Дисертації з теми "Colloids"
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1
Keal, Louis. "Dynamics of hard and soft colloids at aqueous interfaces." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066361/document.
Анотація:
Dans cette these nous avons étudié la dynamique de colloides aux interfaces fluides. Dans une première partie nous avons étudié la dynamique de drainage de films minces liquides contenant des particules de microgels de PNiPAM. Ces systèmes sont de plus en plus utilisés pour stabiliser et déstabiliser des émulsions sur demande en jouant sur la température. Nous avons montré que la dynamique de drainage et l'épaisseur des films dépend de la concentration et du degré de réticulation des particules. Nous avons pu à partir des épaisseurs des films remonter à la conformation des particules. Les microgels moins réticulés s'étalent davantage aux interfaces à basse concentration que les particules ayant un taux de réticulation plus élevé. En revanche à haute concentration, les particules moins réticulées forment des couches plus compactes, ce qui induit des films moins stables. Dans la deuxième partie nous avons étudié la dynamique d'adsorption de particules colloidales dans des systèmes eau dans eau, obtenus par la séparation de phase de deux solutions de polymères. A temps courts, la position de la particule varie exponentiellement avec le temps alors qu'aux temps plus longs l'évolution est logarithmique. De façon surprenante, nous trouvons que dans le régime exponentiel, le temps caractéristique, qui résulte théoriquement d'un équilibre entre les forces de tension interfaciale et la friction visqueuse est trop lent par rapport à la théorie. De plus l'existence d'un régime logarithmique (habituellement attribué à un piégeage/dépiégeage de la ligne de contact) est également surprenante puisque notre système présente des tensions interfaciales très faibles, de l'ordre de 100 µN/mThis thesis examines interfacial colloidal dynamics in two separate aqueous systems. The first part aims to improve understanding of thermoresponsive microgel-stabilised emulsions. Many emulsion properties are determined by the behaviour and drainage dynamics of the thin films that form between droplets. This study reveals these drainage dynamics, achieved through observing a model thin film of PNiPAM microgel solution in air. We explore why, as other studies have shown, less cross-linked microgels stabilise emulsions more effectively than more cross-linked microgels, concluding that both adsorption dynamics and particle rearrangement under pressure play a role. Through a simple calculation, we are able to estimate the conformation of microgels at the interface, showing that microgel concentration in bulk determines the concentration at interface due to differences in adsorption kinetics, and microgel excess does not play a role. The second part of the thesis investigates behaviour of spherical colloidal particles within an Aqueous Two-Phase System (ATPS) composed of non-mixing polymer solutions of fish gelatin and dextran, with applications in low-fat foods. Additionally, the very low surface tension of these systems allows studing fast interfacial processes at experimentally accessible timescales. In this work, we examine adsorption dynamics of spherical particles, observing for the first time the theoretically-predicted exponential ‘snap-in’ stage of particle adsorption. Surprisingly, even at this low surface tension, a slower logarithmic relaxation is subsequently observed which at the oil/water interface is ascribed to pinning of the contact line on surface defects
2
Russell, Emily Ruth. "Structure and Properties of Charged Colloidal Systems." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11413.
Анотація:
This dissertation explores the changes in structure of colloidal systems on the introduction of repulsive interactions. Colloidal gels are well understood when all particle interactions are attractive, but their structure is fundamentally changed when repulsive interactions compete with those attractive interactions, as in the case of a binary gel of oppositely charged particles. Similarly, colloidal crystals are well understood when interactions are approximately hard-sphere, but again, the structure and material properties change when a long-range repulsion is introduced, giving a colloidal `Wigner' crystal. My research quantitatively investigates these effects in experimental model systems. I use confocal microscopy to directly image in three dimensions suspensions of micron-scale colloidal particles which are monodisperse, index- and density-matched, fluorescent, and electrostatically charged. I use standard image-processing techniques to obtain the precise location of each particle in the imaging volume in order to analyze both global and local structure. In the case of the binary gel, I observe gelation of oppositely charged particles, controlled by varying the total particle volume fraction, the interaction strength, and the mixing ratio of the two particle species. I find that contrary to commonly studied purely attractive gels, in which weakly quenched gels are more compact and less tenuous, particles in these binary gels form fewer contacts and the gels become more tenuous as we approach the gel line, and the average attractive bond number emerges as a critical parameter for gelation. This suggests that a different mechanism governs gel formation and structure in binary gels, in which attractive and repulsive interactions compete. In the case of the long-range-repulsive colloidal `Wigner' crystals, I find a body-centered-cubic crystalline phase at particle volume fractions near 15%, in contrast to the face-centered-cubic crystalline phase found at volume fractions above 50% for hard spheres. The soft interactions in these repulsive crystals permit large fluctuations, with typical particle displacements up to 20% of the nearest-neighbor spacing. I determine the three independent crystalline elastic constants, and find that the crystals are very compliant (c ~ 5-40mPa), and strongly anisotropic at all volume fractions studied. I also observe a sharp interface between the fluid and crystalline phases.Physics
3
Keal, Louis. "Dynamics of hard and soft colloids at aqueous interfaces." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066361.
Анотація:
Dans cette these nous avons étudié la dynamique de colloides aux interfaces fluides. Dans une première partie nous avons étudié la dynamique de drainage de films minces liquides contenant des particules de microgels de PNiPAM. Ces systèmes sont de plus en plus utilisés pour stabiliser et déstabiliser des émulsions sur demande en jouant sur la température. Nous avons montré que la dynamique de drainage et l'épaisseur des films dépend de la concentration et du degré de réticulation des particules. Nous avons pu à partir des épaisseurs des films remonter à la conformation des particules. Les microgels moins réticulés s'étalent davantage aux interfaces à basse concentration que les particules ayant un taux de réticulation plus élevé. En revanche à haute concentration, les particules moins réticulées forment des couches plus compactes, ce qui induit des films moins stables. Dans la deuxième partie nous avons étudié la dynamique d'adsorption de particules colloidales dans des systèmes eau dans eau, obtenus par la séparation de phase de deux solutions de polymères. A temps courts, la position de la particule varie exponentiellement avec le temps alors qu'aux temps plus longs l'évolution est logarithmique. De façon surprenante, nous trouvons que dans le régime exponentiel, le temps caractéristique, qui résulte théoriquement d'un équilibre entre les forces de tension interfaciale et la friction visqueuse est trop lent par rapport à la théorie. De plus l'existence d'un régime logarithmique (habituellement attribué à un piégeage/dépiégeage de la ligne de contact) est également surprenante puisque notre système présente des tensions interfaciales très faibles, de l'ordre de 100 µN/mThis thesis examines interfacial colloidal dynamics in two separate aqueous systems. The first part aims to improve understanding of thermoresponsive microgel-stabilised emulsions. Many emulsion properties are determined by the behaviour and drainage dynamics of the thin films that form between droplets. This study reveals these drainage dynamics, achieved through observing a model thin film of PNiPAM microgel solution in air. We explore why, as other studies have shown, less cross-linked microgels stabilise emulsions more effectively than more cross-linked microgels, concluding that both adsorption dynamics and particle rearrangement under pressure play a role. Through a simple calculation, we are able to estimate the conformation of microgels at the interface, showing that microgel concentration in bulk determines the concentration at interface due to differences in adsorption kinetics, and microgel excess does not play a role. The second part of the thesis investigates behaviour of spherical colloidal particles within an Aqueous Two-Phase System (ATPS) composed of non-mixing polymer solutions of fish gelatin and dextran, with applications in low-fat foods. Additionally, the very low surface tension of these systems allows studing fast interfacial processes at experimentally accessible timescales. In this work, we examine adsorption dynamics of spherical particles, observing for the first time the theoretically-predicted exponential ‘snap-in’ stage of particle adsorption. Surprisingly, even at this low surface tension, a slower logarithmic relaxation is subsequently observed which at the oil/water interface is ascribed to pinning of the contact line on surface defects
4
Ryan, Joseph Nolte. "Groundwater colloids in two Atlantic coastal plain aquifers : colloid formation and stability." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14560.
5
Drube, Fabian. "Selfdiffusiophoretic Janus colloids." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-173348.
6
Reynolds, Matthew Drake. "Colloids in groundwater." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15311.
Анотація:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Bibliography: leaves 94-97.
by Matthew Drake Reynolds.
M.S.
7
Batista, Vera Mónica de Oliveira. "Deformable spherical colloids." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610066.
8
Chu, Fangfang. "Dumbbell-shaped colloids." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2014. http://dx.doi.org/10.18452/17062.
Анотація:
In der vorliegenden Arbeit wurde das Phasenverhalten von harten Hantelteilchen (Dumbbells) als Funktion des Aspektverhältnisses (L*, der Quotient aus dem Abstand der Massenzentren zum Durchmesser der Kugel) und der Volumendichte untersucht. Bragg-Reflexe weisen darauf hin, das harte Dumbbells mit L* < 0.4 einen Phasenübergang von einer Fluid-artigen Phase zu einem plastischen Kristall zeigen. Die experimentellen Phasendiagramme bei L* ~ 0.24 und L*~ 0.30 sind vergleichbar mit Vorhersagen aus Monte Carlo-Simulationen. Rheologie Messungen zeigen, dass harte Dumbbells verschiedene Gleichgewichts- und Nichtgleichgewichtsphasen annehmen. Suspensionen von harten Dumbbells im Zweiphasenbereich zeigen ein einziges Fließgrenzen-Ereignis, wohingegen in der plastischen Kristallphase zwei Fließgrenzen-Ereignisse beobachtet werden. Diese, im Folgenden als „double yielding“ bezeichneten Ereignisse, hängen mit der Kristallisation der Suspensionen von harten Dumbbells zusammen. Die entsprechende Strukturentwicklung wurde mit rheo-SANS-Experimenten untersucht und mithilfe von BD Simulationen interpretiert. Es konnte gezeigt werden, dass die plastische Kristallphase polykristallin im Ruhezustand ist. Unter schwacher Scherung wird eine fcc-Schwerzwilling Struktur ausgebildet. Bei hoher Scherung formt sich eine teilweise orientierte Struktur aus gleitenden Schichten. Zwischen diesen beiden Strukturen existiert eine ungeordnete Übergangsphase. Die Scher-induzierte Strukturausbildung eintspricht dem „double yielding“ Ereignis der kristallinen harten Dumbells. Es wurde gezeigt, dass ein größeres L* (L* < 0.4) die Strukturentwicklung unter Scherung qualitativ nicht beeinflusst. Aufgrund verlangsamter Dynamik in der Nähe des Glasübergangs sind lediglich stärkere oder längere Oszillationen von Nöten, um Scher-induzierte Kristallisation zu erzeugen. Im zweiten Teil dieser Arbeit werden Systeme aus hohlen Kugeln und „Janus“-Dumbbells vorgestellt, die als kolloidale Modellsysteme dienen können.In the present work the phase behaviour of hard dumbbells has been explored as a function of aspect ratio (L*, the center to center distance to the diameter of one composed sphere) and volume fractions using thermosensitive dumbbell-shaped microgels as the hard dumbbell model system. A fluid-to-plastic crystal phase transition indicated by Bragg reflections has been observed for L* < 0.4. The experimental phase diagrams at L* ~ 0.24 and L* ~ 0.30 are comparable to the theoretical prediction of the Monte Carlo simulations. Rheological measurements reveal that the hard dumbbells in the biphasic gap show the yielding behaviour with a single yielding event, while two yielding events have been observed for the plastic crystalline phase. The two yielding events, referred to as the double yielding behaviour, are proved to be related to the crystallization of hard dumbbells. The underlying structural evolution has been investigated by rheo-SANS experiments and the scattering data has been interpreted by BD simulations. It is demonstrated that the plastic crystal structure of the hard dumbbells is polycrystalline at rest, which has been induced into the twinned fcc structure at low strain, the partially oriented sliding layers at high strain and the intermediate state at the strain in-between. The shear-induced structural evolution corresponds to the double yielding events of the fully crystallized hard dumbbells. Additionally, we prove that the increase of L* (L* < 0.4) does not change the structural evolution of the sheared hard dumbbells. Only more extensive or longer oscillations are required to form the shear-induced crystal structures due to the slowdown of the dynamics in the vicinity of the glass transition. In a second part, the work of this thesis is extended to hollow systems composed of hollow spheres and hollow Janus dumbbells that can be used as model systems to probe phase behaviour of hollow capsules.
9
Shvets, Alexey. "Theory of colloidal stabilization by unattached polymers." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE025/document.
Анотація:
Les dispersions colloïdales ont beaucoup d’applications technologiques importantes. A cause du mouvement brownien, les particules ont des collisions fréquentes entre elles. Les forces d’attraction de van der Waals,dérivant de potentiels à longue portés, conduisent à l’agrégation et à la précipitation des particules. Plusieurs méthodes ont été proposées pour diminuer ou contrebalancer l’effet d’attraction de van der Waals et augmenter la stabilité colloïdale. Par exemple, le choix du solvant possédant l’indice de réfraction le plus proche possible de celui des particules peut diminuer les forces de van der Waals. D'autres facteurs influencent la stabilité comme les interactions électrostatiques et les interactions spécifiques liées aux chaînes de polymères. Dans le cas des polymères, les chaînes peuvent être greffées à la surface des particules ou être dissoutes dans le solvant (chaînes libres). Dans ce travail de thèse, nous avons étudié l’effet de la stabilisation par déplétion dans le cas des chaînes de polymères libres (FPI, "free polymer induced interaction"). Des modèles théoriques précédents portent un caractère trop simplifié et utilisent des approximations sans vérification. De plus, l’influence des paramètres de la solution, c’est-à-dire, de la structure de polymères et de son interaction avec la surface de particule, n’a pas été étudiée.Les chaînes polymères libres ont été modélisées comme des marches aléatoires dans un champ moléculaire auto-cohérent qui satisfait à l'équation intégro-différentielle de diffusion. Pour le domaine moléculaire, nous avons utilisé un potentiel chimique qui, pour la solution de polymère semi-dilué, peut être représenté comme une expansion du viriel où nous n’avons pris en considération que les deuxième et troisième coefficients du viriel de la solution de polymère. En variant des paramètres tels que la rigidité du polymère, la longueur du polymère, la concentration en polymère et le régime du solvant (comme le solvant thêta), que ce soit pour une surface colloïdale purement répulsive, pour une surface adsorbée ou pour la surface d'une couche de polymère greffé, nous avons été en mesure d'améliorer la barrière répulsive due aux polymères libres entre les particules et donc nous avons trouvé des conditions de la stabilisation cinétique du systèmeStable colloidal dispersions with evenly distributed particles are important for many technological applications. Due to Brownian motion colloidal particles have constant collisions with each other which often lead to their aggregation driven by the long range van der Waals attraction. As a result the colloidal systems often tend to precipitate. A number of methods have been devised to minimize the effect of long-range van der Waals attraction between colloidal particles or to override the influence of the attraction in order to provide the colloidal stability.In the PhD thesis we investigated the colloidal stabilization in solutions of free polymers which is commonly referred to as depletion stabilization. Previous theoretical studies of free-polymer induced (FPI) stabilization were based on oversimplified models involving uncontrolled approximations. Even the most basic features of the depletion stabilization phenomenon were unknown. It was unclear how the PI repulsion depends on the solution parameters, polymer structure and monomer/surface interactions.The free polymer chains were modeled as random walks in a self-consistent molecular field that satisfied to diffusion-like integro-differential equation. As the molecular field we used the chemical potential that for semi-dilute polymer solution can be represented as a virial expansion where we took into account only second and third virial coefficients of the polymer solution. Varying the parameters like polymer stiffness, polymer length, polymer concentration and solvent regime (like theta solvent) whether it is for purely repulsive colloidal surface, adsorbed surface or surface with grafted polymer layer we were able to enhance the repulsive barrier due to the free polymers between the particles and therefore found conditions for kinetic stabilization of the system
10
Kemp, Roger. "Colloids in external fields." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508084.
11
Clements, Andrew Franklin. "Photophysics of C60 Colloids." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/265338.
Анотація:
The goal of this dissertation is to study the photophysics of suspensions of colloidal C₆₀ particles to determine if their nonlinear optical (NLO) response is superior in any way to benchmark NLO materials such as molecular solutions of C₆₀ and carbon black suspensions (CBS). C₆₀ in molecular form is known to exhibit strong reverse saturable absorption (RSA) and it is posited that colloidal particles composed of many C₆₀ molecules would maintain some degree of RSA behavior upon association, although some quenching is to be expected. CBS is known to have an NLO response that is dominated by nonlinear scattering resulting from a phase change due to heating of the carbon black particles by absorbed energy. Colloidal C₆₀ particles that are many nanometers in diameter are similar to CBS, so it is posited that they would also have a nonlinear scattering mechanism contributing to their NLO response. Three samples of C₆₀ colloids are characterized by several techniques, along with two carbon black suspensions and one molecular solution of C₆₀. Transmission electron microscopy is used to determine morphology. Femtosecond pump-probe spectroscopy is used to determine the absorption spectrum and the relaxation kinetics of the first excited singlet state. Nanosecond laser flash photolysis is used to determine the absorption spectrum and the relaxation kinetics of the first excited triplet state. Z-scan is used to determine triplet-triplet absorption cross-sections. An experiment is performed to determine the percentage of the input energy that is transmitted, scattered, or absorbed by each sample. Computer modeling is performed to compare the experimental results to theory. Results show that all materials that exhibit nonlinear scattering have a constant extinction coefficient in the nonlinear regime, implying a characteristic size for the scattering centers that is independent of input energy. Quenching processes in C₆₀ colloids are found to be morphology dependent, with more crystalline structures resulting in stronger quenching and less RSA. C₆₀ colloids with stronger RSA are found to result in less nonlinear scattering than strongly quenched colloids. Highly crystalline C₆₀ colloids were shown to have a stronger NLO response than the benchmark materials at medium to high energies.
12
Quarcoo, Naa Larteokor. "Modeling polymer-colloid phase behavior." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 152 p, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1440615.
13
Boniello, Giuseppe. "Mouvement brownien des particules colloïdales partiellement mouillées." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS068/document.
Анотація:
La dynamique de particules colloïdales à l'interface entre deux fluides joue un rôle central dans la micro-rhéologie, l'encapsulation, l'émulsification, la formation de biofilms, la décontamination de l'eau. En outre, ce sujet est également stimulant d'un point de vue théorique en raison de la complexité de l'hydrodynamique à l'interface et du rôle de la ligne de contact. Malgré ce grand intérêt, le comportement d'une particule à une interface fluide n'a jamais été caractérisé directement. Dans cette thèse, nous étudions le mouvement brownien de billes micrométriques de silice et de sphéroïdes de polystyrène à une interface eau-air. Nous contrôlons expérimentalement tous les paramètres d'intérêt. L'angle de contact des billes est finement ajusté dans la gamme 30°-140° par des traitements chimiques de surface et mesuré in situ par interférométrie. Le rapport d'aspect de particules sphéroïdales varie dans la gamme 1 -10 par étirage de billes sphériques commerciales. Les dynamiques de translation et de rotation sont suivies par particle tracking. Contre intuitivement et contre tous les modèles hydrodynamiques la diffusion est beaucoup plus lente que prévu. Pour expliquer cette dissipation supplémentaire nous concevons un modèle tenant compte de la contribution des fluctuations thermiques de l'interface à la ligne de contact. Les fluctuations donnent origine à des forces aléatoires qui s'ajoutent à celles dues aux chocs de molécules. Le théorème de fluctuation-dissipation permet d'obtenir la friction supplémentaire associée à ces forces flottantes. La friction totale est discutée en termes d'hétérogénéités de la surface des particules et d'ondes capillaires à l'interfaceThe dynamics of colloidal particles at the interface between two fluids plays a central role in micro-rheology, encapsulation, emulsification, biofilms formation and water remediation. Moreover, this subject is also challenging from a theoretical point of view because of the complexity of hydrodynamics at the interface and of the role of the contact line. Despite this great interest, the behavior of a single particle at a fluid interface was never directly characterized.In this thesis, we study the Brownian motion of micrometric spherical silica beads and anisotropic polystyrene spheroids at a flat air-water interface. We fully characterize and control all the experimentally relevant parameters. The bead contact angle is finely tuned in the range 30-140° by surface treatments and measured in situ by a homemade Vertical Scanning Interferometer. The spheroid aspect ratio varies in the range 1 – 10 by stretching of commercial beads. The translational and the rotational dynamics are followed by particle tracking.Counter-intuitively, and against all hydrodynamic models, the diffusion is much slower than expected. To explain this extra dissipation we devised a model considering the contribution of thermally activated fluctuations of the interface at the triple line. Such fluctuations couple with the lateral movement of the particle via random forces that add to the ones due to the shocks of surroundings molecules. Fluctuation-dissipation theorem allows obtaining the extra friction associated to this additional mechanism. The fitting values of the total friction are discussed in term of the typical scales of particle surface heterogeneities and of surface capillary waves
14
Pierce, Flint G. "Aggregation in colloids and aerosols." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/348.
15
Williams, Ian. "Colloids in optically defined confinement." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633436.
Анотація:
Materials under spatial confinement are subject to volume exclusion conditions differing from those of a bulk material. On reducing a system to a lengthscale of the order of a few particles onc can observe new structures, modified dynamics and phase behaviour dramatically differing from that of the bulk system. Through understanding and controlling the boundaries confining a system one can alter the energy landscape it experiences. Three colloidal model systems are realised using holographic optical tweezers to investigate confinement phenomena in quasi two dimensions. ~Whereas the bulk of existing rescarch is concerned with confinement by hard boundaries, the systems presented here employ an adaptive, deformable wall or a soft confining potential. The first system, dubbed the colloidal corral consists of a circular boundary of optically trapped colloids confining additional colloids to its interior. Despite the fact that boundary curvature inhibits hexagonal ordering within this geometry, a bistability is observed between locally favoured hexagonal structures and globally preferential configurations mimicking the symmetry of the confinement. Such behaviour is not observed with hard wall confinement and is entirely due to the adaptivity of the boundary. Additionally, a novel technique for the mechanical measurement of pressure is presented, facilitated by the deformable wall. The second system introduces shear to the colloidal corral through rotation of the boundary and is known as the colloidal washing machine. The flow behaviour in this rotating confinement is investigated for a range of rotation rates. Rigid-body- like and shear melted regimes are identified and their structural behaviours characterised. The final system confines colloids within a circularly symmetric optical potential without a boundary. The result is the assembly of two-dimensional clusters, which are characterised for a range of potential widths and depths. The absence of a curved wall allows enhanced hexagonal ordering compared to the colloidal corral.
16
Köhler, Werner. "Hot colloids in polymer networks." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-179496.
17
Bakewell, David John Guy. "Dielectrophoresis of colloids and polyelectrolytes." Thesis, University of Glasgow, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416521.
18
Archer, Richard. "Catalytic self-phoretic active colloids." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19453/.
Анотація:
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.
19
Pawsey, Anne Claire. "Colloids at liquid crystal interfaces." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8969.
Анотація:
This thesis presents a study of colloidal particles dispersed in thermotropic liquid crystals. It has a specific focus on colloids in the presence of an interface between the liquid crystal and an isotropic fluid. Three systems are studied: colloids trapped at a planar interface between a cholesteric liquid crystal (CLC) and an isotropic oil, nematic emulsions with interfacial colloids and the influence of colloids on the phase transition kinetics of the cholesteric blue phase. Experiments are carried out using polarising optical and confocal microscopy. By combining these techniques, the director field of the liquid crystals could be imaged in combination with precise observation of the colloid locations. Custom image analysis algorithms are developed to extract the information. In the first system, we create an interface between a cholesteric liquid crystal and an isotropic liquid. Homeotropic anchoring leads to a well aligned cholesteric layer and the formation of the fingerprint texture. Fluorescent colloidal particles with planar surface anchoring are dispersed in the CLC. A majority of these particles decorate the interface. The final distribution of particles perpendicular to the interface has a clear dependence on the particle size. In the plane of the interface, surface defects form a template for the colloids. The second system is a particle dispersion within a short pitch CLC which exhibits a blue phase. The colloidal particles and associated defects act as nucleation sites for the blue phase in the cholesteric to blue phase transition. Colloidal particles cause localised melting from the blue phase to the isotropic phase and lead to a larger temperature range for coexistence between isotropic and blue phases. Furthermore, the isotropic regions can be faceted, their shape and size is controlled by the blue phase elasticity. In the final system, a nematic emulsion is created. Droplets of nematic LC are dispersed in water. Colloidal particles initially mixed into the liquid crystal decorate the interface between the two fluids. The addition of a surfactant switches the liquid crystal alignment at the fluid-fluid interface from planar to homeotropic. This forces a change in defect structure, from two boojums at the poles to a hedgehog defect in the droplet centre. The presence of colloids affects the switching dynamics and alters the final liquid crystal alignment preventing the droplets from forming a central radial defect. There is a symbiotic relationship between the particle properties - size and anchoring at the surface - and the elastic properties of the liquid crystal in the bulk and in the presence of an interface with an isotropic fluid. How the systems respond when the balance of these factors is altered is explored throughout the thesis.
20
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.
Анотація:
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.
21
Theurkauff, Isaac. "Collective Behavior of active colloids." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10251/document.
Анотація:
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 proposéeWe 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
22
Smith, Gregory N. "Charging colloids in nonpolar solvents." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683919.
Анотація:
Stabilizing charged species in nonpolar solvents is difficult due to their low relative permittivity (Er); therefore, surfactants that form inverse micelles are often used as charge control additives (CCAs). In this Thesis, the structural and electrokinetic properties of surfactants and surfactant-charged colloids in nonpolar solvents were studied. The aggregation of surfactants was studied using high-resolution small-angle neutron scattering (SANS) measurements. Critical micelle concentrations (CMCs) for inverse micelle formation were measured for an anionic and a nonionic surfactant, and the transition was different for the two types. However, variations to the surfactant counterion and the solvent did not influence the CMC. Contrast-variation SANS (CV-SANS) was used to study the interaction of surfactant with polymer latexes. The surfactant did not strongly interact with the steric stabilizer polymer and, rather, was located throughout the entire latex. Such a distribution of surfactant differs from other model colloids in nonaqueous solvents where the surfactant is assumed to be adsorbed at the core-solvent interface. Molecular variations to the surfactant structure resulted in differences to the charge of particles. Modifying the surfactant tail groups resulted in more effective CCAs. Triple-chain surfactants were more effective, and this may be due to the larger number of inverse micelles. Changing the surfactant counterion resulted in instability of the particles. This may be due to decreased particle charge and increased electrolyte screening. The results presented in this Thesis provide much-needed structural information and systematic variations to the field of charging in nonpolar solvents. Determining the chemical interactions between surfactants and solvents or colloids is important for understanding how surfactants form inverse micelles, stabilize particles, and generate charge.
23
Kim, Anthony Young. "Heteroaggregation of oppositely charged colloids /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/9834.
24
Labalette, Vincent. "Structure and rheology of anisotropic colloids." Thesis, Toulouse, INPT, 2020. http://www.theses.fr/2020INPT0068.
Анотація:
Les argiles colloïdalles sont des phillosilicates d’hydrure de magnésium (ou d’aluminium) pouvant, de part des substitutions isomorphiques, acquérir une charge négative structurale compensée par la présence de cations au niveau de l’espace interfoliaire ou en surface même du colloïde. Ces nanoparticules ont une forme de palet avec un rapport de forme pouvant varier entre 20 et 100. Lors de leur mise en suspension, les colloïdes s’hydratent provoquant ainsi leur gonflement et le relargage des cations. Les groupements hydroxyles présents en bordure des argiles sont extrêmement dépendants du pH et peuvent ainsi générer une charge de bord positive à bas pH, ou négative à pH élevé. Ainsi les argiles colloïdales en suspension présentent à la fois une anisotropie de forme et de charge. Ces caractéristiques confèrent aux dispersions d’argile des propriétés optiques (argiles ocreuses), mécaniques (fabrication de tuile, enduit) ou même nettoyantes (pouvoir dégraissant) intéressantes. Bien qu’étudié depuis de nombreuses années, le comportement des argiles en suspension reste controversé. C’est dans ce contexte que s’inscrit cette thèse dont l’objectif est de proposer un modèle de simulation « gros-grains » de particules présentant une anisotropie à la fois structurale et de charge et ainsi d’étudier le comportement à l’équilibre et hors équilibre d’une suspension de particules anisotropes. Contrairement au modèle Monte-Carlo habituellement utilisé pour modéliser le comportement à l’équilibre d’une suspension de particules anisotropes, le modèle présenté ici tient compte des interactions hydrodynamiques et permet ainsi d’étudier la dynamique du système, que ce soit lors de la formation de structures à l’équilibre ou suite à l’application de force de cisaillement. Les particules sont modélisées à l’aide d’agrégats de sphères liées entre elles par des ressorts, ou contraintes à un mouvement de corps rigide via les équations de la mécanique du solide. La dynamique des agrégats est étudiée à l’aide du code de simulations de type Accelerated Stokesian Dynamics (ASD) et les interactions électrostatiques modélisées suivant le principe d’additivité de paires avec un potentiel de Yukawa. L’implémentation du modèle à « gros-grain » de particules anisotropes dans le code ASD a ainsi permis d’étudier les structures à l’équilibre et sous écoulement de particules présentant des caractéristiques communes avec la Laponite, une smectite de type 2:1 largement étudiée expérimentalement et numériquement dans la littérature. Dans ce manuscrit, des études concernant ces particules anisotropes sont présentées pour différentes fraction volumique et portées d’interactions électrostatiques. La dynamique de formation des structures au repos (Wigner glass, gel, overlapping coin...) ainsi que leurs évolutions sont discutées. Enfin, la réponse rhéologique de ces structures lors de l’application d’un écoulement cisaillant est étudiée, mettant en lumière l’importance du ratio entre les forces électrostatiques et hydrodynamiques au sein de la dynamique du système. Pour des structures initialement percolées, la réponse du stress à la déformation du système dépend de la microstructure initiale aux temps courts, et possède un comportement rhéofluidifiant ainsi qu’une viscosité finale indépendants de la microstructure initialeColloidal clays are hydrous magnesium phyllosilicates (sometimes aluminum), usually bearing a negative structural charge coming from isomorphic substitution compensated by the presence of cations in the basal spacing or on the surface of the colloid. These nanoparticles have a platelet shape with an aspect ratio going from 20 to 100. When immersed in water, clays hydrate and swell, leading to the release of the cations. The hydroxyl group presents on the edge of the particles are sensitive to the pH (titrable sites) resulting in an amphoteric edge charge. At low pH the rim is positively charged and becomes neutral or negative at pH 11. Therefore, suspensions of colloidal clays have both charge and shape anisotropies. Thanks to these features, clay dispersions exhibit interesting optical properties (ochreous clays), mechanical properties (tile manufacturing, surface coating) and even cleaning properties (grease-removing). Although studied for decades, the behavior of colloidal clays remains controversial. In this manuscript, we propose a coarse-grained model to simulate particles with both structural and charge anisotropy. This model allows studying the behavior of colloidal suspensions at equilibrium and under shear flow. Contrary to the Monte-Carlo method usually employed to model the equilibrium behavior of anisotropic particles, the model presented in this thesis takes into account hydrodynamic interactions, allowing the dynamics of the system to be studied. The particles are coarse-grained as clusters of spheres bound by springs or constrained to a rigid body motion thanks to solid mechanics equations. The dynamics of the particles are computed using the Accelerated Stokesian Dynamics code (ASD), and the electrostatic interactions are computed in a pairwise additive fashion with a Yukawa potential. The implementation of this coarse-grained model in the ASD method allows studying the microstructure of anisotropic particles presenting similar features than Laponite, a 2:1 synthetic smectite clay widely studied experimentally and numerically in the literature. Several studies are presented here while varying the volume fraction and the range of electrostatic interactions. The dynamics of formation of the observed structures (Wigner glass, gel, overlapping coin, etc.) and their structural evolution behavior are then discussed. Finally, the rheological response of the different structures to a start-up shear has been studied, highlighting the importance of the ratio between the electrostatic and the hydrodynamic forces. For initially percolated systems, it has been shown that the stress response on the applied strain depends on the initial microstructure at short times, and exhibits shear-thinning and final viscous response independent of the initial structure
25
Higginbotham, Catrena Pearl. "The characterization and manipulation of the internal pore structure of tetramethoxysilane sol-gels and polymer hybrid gels." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/30556.
26
Shang, Jianying. "Surface thermodynamic properties of subsurface colloids." Online access for everyone, 2008. http://www.dissertations.wsu.edu/Dissertations/Summer2008/J_Shang_072108.pdf.
27
Neyland, Ryan P. "Colloid Detachment from Rough Surfaces in the Environment." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-050505-114151/.
28
Ramakrishnan, Ramaa N. "Surface enhanced Raman spectroscopic studies of the orientation of organonitriles on metal colloids." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1583.
Анотація:
Thesis (M.S.)--West Virginia University, 2000.Title from document title page. Document formatted into pages; contains xi, 81 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.
29
Palacci, Jérémie. "Manipulation of Colloids by Osmotic Forces." Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00597477.
30
Sano, Masaki, Hong-ren Jiang, and Daiki Nishiguchi. "Self-organization dynamics of active colloids." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-179578.
31
Robinson, Derek James. "Structure and dynamics of interfacial colloids." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334638.
32
Chapman, John Richard. "Ultrasonic wave interactions with magnetic colloids." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366409.
33
Irfachsyad, Danial. "Mesoscopic simulation of polymers and colloids." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252212.
34
Hinds, Ian Charles. "Characterisation of colloids by electric birefringence." Thesis, London South Bank University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336307.
35
Francis, Paul Anthony. "Production and stabilisation of copper colloids." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46299.
36
Law, Clement. "Simulations of lock and key colloids." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675695.
Анотація:
We introduce the concept of self-assembly and describe how it can explored with a system of colloids. We introduce the lock and key colloid, and describe how it can be useful probe for exploring a specific, geometry-centric, type of colloidal self-assembly called the depletion interaction. We illustrate some of the problems with simulating the lock and key colloid, and intro duce a novel simulation method to side-step many of these problems. Using this simulation technique, and derived theoretical thermodynamic apparatus, we show a methodology for parametrising the depletion drive self-assembly of colloids. This parametrisation allows us to avoid explicitly modelling the nanoparticles that mediate depletion-driven self-assembly and thereby speeds up any subsequent simulations by an order of magnitude compared to the novel simulation technique. Using our parametrisation, we repeat some measurements of explicitly modelled lock and key simulations and find good agreement. As a small aside, we also simulate a sedimenting, lock-only system in the same spirit as a published work. In this work, the authors find an interesting decrystallisation over time from a solid to liquid-like phase. We do not observe this in our experiment but instead note that we can induce a liquid-solid phase transition by varying the depth of the lock mouth. To end, we discuss the quality of our findings and what future avenues of work they may lead to.
37
Golz, Paul Michael. "Dynamics of colloids in polymer solutions." Thesis, University of Edinburgh, 1999. http://hdl.handle.net/1842/10922.
Анотація:
The dynamics of a dilute suspension of colloids diffusing in a simple liquid are well understood and are characterised by the Stokes-Einstein equation. However the validity of this equation for describing the diffusion of a colloid through a polymer solution has been questioned. In this work the motion of dilute poly-methylmethacrylate spheres diffusing through a solution of flexible polystyrene polymers has been studied. Dynamic light scattering was used to measure the self-diffusion of the spheres and the diffusion coefficient for this motion was found to exhibit time dependence. At short times the colloid moves faster than expected from a simple 'polymer solution as a continuum' assumption whereas at longer times this assumption appears valid. Solutions with polymer concentrations up to half the overlap concentration were investigated: the ratio of short to long time diffusion Ds/DL was found to increase with concentration. The effect of changing the quality of the solvent from theta to good was also investigated and no qualitative difference was found. In these experiments it was found that the effect of scattering from the polymer was more significant that initially expected. In particular, the presence of cross scattering, in which the electric field scattered from the colloid is correlated with that from the polymer, can be as high as 30%, despite the polymer scattering being only a few percent. A method for both calculating and experimentally measuring the magnitude of the cross scattering has been described. A new experimental methodology is proposed to minimise the cross and polymer scattering, allowing for measurement of the colloid scattering alone.
38
Hussain, Shahid. "The electromagnetic properties of nanoparticle colloids." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1445659/.
Анотація:
Electromagnetic applications have been at the forefront of technological advancements for many years. As demand for these grows, the need for materials possessing unique electromagnetic properties increases. The aim of this research is therefore to investigate the electromagnetic properties of the nanoparticle colloids in the frequency range of 1 MHz to 20 GHz, with focus on the electromagnetic absorption mechanisms at microwave frequencies. A broad range of magnetic and dielectric properties are investigated using novel, as well as conventional, theoretical and experimental techniques. A number of mechanisms are highlighted for tailoring the electromagnetic performance. Results from the CoxNii.x series, with particle sizes ranging from 25 nm to 200 nm, show particle size related dielectric and magnetic properties, which aid the optimisation of resulting properties, in addition to conventional mechanisms, which are also demonstrated in colloidal form. Further reduction in particle size to below 20 nm, leads to single magnetic domain particles, which also exhibit enhanced electromagnetic properties, as demonstrated with broadband magnetic performance achieved for Co ferrofluid with an average particle size of 5 nm. Charged particle colloids, which typically consist of particles with negative surface charge suspended in an aqueous electrolyte solution, have also been investigated. These exhibit interesting dielectric properties, which occur over a range of timescales determined by various aspects of the system. It is shown that the small nanoparticle sizes, ranging from 20 nm to 220 nm, lead to faster charge dynamics than those expected from conventional micron particle sizes, such that the loss extends to microwave frequencies. The results are fitted to various models, which are validated through experiment and used to establish the origin of the results. These are used to further optimise the electromagnetic properties achievable from nanoparticle colloids and assess their potential benefits.
39
Hunt, Paul Edward. "Protective colloids : understanding nucleation and grafting." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/protective-colloids-understanding-nucleation-and-grafting(a5f5c8c9-acc7-492b-bf81-3cf327af98cf).html.
Анотація:
Alkali-soluble resins (ASRs) were prepared by (i) solution and (ii) emulsion polymerization. All ASRs were synthesized with number-average molar masses < 20,000 g mol-1 and all had 15 wt% methacrylic acid 5 wt% styrene, the remaining 80 wt% was composed of either methyl methacrylate or a combination of methyl methacrylate and ethyl acrylate. All emulsion ASRs were made to 20% solids, with volume-average particle diameters (dv) in the region 30 – 50 nm, with a glass transition temperature of 80 – 120 °C. Emulsion polymerization was the preferred route for ASR synthesis, to allow further studies on their dissolution behaviour. Before their use as colloidal stabilizers, the dissolution behaviour of the ASRs needed to beinvestigated e.g. effect of temperature, molar mass, and composition. Particle size and absorbance measurements were taken during dissolution of ASRs to achieve 100%neutralization and these were shown to have two stages, an apparent particle swelling (whichwas rapid), and a slower, decrease in particle size as water-soluble polymeric material wasdiffusing out of the ASR particles. From this, further interpretation allowed for calculating the diffusion coefficient of the ASR polymer using the Stokes-Einstein equation. Time-domain nuclear magnetic resonance (TD-NMR) was employed to enhance understanding of what is occurring in the ASR particles, and in the aqueous, continuous phase. The final aspect of this project was to use the ASRs prepared as colloidal stabilizers in emulsion polymerizations of butyl acrylate (BA) and butyl methacrylate (BMA) using varying levels and also the effect of adding additional surfactant. The results show that the effect of ASR molar mass, the concentration of stabilizer, and also the impact of the EA-containing ASR greatly influence stability, whereby lower ASR molar mass, higher levels of stabilizer and including EA greatly benefit colloidal stability in PBA latexes. In PBMA latexes, a similar trend was also observed, but, the presence of ethyl acrylate (EA) in the ASR backbone has a detrimental effect on the colloidal stability, caused by the inability of grafting to occur between the ASR and PBMA.
40
Sano, Masaki, Hong-ren Jiang, and Daiki Nishiguchi. "Self-organization dynamics of active colloids." Diffusion fundamentals 20 (2013) 17, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13541.
41
Tu, Mei Hsien. "Physical characteristics of chemically propelled colloids." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/4531/.
Анотація:
Understanding the transport properties of microorganisms in fluid is a fundamental problem in soft matter physics, and the dynamics of an active colloid in non-equilibrium statistical mechanics has recently attracted pioneering investigations into the design of artificial swimming robots at the microscale. A topical review of the remarkable discoveries in the field, both theoretically and experimentally, is first addressed. The mechanism of interfacial phoretic transport is used for an active colloid achieving autonomous propulsion by diffusiophoresis. A theoretical framework has been established to ascertain the generic properties of the active motion of such a self-propelled colloid, driven by the use of surface catalytic reactions. The kinetic route for the chemical reaction is considered as a two-step process, followed by quantitative procedures that examine the influence of fuel concentration and colloid size on the propulsion velocity. Specifically, both Janus and inhomogeneous colloids are studied, and their propulsion velocities rise linearly with the fuel concentration in a dilute solution and decay with the size scale in the small size limits. The theoretical results for a Janus sphere are consistent with the experimental observation. Furthermore, to what extent can the incorporation of advection into the diffusion be interpreted as a means of self-propulsion. An advection-diffusion model is constructed to compute the concentration distribution of the solute and propulsion velocity, aiming to explore the role played by the advection effects on the movement of Janus particles. The numerical results show that while Janus particle can achieve an autonomous propulsion at a small P\'eclet number, the accumulation of solute particles in the upstream of the colloid disappears at the large Pe limit. In conclusion, the major outcome of this work is the demonstration of the qualitative agreement with the present analysis of mobility to explain the observed size dependence. Lastly, the results suggest that a catalytic colloid powered by diffusiophoresis is a useful model for self-propulsion and indicate what still needs to be done to obtain a full understanding of the swimming characteristics of colloidal dispersions.
42
Yang, Zhimou. "Molecular hydrogels : design, synthesis, enzymatic regulation, and biological applications /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202006%20YANG.
43
Tan, Chai Geok. "Deposition of colloidal spheres under quiescent conditions." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26744.
Анотація:
The phenomenon of deposition (or release) of fine particles or other microscopic species, suspended in a liquid, onto (or from) a foreign substrate surface plays a critical role in many natural and industrial processes. Traditionally, the analysis of this phenomenon has been conceptually divided into two steps — the transport step and the adhesion step. Attempts to understand the role of the adhesion step on the overall deposition process under most practical situations are complicated by the presence of a large number of interdependent parameters such as double layer thickness, particle and wall zeta-potential, particle size and flow, amongst others. Thus, as a first step towards gaining a better understanding of the phenomenon, an experimental study of a very simple deposition system, where only the random nature of the deposition process and the double layer interactions between deposited particles are important, was undertaken.
In this idealized system, a stable suspension of monodispersed, negatively charged colloidal silica spheres one micron in diameter, suspended in an aqueous medium in a specially constructed deposition cell, were allowed to settle by gravity and be deposited permanently onto a cationic polymer-coated glass cover slip. The magnitude of surface potential was altered by adjusting the pH of the suspension using NaOH and HC1, while the electrical double layer thickness was varied by dissolving different predetermined quantities of KC1 into the suspension.
The results showed that the trends in the experimental surface coverages obtained were in accordance with expectation in that as the double layer thickness, 1/К, or the particle zeta potential, ζ⍴’ , increased (leading to an increase in the interaction energy between the particles), the surface coverage decreased. Furthermore, the extent of surface coverages obtained when both 1/К and ζ⍴ were changed was found to be greater than that when 1/К alone was used as the controlling variable. A separate series of studies examining the effect of substrate double layer thickness on surface coverage was also performed by dissolving different predetermined quantities of K₃PO₄, into the suspension so that the substrate and the particles could differ in their respective double layer thicknesses. The results of surface coverages obtained in this study showed that the influence exerted by the substrate double layer was negligible. Besides these findings, the presence of geometric exclusion due to the random nature of the deposition process was also noted, although its effect was difficult to quantify.
Besides the systematic experimental study of colloidal deposition, attempts were made to develop two computer simulation models to generate deposition prediction which could be compared with results measured experimentally. The first scheme involved a two-dimensional simple rejection model where only non-overlapping particles were deposited, while the second scheme consisted of a three-dimensional model where the rolling of sedimenting particles over the surfaces of previously-deposited particles as well as the stacking of particles were allowed. Comparison of experimental results with those obtained using the two-dimensional model revealed that for all cases, the simulated results consistently underpredicted the experimental results due to the oversimplifying nature of the simulation. The trends in the experimentally obtained results, however, were approximated by the simulated results. Owing to its very complex nature, successful completion of the three-dimensional model simulation did not materialize. It is expected, however, that when such a model is successfully completed, it will yield predicted results which are in better quantitative agreement with those measured experimentally.
Besides the above, a separate study examining the effects of reaction temperature and the types of alcoholic solvent used on the properties of silica particles produced was also performed. This study led to the development of a novel method in which dispersed, uniform-sized, spherical silica particles in the size range of 0.2 to 2.0 µm can be produced by simply varying the reaction temperature and the type of alcoholic solvent used.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
44
Lu, Yu. "Engineering the structures and shapes of colloidal particles /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/10615.
45
Dersoir, Benjamin. "La physique du colmatage : de la particule colloïdale au bouchon." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S010/document.
Анотація:
La formation de bouchon est un problème récurrent et presque inévitable lors de l'écoulement de solutions diluées dans des milieux poreux. Actuellement, on ne sait pas comment, à partir du processus initial de déposition de particules à la paroi, ces dernières s'accumulent dans le pore et finissent par le boucher. L'idée générale de ce travail est d'étudier la dynamique de formation de bouchon lors l'écoulement de particules colloïdales au sein de matériaux poreux modèles (canaux microfluidiques). Nous décrivons dans un premier temps, les différents phénomènes physiques impliqués dans la capture de particules et dans l'agrégation colloïdale. Nous faisons également une brève présentation des différentes techniques d'imagerie utilisées dans ce travail et des méthodes de préparation des solutions colloïdales ainsi que des dispositifs microfluidiques. Le troisième chapitre est consacré à l'étude du processus de colmatage en situation de fort confinement (2d). Nous avons identifié deux régimes de colmatage (régime de ''ligne'' et ''d'invasion''). Nous avons ensuite déterminé les processus de capture de particules à l'origine de ces deux régimes, à l'échelle de la particule. Nous avons montré que le processus de colmatage correspond à un phénomène d'auto-filtration. Alors que les premières particules sont capturées de manière « directe » par les parois du pore, la déposition de toutes les suivantes résulte systématiquement d'une interaction avec ces dernières. Finalement, nous avons abordé le colmatage de pore 3d, dont la hauteur est égale à la largeur du pore. Nous avons fourni une description détaillée de l'ensemble du processus de colmatage, à l'échelle du pore et de la particule. Nous avons déterminé les conditions d'adhésion des premières particules à la paroi du pore, les propriétés de croissance des agrégats, ainsi que la manière dont ils se connectent pour obstruer le pore. Nous avons montré que cette dynamique de formation conduit à une structure finale de bouchon très ténueClog formation is a recurring and almost inevitable issue when dilute solution of particles flows in porous media. Currently, we do not know how, from the initial process of particle deposition on the pore wall, particles accumulate in the pore leading to its blocking. The main idea of this work is to study the dynamics of the clog formation, when colloidal particles flow through a single pore (microfluidics channels). In a first part, we describe the various physical phenomenon involved in the particle capture and the colloidal aggregation. We also describe briefly the imaging techniques used in this work as well as the colloidal solution and micro-fluidics chips preparation. The third chapter is devoted to the study of the clogging process in high confinement (2d). We identified two clogging regimes (“line” and “invasion”). We then studied the underlying capture mechanisms, at the particle scale, related to both clogging regimes. We showed that the blockage process corresponds to a self-filtration process. The first particles are captured “directly” by the pore walls, while the deposition of all the following ones systematically results from hydrodynamic interactions with those first still particles. Finally, we addressed the clogging of a 3d pore, in which the height of the pore is equal to its width. We gave a detailed description of the whole clogging process at the pore and at the particle scale. We provided the conditions for the adhesion of the first particles on the pore walls, the properties of subsequent aggregates growth, and how the aggregates eventually merge in order to block the pore. We showed that this dynamics of formation leads to a very loose clog structure
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Zimmermann, Urs [Verfasser]. "Colloids in Non-Equilibrium: Dynamical Density Functional Theory of Colloidal Suspensions under External Forcing / Urs Zimmermann." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2018. http://d-nb.info/1151698288/34.
47
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.
48
Chowdhury, Zaid Kabir. "Coagulation of submicron colloids in water treatment." Diss., The University of Arizona, 1988. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1988_35_sip1_w.pdf&type=application/pdf.
49
Chinas, Fernando. "The behaviour of colloids in lubricated contacts." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325565.
50
Wu, Lin. "Synthesis, modification and applications of polymer colloids." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581974.
Анотація:
Three approaches were used for the preparation of polymer colloids, including block copolymer micellization, miniemulsion and dispersion polymerisation. Polymers, ego PDMAEMA, PDMAEMA-b-PBMA, P(PDMA-PS)4, P(PS-PDMA)4, involved in the preparation were synthesized using reversible addition fragmentation chain transfer (RAFT) polymerisation. The details of each approach are given below. In the first approach, well-defined amphiphilic star block copolymers, P-(PS- PDMA)4 and P-(PDMA-PS)4 (P: porphyrin) were prepared from a free base porphyrin-cored chain transfer agent (CTA-FBP) and used for self-assembly studies. In methanol, a selective solvent for PDMA, spherical micelles were observed for both block copolymers, as characterized by TEM. UV-VIS studies suggested that star-like micelles were formed from P-(PS-PDMA)4, while P-(PDMA-PS)4 aggregated into flower-like micelles. In the second approach, miniemulsions, prepared using PDMAEMA-b-PBMA or PDMAEMA polymers were used as templates for the synthesis of polymer nanocapsules via the quaternization cross-linking of PDMAEMA (block), using 1, 2- bis(2-iodoethoxy)ethane (BIEE) as a bifunctional crosslinker. The miniemulsion prepared from block copolymers of PDMAEMA-b-PBMA were used as templates for the synthesis of Prussian Blue nanoshells, while cross-linked PDMAEMA homopolymer miniemulsions were used as capsules for hydrophobic dyes. In the last approach, PDMS-CTAs (poly(dimethylsiloxane)-based chain transfer agents) were prepared and used as stabilizers in the dispersion polymerisation of methyl methacrylate (MMA) in hexane. The effect of several factors, including the molecular weight of the PDMS and the concentration of the initiator, on the MMA polymerisation was investigated. The kinetics of the polymerisation in the presence of two CTAs were also investigated.