Janus particles, named after the two faced Roman god Janus, possess unique asymmetry and combine two distinct functions at their opposite sides, allowing them to target complex self-assembled architectures and materials inaccessible for homogeneous building blocks. In this study, three areas regarding the topic of Janus particles were explored: the synthesis of Janus particles, their (self-) assembly, and applications. In the first part of the work, we have drawn our attention to the optimization of the synthetic procedures concerning the preparation of Janus particles and to the extending of the current Janus particle library by adding new geometries to the list. In the case of spherical Janus particles, we have developed an easy approach to tailor the Janus ratio of the resulting particles, thus, extending the possibilities of the Pickering emulsion approach for the creation of a variety of Janus particle architectures. Additionally, a new methodology was employed to measure directly and in situ the position/contact angle of the prepared Janus particles with different Janus ratios at a water-oil interface. It was further concluded that having simply two different functionalities on a particle surface does not necessarily imply amphiphilic behavior: only in the case of large wettability contrasts our particles were in a true Janus regime. In the case of platelet-like Janus particles, we have developed a completely new approach for their large-scale synthesis, which involved a reduced number of steps compared to the spherical Janus particles. In the second part of the work, the assembly behavior of various kinds of functional spherical Janus particles was investigated depending on the nature of the Janus particles and the surrounding media conditions. Oppositely charged, uncharged amphiphilic, and charged amphiphilic Janus particles were fabricated comprising different responsive polymers on their surface, and their assembly was investigated depending on the pH value of the dispersion, the ionic strength, or the solvent. It was found that, under specific conditions, the Janus particles formed hierarchical chain-like structures in solutions, which were not observed in the case of the homogeneous particle mixtures. The obtained results indicate that the fundamental understanding of the Janus particle assembly mechanisms is crucial for the programmed formation of desired structures. In the third part of the work, we have focused on the applications of our developed hybrid hairy Janus particles and proposed two main directions that would benefit from the unique properties or architecture of the Janus particles. The first direction is based on the exploitation of the superior interfacial activity of the Janus particles and their use for interfacial catalysis. The second proposed direction for the application of Janus particles is based on their use as building blocks for functional structured surfaces. The prepared surfaces were thoroughly characterized and tested for their performance toward anti-icing as well as anti-fouling applications. Ultimately, the developed functional surfaces based on Janus particles as building blocks are very promising for their future application in the coating technology.

Janus particles, named after the two faced Roman god Janus, possess unique asymmetry and combine two distinct functions at their opposite sides, allowing them to target complex self-assembled architectures and materials inaccessible for homogeneous building blocks. In this study, three areas regarding the topic of Janus particles were explored: the synthesis of Janus particles, their (self-) assembly, and applications. In the first part of the work, we have drawn our attention to the optimization of the synthetic procedures concerning the preparation of Janus particles and to the extending of the current Janus particle library by adding new geometries to the list. In the case of spherical Janus particles, we have developed an easy approach to tailor the Janus ratio of the resulting particles, thus, extending the possibilities of the Pickering emulsion approach for the creation of a variety of Janus particle architectures. Additionally, a new methodology was employed to measure directly and in situ the position/contact angle of the prepared Janus particles with different Janus ratios at a water-oil interface. It was further concluded that having simply two different functionalities on a particle surface does not necessarily imply amphiphilic behavior: only in the case of large wettability contrasts our particles were in a true Janus regime. In the case of platelet-like Janus particles, we have developed a completely new approach for their large-scale synthesis, which involved a reduced number of steps compared to the spherical Janus particles. In the second part of the work, the assembly behavior of various kinds of functional spherical Janus particles was investigated depending on the nature of the Janus particles and the surrounding media conditions. Oppositely charged, uncharged amphiphilic, and charged amphiphilic Janus particles were fabricated comprising different responsive polymers on their surface, and their assembly was investigated depending on the pH value of the dispersion, the ionic strength, or the solvent. It was found that, under specific conditions, the Janus particles formed hierarchical chain-like structures in solutions, which were not observed in the case of the homogeneous particle mixtures. The obtained results indicate that the fundamental understanding of the Janus particle assembly mechanisms is crucial for the programmed formation of desired structures. In the third part of the work, we have focused on the applications of our developed hybrid hairy Janus particles and proposed two main directions that would benefit from the unique properties or architecture of the Janus particles. The first direction is based on the exploitation of the superior interfacial activity of the Janus particles and their use for interfacial catalysis. The second proposed direction for the application of Janus particles is based on their use as building blocks for functional structured surfaces. The prepared surfaces were thoroughly characterized and tested for their performance toward anti-icing as well as anti-fouling applications. Ultimately, the developed functional surfaces based on Janus particles as building blocks are very promising for their future application in the coating technology.

The main subject of this thesis is to examine thermo-osmotic flows, which occur on interfaces of non-uniform temperature. Such thermo-osmotic flows are purely non-thermal equilibrium phenomena. Along the non-isothermal interface, specific interaction of a liquid and its solutes with a boundary vary in strength across the interface, according to the local temperature. This boundary can be a solid, a membrane or a phase boundary. The flow is thereby continuously pumping fluid across the interface in direction of the local temperature gradient, resulting in an extended flow pattern in the bulk due to mass conservation. In a system containing particles and heat sources in a liquid under spatial confinement, the thermo-osmotic flow may drive particles in a directed manner, or can lead to collective phenomena. To approach this broad topic of (self-)thermophoresis and collective motion of active particles and quantify the role of the thermo-osmotic flow upon the latter effects, different experiments have been performed: The first experiments aim to quantify the thermo-osmotic flow at a non-isothermal liquid/solid interface for two fundamentally different substrate properties. Further, the bulk flow was investigated for two different systems. The form and spatial extension of this bulk flow pattern depends sensitively on the form of the container and the interface, as well as on the thermo-osmotic flow. The first system is a liquid film confined between two planar glass cover slips. The second case is a Janus particle immobilized on one of the glass slips. In the first case, the non-uniform temperature profile is generated by optical heating of a nanometer sized gold colloid, and in the second case, the heat source is the Janus particle. The bulk flow pattern consists, for the second case, of the flow pattern created by the glass cover slips and the one created by the Janus particle. The following experiments are focusing on the dynamics of mobile self-thermophoretic Janus particles. In particular, their dynamics and the contributions of the thermo-osmotic flow to the interaction of multiple active particles are investigated. To investigate those particles under controlled conditions and examine their interactions at low concentrations for an effectively unlimited amount of time, a real-time feedback algorithm was co-developed to gain control of the motion of multiple active particles simultaneously, called ”photon nudging”. With the help of this method, first experiments have been performed to quantify the dynamics of a Janus particle located close to a heat source.

No description available.

Beams are ubiquitous in our everyday life and can be found in a variety of length scales, from large supports of buildings to carbon nanotubes. Similarly, bubbles can also span a variety of scales, ranging from tiny bubbles in a glass filled with champagne to the giant soap bubbles formed by artists to attract crowds. Yet, the behavior of beams and bubbles can often occur so fast that the dynamics go unnoticed. This dissertation aims to understand the mechanics of beams and bubbles in four different examples. We combine table-top experiments with mathematical models to predict how each system will behave when exposed to different extreme conditions. We start by examining the retraction of a rubber band once it has been stretched and released. This process is similar to plucking a string, where the dynamics are governed by tensile and inertial forces, resulting in a trapezoidal shape during retraction. However when a rubber band is stretched and released, a region of high-curvature develops. Our experiments and mathematical model highlight that bending forces can be significant and give rise to a curved self-similar shape to the retracting rubber band. The next example involves the competition of surface tension and twisting on a flexible rod. Most studies in the field of elasto-capillarity have focused on how surface tension can bend an elastic structure, leaving the possibility of twisting unexplored. Here we utilize particles with discrete wettabilities -- or Janus particles -- at liquid interfaces that can be used to twist a flexible cylinder. The third system is focused around the spreading behavior of bubbles on submerged surfaces coated with a layer of oil. These liquid-infused surfaces have remarkable applications due to their ability to minimize contact line pinning. However, this property has mostly been exploited using liquid drops. We here study the early spreading behavior of a bubble once it has made contact with the liquid-infused surface. The final chapter is centered around the collapse of bubbles resting on the surface of an ultra viscous liquid. When a bubble on such a surface is ruptured, the bubble film collapses vertically downwards, leading scientists to believe that gravity is driving the collapse. Yet, interfacial forces are dominant in highly curved liquid surfaces and exceed gravitational forces. By turning the setup upside-down, we show that surface tension is indeed responsible for the collapse and the subsequent wrinkling instability that develops.

No description available.

No description available.

L’électrochimie bipolaire est un phénomène générant une réactivité asymétrique à la surface d’objets conducteurs, sans contact électrique direct. Ce concept est basé sur le fait que lorsqu’un objet conducteur est localisé dans un champ électrique, il se polarise. Par conséquent, une différence de potentiel est générée entre ses deux extrémités, et peut être utilisée pour induire des réactions redox localisées. Dans cette thèse, l’utilisation de l’électrochimie bipolaire pour la science des matériaux et pour la locomotion d’objets est présentée.Jusqu’à présent, la plupart des méthodes ou procédés utilisés pour générer des objets asymétriques,appelés aussi objets « Janus », nécessitent l’introduction d’une interface pour briser la symétrie. Nous avons développé une nouvelle approche basée sur l’électrodéposition bipolaire pour générerce type d’objet en grande quantité. Grâce à cette technologie différents matériaux tels que des métaux, des polymères et des semi‐conducteurs ont pu être déposés sur diverses particulesconductrices. Il a été aussi démontré que l’électrochimie bipolaire pouvait être utilisée pour lamicrostructuration de substrats conducteurs.Nous avons induit des mouvements à des objets conducteurs en exploitant le phénomèned’électrochimie bipolaire. Certains objets Janus synthétisés par l’approche précédente ont pu être utilisés comme micronageurs. La brisure de symétrie qui est générée par l’électrochimie bipolaire peut être aussi utilisée directement pour générer un mouvement de particules isotropes. En employant ce concept, nous avons pu provoquer des mouvements de translation, rotation et lévitation pour des particules de carbones ou métalliques. / The phenomenon of bipolar electrochemistry generates an asymmetric reactivity on the surface ofconductive objects in a wireless manner. This concept is based on the fact that when a conducingobject is placed in an electric field, it gets polarized. Consequently, a potential difference appearsbetween its two extremities, that can be used to drive localized redox reactions. In the presentthesis, bipolar electrochemistry was used for material science and the locomotion of objects.So far, the majority of methods and processes used for the generation of asymmetric objects, alsocalled “Janus” objects, is based on using interfaces to break the symmetry. We developed a newapproach based on bipolar electrodeposition for generating this type of objects in the bulk. Using thistechnology, various materials like metals, polymers and semiconductors could be deposited ondifferent types of conducting particles. We also showed that bipolar electrochemistry can be used forthe microstructuration of conducting substrates.Motion generation by bipolar electrochemistry has also been demonstrated. Some of the Janusobjects synthesized by the previous approach can be used as microswimmers. The asymmetricreactivity that is induced by bipolar electrochemistry can also be used directly to generate motion ofnon‐hybrid objects. With this concept we induced translations, rotations and levitations of carbonand metal particles.

This study is focused on the fabrication of plasma polymerized ultrathin films and the elucidation of their unique properties with an emphasis on the solvent-less, dry polymerization process to introduce post-deposition functionality, robustness, and shape preservation. Two major classes of materials are the subject of this study: biological monomers, specifically the amino acids tyrosine and histidine and synthetic organic and inorganic monomers including acrylonitrile, 2-hydroxyethyl methacrylate, N-isopropylacrylamide, titanium isopropoxide and ferrocene. The unique chemical and physical properties of highly cross-linked ultrathin plasma polymerized amino acid and synthetic polymer films are demonstrated along with their functional response and robustness on both planar and complex surface structures. The work emphasizes the facile ability of plasma polymerization to create unique, tailored ultrathin coatings. Chemical functionality retention (OH, NH₂) of the tyrosine and histidine amino acids is demonstrated by the subsequent mineralization of gold or titania nanoparticles on the plasma polymerized ultrathin films using a wet chemical approach. Inorganic nanoparticle mineralization is further investigated as a method to modify the optical properties of composite nanocoatings. Plasma co-polymerization of tyrosine and synthetic monomers is used to create nanocomposite coatings with unique surface functionalities, responsive behavior, optical characteristics and a high level of integration between monomers. The fabrication of novel plasma polymerized Janus microspheres, micropatterned substrates and free-standing films also demonstrate numerous plasma polymerized materials which exhibit unique structural properties. Overall, facile plasma polymerization of novel, functional ultrathin films and complex topological coatings having potential biocompatible and optical applications is established.

Bipolar electrochemistry deals with the exposure of an isolated conducting substrate that has no direct connection with a power supply except via an electric field. Therefore it can be considered as a "wireless technique". The polarization of the substrate with respect to the surrounding medium generates a potential difference between its opposite ends which can support localized electrochemical oxidation reduction reactions and break the surface symmetry of the substrate. The method was applied in the present thesis to materials science and biological systems. In the frame of designing asymmetric particles, also called "Janus" particles, bipolar electrochemistry was adapted for the bulk preparation of these objects. Conductive substrates with different nature, sizes and shapes have been modified with various materials such as metals, ionic and inorganic compounds using this approach. Moreover, a control over the deposit topology could be achieved for substrates at different length scales. Bipolar electrodeposition is also a good tool for investigating the generation of different metal morphologies. Further developments in the bipolar setup allowed us to use the technology for microstructuration of conductive objects. Furthermore the concept has shown to be very useful in the field of the induced motion of particles. The asymmetric objects that have been prepared by bipolar electrodeposition were employed as microswimmers which could show both translational and rotational motion. The application of electric fields in the bipolar setup can be used for the direct generation of motion of isotropic objects through bubble generation. A levitation motion of objects combined with light emission was possible using this concept. Finally, bipolar electrochemistry was also used for studying the intrinsic conductivity of biological molecules (DNA), which is of great importance in the nanotechnology.