ambient water, with the 20% w/w solution proving to be the most stable. / Gränsskiktsstrukturen hos tre olika icke-halogenerade jonvätskor undersöktes vid luft-vätskegränsskiktet för både torra och fuktiga förhållanden genom analys av data från en röntgen reflektometer med en “slab model approach”. Målet var att undersöka effekten av luftfuktighet på luft-vätskagränsskiktet. Rena jonvätskor såväl som lösningar av 5 och 20 vikt-% utspädda i propylenkarbonat undersöktes. Tre olika katjoner användes, en fosforkatjon ([P6,6,6,14]+) samt två dialkylimidazoliumkatjoner ([C6C1Im]+ och [C10C1Im]+). Anjonen var bis(madelato)borat ([BMB]-), vilket är en icke-kommersiell anjon som har visat bra tribologiska egenskaper. Resultatet visar att närvaron av omgivande vatten har en påverkan på gränsskiktsstrukturen samt skiktning hos alla rena jonvätskor och de flesta utspädda lösningar. Exponering för fuktighet hade den största inverkan på alla rena och utspädda lösningar av [C6C1Im][BMB], för vilka en mer distinkt skiktning kunde observeras. [P6,6,6,14][BMB] lösningar uppvisade inga signifikanta ändringar vid exponering till fuktig luft, där den lösning med 20 vikt-% visade sig vara mest stabil.

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<p>The structural and thermodynamic properties of a crystal-melt interface in</p> <p>elemental magnesium have been investigated using molecular dynamics (MD)</p> <p>simulations with an embedded atom method description of the interatomic potential.</p> <p>Three low index interfacial orientations, (0001), (1101) and (1120), have been studied.</p> <p>From fine-grained atomic density profiles, the structural interfacial widths show obvious anisotropy and the variation of interatomic planar spacing as a function of distance through the crystal-melt boundary is established. Mainly from the coarse-grained density profiles, the effective 10-90 width of the interface region, defined as the intrinsic width, in each orientation has been determined. In addition, the interfacial stresses are obtained from an integration of the interfacial stress profiles and the results show significant anisotropy, which is possibly related to the anisotropy of occupation fraction profiles. Finally, from a determination of the excess energy and interfacial stress of the solid-liquid interface and from previous published results for the interfacial free energy at the melting point, the Gibbs-Cahn integration is employed to derive an estimation of the temperature dependence of the interfacial free energy at non-equilibrium temperatures. All of the crystal-melt interfacial properties for magnesium are compared with simulation data from other elemental metals and alloys, as well as from other model systems such as Lennard- Jones and hard spheres.</p> / Master of Applied Science (MASc)

Ionic liquids (ILs) present new approaches for controlling interactions at the solid-liquid interface. ILs are defined as liquids consisting of bulky and asymmetric ions, with a melting point below 373 K. Owing to their amphiphilic character they are powerful solvents but also possess other interesting properties. For example, ILs can self-assemble and are attracted to surfaces due to their charged nature. As a result, they are capable of forming nanostructures both in bulk and at interfaces. This thesis describes how the solid-IL interface responds to external influences such as elevated temperatures, the addition of salt and polarisation. An improved understanding of how these factors govern the surface composition can provide tools for tuning systems to specific applications such as friction. Normal and friction forces are measured for ethylammonium nitrate (EAN) immersed between a mica surface and a silica probe, at different temperatures or salt concentrations. The results demonstrate that an increase in temperature or low concentrations of added salt only induce small changes in the interfacial structure and that the boundary layer properties remain intact. In contrast, at sufficiently large salt concentrations the smaller lithium ion prevails and the surface composition changes. The interfacial layer of a similar IL is also investigated upon the addition of salt and the results reveal that lithium ions affect the surface composition differently depending on the ion structure of the IL. This demonstrates that the surface selectivity strongly depends on the ion chemistry. Remarkably, a repulsive double layer force manifests itself for EAN at 393 K, which is not observed for lower temperatures. This indicates a temperature dependent change in EAN’s microscopic association behaviour and has general implications for how ILs are perceived. A new method is developed based on a quartz crystal microbalance to investigate how the surface compositions of ILs respond to polarisation. The approach demonstrates that interfacial layers of both a neat IL and an IL dissolved in oil can be controlled using potentials of different magnitudes and signs. Furthermore, the method enables two independent approaches for monitoring the charges during polarisation which can be used to quantify the surface composition. The technique also provides information on ion kinetics and surface selectivity. This work contributes to the fundamental understanding of the solid-IL interface and demonstrates that the surface composition of ILs can be controlled and monitored using different approaches. / Jonvätskor möjliggör nya tillvägagångssätt för att kontrollera interaktioner vid gränsskiktet mellan fasta ytor och vätskor. Jonvätskor definieras som vätskor som består av stora och asymmetriska joner med en smältpunkt under 373 K. På grund av sin amfifila karaktär är de starka lösningsmedel men har också andra intressanta egenskaper. Jonvätskor kan till exempel självorganisera sig och attraheras till ytor på grund av sin laddning. En följd av detta är att de bildar nanostrukturer både i bulk och på ytor. Denna avhandling beskriver hur gränsskiktet mellan fasta ytor och jonvätskor svarar på yttre påverkan såsom en ökning i temperatur, tillsättning av ett salt samt polarisering. En ökad förståelse för hur dessa faktorer styr ytkompositionen av jonvätskor kan bidra med verktyg för att kontrollera system till specifika applikationer såsom friktion. Normala- och friktionskrafter mäts för etylammonium nitrat (EAN) mellan en glimmeryta och en kolloidprob vid olika temperaturer eller saltkoncentrationer. Resultaten visar att en ökning av temperatur eller låga koncentrationer av tillsatt salt bara marginellt framkallar ändringar i strukturen på gränsytan och att det adsorberade lagret förblir intakt. När saltkoncentrationen emellertid var tillräckligt hög får den mindre litiumjonen överhanden och ytsammansättningen ändras. Ytlagret av en liknande jonvätska undersöks också vid tillsättning av salt och resultaten avslöjar att litiumjoner påverkar ytsammansättningen annorlunda beroende på jonstrukturen av jonvätskan. Detta visar att ytselektiviteten starkt beror på jonkemin. En repulsiv dubbellagerkraft yttrar sig anmärkningsvärt för EAN vid 393 K vilket inte observeras vid lägre temperaturer. Detta indikerar en ändring i EANs mikroskopiska sammansättningsbeteende och har generella återverkningar för hur jonvätskor uppfattas. En ny metod har utvecklats baserad på en kvartskristall mikrovåg för att undersöka hur ytsammansättningen av jonvätskor reagerar på polarisering. Denna metod visar att det adsorberade lagret av både en ren jonvätska och en jonvätska löst i olja kan kontrolleras genom att applicera spänningar med olika tecken och storlekar. Dessutom möjliggör metoden två oberoende tillvägagångssätt för att övervaka laddningarna under polarisering vilket kan användas för att kvantifiera ytsammansättningen. Tekniken ger också information om jonkinetik och ytselektivitet. Detta arbete bidrar till den grundläggande förståelsen av gränsskiktet mellan fasta ytor och jonvätskor och visar att ytsammansättningen av jonvätskor kan kontrolleras och övervakas med olika tillvägagångssätt. / <p>QC 20160518</p>

The process of assembling metal nanoparticles at the interface of two liquids has received a great interest over the past few years due to a wide range of important applications and their unusual properties compared to bulk materials. The work in this thesis presents a low cost, simple and cheap synthesis of metal nanoparticles, core/shell structures and semiconductors followed by assembly of these particles between immiscible liquids. The aim of this thesis is divided to three parts (Summary of the experimental work of this thesis is in Table A1):1) To achieve a closed loop recycling for producing cadmium sulfide as powders and/or nanostructured thin films for solar cells or other optoelectronic devices applications. A series of bis(dialkyldithiocarbamato)cadmium(II) were used for this approach. Bis(dioctyldithiocarbamato)cadmium(II) complexes proved to be the optimal alkyl chain for this process. The approach can be extended to other metal sulfides such as those of Zn, Pb, Cu, or Fe and many transition metals and oxides.2) To explore the phenomena of exchange bias in very small size particles (5 nm) of Ni/NiO (core/shell structure) obtained by solution phase synthesis. Ferromagnetism (FM) due to exchange bias is well established in the case of larger particles with diameters over 10 nm. However, sub 10 nm magnetic structures synthesized by solution phase have never been found to be ferromagnetic at room temperature. These Ni/NiO nanocrystals with ferromagnetic properties at room temperature were among the smallest and strongest magnets made in solution. Similar magnets can be obtained using a rare class of high anisotropy materials nearly all of which feature precious metals. This work would lead to significantly cheaper magnetic particles suited for the mass market. The applications of this work can be applied to produce viable storage devices and the other possibility is to disperse these nanocrystals in solution and use it to make ferrofluids which have a number of mature applications. Functional device architectures of these particles were rapidly and inexpensively produced as thin films using self-assembly of liquid/liquid interface process at room temperature by using octylamine as a surfactant.3) To synthesise and assemble submicron particles of silver, cobalt and nickel by using polyol methods and liquid/liquid interface, respectively. The effect of reaction conditions (solvent, precursor concentration, temperature, etc.) on synthesis and assembly of the particles was studied. Assembled cobalt and nickel as films are promising materials for spintronics, magnetic and magneto-electronics and biomedics. The nature and characteristics of the particles and their films were studied by a number of techniques such as SEM, EDX, TEM, p-XRD, UV-Vis, PL, FTIR, DLS and SQUID for magnetic measurements.

Le présent manuscrit présente le développement méthodologique du calcul de la tension de surface d’interfaces solide-liquide via des simulations de dynamique moléculaire. Après une courte présentation des avancées dans le domaine du calcul de la tension de surface pour les interfaces fluide-fluide et solide-fluide, les principales méthodes de calcul de la tension de surface d’un point de vue théorique sont montrées et généralisées pour le cas des interfaces solide-liquide, puis mises en oeuvre dans le cas de simulations de dynamique moléculaire. Un système école, constitué d’une feuille de graphène pour la phase solide et d’un bain de méthane pour la phase liquide, est ensuite étudié pour observer l’influence des artefacts de simulation sur le calcul de la tension de surface, montrant en particulier des effets de taille bien plus importants que pour le cas des interfaces liquide-liquide. Un autre système constitué d’une tranche de cuivre pour la phase solide, et d’un bain de méthane pour la phase liquide, a permis d’étudier l’effet inédit aux systèmes solide-liquide appelé anisotropie, montrant en particulier l’importance du caractère tensoriel de la tension de surface pour ce type de système. L’influence des paramètres du potentiel croisé entre les atomes de cuivre et de méthane est ensuite étudié. Finalement, deux systèmes applicatifs sont abordés, d’une part le système graphène-eau permettant d’étudier les effets de l’interaction électrostatique, et d’autre part un système constitué d’un solide explosif, le 1,3,5-triamino-2,4,6-trinitrobenzène (TATB) en contact avec un bain polymère pour la phase liquide, représentatif d’un cas réel d’intérêt. / This manuscript presents the methodological development of surface tension calculation of solid-liquidinterfaces via molecular dynamics simulations. After a short presentation of the advances in the field ofsurface tension calculation for fluid-fluid and solid-fluid interfaces, the main methods of surface tensioncalculation from a theoretical point of view are shown and generalized for solid-liquid interfaces, thenimplemented in the case of molecular dynamics simulations. A school system, consisting of a graphenesheet for the solid phase and a methane bath for the liquid phase, is then studied to observe the influenceof simulation artifacts on the surface tension calculation, showing in particular much larger size effectsthan in the case of liquid-liquid interfaces. Another system consisting of a copper slice for the solid phaseand a methane bath for the liquid phase made it possible to study the novel effect of solid-liquid systemscalled anisotropy, showing in particular the importance of the tensor character of the surface tension forthis type of system. The influence of the parameters of the cross potential between copper and methaneatoms is then studied. Finally, two application systems are discussed, on the one hand the graphene-watersystem for studying the effects of electrostatic interaction, and on the other hand a system consisting ofan explosive solid, 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in contact with a polymer bath for theliquid phase, representing a real case of interest.

Les charges à l'interface liquide/solide sont un élément originel majeur des phénomènes électrocinétiques observés en micro/nanofluidique. Elles sont donc la colonne vertébrale de mon manuscrit de thèse, qui se décompose en trois parties : Dans la première partie, un rappel des concepts de base sur les interfaces liquides/solides est proposé au lecteur. Il est suivi d'une description des différentes méthodes expérimentales permettant de mesurer le potentiel zeta de couples solide/électrolyte, puis d'une présentation des travaux de la littérature exploitant les charges aux interfaces pour la préconcentration de molécules biologiques dans des systèmes Micro-Nano-Micro (MNM) fluidiques. Ensuite, une deuxième partie est consacrée à la mesure du potentiel zeta par la méthode des courants d'écoulement. Nous y présentons l'amélioration du banc expérimental issu des travaux antérieurs à ma thèse, ainsi que le développement de nouveaux protocoles de préparation des surfaces permettant de rationaliser et de stabiliser les mesures. Une application à un détecteur original de molécules biologiques clos cette deuxième partie. Enfin, la troisième et dernière partie s'intéresse à la préconcentration de molécules biologiques. Une méthode originale de fabrication des dispositifs MNM et les résultats de préconcentration obtenus, très encourageants, sont décrits. Des premiers modèles numériques et phénoménologiques sont proposés, qui mettent en avant l'originalité de notre travail / The charges at liquid/solid interfaces are a key element for both understanding and exploiting the electrokinetic phenomena in micro/nanofluidics. The manuscript of my Ph.D thesis is dedicated to these phenomena, which is divided into three main parts: Above all, a simple overview of charges at the liquid/solid interface is proposed. Then, several common methods for measuring the zeta potential at the liquid/solid interface are described. Next, various effective methods to preconcentrate the biological molecules is presented with the help of the surface charges. Secondly, the streaming current, which is a standard method to measure the zeta potential in our laboratory, is detailed. It contains the upgrade of the experimental setup from the previous version and the development of new protocols, which improve dramatically the stabilization and the reproducibility of the measurements. In addition, an original biological sensor is briefly presented based on these advancements. Lastly, in the final part, we describe a method which is primitively utilised in the fabrication of Micro-Nano-Micro fluidic system. Based on this system, some favorable preconcentration results is obtained. Moreover, numerical simulations are presented to prove the originality of our work