Tesis: "Colloides actifs"

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Nidhi, Vagisha. "Radiotactic colloids : towards the Decontamination Nanobots". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASF052.

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Les méthodes traditionnelles de décontamination restent confrontées à des défis importants, tels que la difficulté d'accès aux espaces complexes ou confinés, la quantité élevée de déchets, etc. Il est encore nécessaire aujourd'hui d'explorer de nouvelles méthodes permettant d'atteindre des géométries complexes avec des processus de décontamination efficaces. Même si les macrorobots se révèlent utiles dans les tâches de décontamination à grande échelle, leur taille limite leur capacité à naviguer dans des environnements complexes et confinés. Les micro ou nano robots, quant à eux, pourraient traverser de tels espaces et cibler des sites de contamination spécifiques, ce qui les rendrait plus adaptés aux travaux de décontamination en milieu confinés et complexes. Dans ce contexte, cette thèse porte sur la synthèse à grande échelle et l'étude de la mobilité de colloïdes actifs, en particulier de particules Janus, susceptibles d'être utilisés comme brique dans de nouvelles méthodes de décontamination. À cette fin, différents assemblages de particules d'or sur silice (assemblage isotrope ou Janus, nanoparticules discrètes ou couche d'or continue) ont été préparés, caractérisés et comparés. Leurs mouvements 3D et 2D ont été suivis dans différents environnements. Un élément clé de ce travail a consisté en particulier à développer un dispositif microfluidique capable de générer des gradients stables d'eau oxygénée, produit de la radiolyse de l'eau. Ce dispositif s'est révélé essentiel pour l'analyse directionnelle du mouvement des différentes particule. Ces travaux ont montré que les assemblages or silice pouvaient se déplacer de manière autonome vers une source d'H₂O₂, ce qui pourrait les rendre efficaces pour cibler les sites de contamination radioactives. Nous avons également montré que des assemblages isotropes, plus simples à préparer, pouvaient également présenter un mouvement directionnel
Traditional methods of decontamination face significant challenges, such as difficulty in accessing complex or confined spaces, high amount of waste, etc. There is still a need for the development of new methods to reach complex geometries with effective decontamination processes. While macro-robots have been useful in large-scale decontamination tasks, their size limits their ability to navigate in intricate environments. Micro or nano robots, on the other hand, can traverse small, complex spaces and target specific contamination sites, making them more suitable for detailed decontamination work. In this context, this thesis studies the capacities of micro/nanoparticles to move towards contaminated spot in complex geometries, by mimicing the chemotaxism guided by H₂O₂ (product of water radiolysis). To this end, the large-scale synthesis and mobility of active colloids, in particular Janus particles is described. A set of different assemblies of gold particles on silica (isotropic or Janus assembly, discrete nanoparticles or continuous gold layer) were prepared, characterized and compared. Their movements were monitored in different environments. A key part of this work was the developement of a microfluidic device capable of generating stable hydrogen peroxide gradients. This device was essential to study the directionnal orientation of the different particles. This work showed that silica-gold assemblies could move autonomously towards a source of H₂O₂, which could make them effective for targeting radioactive contamination sites. We have also shown that isotropic assemblies, which are simpler to prepare, can also exhibit directional movement

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2

Wang, Xiaolu. "Janus Colloids Surfing at the Surface of Water". Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS272/document.

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Considérant une particule isolée, la différence principale entre un colloïde actif et un colloïde passif réside dans le temps de persistance du régime balistique. La transition du régime balistique vers le régime diffusif est déterminée dans les deux cas par des coefficients de friction ou de manière équivalente par des coefficients de diffusion. Le mouvement d’une particule colloïdale passive micrométrique est diffusif lorsqu’il est observé sur des intervalles de temps d’au moins une microseconde, suffisamment longs pour que la direction de la quantité de mouvement soit rendue aléatoire par des collisions avec les molécules de solvant. A l’échelle macroscopique ces collisions se traduisent par un coefficient de friction de translation. Pour une particule colloïdale active, un mouvement diffusif est observé pour des intervalles de temps de plusieurs secondes, suffisamment longs pour que la direction d’auto-propulsion soit rendue aléatoire par la diffusion rotationnelle de la particule.Dans cette thèse, nous étudions le mouvement d’une particule colloïdale active déposée à la surface de l’eau. Des particules Janus aux propriétés catalytiques ont été préparées par dépôt de platine métal à la surface de particules de silice. La profondeur d’immersion des particules ainsi que leur orientation par rapport à la surface de l’eau ont été caractérisées et discutées en tenant compte des propriétés de mouillage non-uniformes de la surface des particules Janus. Le mouvement de particules isolées en présence de quantités variables d’eau oxygénée utilisée comme source d’énergie, a été enregistré par vidéo-microscopie optique et les trajectoires analysées en termes de déplacement carré moyen et de fonction d’auto-corrélation des vitesses. L’observation de deux types de trajectoires, rectilignes et circulaires, révèle la force effective ainsi que le couple induit par la décomposition catalytique de l’eau oxygénée à la surface de la particule Janus. Le résultat principal de ce travail est que le mouvement des particules actives confinées à l’interface persiste plus longtemps dans le régime balistique que celui de particules actives totalement immergées en solution. Ceci est dû au confinement qui réduit le nombre de degrés de liberté de rotation mais aussi aux conditions de mouillage partiel qui font apparaître des contributions supplémentaires à la friction de rotation
At the single-particle level, the main difference between active colloids and passive ones is the time scale over which the motion crosses over from ballistic to diffusive regime. In both cases, friction coefficients or equivalently diffusion coefficients determine this time scale. For instance, the motion of a passive colloid of 1m radius is diffusive when observed over lag times longer than a microsecond, once the direction of its momentum has been randomized by collisions with solvent molecules. At the macroscopic scale these collisions are accounted for by the translational friction coefficient. For an active colloid the effective diffusive behavior observed over lag times larger than few seconds results from the randomization of the direction of self-propulsion by rotational diffusion. In this thesis we investigated the motion of an active Janus colloid trapped at air-water interface. Spherical catalytic Janus colloids have been prepared through the deposition of platinum metal at the surface of silica particles. Immersion depth of the Janus colloid as well as their orientation with respect to the water surface, has been characterized and interpreted in terms of the non-uniform wetting properties of the Janus particles. The motion of the active Janus colloids in the presence of various concentration of hydrogen peroxide H2O2 as fuel was characterized by video microscopy and the trajectories analyzed through the mean square displacement and the velocity autocorrelation function. The types of trajectories, directional and circular ones that we observed in our experiments, revealed the effective force and torque induced by the catalytic decomposition of H2O2. At the water surface, active colloids perform more persistent directional motions as compared to the motions performed in the bulk. This has been interpreted as due to the loss of degrees of freedom resulting from the confinement at interface and also to the partial wetting conditions that possibly bring new contributions to the rotational friction at interface

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Archer, Richard. "Catalytic self-phoretic active colloids". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19453/.

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Active Janus colloids are nano to micron sized colloids, capable of propelling themselves through fluidic environments. Localised, asymmetric catalytic reactions on the colloidal bodies are used to decompose a dissolved ‘fuel’ to produce motion. Active Janus colloids have been proposed for applications in microfluidic transport. Currently active Janus colloids are restricted in their practical applications due to the randomised nature of their trajectories over time and their low yielding production methods. This thesis is focused on active Janus colloids prepared by physical vapour deposition, which utilise hemispherically coated platinum as a catalyst to decompose aqueous hydrogen peroxide. Many theories and mathematical models have been reported and are discussed in this thesis as to the precise nature of the mechanism of motion. To contribute to this discussion, active colloids were prepared with different surface functionalities on the non-catalytic section of the Janus colloids. The results indicated that the hydrophobicity of the non-catalytic face influenced the propulsive velocity of the active colloid which informs on the relationship between the fluid and the phoretic body. In an effort to produce active colloids with non-random, prescribed trajectories, the symmetry of the catalytically active layer was incrementally broken and found to introduce an additional angular velocity. The magnitude of angular velocity was controllable through production parameters. An alternative, more scalable fabrication method was developed during the course of this work. A solution based fabrication method was found to successfully produce active colloids in high concentrations which were phoretically analogous to those previously fabricated. Finally, an investigation into the effect of the active cap shape and surface coverage was conducted. Significantly, this study found that symmetrically active colloids displayed propulsive behaviour. The suggestion that asymmetry is not required for producing enhanced motion can be used to inform and simplify future fabrication methods.

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Cohen, Jack Andrew. "Active colloids and polymer translocation". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:e8fd2e5d-f96f-4f75-8be8-fc506155aa0f.

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This thesis considers two areas of research in non-equilibrium soft matter at the mesoscale. In the first part we introduce active colloids in the context of active matter and focus on the particular case of phoretic colloids. The general theory of phoresis is presented along with an expression for the phoretic velocity of a colloid and its rotational diffusion in two and three dimensions. We introduce a model for thermally active colloids that absorb light and emit heat and propel through thermophoresis. Using this model we develop the equations of motion for their collective dynamics and consider excluded volume through a lattice gas formalism. Solutions to the thermoattractive collective dynamics are studied in one dimension analytically and numerically. A few numerical results are presented for the collective dynamics in two dimensions. We simulate an unconfined system of thermally active colloids under directed illumination with simple projection based geometric optics. This system self-organises into a comet-like swarm and exhibits a wide range of non- equilibrium phenomena. In the second part we review the background of polymer translocation, including key experiments, theoretical progress and simulation studies. We present, discuss and use a common model to investigate the potential of patterned nanopores for stochastic sensing and identification of polynucleotides and other heteropolymers. Three pore patterns are characterised in terms of the response of a homopolymer with varying attractive affinity. This is extended to simple periodic block co-polymer heterostructures and a model device is proposed and demonstrated with two stochastic sensing algorithms. We find that mul- tiple sequential measurements of the translocation time is sufficient for identification with high accuracy. Motivated by fluctuating biological channels and the prospect of frequency based selectivity we investigate the response of a homopolymer through a pore that has a time dependent geometry. We show that a time dependent mobility can capture many features of the frequency response.

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5

Theurkauff, Isaac. "Collective Behavior of active colloids". Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10251/document.

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Nous étudions le comportement collectif d'une assemblée de colloïdes Janus, des sphères d'or de 1µm dont une moitié est recouverte de platine. Lorsqu'ils sont immergés dans une solution d'eau oxygénée, ils se déplacent à des vitesses de l'ordre de 5µm/s, contrôlable par la concentration en peroxyde. Individuellement, ces colloïdes suivent une marche aléatoire persistante ; Ils interagissent par effets phorétiques, formant des clusters dynamiques de quelques dizaines de colloïdes. Ces clusters, mobiles, échangent continuellement des colloïdes, se divisent et se fusionnent, formant une phase stationnaire. Nous avons développés ces colloïdes, ainsi qu'un système d'acquisition pour détecter et reconstituer les trajectoires des colloïdes. La taille moyenne des clusters augmente linéairement avec l'activité, définie comme la vitesse moyenne des colloïdes en dehors des clusters. La fonction densité de probabilité de la taille des clusters est une loi de puissance d'exposant -2. Nous quantifions les vitesses de translation et de rotation des clusters. Pour réaliser une étude thermodynamique, nous réalisons des expériences de sédimentation. Une transition est observée, entre une phase peu dense, un gaz parfait, dans lequel on mesure une température effective, et une phase dense à la dynamique hétérogène. L'équation d'état du système est mesurée, et une forme analytique heuristique est proposée
We study the collective behavior of an assembly of Janus Colloids. These are 1µm gold colloids with one half coated in platinum. When immersed in a peroxide bath, they self-propel, owing to diffusiophoresis and electrophoresis, moving at velocities of order 5µm/s. The velocity can be tune by adjusting the amount of peroxide in the bath. At the single particle level, the colloids undergo a persistent random walk. When in denser groups, the colloids interact through chemical and steric effects. The combination of these interactions, with the colloids activity, leads to collective effects. A dynamic cluster phase is observed, the formation of motile clusters of colloids, formed of up to 100 colloids. The clusters are in a stationary state, constantly moving, and exchanging colloids, they are also colliding, merging and breaking apart. We developed both the colloids, whose synthesis is described, and a high-throughput acquisition and analysis system. We measure the positions, and reconstruct the trajectories of thousands of colloids for a few minutes. From the trajectories, we extract statistical observables. We show that the sizes of clusters increases linearly as a function of the activity of the colloids. The probability distribution functions of sizes are power laws. As the density increases, a jamming transition is observed. The dense phase heterogeneous dynamics is characterized. We study the transition from the dense phase to a low density assembly with sedimentation experiments. The low density phase behaves as an ideal gas, allowing the definition of an effective temperature. We measure an equation of state for the system, and propose a heuristic collapse

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Sano, Masaki, Hong-ren Jiang y Daiki Nishiguchi. "Self-organization dynamics of active colloids". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-179578.

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Sano, Masaki, Hong-ren Jiang y Daiki Nishiguchi. "Self-organization dynamics of active colloids". Diffusion fundamentals 20 (2013) 17, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13541.

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Semeraro, Enrico Federico. "Interactions effectives et dynamiques en systèmes actifs de colloïdes autopropulsés". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAV017/document.

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L’objectif de ce projet était l’étude systématique des interactions, de la microstructure et de la dynamique de suspensions de colloïdes qui imitent les mouvements de systèmes auto-propulsés (actifs), au moyen de techniques de diffusion : diffusion des rayons X aux (ultra) petits angles (USAXS/SAXS) et spectroscopie de corrélation de photons X (XPCS).À la différence des colloïdes passifs conventionnels (particules browniennes), les colloïdes actifs sont des systèmes hors équilibre faits d’objets auto-propulsés. Ces systèmes montrent une dynamique fascinante qui s’apparente aux mouvements de volée d'oiseaux, d’essaim d’insectes, etc.Les micro-organismes mobiles sont des exemples types de colloïdes actifs, notamment certaines variétés de bactéries, ou les colloïdes de type Janus caractérisé par une composition asymétrique de leur surface qui peux engendrer une propulsion, l’auto-diffusiophorèse. Les thèmes principaux de cette thèse sont les interactions inter-particule, les interactions particule-solvant et les dynamiques phorétiques des systèmes actifs.En premier lieu, la structure et la mobilité de la bactérie Escherichia coli ont été étudiées au moyen de SAXS/USAXS . Comme projet secondaire, l’obtention de données couvrant une très large gamme de vecteur de diffusion (q) a permis de dériver un modèle structural multi-échelle de la bactérie, en combinant les caractéristiques de colloïdes (corps cellulaire), de membranes (enveloppe cellulaire) et de polymères (flagelles). Ce modèle a été affiné au moyen de mesures complémentaires de diffusion de neutrons aux petits angles (SANS) sur des suspensions de la bactérie E. coli en variant le contraste externe (remplacement isotopique partielle du solvant) afin d’aboutir à une détermination quantitative de la densité électronique des membranes et des distances entre membranes.Ces bactéries ont ensuite été utilisées comme éléments actifs en mélange avec des colloïdes passifs de silice de taille sub-micrométrique, pour comprendre comment la présence de bactéries actives mobiles affecte les interactions effectives et la dynamique des colloïdes passifs. Des mesures USAXS et XPCS simultanées ont permis de déduire les propriétés statiques et hydrodynamiques de ces colloïdes passifs. Les données suggèrent que les bactéries actives se comportent comme un fluidifiant pour les colloïdes passifs, en réduisant leurs interactions attractives et en augmentant leur dynamique ; réciproquement, ces derniers sont affectés par la solution tampon et par la présence de bactéries augmente la viscosité environnante effective.Enfin, les mouvements phorétiques de colloïdes de silice et de type Janus (silice partiellement recouvert de nickel) suspendus dans un mélange de 3-methylpyridine (3MP) + eau/eau lourde pendant la séparation de phase liquide-liquide ont été investigués par USAXS et XPCS. Les mouvements des colloïdes sont fortement corrélés à la dynamique de la séparation de phase du fait de l’absorption préférentielle de 3MP à la surface de silice. Les colloïdes de silice montrent une dynamique advective avec une diffusion amélioré en direction des microdomaines riches en 3MP, évoquant la dynamique des systèmes auto-propulsés, jusqu’à l’aboutissement de la séparation de phase. Les suspensions de colloïdes de type Janus ont un comportement beaucoup plus complexe, la dynamique étant fortement corrélée aux interactions asymétriques avec le solvant. Cette dynamique est soit augmentée soit supprimée en fonction de la concentration en 3MP qui modifie aussi la micro-structure du système. Au lieu que les colloïdes de silice migrent vers la phase riche en 3MP, les colloïdes de type Janus agissent comme des tensioactifs en se plaçant à l’interface.Cette thèse démontre l’intérêt des techniques de diffusion pour explorer les propriétés des systèmes actifs et examiner leur comportement en thermodynamique hors équilibre afin de compléter les informations obtenues par observations microscopique
This project aimed to systematically investigate the interactions, microstructure and dynamics in suspensions of colloidal particles that mimic active motions, using (Ultra) Small- Angle X-ray Scattering (USAXS/SAXS) and X-ray Photon Correlation Spectroscopy (XPCS). As opposed to the conventional passive colloids (Brownian particles), active colloids are non-equilibrium systems consisting of self-propelled particles that display many fascinating dynamics, such as streaming, swarming, flocking, etc. in appropriate media. Practical examples of active systems are motile microorganisms, such as some species of bacteria, or synthetic Janus colloids – characterized by an asymmetric chemical composition of their surface – that can induce a propulsion mechanisms, like self-diffusiophoresis. The foci of this thesis are on interparticle interactions, particle-medium interactions and the phoretic dynamics in active systems.Firstly, the structure and motility of Escherichia coli bacteria were investigated by combined USAXS and SAXS methods. As an offshoot, the scattering data spanning a broad scattering vector (q)-range permitted the derivation of a multiscale structural model by combining colloidal (cell-body), membrane (cell-envelope) and polymer (flagella) features. This model was further refined by contrast-variation Small Angle Neutron Scattering (SANS) measurements on E. coli suspensions at three match points and the full contrast which allowed the determination of the membrane electron-density and the inter-membrane distances on a quantitative scale.These bacteria were then used as active component in a mixture with micron-sized passive silica colloids, with the aim of investigating how the effective interactions and dynamics of passive colloids are affected by the presence and the motility of active E. coli. Both static and hydrodynamic information were obtained via the simultaneous use of USAXS and XPCS techniques. Data suggested active bacteria act as a fluidizing agent in such systems, reducing attractive interactions and enhancing the dynamics of passive colloids, which, at the same time, are affected by the buffer and more viscous environment due to the bacterial presence.Finally, the phoretic motions of micron-sized silica colloids and half-coated silica/nickel Janus colloids suspended in a mixture of 3-methylpyridine (3MP) and water/heavy water undergoing liquid-liquid phase separation were investigated using USAXS and XPCS. Due to the preferential wetting of 3MP on the silica surface, the motion of the colloids is strongly correlated to the dynamics of phase separation.Silica colloids displayed advective motion with enhanced diffusion toward the 3MP-rich phase reminiscent of self-propelled motion until the phase separation is completed. Suspensions of Janus colloids showed a much richer scenario, where colloid dynamics are strongly influenced by the asymmetric interactions with the solvent. The dynamics of Janus colloids were either enhanced or suppressed depending on the 3MP concentration, which, concurrently, affected the microstructure of the system. As opposed to the partitioning in 3MP-rich phase in the case of silica colloids, Janus particles behave like surfactants at the interface.The thesis demonstrates the ability of studying active systems by means of scattering methods and probe their behaviour in the thermodynamic limit and complement the information derived from direct microscopy observations

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Ibrahim, Yahaya. "Phoretic self-propulsion of chemically active colloids". Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.723473.

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Harrer, Christian, Igor Gazuz, Thomas Voigtmann y Matthias Fuchs. "Driven motion of colloids in active microrheology". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-179429.

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Harrer, Christian, Igor Gazuz, Thomas Voigtmann y Matthias Fuchs. "Driven motion of colloids in active microrheology". Diffusion fundamentals 20 (2013) 7, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13529.

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Peng, Chenhui. "ACTIVE COLLOIDS IN ISOTROPIC AND ANISOTROPIC ELECTROLYTES". Kent State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=kent1480622734084146.

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13

Navarro, Argemí Eloy. "Hydrodynamic effects on active colloidal suspensions". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/665006.

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The goal of this thesis is studying hydrodynamic effects on active colloidal suspensions. Hydrodynamic interaction is propagated through the fluid in which the colloids displace due to the flow they create during their motion. It can lead to the emergence of collective phenomena, such as the self-assembly of more complex structures. Hydrodynamic interactions are not the only present in the system, since other forces may be acting between colloids, or there can be external fields acting on them such as gravity. We present our study for two different systems: magnetic colloids and Janus particles. When applying a circular magnetic field, we can induce a rotation to a particle possessing a magnetic moment. Due to the coupling of the flow with the one created by surrounding particles and with system interfaces, a rotor will eventually self-propel. Two magnetic moments interact with each other through the magnetic dipole-dipole force, which tends to align them into arrays. We study how the balance between hydrodynamic, magnetic and gravitational forces determines the morphology of the structures magnetic colloids can form. Janus particles have two faces with different chemical properties, thus the interaction between them depends on their relative orientation. We study the morphology and order of the structures that can emerge for these particles as a function of the intensity, sign and reach of the interaction between them, as well as the type of flow they create when self-propelling. Methodologically, we have combined the use of far-field theory to draw analytical expressions that have given us qualitative insight on the results we could expect with high-performance computing simulations which have allowed us to extend our study to bigger systems.
En aquesta tesi ens proposem estudiar els efectes hidrodinàmics en suspensions col·loidals actives. La interacció hidrodinàmica es propaga a través del fluid en el que es desplacen els col·loids degut al flux que ells mateixos creen durant el seu moviment, podent donar lloc a l’emergència de fenòmens col·lectius, com l’autoorganització en estructures més complexes. Les interaccions hidrodinàmiques no són les úniques presents en el sistema, ja que pot haver-hi d’altres forces actuant entre els col·loids, o podem considerar l’efecte d’altres camps com la gravetat. Presentem el nostre estudi per a dos sistemes diferents: col·loids magnètics i partícules Janus. En aplicar un camp magnètic circular, es pot induir una rotació a una partícula que posseeixi un moment magnètic. Degut a l’acoplament del flux amb el creat per altres partícules i les parets del sistema, un rotor pot acabar desplaçant-se. Dos moments magnètics interactuen entre ells mitjançant la força dipolar, que afavoreix el seu alineament i la formació de cadenes de col·loids. Estudiem com el balanç entre interaccions hidrodinàmiques, magnètiques i efectes gravitatoris afecta a la morfologia de les estructures que poden formar els col·loids magnètics. Les partícules Janus tenen dues cares amb propietats químiques diferents, quelcom que dóna lloc a una interacció entre elles que depèn de la seva orientació relativa. Estudiem les estructures que poden aparèixer per a aquestes partícules com a funció de la intensitat, signe i abast d’aquesta interacció, així com de la forma del flux que creen en desplaçar-se. Metodològicament, hem combinat expressions analítiques aproximades per tenir una idea qualitativa dels fenòmens que hom pot esperar amb simulacions per ordinador per poder estudiar els fenòmens col·lectius en sistemes de més partícules.

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Popovic, Suzana. "Design of electro-active polymer gels as actuator materials /". Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/7053.

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15

Massana-Cid, Helena. "Out-of-equilibrium dynamics in driven and active magnetic colloids". Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668374.

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In this thesis we investigate the structure formation and the out-of-equilibrium dynamics of driven and active magnetic colloids. The interactions in our system were tuned in situ by using external fields, with the aim of finding novel approaches to drive and engineer these microparticles into a rich variety of microstructures. The colloids formed chains and clusters able to transport cargos, space-filling gels and self-healing crystals. Moreover, we demonstrated the bidirectional transport of paramagnetic particles on top of a structured magnetic substrate. Because of their associated length-scale, colloids are experimentally accessible with traditional optical microscope techniques. We analysed the data extracted from digital video microscopy and used such information to infer the particle dynamics. Colloids have been proven to be excellent model systems for structures across different length scales that are more difficult to observe, such as collections of atoms and molecules. Furthermore, they are helpful test-beds to investigate fluid dynamics at low Reynolds number and can form artificial micromachines that are essential for the realization of disparate functional tasks at the microscale.
En aquesta tesi hem investigat la dinàmica fora de l'equilibri de col·loides magnètics i el seu comportament individual i col·lectiu. Controlant les interaccions utilitzant camps magnètics externs i l'activitat química de col·loides especialment sintetitzats, vam construir microdispositius nedadors capaços de transportar altres materials i formar cadenes, agrupacions, gels, i cristalls amb l'habilitat de reordenar-se. A més, vam demostrar el transport bidireccional de partícules paramagnètiques sobre un substrat magnètic. A causa de la seva mida, els col·loides són fàcilment accessibles experimentalment i es poden observar amb microscopis òptics tradicionals. Mitjançant tècniques de videomicroscopia, vam obtenir informació sobre la dinàmica fora d'equilibri dels sistemes estudiats. S'ha demostrat que els col·loides poden ser sistemes model excel·lents per estructures amb diferents escales de longitud que són més difícils d’observar. D'altra banda, els col·loides ens van ajudar a comprendre la dinàmica de fluids a baix nombre de Reynolds, el que té aplicacions en estudis de microfluídica. Aquest treball és un pas més que ens acosta a trobar un microdispositiu òptim basat en partícules col·loïdals per manipular, transportar i controlar processos a aquestes escales.

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Ginot, Félix. "Dynamical aspects of active colloids : from dilute to dense systems". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1213/document.

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Les effets collectifs sont présents dans la nature à de nombreuses échelles et dans des systèmes très différents.On peut notamment citer les vols d'oiseaux, les bancs de poissons, les nuages d'insectes, ou encore les troupeaux de moutons.Pour pouvoir décrire ces effets collectifs, il est nécessaire de disposer de systèmes expérimentaux abiotiques modèles.Dans cette thèse nous présentons un système expérimental composé de colloïdes Janus or et platine. Au contact d'eau oxygénée ces colloïdes se mettent en mouvement tout en consommant ce carburant.Ce système est donc fondamentalement hors équilibre puisque de l'énergie est consommée à l'échelle des individus. Il a la particularité de présenter des effets collectifs sous la forme de l'apparition de clusters, agrégats dynamiques de colloïdes
Collective motion are present at every scales and in very various biological systems. For example one can observe flocks of birds, schools of fishes, or swarms of insects. To be able to describe and understand these collective effects, it is necessary to have experimental abiotic model systems.In this PhD we present an experimental system made of Janus colloids of gold and platinum. When putted in an hydrogen peroxide bath, they set in motion, consuming fuel.This system is fully out of equilibirum because energy is consumed at the scale of individuals. It presents collective motion with the apparition of clusters, dynamical aggregates of active colloids.This PhD is structured around three parts :- the study of the kinetics and dynamics of the clusters- the achievement of sedimentation experiments- the study of the system in dense assemblies, forming an active colloidal glass

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17

Many, Véronique. "Synthèse et design de nanorésonateurs optiques actifs dans le visible". Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0325.

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L’étude et la réalisation de métamatériaux auto-assemblés possédant une réponse magnétique aux fréquences optiques font l’objet d’un champ de recherche très actif depuis plusieurs années. De nombreux calculs théoriques ont prédit qu’un arrangement dense de briques élémentaires plasmoniques, « les méta-atomes », conduirait à des matériaux à indice négatif actifs dans le domaine du visible. Il a été démontré qu’un nano-objet ayant un coeur de silice décoré de 12 nanoparticules d’or sphériques permettrait d’optimiser le phénomène de magnétisme optique. Ma thèse repose sur l’élaboration de ces objets à partir de particules colloïdales, parfaitement symétriques, constituées d’un coeur de silice et 12 nodules de polystyrène. Ces nodules de PS pouvant être éliminés ultérieurement par dissolution. Ces objets ont permis de fabriquer des particules de silices décorées d’un nombre précis de « patchs » ou de « fossettes ». Ces objets ont été formés en grande quantité. Nous sommes parvenus à rendre les cavités de surface des particules à fossettes collantes pour des germes d’or de 2-3 nm de diamètre et initier leur croissance. Les mesures de propriétés optiques de ces dodécapodes dorés ont reflété le couplage intense existant entre les nanoparticules plasmoniques autour du coeur diélectrique. La possibilité de faire croitre de l’argent à la surface des germes d’or permet de générer des nanorésonateurs avec des modes magnétiques optiques encore plus intenses que ceux observés pour les systèmes à base d’or
Over the last decade, the field of self-assembled metamaterials exhibiting unusual properties such as a magnetic response in the visible range represents a challenging and attracting area. Many simulations reported that a dense arrangement of specific plasmonic sub-units called “meta-atoms”, may lead to a material with a negative refractive index. It was reported by computational modelling that a dodecapod clusters made of a central dielectric core and surrounded by a controlled number of satellites (12 satellites, here) with a specific size can exhibited some interesting properties. Here, the purpose was to fabricate such clusters from colloidal particles, which are perfectly symmetrical, made of a silica core and 12 polystyrene nodules. Subsequently, those polystyrene nodules can be dissolved to get silica particles with a specific number of “patches” or “dimples”. Those objects were synthesized in a large quantity. We were able to make those dimples sticky to tiny gold seed of 2-3 nm size and to grow then for a specific size. Optical measurements reported the strong magnetic coupling in-between the plasmonic nanoparticles around the dielectric core. We also reported that growing silver on tiny gold seeds generates stronger magnetic responses than those observed from gold clusters

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18

Palla, Byron Joseph. "Mixed surfactant systems to control dispersion stability in severe environments for enhancing chemical mechanical polishing (CMP) of metal surfaces". [Florida] : State University System of Florida, 2000. http://etd.fcla.edu/etd/uf/2000/ana6408/byronpalla.PDF.

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Thesis (Ph. D.)--University of Florida, 2000.
Title from first page of PDF file. Document formatted into pages; contains xvii, 174 p.; also contains graphics. Vita. Includes bibliographical references (p. 165-173).

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19

Foffano, Giulia. "Colloidal dispersions in active and passive liquid crystalline fluids : a simulation study". Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/11756.

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In this thesis we study the physics of colloidal dispersions in active and passive liquid crystals by computer simulations. Liquid crystals are materials that exhibit long-range orientational order, with characteristics intermediate between the ones of simple, isotropic fluids and the ones of crystalline solids. Active fluids are suspensions of particles that continuously stir their ambient fluid. Like liquid crystals, active fluids undergo phase transitions to orientationally ordered phases. The framework that we apply here to describe them extends hydrodynamic equations for liquid crystals to the active case, in which their constituent particles exert local stresses on the simple fluid in which they are embedded. Studying systems of colloids embedded in these materials can be done with multiple aims. Here we use colloids as probe particles to investigate the rheological properties of active nematics. To do so we apply a constant force to a spherical particle embedded therein and define an effective viscosity, which we determine by measuring the velocity in steady state. We find an important dependence of the effective viscosity on the size of the particle, and a regime characterised by a steady state of negative drag. We also consider collective properties for systems of many colloids and analyse how they are affected by activity. We find that spontaneous flow can either hinder or favour colloidal aggregation, depending mainly on whether a fixed orientation of the liquid crystal is imposed close to the colloidal surface. This remains true independently of the initial condition chosen for the liquid crystal, which only affects the transition to spontaneous flow.

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20

Gazuz, Igor. "Active and passive particle transport in dense colloidal suspensions". [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-66299.

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21

Morin, Alexandre. "Colloidal flocks in challenging environments". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN047/document.

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Le déplacement cohérent dirigé au sein de troupeaux, d’essaims, de nuées, prend place à toutes les échelles du vivant. En cherchant à rationaliser l’émergence de tels mouvements collectifs, les physiciens ont décrit ces assemblées comme des matériaux actifs. Ces matériaux sont formés de constituants auto-propulsés qui se déplacent spontanément dans une direction commune. Cette thèse expérimentale s’appuie sur la réalisation de troupeaux synthétiques pour explorer les propriétés de la matière active polaire dans des situations défavorables à son auto-organisation : leur dynamique en milieux désordonnés et leur réponse à des perturbations externes. Des rouleurs colloïdaux aux interactions d’alignement sont confinés au sein de dispositifs microfluidiques. Au-delà d’une densité seuil, ils forment un troupeau caractérisé par l’émergence d’un ordre en orientation de longue portée. Ces troupeaux colloïdaux font office de prototypes de la matière active polaire. Nous avons étudié la réponse d’un liquide actif polaire assemblé à partir de rouleurs colloïdaux. Nous avons montré que face à une perturbation longitudinale leur réponse est hystérétique. Nous avons expliqué théoriquement ce comportement non-linéaire et l’avons exploité pour réaliser des oscillateurs microfluidiques autonomes. Nous avons également étudié la dynamique de troupeaux colloïdaux qui se propagent dans des environnements hétérogènes. La présence d’obstacles distribués aléatoirement focalise les troupeaux le long de chemins privilégiés qui forment un réseau épars et tortueux. Augmenter le désordre conduit à la destruction du troupeau. Nous avons démontré que la suppression du mouvement collectif consiste en une transition discontinue, générique à tous les matériaux actifs polaires
Directed collected motion within herds, swarms and flocks, is a phenomenon that takes place at all scales in living systems. Physicists have rationalized the emergence of such collective behavior. They have described these systems as active materials. These materials are assembled from self-propelled units that spontaneously move in the same direction. By experimentally studying synthetic flocks, this work uncovers some properties of polar active materials in situations that disfavor their self-organization: their dynamics in disordered environments and their response to external perturbations. Colloidal rollers with alignment interactions are confined within microfluidic devices. At high density, they spontaneously form a flock which is characterized by the emergence of orientational long-ranged order. These colloidal flocks are prototypical realizations of polar active matter. We have studied the response of a polar active liquid assembled from colloidal rollers. We have shown that they display a hysteretic response to longitudinal perturbations. We have theoretically accounted for this non-linear behavior. We have used this behavior to realize autonomous microfluidic oscillators. We have also studied the dynamics of colloidal flocks that propagate through heterogeneous environments. Randomly positioned obstacles focalize flocks along favored channels that form a sparse and tortuous network. Increasing disorder leads to the destruction of flocks. We have demonstrated that the suppression of collective motion is a discontinuous transition generic to all polar active materials

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22

Balin, Andrew. "Statistical mechanics of colloids and active matter in and out of equilibrium". Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:2941a082-82ca-400b-ae6b-7c22e75cc90c.

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Thermal and viscous forces compete for dominance at the microscopic length-scales which govern the behaviour of many soft or biological systems. We study three systems of increasing complexity with the central goal of understanding the statistical or hydrodynamic nature of their mechanics. First we study experiments that have been conducted on ferromagnetic colloidal rods. At equilibrium, the magnetically pinned rod is observed to randomly flip between two orientational states, which our theoretical analysis shows is due to a competition between entropic and Hamiltonian forces. We show analytically how entropic forces can arise by considering the coupling between observed and unobserved variables of a system. Experiments in which a rod is driven out of equilibrium by a rotating field display three phases of steady-state behaviour as a function of driving frequency. Using Brownian dynamics simulations we match the lower critical frequency to the experimentally obtained values, showing that thermal fluctuations play an important role in this regime and propose a simple argument to demonstrate that hydrodynamic interactions between the substrate and rod affect the upper critical frequency. We then turn to the biophysical topic of cell locomotion in viscoelastic media. In order to study how bacterial flagella interact with similarly-sized polymers in their environment, we construct a Stokesian dynamics model of a helical filament and bead--spring polymer. Simulating their interaction first for a pinned--rotating helix, then for a swimming helix, we demonstrate that large polymers become hydrodynamically entrained by the flagellum and coil around it, causing both pinned and swimming flagella to expend more work. For the swimming helix, this results in a reduction of swimming speed on average. Finally, we consider an active nematic fluid confined to a channel and show that the inclusion of a passive colloid induces a global state of coherent flow maintained by the intrinsic activity of the system. This flow is persistent, and transports the colloid with it along the channel. By this mechanism, a passive colloid is able to spontaneously induce its own transport through an otherwise quiescent fluid.

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23

Katuri, Jaideep. "Guiding active particles through surface interactions". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/663989.

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Living organisms and systems are continually converting energy, either internally stored or transduced from their surroundings, into motion. This activity and the resulting self-propulsion constantly push these biological systems out of thermal equilibrium. A number of exotic phenomenon result from the intrinsic non-equilibrium nature of these living systems, that are not accessible in a system at thermal equilibrium. In recent years, these ubiquitous non-equilibrium systems have come to be classified as active matter. Active matter, by definition, refers to systems composed of active units, each capable of converting ambient or stored energy into systematic movement. Examples range from the sub-micrometer scale, with microtubules associated with motor proteins in the cytoplasm, to the micrometer length scales of swimming bacteria, and the meter-length scales of greater familiarity, such as that of fish and birds. There are two common themes that run through all these active matter systems. The first is the emergence of correlated collective phenomenon through particle-particle interactions as exemplified in flocking of birds, swarming of bacteria and crystallization of self-propelled particles. And the second is the ability of the active units to interact with their surroundings through self-propulsion. Common examples of this include chemotaxis and rheotaxis, observed in many biological systems. In this thesis, I have focussed on studying the ability of artificial active matter systems to respond to their local environment. As a model active matter system, we use colloidal active particles, that propel due to self-diffusiophoresis. These particles coated with two different materials on each half are referred to as Janus particles. In a solution of H2O2, one of the sides has catalytic properties (Pt), while the other half remains inert (SiO2). This creates a concentration gradient of the reaction product along the surface of the particle and induces a phoretic slip, which propels the particle. We study the dynamics of these self-phoretic particles close to solid surfaces. The particles interact with their surroundings via hydrodynamic and phoretic effects and we observe that when confined closed to a surface, a strong alignment interaction comes into play. This effect can be used to guide micron sized active particles along predetermined pathways. We then exploit this alignment interaction to design micropatterned ratchets capable of generating a strong directional flow of active particles. A different geometry of the same system can also be used to accumulate active particles in confined areas. Finally, we study the influence of an applied external shear flow on the dynamics of active particles near surfaces. We find that a strong directional response emerges for the active particles in the direction perpendicular to the flow direction leading to the cross-stream migration of active particles. This response is dependent on the applied shear flow and the propulsion velocity of the particle, potentially opening up a possibility to sort particles of different activities based on their response to shear flows. Overall, our results indicate that active particles can have a strong directional response in certain environments allowing us to engineer ways of guiding them.
Los organismos y sistemas vivos convierten energía almacenada internamente o derivada de sus alrededores en movimiento de forma continua. Esta actividad puede causar una constante auto-propulsión que lleva a estos sistemas a un estado fuera de equilibrio térmico. Gracias a esto, aparecen un gran número de fenómenos exóticos que no son accesibles para un sistema que se encuentra en equilibrio térmico. En los últimos años se ha clasificado a estos sistemas de no equilibro como “material activa”. La materia activa, por definición, incluye los sistemas compuestos de unidades activas, cada una de ellas capaz de convertir la energía almacenada o del entorno en movimiento sistemático. Existen varios ejemplos que van desde la escala sub-micrométrica, donde podemos encontrar a los microtúbulos asociados a proteínas motoras en el citoplasma, a las grandes escalas, donde se encuentran sistemas más familiares como peces o pájaros, pasando por la escala micrométrica, donde nadan las bacterias. Podemos diferenciar dos temas principales que se manifiestan en todos estos sistemas de materia activa. El primero es la aparición de fenómenos colectivos correlacionados a través de interacciones partícula-partícula, como ocurre en bandadas de pájaros, enjambres bacterianos y la cristalización de partículas auto-propulsadas. El segundo es la capacidad de estas unidades activas de interaccionar con sus alrededores a través del fenómeno de la auto-propulsión, por ejemplo, a través de quimiotaxia o reotaxia, como se puede observar en muchos sistemas biológicos y que ya han sido reportados en varios estudios. En esta tesis, me he enfocado en el estudio de este último tema principal: la interacción de partículas activas con su entorno local. Como modelo de sistema de materia activa, usamos partículas activas coloidales que se propulsan gracias al fenómeno de auto-difusioforesis. Estas partículas están recubiertas por dos materiales diferentes en cada una de sus caras, y son comúnmente llamadas “partículas Janus”. Una de sus caras está recubierta con Pt, material que cataliza la descomposición de H2O2, mientras que la otra cara está recubierta de un material inerte (SiO2). En una solución de H2O2, la reacción que ocurre en la parte catalítica produce un gradiente de concentración de producto a lo largo de la superficie de la partícula e induce un deslizamiento forético que la propulsa. En esta tesis se ha estudiado la dinámica de estas partículas "autoforéticas" cerca de superficies sólidas. De manera natural, las partículas interaccionan con su alrededor debido a los efectos foréticos e hidrodinámicos. Cuando estas partículas se hayan confinadas cerca de una superficie, observamos que se origina en ellas una fuerte interacción de alineamiento. A partir de ello, consideramos interesante diseñar ratchets micro estampados capaces de generar un flujo direccional de partículas activas. Por otra parte, estudiamos la influencia de aplicar un flujo de cizalla externo en la dinámica de las partículas activas cerca de superficies. A consecuencia del flujo externo, encontramos que en el sistema emerge una respuesta fuertemente direccional para las partículas activas en la dirección perpendicular al flujo provocando una migración "cross-stream" de partículas activas.

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24

Wittkowski, Raphael [Verfasser]. "Brownian dynamics of active and passive anisotropic colloidal particles / Raphael Wittkowski". Aachen : Shaker, 2012. http://d-nb.info/1066197733/34.

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25

Harrer, Christian Josef [Verfasser]. "Active and Nonlinear Microrheology of Dense Colloidal Suspensions / Christian Josef Harrer". Konstanz : Bibliothek der Universität Konstanz, 2013. http://d-nb.info/1041224648/34.

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26

Guillamat, Bassedas Pau. "Control of active flows through soft interfaces". Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/404355.

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Groups of animals, bacterial colonies, cellular tissues and assemblies of subcellular extracts are some examples of experimental systems studied in the field of Active Soft Matter. All of them are composed of autonomous self-propelled units that consume and transform energy to generate mechanical work. The interaction between these motile units lead to the emergence of cooperative spatiotemporal patterns, not observed in complex fluids in equilibrium. Despite the morphology and dynamics of these systems are being studied in detail, there is still absence of true control capabilities, which could bring new possibilities in the use or application of active flows. To this end, this thesis aims at the development of strategies to condition active flows by means of non-invasive bounds, namely rheological patterning and confinement, as a tool towards the control of the intrinsic unpredictable chaotic behaviour of active matter systems. The experimental system used here is an active gel based on a mixture of cytoskeletal proteins, created in the laboratory of Z. Dogic from Brandeis University (MA, USA) in 2012. In brief, ATP-fuelled kinesin motor clusters crosslink and drive bundled microtubules, giving rise to an active network of biofilaments that develops far from thermodynamic equilibrium. The active gel can also self-organize at soft interfaces, where it forms a quasi-2d active nematic liquid crystal, which features spontaneous turbulent-like flows. In this thesis, first, we report experimental evidence of the existence of strong hydrodynamic coupling at the oil/water interface, where the active nematic resides, and the influence of the rheological properties of the oil phase. By changing the viscosity of the contacting oily fluid, we alter the morphology and dynamics of the active nematic, which we have characterized. In addition, in collaboration with M. C. Marchetti and S. Shankar from Syracuse University (NY, USA), we have fitted specific data to a hydrodynamical model in order to extract an estimate value for the viscosity of the active material. Second, based on these observations, and with the objective of steering the active flows, we impose viscosity patterns at the interface. For this purpose, we use a thermotropic liquid crystal, which self-assemble in well-known structures with marked anisotropic viscosity, externally- and in situ-tuneable by means of temperature and/or external fields. Under such rheological constraints, the active nematic flows are commanded at will, rapidly organizing either in localized rotating swirls or parallel stripes of aligned microtubule bundles. Through this process, we have also had the opportunity to study the interaction between active and passive nematic liquid crystals, which in this case, serve as reporters of the active flows. Finally, we prepare active emulsions by dispersing droplets of active gel in different fluids. Inside droplets, the active gel condenses at the inner surfaces to create an active nematic spherical shell, which develops in geometrically and topologically constrained conditions. Due to the confinement restrictions, the active nematic develops strikingly periodic dynamics that transmit coherent flows into the confining phase. Here, with experiments and simulations performed by M. Ravnik and Ž. Kos from the University of Ljubljana (Slovenia), we study emulsions of droplets with an active nematic shell dispersed in thermotropic nematic liquid crystals. In particular, we focus on the interaction between active flows and the usually static topological defects induced around inclusions in liquid crystals. To conclude, this work not only increases our fundamental knowledge of both thermotropic (passive) and active nematic liquid crystals but it serves as a starting platform to explore the interaction between these two fluid ordered analogues at the interface. Special emphasis will be put on the implementation of anisotropic patterns at interfaces as it has demonstrated to be key towards controlling active flows.
Sistemes compostos per grups d’animals, colònies de bacteris, teixits de cèl·lules o assemblatges d’extractes cel·lulars, mostren comportaments dinàmics complexos significativament similars tot i que, evidentment, es desenvolupen a escales espai-temps molt diverses. Aquests sistemes, anomenats sistemes actius, estan generalment formats per unitats individuals auto-propulsades que consumeixen energia de l’ambient, a partir de la qual generen forces i treball mecànic. La interacció entre els constituents d’aquests sistemes propicia moviments col·lectius i cooperatius, així com patrons de flux que no s’observen en sistemes similars en equilibri termodinàmic. Tot i que les característiques morfològiques i dinàmiques d’aquests sistemes s’estan estudiant amb detall, manquen encara estratègies per controlar els fluxos actius que se’n deriven. L’habilitat de controlar sistemes actius, no només en facilita la seva caracterització sinó que possibilita l’aplicació dels fluxos que se’n deriven, per exemple, en dispositius. Amb aquest objectiu, aquesta tesi se centra en el desenvolupament d’estratègies per al condicionament i control de fluxos actius mitjançant constriccions que procuren ser no invasives per als materials implicats. El material estudiat consisteix en un gel actiu aquós format per agregats de microtúbuls, reticulats per complexos de motors moleculars. En presència d’Adenosina trifosfat (ATP), els complexos motors exerceixen forces de cisalla locals entre els microtúbuls que, globalment, provoquen contínuament l’extensió, flexió i trencament dels agregats filamentosos. La interacció entre els constituents actius genera fluxos turbulents a escales molt més grans que les pròpies de les unitats constitutives del material. D’altra banda, en presència d’una interfície aigua/oli correctament funcionalitzada, el gel es pot densificar, desenvolupant els seus fluxos en contacte amb la fase oliosa. D’aquesta manera, s’obté un material actiu quasi-bidimensional molt dens, en el qual els filaments interaccionen entre si i s’organitzen en el pla donant lloc a un gel actiu amb ordre orientational. En particular, en aquesta tesi, s’estudiarà l’efecte de l’acoblament hidrodinàmic d’aquest material amb fluids viscosos isotròpics, amb patrons reològics imposats per cristalls líquids i en confinament, com a eines per al control dels fluxos, fins ara, aparentment caòtics i impredictibles d’aquests sistemes actius.

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27

Da, Rocha Sandro Roberto Possatti. "CO₂-water interface : interfacial tension, emulsions, microemulsions, and computer simulations /". Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004246.

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Das, Shibananda [Verfasser], Gerhard [Gutachter] Gompper y Andreas [Gutachter] Schadschneider. "Dynamical structure formation in passive and active colloidal systems / Shibananda Das ; Gutachter: Gerhard Gompper, Andreas Schadschneider". Köln : Universitäts- und Stadtbibliothek Köln, 2018. http://d-nb.info/1160379327/34.

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29

El, Ismaili Mohammed. "Out-of-equilibrium Binary Colloidal Mixtures : Experimental magnetic system and simulations of active Lennard-Jones mixtures". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0172.

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Les systèmes vivants consomment continuellement de l'énergie et ont ainsi accès à des états hors-équilibre qui leur confèrent des propriétés fascinantes. L'étude physique des systèmes vivants repose souvent sur des analogies avec des systèmes de la matière molle, tels que les colloïdes. Dans cette thèse, nous investiguons deux systèmes colloïdaux bidimensionnels hors l'équilibre thermodynamique, qui présentent des phénomènes d'auto-assemblage, de viscoélasticité, de transitions de phase et de ségrégation semblables à ceux de certains systèmes biologiques. Dans la première partie de la thèse, nous étudions expérimentalement et théoriquement la dynamique des agrégats de colloïdes paramagnétiques sous un champ magnétique tournant, qui agit comme une source constante d'énergie. Nous caractérisons la dynamique de rotation des agrégats, que nous expliquons par un modèle théorique qui décrit l'émergence de propriétés viscoélastiques collectives. Le modèle capture avec succès la dépendance entre la vitesse de rotation mesurée et les caractéristiques des particules, des agrégats et du champ, et il fournit une estimation de la viscoélasticité de l'agrégat. Nous étendons notre étude au cas des agrégats binaires de deux types de colloïdes, qui ont des tailles et des susceptibilités magnétiques différentes. La dynamique des agrégats en fonction des compositions est correctement décrite par notre modèle théorique généralisé. Nous caractérisons également l'évolution de la structure de ces agrégats binaires, qui rappelle la ségrégation entre deux liquides non miscibles. Motivés par les phénomènes d'étalement des agrégats vivants, nous étudions ensuite le désassemblage d'un agrégat de colloïdes en réponse à un changement du champ magnétique externe, par expérience et théorie. Dans la deuxième partie de la thèse, nous étudions un mélange binaire de colloïdes de Lennard-Jones actifs et passifs, caractérisés par deux températures effectives différentes, ce qui correspond à une différence d'activité scalaire. Nous effectuons des simulations de dynamique moléculaire où les deux types de colloïdes sont couplés à deux thermostats différents. Nous nous intéressons à deux systèmes de référence à l'équilibre thermodynamique : un mélange homogène et un système interfacial gaz-liquide. Nous amenons ces systèmes à des états stationnaires hors-équilibre en introduisant une différence de température effective entre les deux espèces, et nous étudions systématiquement les changements de structure et propriétés qui en résultent. Pour le système homogène, l'introduction d'une différence d'activité entre les deux espèces déplace le mélange du solide vers l'état liquide et le rend plus déformable que ce qui correspondrait à la température effective moyenne du système. Lorsque la différence d'activité dépasse un certain seuil, des phénomènes de ségrégation sont observés. Pour le système interfacial, nous étudions l'effet de l'activité sur une interface gaz-liquide pré-existante entre deux espèces séparées. Nous constatons qu'une différence d'activité élevée induit la formation de nouvelles interfaces solide-liquide, tandis qu'une différence faible déstabilise les interfaces liquide-gaz préexistantes. De plus, la combinaison d'une interface préexistante avec une activité différentielle conduit à une cristallisation partielle et donc à une coexistence de trois phases (solide, liquide et gaz). Les résultats obtenus dans ces systèmes idéalisés pourraient guider notre compréhension et mettre en évidence des mécanismes physiques présents dans les systèmes biologiques, où des comportements dynamiques similaires sont observés
Living systems generally operate in non-equilibrium states by continuously consuming energy, thus exhibiting rich collective dynamics and properties. Physical investigations often rely on analogies with model systems in soft matter, such as colloids. In this thesis, we develop two colloidal model systems that operate in non-equilibrium states and exhibit interesting phenomena similar to those of certain biological systems, such as self-assembly, viscoelasticity, phase transitions, and segregation. In the first part of this thesis, we study experimentally and theoretically the dynamics of two-dimensional clusters of paramagnetic colloids under a time-varying magnetic field. Due to the continuous energy input by the rotating field, these self-assembled clusters are at a dissipative non-equilibrium state. We experimentally characterize the dynamics of cluster rotation and we develop a theoretical model to explain the observations by the emergence of collective viscoelastic properties. The model successfully captures the observed dependence on particle, cluster, and field characteristics, and it provides an estimate of cluster viscoelasticity. We extend our study to the case of binary clusters of colloids of two different sizes and magnetic susceptibilities. The composition dependence of the rotation dynamics is successfully captured by a generalization of our theoretical model. We also investigate the evolution of the internal distribution of the two particle types, reminiscent of segregation in a drop of two immiscible liquids, and the effect of such structure on the rotation dynamics. Next, we study cluster disassembly in response to a change in the external field. The experimentally observed disassembly dynamics are successfully described by a model, which moreover provides an estimate of the particle-substrate friction coefficient. In the second part of the thesis, we investigate a two-dimensional binary mixture of active and passive Lennard-Jones colloids, characterized by different degrees of scalar activity, modeled by an effective temperature difference. We perform molecular dynamics simulations of this system using two different thermostats. We consider two equilibrium reference systems: a homogeneous system and a gas-liquid interfacial system. We drive these systems out-of-equilibrium by increasing the effective temperature difference and we systematically investigate the effect on their behaviors and properties. For the homogeneous system, our results indicate that the presence of differential activity shifts the mixture from solid towards the liquid state and renders it more deformable than a homogeneous state at the average temperature. The binary mixture remains homogeneous for moderate activity difference between the two species, and segregation arises for a sufficiently large activity difference. For the interfacial system, we investigate the effect of activity on a pre-existing gas-liquid interface between two separated species. We find that a high activity difference induces the formation of new solid-liquid interfaces, whereas a low difference destabilizes pre-existing liquid-gas interfaces. Moreover, the combination of a pre-existent interface with differential activity leads to partial crystallization and thus to triple phase coexistence (solid, liquid, and gas), which is observed over a wide range of differential activities. Our findings from these idealized systems could guide our understanding and point to certain physical mechanisms at play in biological systems, where similar dynamical behaviors are observed

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30

Hardin, James. "Encapsulation and controlled release of active DNA from uncrosslinked gelatin microspheres". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43735.

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Cancer is a disease that varies dramatically from person to person due to the specifics of the individual's physiology and the source of the cancer. In most cases, the origin of the cancer can be determined but metastasis can lead to tumors anywhere and thus many cancers require treatment of the whole body. Since many of the drugs that are used to treat cancer are toxic to healthy cells as well as cancerous ones, there has been considerable interest in developing ways to convey the drug specifically to the cancer cells with minimal exposure to healthy cells. Colloid drug delivery vehicles have shown considerable progress toward this end, while also reducing degradation of the drug prior to delivery to targeted sites (particularly important for oligonucleotide and protein therapeutics), and controlling release rates. Toward the end of improved drug delivery, this thesis work investigates the encapsulation of DNA in gelatin microspheres (GMS) and the subsequent temperature controlled release of the encapsulated DNA from these GMS. DNA-loaded GMS were then used as templates for colloidal satellite assemblies and the released DNA was shown to competitively displace the original partner strands of immobilized DNA on the surface of the assemblies. To support these investigations, hybridization of DNA at colloidal surfaces was also investigated using in situ measurements and found to significantly deviate from solution behavior. DNA hybridization is of particular interest as means of controlling the functionality of colloidal structures because it is uniquely reversible and tunable as well as biocompatible. Gelatin was chosen as the encapsulation matrix for its superior biocompatibility, convenient gel to liquid phase transition at ~35 oC, and economical availability.

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Choimet, Maëla. "Particules colloïdales multifonctionnalisées pour la vectorisation d'un principe actif : vers une nouvelle formulation pour la dermatologie". Thesis, Toulouse, INPT, 2016. http://www.theses.fr/2016INPT0129/document.

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L’acné est la dermatose la plus courante dans le monde. Cette pathologie, à causes multiples, peut impliquer des traitements longs dont l’efficacité reste à améliorer. Au niveau topique, le ciblage de la surface cutanée et en particulier des foyers infectieux (impliquant notamment la bactérie P. acnes) est un axe de recherche visant un meilleur traitement de la pathologie. Ces travaux de thèse s’inscrivent dans cet objectif, et portent sur l’utilisation de particules submicroniques minéral-organiques à base d’apatites bio-inspirées pour le traitement de l’acné en vue de la vectorisation d’un antibiotique via une nouvelle formulation galénique. Dans un premier temps, les recherches se sont focalisées sur l’élaboration et la caractérisation physico-chimique de particules apatitiques préparées en présence d’un agent dispersant. Parmi les conditions testées, un protocole de référence permettant d’obtenir une suspension colloïdale de particules d’apatite de diamètre hydrodynamique moyen (DLS) de 180 nm, stabilisées à l’aide d’un polyéthylène glycol phosphonaté, a été retenu. L’analyse des particules par DRX et IRTF a mis en évidence le caractère nanocristallin biomimétique de la phase apatitique. Dans un second temps, l’adsorption d’une molécule modèle phosphatée puis d’un antibiotique – le phosphate de clindamycine (ClindP) – a été quantifiée et analysée à l’aide de différents modèles d’adsorption. Par ailleurs, la possibilité d’une incorporation d’ions biologiquement actifs (ex : antibactériens, antiinflammatoires) tels que Cu2+ et/ou Zn2+ dans l’apatite colloïdale a été établie. Dans un troisième temps, des évaluations biologiques ainsi que divers essais de suivi des particules ont été entrepris. L’interaction avec des éléments du sang – globules rouges et protéines plasmatiques – a été explorée (dans l’éventualité d’une application sur peau lésée), mettant en évidence l’excellente hémocompatibilité de ces particules colloïdales. Différentes techniques de suivi des particules ont ensuite été abordées sur membranes synthétiques et sur explants d’oreilles de porcs, telles que l’utilisation de cellules de Franz en modes statique et dynamique, ou encore la microscopie confocale Raman. Les résultats obtenus indiquent que cette dernière technique est adaptée à l’étude de la localisation cutanée de ces particules colloïdales, et montrent une accumulation de celles-ci au niveau de l’épiderme et des follicules pileux. Enfin, une étude préliminaire d’élaboration et de caractérisation d’une forme galénique (bigel) a été abordée
Acne is the most frequent dermatosis in the world. This multifaceted pathology may necessitate long-term treatments which can be improved. For a topical application, the idea of targeting the skin surface and in particular infected pilosebaceous units (involving bacteria such as P. acnes) is one approach for a better treatment of this pathology. This thesis work follows this objective, and deals with the use of submicron mineral-organic particles based on bio-inspired apatite for the treatment of acne, in view of drug delivery via a new galenic formulation. In a first stage, research was focused on the synthesis and physicochemical characterization of apatitic particles prepared in the presence of a dispersing agent. Among the tested conditions, a reference protocol was retained, allowing the obtainment of a colloidal suspension of apatite particles with a mean hydrodynamic diameter (DLS) of 180 nm, stabilized with phosphonated polyethyleneglycol. XRD and FTIR evidenced the biomimetic nanocrystalline nature of the apatitic phase. In a second stage, the adsorption of a model phosphate molecule and then of an antibiotic – clindamycin phosphate (ClindP) – was quantified and analyzed with regard to various adsorption models. Moreover, the possibility to incorporate biologically-active ions (e.g. antibacterial, antiinflammatory) such as Cu2+ and/or Zn2+ in colloidal apatite was established. In a third part, biological evaluations as well as particle follow-up experiments were performed: the interaction with blood components – red blood cells and plasma proteins – was explored (in the eventuality of application on damaged skin), evidencing the excellent hemocompatibility of these colloidal particles. Various particle follow-up techniques were then considered, involving synthetic membranes and porcine ear skin, such as the use of Franz cells in static and dynamic modes or else Raman confocal microscopy. Results indicate that the latter technique is suitable for the study of the localization of these colloidal particles within the skin, and point out their accumulation on the epidermis and hair follicles. Finally, a preliminary study was carried out on the setup and characterization of a galenic form (bigel)

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Wittkowski, Raphael [Verfasser], Hartmut [Akademischer Betreuer] Löwen, Helmut [Akademischer Betreuer] Brand y Holger [Akademischer Betreuer] Stark. "Brownian dynamics of active and passive anisotropic colloidal particles / Raphael Wittkowski. Gutachter: Helmut Brand ; Holger Stark. Betreuer: Hartmut Löwen". Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2012. http://d-nb.info/1024161064/34.

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Liao, Guo-Jun [Verfasser], Sabine [Akademischer Betreuer] Klapp, Sabine [Gutachter] Klapp y Felix [Gutachter] Höfling. "Self-assembly and pattern formation of complex active colloids in two dimensions / Guo-Jun Liao ; Gutachter: Sabine Klapp, Felix Höfling ; Betreuer: Sabine Klapp". Berlin : Technische Universität Berlin, 2021. http://d-nb.info/1238143105/34.

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Planade, Jessica. "Etude du rôle des protéines partenaires de l'actine dans la mécanique des gels branchés de levure". Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC285/document.

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Par ce travail expérimental, nous essayons d’établir un lien entre les propriétés mécaniques de gels d’actine branchés de levure et la composition biochimique des réseaux. L’actine est un polymère semi-flexible qui fait partie du cytosquelette. De nombreux partenaires protéiques de l’actine (notés ABPs par la suite) se lient aux filaments d’actine et les agencent en différents types de réseaux. Arp2/3 est un complexe protéique qui génère la croissance de réseaux d’actine branchés. Les réseaux d’actine branchés en croissance intéressent tout particulièrement physiciens comme biologistes car ils sont capables de développer des forces nécessaires à de nombreux processus vitaux pour la cellule, comme l’endocytose. Nous avons ici étudié les propriétés mécaniques de gels d’actine branchés reconstitués in vitro, en nous focalisant sur le rôle d’un type d’ABPs en particulier, les protéines de réticulation. Il nous a été possible de quantifier et de comparer l’effet de trois protéines de réticulation différentes sur la mécanique des réseaux d’actine branchés de levure.Afin de mener à bien cette étude, nous avons combiné deux puissantes techniques expérimentales.Nous avons utilisé une technique de mesure des propriétés mécaniques basée sur l’utilisation de colloïdes superparamagnétiques développée au laboratoire. Cette technique permet de réaliser des mesures quantitatives et à haut débit sur des gels polymères très fins (quelques centaines de nanomètres d’épaisseur). Les réseaux ont été reconstitués in vitro grâce à la fonctionnalisation des billes superparamagnétiques avec Las17, une protéine que notre collaborateur biologiste a identifiée comme suffisant à activer Arp2/3 chez la levure. Nous avons de plus combiné deux approches complémentaires en travaillant à la fois sur des extraits cellulaires de levure contenant toutes les ABPs des réseaux Arp2/3 et à la fois sur des mélanges de quelques protéines purifiées.L’approche « top-down » est basée sur l’utilisation d’extraits cellulaires de mutants de la levure n’exprimant pas une ou des protéine(s) d’intérêt(s), et l’approche « bottom-up » sur l’addition de la protéine étudiée dans le système simplifié de quelques protéines purifiées
In this experimental work we tried to quantify the mechanical properties of yeast branchedactin networks with regard to their biochemical composition. Actin is a semi-flexible biopolymerthat is assembled as part of the cytoskeleton. Proteins partners of actin (ABPs) shape itsfilaments into different type of networks. Arp2/3 is a protein complex that has the propertyto generate branched actin gels. Growing branched actin networks are of particular interest forboth biologists and physicists because of their ability to generate forces necessary to many vitalprocesses such as endocytosis. Here we study in vitro the mechanical properties of such networks,and we focus on the role of one type of actin binding proteins, the crosslinkers. This family ofproteins appears to play a role in both the elastic, viscous and plastic properties of the gels. Weare able to quantify and to compare the impact of three different crosslinkers on branched actinnetworks in yeast.In order to conduct said study, we combined two powerful experimental methods. We used asuperparamagnetic particle-based mechanical measurement technique that was developed in thelab and allows quantitative, high-throughput measurements on very thin gels. And the networkswere reconstituted in vitro by functionalization of the magnetic particles with Las17, which hasbeen showed to activate Arp2/3 for the yeast by our biologist collaborator. We furthermoreworked on both yeast extracts containing all the ABPs of the Arp2/3 networks, and with setsof a few purified proteins, in order to combine a « top-down » (use of mutations in yeast toprevent the expression of protein(s) of interest) and a « bottom-up » (addition of a protein ofinterest in a simplified system) approaches

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Li, Run [Verfasser], Gerhard [Gutachter] Gompper, Matthias [Gutachter] Sperl y Marisol [Gutachter] Ripoll. "Hydrodynamics of colloidal ellipsoids and helices under shear flow and active deformation / Run Li ; Gutachter: Gerhard Gompper, Matthias Sperl, Marisol Ripoll". Köln : Universitäts- und Stadtbibliothek Köln, 2019. http://d-nb.info/1188810847/34.

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Arya, Pooja [Verfasser], Svetlana [Akademischer Betreuer] Santer, Svetlana [Gutachter] Santer, Carsten [Gutachter] Beta y Holger [Gutachter] Stark. "Light controlled active and passive motion of colloidal particles / Pooja Arya ; Gutachter: Svetlana Santer, Carsten Beta, Holger Stark ; Betreuer: Svetlana Santer". Potsdam : Universität Potsdam, 2020. http://d-nb.info/1223022471/34.

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Arya, Pooja [Verfasser], Svetlana [Akademischer Betreuer] Santer, Svetlana Gutachter] Santer, Carsten [Gutachter] [Beta y Holger [Gutachter] Stark. "Light controlled active and passive motion of colloidal particles / Pooja Arya ; Gutachter: Svetlana Santer, Carsten Beta, Holger Stark ; Betreuer: Svetlana Santer". Potsdam : Universität Potsdam, 2020. http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483880.

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38

Lefranc, Thibault. "Quorum sensing dans des assemblées de particules actives synthétiques : Séparation de phase induite par la motilité". Electronic Thesis or Diss., Lyon, École normale supérieure, 2023. https://theses.hal.science/tel-04510010.

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On définit la matière active comme une assemblée de particules capables de transformer à leur échelle l'énergie en mouvement. Les exemples de matière active sont nombreux dans la nature, allant de la colonie de bactérie au troupeau de zèbres en passant par les bancs de poissons et les foules humaines. Malgré ce mouvement perpétuel des individus, il est possible dans certains cas d'observer une séparation de phase, c'est-à-dire la formation de zones définies de densités différentes. Ceci peut s'expliquer par la détection de quorum : les particules tiennent compte de leurs voisines pour ajuster leur activité. Depuis une dizaine d'années, l'ensemble des briques élémentaires de la matière molle (polymères, colloïdes, ...) ont été motorisées pour fabriquer de la matière active en laboratoire. Cependant aucune forme de détection du quorum synthétique n'a été rapportée jusqu'à aujourd'hui. Dans cette thèse, nous présentons les premiers résultats permettant de montrer la possibilité de créer une forme simple de détection de quorum en laboratoire. Pour cela nous avons choisi comme élément de base un bâtonnet colloïdal. Nous présentons d'abord une analyse théorique expliquant le comportement de bâtonnets actifs. Cette analyse est une extension aux particules anisotropes du phénomène d'électrorotation de Quincke, déjà utilisé pour rendre des sphères actives. Elle permet de mettre en lumière le comportement plus riche des bâtonnets. Puis nous détaillons la démarche expérimentale pour la mise en œuvre concrète de la motorisation de ces colloïdes actifs, qui est au cœur de ces travaux de thèse. Enfin, nous rapportons les résultats obtenus, qui indiquent une première réalisation expérimentale de détection de quorum artificielle, avec notamment l'observation et la caractérisation d'une séparation de phase induite par la motilité conditionnelle des particules
Active matter is defined as an assembly of particles capable of transforming energy into movement on their own scale. There are many examples of active matter in nature, from a colony of bacteria to a flock of zebras, from school of fishes to human crowds. Despite this perpetual movement of individuals, it is possible in some cases to observe phase separation, i.e. the formation of defined zones of different densities. This can be explained by the detection of quorum: particles take account of their neighbors to adjust their activity. Over the last ten years or so, all the building blocks of soft matter (polymers, colloids, etc.) have been motorized to produce active materials in the laboratory. However, no form of synthetic quorum sensing has yet been reported. In this thesis, we present the first results demonstrating the possibility of creating a simple form of quorum sensing in the laboratory. For this purpose, we have chosen a colloidal rod as the basic element. We first present a theoretical analysis explaining the behavior of active rods. This analysis is an extension to anisotropic particles of Quincke's electrorotation phenomenon, already used to render spheres active. It sheds light on the richer behavior of rods. We then detail the experimental approach for the concrete implementation of motorization of these active colloids, which is at the heart of this thesis work. Finally, we report on the results obtained, which indicate a first experimental realization of artificial quorum sensing, including the observation and characterization of a phase separation induced by conditional particle motility

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Aland, Sebastian. "Modelling of two-phase flow with surface active particles". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-92397.

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Kolloidpartikel die von zwei nicht mischbaren Fluiden benetzt werden, tendieren dazu sich an der fluiden Grenzfläche aufzuhalten um die Oberflächenspannung zu minimieren. Bei genügender Anzahl solcher Kolloide werden diese zusammengedrückt und lassen die fluide Grenzfläche erstarren. Das gesamte System aus Fluiden und Kolloiden bildet dann eine spezielle Emulsion mit interessanten Eigenschaften. In dieser Arbeit wird ein kontinuum Model für solche Systeme entwickelt, basierend auf den Prinzipien der Massenerhaltung und der themodynamischen Konsistenz. Dabei wird die makroskopische Zwei-Phasen-Strömung durch eine Navier-Stokes Cahn-Hilliard Gleichung modelliert und die mikroskopischen Partikel an der fluiden Grenzfläche durch einen Phase-Field-Crystal Ansatz beschrieben. Zur Evaluation des verwendeten Strömungsmodells wird ein Test verschiedener Navier-Stokes Cahn-Hilliard Modelle anhand eines bekannten Benchmark Szenarios durchgeführt. Die Ergebnisse werden mit denen von anderen Methoden zur Simulation von Zwei-Phasen-Strömungen verglichen. Desweiteren wird eine neue Methode zur Simulation von Zwei-Phasen-Strömungen in komplexen Gebieten vorgestellt. Dabei wird die komplexe Geometrie implizit durch eine Phasenfeldvariable beschrieben, welche die charakteristische Funktion des Gebietes approximiert. Die Strömungsgleichungen werden dementsprechend so umformuliert, dass sie in einem größeren und einfacheren Gebiet gelten, wobei die Randbedingungen implizit durch zusätzliche Quellterme eingebracht werden. Zur Einarbeitung der Oberflächenkolloide in das Strömungsmodell wird schließlich die Variation der freien Energie des Gesamtsystems betrachtet. Dabei wird die Energie der Partikel durch die Phase-Field-Crystal Energie approximiert und die Energie der Oberfläche durch die Ginzburg-Landau Energie. Eine Variation der Gesamtenergie liefert dann die Phase-Field-Crystal Gleichung und die Navier-Stokes Cahn-Hilliard Gleichungen mit zusätzlichen elastischen Spannunngen. Zur Validierung des Ansatzes wird auch eine sharp interface Version der Gleichungen hergeleitet und mit der zuvor hergeleiteten diffuse interface Version abgeglichen. Die Diskretisierung der erhaltenen Gleichungen erfolgt durch Finiten Elemente in Kombination mit einem semi-impliziten Euler Verfahren. Durch numerische Simulationen wird die Anwendbarkeit des Modells gezeigt und bestätigt, dass die oberflächenaktiven Kolloide die fluide Grenzfläche hinreichend steif machen können um externen Kräften entgegenzuwirken und das gesamte System zu stabilisieren
Colloid particles that are partially wetted by two immiscible fluids can become confined to fluidfluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids compose an emulsion with interesting new properties and offer an important route to new soft materials. Based on the principles of mass conservation and thermodynamic consistency, we develop a continuum model for such systems which combines a Cahn-Hilliard-Navier-Stokes model for the macroscopic two-phase fluid system with a surface Phase-Field-Crystal model for the microscopic colloidal particles along the interface. We begin with validating the used flow model by testing different diffuse interface models on a benchmark configuration for a two-dimensional rising bubble and compare the results with reference solutions obtained by other two-phase flow models. Furthermore, we present a new method for simulating two-phase flows in complex geometries, taking into account contact lines separating immiscible incompressible components. In this approach, the complex geometry is described implicitly by introducing a new phase-field variable, which is a smooth approximation of the characteristic function of the complex domain. The fluid and component concentration equations are reformulated and solved in larger regular domain with the boundary conditions being implicitly modeled using source terms. Finally, we derive the thermodynamically consistent diffuse interface model for two-phase flow with interfacial particles by taking into account the surface energy and the energy associated with surface colloids from the surface PFC model. The resulting governing equations are the phase field crystal equations and Navier-Stokes Cahn-Hilliard equations with an additional elastic stress. To validate our approach, we derive a sharp interface model and show agreement with the diffuse interface model. We demonstrate the feasibility of the model and present numerical simulations that confirm the ability of the colloids to make the interface sufficiently rigid to resist external forces and to stabilize interfaces for long times

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40

Leroy, Lechat Frédérique. "Investigation de la cytotoxicite et de la capacite de transporteur d'un nouveau systeme colloidal a base de cyclodextrines amphiphiles : application a la vectorisation d'un principe actif anticancereux : la doxorubicine". Paris 11, 1995. http://www.theses.fr/1995PA114829.

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Braunger, Julia. "Ezrin activation in vitro: Investigation of ezrin's conformation and the interaction between ezrin and F-actin". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-609D-5.

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Liu, Bei [Verfasser], Benjamin [Gutachter] Dietzek y Wolfgang [Gutachter] Weigand. "From the inside out : colloidal CdSe/CdS semiconductor nanorods : a study on the influence of their structures, surface ligands, and interactions with Redox-Active (Poly)Dopamine / Bei Liu ; Gutachter: Benjamin Dietzek, Wolfgang Weigand". Jena : Friedrich-Schiller-Universität Jena, 2020. http://d-nb.info/1223981800/34.

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Santos, Ronaldo Gonçalves dos. "Formulação e propriedades reologicas e coloidais de emulsões oleo em agua para aplicação em processos de escoamento de oleos pesados". [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266185.

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Orientadores: Watson Loh, Antonio Carlos Bannwart
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: Emulsões óleo em água (o/a) têm sido propostas como alternativa aos métodos convencionais para redução dos problemas associados ao escoamento, causados pela alta viscosidade destes óleos. Nestas emulsões, o óleo se encontra disperso na fase aquosa sob a forma de gotículas e pode ser bombeado sem necessariamente entrar em contato com as paredes do duto, reduzindo os efeitos viscosos e ampliando a capacidade de transferência. Neste trabalho, realizou-se um estudo experimental sobre a aplicação de emulsões de óleo em água (o/a) no transporte de óleos pesados brasileiros. Emulsões contendo 50-70% de óleo disperso foram preparadas sob diferentes parâmetros da formulação fisico-química, permitindo adequação de suas propriedades às exigência da aplicação. Eficaz protocolo de preparação produziu gotas com diâmetro médio de Sauter D3,2da ordem de 10-50 micrômetros e com distribuição de diâmetros obedecendo a uma distribuição lognormal. A reologia e a estabilidade das emulsões foram dependentes do diâmetro médio de gota e da distribuição de tamanhos. Emulsões mostraram alta estabilidade sob condições severas de avaliação. A emulsificação reduziu a viscosidade de 1.000 cP do óleo original para 30-150 cP da emulsão o/a, produzindo decréscimo de cerca de 30 vezes na viscosidade do óleo. As emulsões mostraram comportamento pseudoplástico descrito pela lei de potência (modelo de Ostwald-de Waele), apresentando influência do envelhecimento. O óleo cru pode.ser recuperado pela quebra da emulsão utilizando desemulsificantes comerciais, produzindo BS&W de cerca de 5%. Um sistema' de fluxo experimental em escala piloto com comprimento reto de teste de 3 m foi constiuído com tubulação de aço API com % in d.i. para ensaios de escoamento das emulsões. A viscosidade foi calculada a partir de dados de queda de pressão. A viscosidade de emulsões óleo em água com 50%, 60% e 70% de óleo disperso foi adequadamente prevista pela lei de potência, mostrando valores até 100 vezes menor que a viscosidade do óleo em escoamento a 500 S.I. As perdas de carga observadas durante o escoamento de emulsões são até 20 vezes inferior às do óleo em fluxo monofásico, o que também se verifica através da estimativa da potência requerida de bombeio. As emulsões óleo em água produzidas neste estudo mostram a viabilidade técnica da aplicação de emulsões óleo em água para o escoamento de óleos pesados, incluindo operações de elevação e transporte em oleodutos convencionais.
Abstract: Use of oil-in-water (o/w) emulsions for transportation of heavy crude oils has been proposed as altemative means of reducing problems associated with difficulties in transport of these fluids for their high viscosity, with some advantages over the currently used methodologies. In these emulsions, oil is dispersed as stabilized droplets allowing its transportation with low pressure drops and avoiding oil contact with the pipeline walls. This study involved the experimental evaluation of o/w emulsions for the transportation of Brazilian crude oils. Emulsions containing 50-70% oi! were prepared with different formulations. An efficient methodology of preparation produced emulsions with droplet diameters (Sauter diameter, D3,2) in the range of 10-50 micrometers and a log-normal size distribution. Rheology and stability of these emulsions depend on their average diameters and size distributions. These emulsions displayed high stability under severe conditions (centrifugation). Using this approach, oil viscosity of around 1 000 cP was reduced to 30-150 cP. These emulsions display a pseudoplastic rheological behavior following the power law described by the Ostwald-de Waele model, which changed with their aging. Crude oil could be recovered after emulsification using commercial additives, producing BS&W values of 5 %, which could be further reduced with more severe treatments (down to 0.5 %). An experimental set-up was built for flow assays in pilot scale with 3 m length for measurements made of API steel with :;4 in (i.d.). Viscosity was obtained from drop pressure data. The power law adequately adjusted emulsions containing several oil contents. Emulsions viscosity was found to. be up to 100 times lower tIutn the oil viscosityat 500 S-I and drop pressure in the emulsion flow was 20 times lower than q,il monophasic flow. In summary, all of these measurements confirm the viability of these emulsions for use in transportation of heavy crude oils, induding their lift and transportation in conventional pipelines.
Doutorado
Engenharia de Processos
Doutor em Engenharia Química

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44

Sartori, Paolo. "The Role of Interfaces in Microfluidic Systems: Oscillating Sessile Droplets and Confined Bacterial Suspensions". Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3423250.

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This PhD thesis is focused on the role of interfaces that characterize microfluidic systems, such as the free air/liquid interface of drops or the liquid/solid interface of fluids enclosed in microchannels. This work has a twofold character: on one side, we studied the dynamics of sessile drops subject to oscillations of the substrate; on the other, we investigated the spatial concentration distribution of suspensions of motile bacteria, as a model system for active collids, tuned by geometrical confinement. Dynamics of sessile drops. The first topic is related to the field of wetting phenomena and open microfluidics, which deals with the behaviour of drops, typically in the nano-/microliter range, deposited on open surfaces. At such length scale, these systems are dominated by capillarity and may give rise to unexpected effects, not commonly observed at the larger scale we are used to. Our studies aim to the achievement of an active control on the motion and shape of drops by means of vibration of the substrates, for chemical or biological applications. In particular, the motion of liquid drops on an inclined substrate subject to vertical harmonic oscillations have been considered. Typically, small droplets on inclined surfaces remain pinned because of contact angle hysteresis. When vertical oscillations are applied the droplets unpin and slide down. Surprisingly, for sufficiently large oscillation amplitude the droplets move upward against gravity. The systematical investigation of the response of drops on varying peak acceleration and frequency of oscillations, for fluids with different surface tensions and viscosity, allowed the control of the unidimensional motion along the substrate. Then, we have studied the interfacial morphologies of water drops confined on the hydrophilic top face of rectangular posts of width 0.5 mm and various length. For small volumes, the liquid film adopts the shape of a homogeneous filament with a uniform cross section close to a circular segment. For larger volumes, the water interface forms a central bulge, which grows with the volume. In the case of posts longer than a characteristic length, the transition between the two film shapes on varying the volume is discontinuous and exhibits the bistability of the two morphologic states associated with a hysteresis phenomenon. Vertically oscillating the post, with fixed water volume corresponding to the bistability, at certain frequencies induces an irreversible transition from the filament to the bulge state. Self-propelled particles under geometrical confinement. The second topic deals with the behaviour of active fluids, i.e. self-propelled colloid suspensions which are intrinsically out of equilibrium systems (Active Matter). In particular, in the presence of geometrical structures, such systems behave in a very different way with respect to equilibrium Browinan colloids. We have analyzed the role of different swimming patterns on the concentration distribution of bacterial suspensions confined between two flat walls, by considering wild-type E. coli and P. aeruginosa, which perform Run and Tumble and Run and Reverse patterns, respectively. The concentration profiles have been obtained by counting motile bacteria at different distances from the bottom wall. In agreement with previous studies, an accumulation of motile bacteria close to the walls was observed. Different fraction of motile bacteria and different wall separations, ranging from 100 μm to 250 μm, have been tested. The concentration profiles resulted to be independent on the walls separation and on the different kind of motility and to scale with the motile fraction. These results are confirmed by numerical simulations, based on a collection of self-propelled rod-like particles interacting only through steric interactions.
Questa tesi di dottorato prende in esame il ruolo delle interfacce che caratterizzano i sistemi microfluidici, come ad esempio l’interfaccia libera aria/acqua delle gocce o l’interfaccia liquido/solido di fluidi racchiusi in microcanali. Questo lavoro ha un duplice carattere: da una parte, abbiamo studiato la dinamica di gocce sessili soggette ad oscillazioni del substrato; dall’altra, abbiamo investigato come la distribuzione spaziale della concentrazione in sospensioni batteriche, prese come sistema modello per colloidi attivi, venga alterata da un confinamento geometrico. Dinamica di gocce sessili. Il primo argomento rientra nel campo dei fenomeni di bagnabilità e della microfluidica aperta, che tratta il comportamento di gocce, tipicamente nel range dei nano- /microlitri, depositate su superfici aperte. A tali scale di lunghezza, questi sistemi sono dominati dalla capillarità a possono produrre effetti inaspettati che non vengono comunemente osservati alle scale macroscopiche a cui siamo abituati. I nostri studi sono volti al raggiungimento del controllo attivo del moto e della forma delle gocce per mezzo di vibrazioni del substrato, con applicazioni dalla Chimica alla Biologia. In particolare, è stato considerato il moto di gocce su in substrato inclinato sottoposto ad oscillazioni armoniche verticali. Normalmente, su superfici inclinate le goccioline rimangono ferme a causa dell’isteresi dell’angolo di contatto. Quando vengono applicate oscillazioni verticali le goccioline si sbloccano e scivolano giù. Sorprendentemente, per ampiezze di oscillazioni sufficientemente grandi le goccioline si muovono verso l’atro contro la forza di gravità. Un’analisi della risposta delle gocce al variare dell’accelerazione di picco e della frequenza di oscillazione, prendendo in esame fluidi con diverse tensioni superficiali e viscosità, ha permesso il controllo del moto unidimensionale lungo il pianoinclinato. Inoltre, abbiamo studiato le morfologie interfacciali di gocce d’acqua confinate sulla faccia superiore idrofilica di post rettangolari con larghezza 0.5 mm e varie lunghezze. Per piccoli volumi, il film liquido prende la forma di un filamento omogeneo con una cross-section uniforme simile ad un segmento circolare. Per volumi più grandi, l’interfaccia acqua/aria forma un rigonfiamento centrale, che cresce con il volume. Nel caso di post più lunghi di una lunghezza caratteristica, la transizione tra le due forme al variare del volume discontinua e mostra la bistabilità dei due stati morfologici associata ad un fenomeno di isteresi. Applicando al post, con volume d’acqua fissato corrispondente alla bistabilità, vibrazioni verticali con determinate frequenze si più indurre una transizione irreversibile dallo stato di filamento omogeneo a quello rigonfiato. Particelle auto-propulse sotto confinamento geometrico. Il secondo argomento riguarda il comportamento di fluidi attivi, cioè sospensioni di colloidi auto-propulsi che costituiscono sistemi intrinsecamente fuori equilibrio (Materia Attiva). In particolare, in presenza di strutture geometriche, tali sistemi si comportano in modo molto differente rispetto a colloidi Browniani all’equilibrio. Abbiamo analizzato il ruolo di diversi schemi di motilità sulla distribuzione di concentrazione di sospensioni batteriche confinate tra due pareti solide. considerando E. coli a P. aeruginosa wild-type, che si muovono secondo gli schemi Run and Tumble e Run and Reverse, rispettivamente. I profili di concentrazione sono tati ottenuti contando i batteri motili a diverse distanze dalle pareti. In accordo con studi precedenti, si osservato un accumulo di batteri motili in prossimit delle pareti. Sono state testate diverse frazioni di batteri motili e diverse distanze di separazione tra le pareti, nel range tra 100μm e 250 μm. I profili di concentrazione risultano indipendenti dalla distanza tra le pareti e dai differenti schemi di motilità e scalano con la frazione di batteri motili. Questi risultati sono confermati da simulazioni numeriche, basate su una collezione di particelle allungate auto-propulse che interagiscono solo tramite interazioni steriche.

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45

Pesesse, Antoine. "Synthèse de nanoparticules contenant des métaux pour la catalyse assistée par des bases de Lewis en suspension colloïdale". Electronic Thesis or Diss., Sorbonne université, 2021. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2021SORUS530.pdf.

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Dans ces travaux, nous avons synthétisé des nanoparticules contenant du cuivre et de l’or dans le but de créer une synergie avec une base de Lewis moléculaire lors de réactions catalytiques en suspension colloïdale. Une étude de la bibliographie, a mis en lumière l’intérêt d’utiliser une base de Lewis forte supplémentaire et encombrée pour réaliser une interaction de type « Paire de Lewis Frustrée » avec la surface de la nanoparticule (Chapitre 1). Des travaux antérieurs ont montré que la formation d’une couche d’oxyde pourrait expliquer l’instabilité des nanoparticules de cuivre vis-à-vis de phosphines tertiaires (Chapitre 2). Pour empêcher sa formation les nanoparticules ont été lavées sous atmosphère inerte (Chapitre 3). De l’oxyde est détecté et les nanoparticules sont sujettes au mécanisme de lixiviation. Le mécanisme de synthèse suggère que l’eau pourrait être responsable de la formation de l’oxyde. Nous avons développé un nouveau protocole de sulfuration de nanoparticules de cuivre. Ces nanoparticules sont instables vis-à-vis des phosphines tertiaires (Chapitre 4). Une nouvelle synthèse de nanoparticules de cuivre stabilisées par des carbènes N-hétérocycliques, utilisant des précurseurs plus accessibles que dans la littérature et sans oxygène, a été proposée et a permis d’obtenir des nanoparticules dépourvues d’oxyde et stabilisées par des ligands très forts. Le mécanisme a été étudié dans le détail (Chapitre 5). L’influence de phosphines sur les propriétés catalytiques de l’or en solution colloïdale pour des réactions de réduction et d’hydrogénation a été évaluée (Chapitre 6)
In this work, we synthesised copper based and gold nanoparticles to produce a catalytic activity in combination with a molecular Lewis base in colloidal suspension. A bibliographic research, showed the potential of using a sterically hindered tertiary phosphine to obtain a “Frustrated Lewis Pair” type of interaction with the nanoparticle surface (Chapter 1). Previous works unveiled that the formation of an oxide shell could explain the lack of stability of copper nanoparticles toward tertiary phosphine (Chapter 2). To prevent its formation, the nanoparticles were washed under inert atmosphere. The oxide was still detected and the nanoparticles were subject to leaching. Mechanistic study suggest that water could be responsible for oxidation formation (Chapitre 3). A new procedure to sulfurize copper nanoparticles was developed but the nanoparticles obtained were unstable toward tertiary phosphines (Chapter 4). A new synthesis of N-heterocyclic carbene stabilized copper nanoparticles using more accessible and oxygen free precursors was proposed and delivered nanoparticles that are both oxide free and stabilized by very strong ligands (Chapter 5). The synthesis mechanism was studied in details. The influence of phosphine on the catalytic activity of gold for reduction and hydrogenation in colloidal suspension were assessed (Chapter 6)

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46

Josefsson, Sarah. "Fate and transport of POPs in the aquatic environment : with focus on contaminated sediments". Doctoral thesis, Umeå universitet, Kemiska institutionen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-42107.

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Persistent organic pollutants (POPs) are hydrophobic substances that readily sorb to organic matter in particles and colloids instead of being freely dissolved in the water phase. This sorption affects the bioavailability and environmental transport of the POPs. The major part of this thesis concerns the role of sediments as secondary sources of POPs. As the primary emissions decrease, contaminated sediments where POPs have accumulated can become the main source of contamination. If the contaminated sediment by time becomes covered with cleaner layers, the POPs are buried and no longer in contact with the aquatic environment. Experiments in this thesis showed, however, that new invading species can alter the sediment-water dynamics as a result of their bioturbation, i.e. mixing of sediment particles and pore-water. Marenzelleria spp., invading species in the Baltic Sea that burrow deeper than native species, were found to increase the remobilization of buried contaminants. The sediment-to-water flux was inversely related to the burial depth (2-10 cm) of the POP congeners (polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers) and also inversely related to the hydrophobicity of the congener. The flux was therefore most pronounced for less hydrophobic contaminants, which was linked to the bioirrigating behaviour of these species. Marenzelleria spp. also accumulated the buried POPs and increased concentrations in surface sediment. Contaminants previously considered buried at a ’safe’ depth can thus be remobilized as a result of the invasion of Marenzelleria spp. in the Baltic Sea. One method to decrease the remobilization of contaminants from sediments is ’capping’, i.e. a layer of clean material is placed as a cap on the sediment. By amending the cap with active materials, which sequester the POPs and decrease their availability, thinner layers can be used (’active capping’ or ’thin-layer capping’). Results from an experiment with thin-layer capping using different active materials (activated carbon (AC) and kraft lignin) showed that both the sediment-to-water flux and the bioaccumulation by benthic species of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), hexachlorobenzene (HCB) and octachlorostyrene (OCS) decreased with increased thickness of the cap layer (0.5-5 cm). Amendments with active materials further increased the cap efficiency. AC was more efficient than kraft lignin, and a 3 cm cap with 3.3% AC reduced the flux and bioaccumulation with ~90%. The reduction of the sediment-to-water flux was inversely related to the hydrophobicity of the POP, and reductions in the flux had similar magnitudes as reductions in the concentration in deep-burrowing polychaetes, demonstrating the importance of bioturbation for sediment-to-water transport. In a one-year study on the levels of PCDD/Fs, PCBs, and HCB in a coastal area of the Baltic Sea, the correlations between the POP levels and the levels of particles and organic carbon in the water were found to differ for POPs of different structure and hydrophobicity. The levels of PCDD/Fs decreased to one third in May, which could be related to the increased sedimentation, i.e. water-to-sediment transport, during spring bloom.

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47

Saha, Suropriya. "Phoretic Motion of Colloids : Single Particle and Collective Behaviour". Thesis, 2014. http://etd.iisc.ac.in/handle/2005/2934.

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In this thesis we have studied systems that driven by mechanisms broadly known as phoresis. More specifically, in the second chapter we calculate the excess noise in electrophoresis of a colloid due to microion fluctuations. In the next three chapters we study in detail a system of self-phoretic colloids, propelled by the energy released when an ambient fuel molecule makes contact with a catalytic region on the particle’s surface. We start with the behaviour of a single particle in a linear substrate gradient, then go on to study interactions between two particles due to their diffusion clouds, and finally obtain the collective equations of motion by a systematic coarse-graining of the microscopic Langevin dynamics. To understand the role of nonequilibrium fluctuations in an electrophoretic system we have theoretically analyzed the dynamics of a single colloidal particle in an externally applied electric field. We have studied the colloidal dynamics in two scenarios: a particle free to move in an unbounded fluid and a colloid near a wall which is stationary due to a balance between gravity and the electric field. The thermal motions of microions lead to an anisotropic, nonequilibrium noise, proportional to the field, in the effective Langevin equation for the colloid. The fluctuation-dissipation ratio depends strongly on frequency, in contrast to an equilibrium system, and the colloid if displaced from its steady-state position relaxes with a velocity not proportional to the gradient of the logarithm of the steady-state probability. Other measurable effects of this noise are a superdiffusive peak at short times and an enhanced diffusity at long times. We have then studied the effective potential and obtained a non-dimensional measure of the size of the excess noise. Possible extensions of this study to include the behaviour of the mean and fluctuation properties in the case of an applied alternating potential, and the effect of the excess noise on electrohydrodynamic aggregation of colloids. We next turn to a phoretic system that has been much studied in the recent years – active Janus colloids . On one hand these colloids are an important contribution to the general class of problems on self-propulsion at low Reynolds number. On the other hand since their behaviour can be tuned at the level of single particle we can ask how their collective behaviour depends on the swimmer design. This makes it a very rich field with lots of challenging questions. We first study the single particle behaviour of an active Janus colloid in an imposed substrate gradient, then build the two-particle interactions and ultimately the collective equations of motion by a generalisation of these results. Our work presents a new approach to active matter. We show theoretically how to design particles that are not only motile but can reorient in response to gradients, thus mimicking chemotaxis. We outline the collective behaviour emerging from these single-particle properties, including colloidal realisations of gravitational collapse, plasma oscillations and spontaneously ringing states, and present a phase diagram, in terms of single particle parameters, that can be tested in experiments. This provides a template to design collective behaviours of interest by tuning the surface properties of the colloids. We can also control the range of the interaction by varying the concentration of reactant. Our coarse-grained equations of motion for the polar orientation and number density fields for a collection of colloids propelled by and interacting through long-ranged dif-fusion fields are novel in a number of ways. This is the first example in active matter literature of a microscopic derivation of collective dynamics for particles interacting via long-ranged diffusion fields. The instabilities and possible phases that we predict are different from those in traditional flocking models, which consider only short-ranged aligning interactions. The long-ranged interactions of interest here cannot produce a globally polar ordered state, and we work in a concentration regime where steric and collisional interactions are not important. Instabilities towards flocking, and the advective nonlinearities of the Toner-Tu model, although not ruled out by the symmetries of our model, do not play a significant role in our system. The collective behaviour we predict will not be seen in purely locally interacting active-particle systems. The mechanisms at work in the “saturated” case where reactant is abundant cannot be viewed as totally generic features of collections of self-driven particles; they require interactions mediated by the production or consumption of long-ranged diffusing solute fields. Earlier work on saturated systems resolved neither interactions mediated by the polarity of the objects nor chemotactic effects. Their treatment truncated the equations at the level of the concentration [1]. In the “unsaturated” case more than one mechanism operates. One is related to the motility-induced phase separation discussed phenomenologically in refs. [2,3] (for which our system provides an important microscopic realisation). The other is due to chemo-taxis and phoresis which we report for the first time. Our expression of the various coefficients in the equaions of motion in terms of the single particle properties can also be used to design systems in which one or the other of these mechanisms dominate. We are now planning to study a collection of these particles in a fluid and examine the diffusion of a tracer particle as was done by Yeomans et al. [4] for hydrodynamic interactions. The Levy flights obtained in [4] is due to the long-ranged nature of the hydrodynamic fields, which cause effects like entrainment leading to interesting tracer dynamics. In this thesis we have considered colloids in which the symmetry axis of the colloid and the catalytic coat coincide. It might be of interest to consider cases when the axes are at an angle making the swimmer biaxial, or more complicated arrangements leading to chirality and thus rotation. Collective dynamics and two particle interaction between such swimmers can also be interesting. The formalism developed for the study of interaction between two active colloids through their diffusion fields and hydrodynamics can be extended to study their interaction with extended passive surfaces like walls or spheres. The collective dynamics of this class of active systems when it is confined between parallel walls is also of interest. Work in progress includes studies of the motion of the swimmer in a periodic array of passive colloids. In this study of collective dynamics, we have ignored the role of hydrodynamics, as the slowest decay of the field is 1/r3, which is subdominant to the decay of the chemical fields and in the dilute limit is expected to change things only qualitatively. However their role would be more important when we consider the stability of ordered structures like an aster in the saturated case. Another effect of hydrodynamics is to stir the fluid. It might be interesting to study the finite-P´eclet number regime [5, 6] of our system particularly in the unscreened region when advection of the scalar fields s and p by the velocity can affect clustering. We have derived the form of the nonlinear equations of motion in both the saturated and the unsaturated regimes. It will be interesting to investigate their relevance in the dynamics and phases that this extremely rich system can form. Even in the overdamped limit where we obtain an effective density equation it is not clear that the dynamics will resemble that of the Keller-Segel model due to the presence of the interesting nonlinear terms. Also, in this thesis, we have only looked at the fluid-like state of the system. We have just started exploring the high concentration regime where we can check the propensity of the system to develop crystalline order. In the screened limit where we obtain a condensation due a negative squared sound speed, it is posssible to study the condensation phenomenon in greater detail. In future we also plan to examine whether the tendency to condense at nonzero wavenumber (See Fig 5.1), i.e., microphase separation, can lead to liquid-crystalline phases like smectics. The systems described in this thesis are extremely rich and the few ideas mentioned above form just a small subset of the plethora of exciting theoretical and experimental explorations that can be performed with them. Since they can be “designed”, unlike biological substances, they can also become a test-bed for testing theoretical predictions of the nonequilibrium statistical mechanics of self-propelled systems.

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48

Saha, Suropriya. "Phoretic Motion of Colloids : Single Particle and Collective Behaviour". Thesis, 2014. http://hdl.handle.net/2005/2934.

Texto completo

Resumen

In this thesis we have studied systems that driven by mechanisms broadly known as phoresis. More specifically, in the second chapter we calculate the excess noise in electrophoresis of a colloid due to microion fluctuations. In the next three chapters we study in detail a system of self-phoretic colloids, propelled by the energy released when an ambient fuel molecule makes contact with a catalytic region on the particle’s surface. We start with the behaviour of a single particle in a linear substrate gradient, then go on to study interactions between two particles due to their diffusion clouds, and finally obtain the collective equations of motion by a systematic coarse-graining of the microscopic Langevin dynamics. To understand the role of nonequilibrium fluctuations in an electrophoretic system we have theoretically analyzed the dynamics of a single colloidal particle in an externally applied electric field. We have studied the colloidal dynamics in two scenarios: a particle free to move in an unbounded fluid and a colloid near a wall which is stationary due to a balance between gravity and the electric field. The thermal motions of microions lead to an anisotropic, nonequilibrium noise, proportional to the field, in the effective Langevin equation for the colloid. The fluctuation-dissipation ratio depends strongly on frequency, in contrast to an equilibrium system, and the colloid if displaced from its steady-state position relaxes with a velocity not proportional to the gradient of the logarithm of the steady-state probability. Other measurable effects of this noise are a superdiffusive peak at short times and an enhanced diffusity at long times. We have then studied the effective potential and obtained a non-dimensional measure of the size of the excess noise. Possible extensions of this study to include the behaviour of the mean and fluctuation properties in the case of an applied alternating potential, and the effect of the excess noise on electrohydrodynamic aggregation of colloids. We next turn to a phoretic system that has been much studied in the recent years – active Janus colloids . On one hand these colloids are an important contribution to the general class of problems on self-propulsion at low Reynolds number. On the other hand since their behaviour can be tuned at the level of single particle we can ask how their collective behaviour depends on the swimmer design. This makes it a very rich field with lots of challenging questions. We first study the single particle behaviour of an active Janus colloid in an imposed substrate gradient, then build the two-particle interactions and ultimately the collective equations of motion by a generalisation of these results. Our work presents a new approach to active matter. We show theoretically how to design particles that are not only motile but can reorient in response to gradients, thus mimicking chemotaxis. We outline the collective behaviour emerging from these single-particle properties, including colloidal realisations of gravitational collapse, plasma oscillations and spontaneously ringing states, and present a phase diagram, in terms of single particle parameters, that can be tested in experiments. This provides a template to design collective behaviours of interest by tuning the surface properties of the colloids. We can also control the range of the interaction by varying the concentration of reactant. Our coarse-grained equations of motion for the polar orientation and number density fields for a collection of colloids propelled by and interacting through long-ranged dif-fusion fields are novel in a number of ways. This is the first example in active matter literature of a microscopic derivation of collective dynamics for particles interacting via long-ranged diffusion fields. The instabilities and possible phases that we predict are different from those in traditional flocking models, which consider only short-ranged aligning interactions. The long-ranged interactions of interest here cannot produce a globally polar ordered state, and we work in a concentration regime where steric and collisional interactions are not important. Instabilities towards flocking, and the advective nonlinearities of the Toner-Tu model, although not ruled out by the symmetries of our model, do not play a significant role in our system. The collective behaviour we predict will not be seen in purely locally interacting active-particle systems. The mechanisms at work in the “saturated” case where reactant is abundant cannot be viewed as totally generic features of collections of self-driven particles; they require interactions mediated by the production or consumption of long-ranged diffusing solute fields. Earlier work on saturated systems resolved neither interactions mediated by the polarity of the objects nor chemotactic effects. Their treatment truncated the equations at the level of the concentration [1]. In the “unsaturated” case more than one mechanism operates. One is related to the motility-induced phase separation discussed phenomenologically in refs. [2,3] (for which our system provides an important microscopic realisation). The other is due to chemo-taxis and phoresis which we report for the first time. Our expression of the various coefficients in the equaions of motion in terms of the single particle properties can also be used to design systems in which one or the other of these mechanisms dominate. We are now planning to study a collection of these particles in a fluid and examine the diffusion of a tracer particle as was done by Yeomans et al. [4] for hydrodynamic interactions. The Levy flights obtained in [4] is due to the long-ranged nature of the hydrodynamic fields, which cause effects like entrainment leading to interesting tracer dynamics. In this thesis we have considered colloids in which the symmetry axis of the colloid and the catalytic coat coincide. It might be of interest to consider cases when the axes are at an angle making the swimmer biaxial, or more complicated arrangements leading to chirality and thus rotation. Collective dynamics and two particle interaction between such swimmers can also be interesting. The formalism developed for the study of interaction between two active colloids through their diffusion fields and hydrodynamics can be extended to study their interaction with extended passive surfaces like walls or spheres. The collective dynamics of this class of active systems when it is confined between parallel walls is also of interest. Work in progress includes studies of the motion of the swimmer in a periodic array of passive colloids. In this study of collective dynamics, we have ignored the role of hydrodynamics, as the slowest decay of the field is 1/r3, which is subdominant to the decay of the chemical fields and in the dilute limit is expected to change things only qualitatively. However their role would be more important when we consider the stability of ordered structures like an aster in the saturated case. Another effect of hydrodynamics is to stir the fluid. It might be interesting to study the finite-P´eclet number regime [5, 6] of our system particularly in the unscreened region when advection of the scalar fields s and p by the velocity can affect clustering. We have derived the form of the nonlinear equations of motion in both the saturated and the unsaturated regimes. It will be interesting to investigate their relevance in the dynamics and phases that this extremely rich system can form. Even in the overdamped limit where we obtain an effective density equation it is not clear that the dynamics will resemble that of the Keller-Segel model due to the presence of the interesting nonlinear terms. Also, in this thesis, we have only looked at the fluid-like state of the system. We have just started exploring the high concentration regime where we can check the propensity of the system to develop crystalline order. In the screened limit where we obtain a condensation due a negative squared sound speed, it is posssible to study the condensation phenomenon in greater detail. In future we also plan to examine whether the tendency to condense at nonzero wavenumber (See Fig 5.1), i.e., microphase separation, can lead to liquid-crystalline phases like smectics. The systems described in this thesis are extremely rich and the few ideas mentioned above form just a small subset of the plethora of exciting theoretical and experimental explorations that can be performed with them. Since they can be “designed”, unlike biological substances, they can also become a test-bed for testing theoretical predictions of the nonequilibrium statistical mechanics of self-propelled systems.

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49

Tung, Clarion K. "Studies of Polymers, Active Colloids, and Proteins". Thesis, 2016. https://doi.org/10.7916/D87H1JSP.

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This thesis describes several molecular dynamics studies of polymers, proteins, and active colloids. These diverse systems fall under the purview of soft matter physics and in Part I, I explain what is soft matter and describe some of its essential features. In Part II, I introduce some basic polymer physics and show how confined polymers can be described using blob theory. I also discuss how phase separation of polymer mixtures can occur. These concepts are applied to systems of mixed polymer brushes on spheroids, objects that have surfaces with non-uniform curvature. I show how the interplay of phase separation and surface curvature give rise to striped patterns, and how an extension of blob theory can give analytical expressions for the free energy. Finally, I show how phase separation of miscible polymers can occur, driven solely by surface curvature. In Part III, I present an overview of self-assembly and describe how active, or self-propelled colloids can be used to assemble new materials. I show how two large colloids immersed in a bath of smaller active colloids exhibit an effective short-ranged repulsion and long-ranged attraction, which stands in contrast to the standard short-ranged depletion attraction. I also explore how self-propulsion changes clustering by focusing on a system with short-ranged attractive and long-ranged repulsive particles, which under equilibrium, exhibit finite-sized clusters. I show that for certain parameters, spheres can form a fluid of living crystals, and dumbbells can form a crystal of rotors. In Part IV, I give a brief introduction to protein folding and describe how molecular chaperones combat misfolding in the human body. Then, taking inspiration from the chaperones, I show that a polymer-grafted “soft” nanopore can be used to unfold misfolded proteins and destroy undesired aggregates. I also show preliminary results for a hydrophobic “smart” nanopore that can selectively capture and unfold misfolded proteins.

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Mallory, Stewart Anthony. "An Active Approach to Engineering the Microscopic". Thesis, 2017. https://doi.org/10.7916/D8D22955.

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Active colloids, which can be thought of as the synthetic analog of swimming bacteria, exhibit remarkable collective behavior. Using a combination of computer simulations and analytical theory, I have looked to provide quantitative answers to fundamental questions concerning the phase behavior and material properties of active suspensions. A primary focus of my Ph.D work has been devoted to developing novel techniques to exploit the active nature of these particles to manipulate and self-assemble matter at the colloidal scale. In the introductory chapter, I discuss recent advances in the self-assembly of self-propelled colloidal particles and highlight some of the most exciting results in this field. The remaining chapters are each self-contained and focus on a particular topic within active colloidal self-assembly. These chapters are ordered in terms of system complexity, and begins with characterizing the thermomechanical properties of an ideal active fluid. The next three chapters are centered around characterizing the effective interactions induced by an active suspension. The last two chapters focus on using self-propulsion as a tool to improve colloidal self-assembly, and understanding the interplay between self-propulsion and anisotropic pair interaction.

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Tesis sobre el tema "Colloides actifs"

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