Dissertations / Theses: 'Anisotropic particles'

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Alzhrani, Attyah. "Fabrication of anisotropic polymer colloid particles." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/46004/.

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The fabrication of complex colloidal particles with anisotropic "patchy" e.g. Januslike, morphology will be studied. Known approaches towards "Janus particles" focus mostly on the micron-sized domain, with common fabrication routes based on monolayer modification or microfluidic production (restricts scale-up). We operate in the submicron regime (typically 100-500 nm) and use scalable emulsion polymerization strategies, in combination with entropic phase separation of swollen cross-linked latex particles and living radical polymerization, i.e. SET-LRP, to prepare our "patchy" amphiphilic particles. In this research, various Cross-linked densities (typically from 1 - 8wt%) poly(styrene) latexes (typically 100-500 nm) functionalized with tert-bromine functional groups, by batch or shot addition of (2-methacryloxyethyl -2- bromoisobutyrate) made via soap-free emulsion polymerization used as the precursor particles. Two synthetic pathways were investigated to make the targeted hairy Janus Particles. Approach one: in which we carried out the domain formation step prior to the fabrication of the polymer brushes, We found out that the effective synthetic way to make Janus hairy dumbbell particles in a reproducible manner is to start the synthesis with light cross-linked density of (1.9 to 3.0 wt% DVB) precursor poly(styrene) latex particles (150-250 nm diameter) made by shot addition method. The direct entropic phase separation from these latex particles leads to the formation of only one new domain with dumbbell shape morphology, when the swelling ratio used between monomer and latex is between 2.0 and 4.0, and with low DVB concentration in the swelling monomer (between 0.15-1.0wt%) using AIBN as initiator. Formation of hydrophilic polymer brushes by SET-LRP resulted in targeted hairy Janus particles with sub-micrometer diameter, in a reproducible manner. The length of the polymer brushes can be controlled by addition of water soluble ATRP initiator to produce shorter polymer brushes. The rate of SET-LRP was ultrafast and the rate can be reduced by addition of deactivator CuBr2. The second approach: water-soluble polymer brushes were grafted onto the surface of latex particles by SET-LRP. These “hairy” cross-linked colloids were swollen with additional monomers and initiator. Elevation of temperature causes entropic phase separation inducing new domains, which were polymerized. This approach leads to mainly popcorn and raspberry particles with some limited cases that are able to make hairy Janus Particles with non reproducible manner. The obtained complex particles show some interesting application such as a stabilization agent for Carbon Nanotubes (CNTs) in aqueous medium, Pickering emulsion stabilizer, and they self assembled upon addition of dilute electrolyte solution.

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Mcbride, John. "Computer simulations of anisotropic colloidal particles." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/computer-simulations-of-anisotropic-colloidal-particles(7c516a14-1be0-4450-a703-7048937f66d0).html.

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Self-assembly of colloidal particles into ordered structures is hailed as the preferred route to production of functional devices on the nanometre and micron length scales. The shape of a colloidal particle is one of the most influential factors determining the type of ordered structure that is assembled. Thus this thesis is devoted to understanding the role of particle shape on phase behaviour of colloidal systems. The effect of particle shape is isolated by using computer simulations to model particles as hard, anisotropic bodies which interact via purely repulsive interactions. Two particle models are studied which are representative of real colloids: non-convex wireframe polyhedra, and convex spherical caps. This thesis investigates the densest packings of several wireframe polyhedra. By comparing packings of six distinct polyhedra some general conclusions are drawn regarding the effects of rounded polyhedra edges, and a new shape descriptor is given which can suggest whether a wireframe polyhedron is likely to form new interpenetrating crystal structures. Wireframe cubes were studied in more detail, where the full phase behaviour was mapped out. A curious phenomenon was found whereby crystals formed by cubic wireframes exhibit plastic fluctuations. This unusual behaviour, if reproduced experimentally, may lead to useful optical properties. A systematic study of spherical caps demonstrates the effect of shape on collective behaviour as the particle model interpolates between a sphere and a thin platelet. Purely repulsive interactions are responsible for a range of different crystal structures, but the nucleation of these structures is challenging due to slow dynamics. Furthermore, there are often many ways for a spherical cap to pack in a given volume, which leads to multiple metastable states. The self-assembly of spherical caps was directed by sedimentation on a solid template which resulted in increased nucleation rates and more stable crystals. However, there is still a lack of control over the exact crystal structure due to the degeneracy in ways to pack.

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Panczyk, Mark M. "Directed assembly and dynamics of anisotropic particles." Thesis, University of Delaware, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3613049.

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Structures of nanometer and micrometer sized particles exhibit a variety of useful properties both as naturally occurring phenomena and in technological applications. In nature, colloidal crystals account for the colors in an opal and colloidal crystals can be used to create materials with photonic or phononic properties or used as coatings or templates. Creating these structures with nonspherical particles allows for a greater variety of properties. However, although the structures are dictated by thermodynamics, whether they are ultimately achievable as well as on what time scale they form, are limited by kinetics. In particular, concentrating particles slows their dynamics and reduces the rate at which they can arrange into the desired crystal. When nonspherical particles are assembled, both translational and orientational order is required to create crystals. Dicolloids, the shape of two overlapping spheres, are a particularly interesting particle shape to study due to the fact that their crystal structure can be changed with aspect ratio. The goal of this thesis is to investigate the kinetic limitations to assembly with increasing volume fraction. Specifically, we focus on concentrated monolayers of particles assembled into two-dimensional structures using oscillating electric fields.

Multiple light scattering is used to probe the dynamics of dicolloid particles with different shapes. With greater anisotropy, an increase in the diffusivity is observed. The diffusivity as a function of volume fraction could also be normalized by the random-close-packed volume fraction onto a master curve. The localization of particles was also characterized as a function of volume fraction and after accounting for repulsive interactions could be used to determine the glass transition of the dicolloids. The response of the localization length also compared well with theoretical predictions.

AC electric field induced assembly provides one potential pathway for directed self-assembly of colloidal particles. The advantage of using electric fields is that they orient and concentrate particles into a close-packed state. The structure of an assembled monolayer of dicolloids is studied both using microscopy and light scattering techniques. The scaling of the order to disorder transition was determined to be similar to that observed for spherical particles and optimal conditions for assembly were discovered. This optimum highlights the balance between creating a structure at thermal equilibrium and concentrating the particles quickly. The assembly of dicolloids is also unique in that the structure at low concentrations and in the initial phases of the assembly demonstrates end-to-end chaining which disappears for concentrated assemblies. Furthermore, orientational defects are apparent even in this low volume fraction case.

Although electric fields are chosen due to their ability to orient and concentrate nonspherical particles into structure, even at low concentration, care must be taken to ensure particles are oriented before concentrated. Otherwise they arrest into nonequilibrium structures. The concentrated particle dynamics, including the localizalization length and glass transitions are mapped out for dicolloid particles of different sizes and shapes. Values for the glass transition and diffusivity provide a metric for where the assembly is inhibited to better understand the optimal conditions for assembly processes.

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Gabrielson, Lynn. "The manufacture and behaviour of anisotropic polymer particles." Thesis, Brunel University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336644.

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Cayre, Olivier Jean. "Preparation and characterisation of anisotropic particles and microstructures." Thesis, University of Hull, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421219.

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Siem, Ellen J. (Ellen Jane) 1979. "Thermodynamic stability and implications of anisotropic boundary particles." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/27874.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 168-180) and index.
(cont.) Generally, a boundary is nonplanar in the neighborhood of an attached particle--even when anisotropic interfacial free energies do not produce faceting-and maintains a icKy = 0 while the boundary particles maintain a nonzero ,Ky. This is consistent with independent observations of Pb-rich particles at grain boundaries in dilute Pb-AI alloys. Predicted particle/boundary morphologies give a trade-off between boundary and particle interface-a particle replaces some boundary but also produces boundary area through local distortions. This result has several implications. The transition to perfect wetting requires a larger boundary energy density. The steady-state heterogeneous nucleation rate is increased when facets appear on the nucleus, but the increase is diminished if the boundary distorts. A corollary result presented in this thesis, that particles can induce rotations or ser- ration through torques, has implications in microstructural stability and illustrates avenues for future research.
Many material properties depend on grain and phase boundary morphology. Equilibrium boundary and particle morphologies are determined by their interactions through interfacial free energy. Currently, the determination of boundary and particle morphology is, for most materials systems, experimentally difficult. This thesis demonstrates that geometric constructions from capillarity theory for anisotropic interfaces cannot predict boundary and particle morphology, even in systems with uniform temperature, pressure, and chemical potentials. In this thesis, numerical methods are developed and implemented for calculations of anisotropic particles of fixed volumes attached to one or more interfaces that are also subject to specified constraints. Some boundary properties can be found experimentally, such as: the crystallographic misorientation across the boundary, the fixed average unit normal to the boundary, the Wulff shape (W') of the boundary, and the particle W'4 within each grain or phase abutting the boundary. These properties become model parameters in addition to the W' associated with each interface. This thesis also presents methods of generating algebraic expressions for interfacial free energy densities, W' (n), that produce W for a given symmetry. Calculated examples show that equilibrium configurations are formed from portions of the boundary and particle /s and do not contain orientations absent from the respective W's. Under the constraint that the pressure difference across a boundary is zero, the boundary will develop a constant weighted mean curvature (Kic) of zero.
by Ellen J. Siem.
Ph.D.

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Dou, Guangbin. "Mechanical and electrical characterisation of anisotropic conductive adhesive particles." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/35569.

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This thesis presents research into the mechanical and electrical characterisation of Anisotropic Conductive Adhesive (ACA) particles and their behaviour within typical joints. A new technique has been developed for study of individual ACA particle mechanical and electrical performance when undergoing deformation. A study of the effects of planarity variations on individual electrical joints in real ACA assemblies is presented firstly, followed by the research on the mechanical deformation and electrical tests of individual ACA particles undergoing deformation. In the co-planarity research, experiments introducing deliberate rotation between a chip and substrate were designed and carried out to simulate planarity variations in ACA assemblies. There are two outputs from this part of the research. One is the planarity variation effects on individual electrical joints in ACA assemblies, and the other is the effect of bond thickness on the resistance of a real joint.

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Brown, Judith. "Synthesis and use of Mesogenic Stabilisers and Anisotropic Dichroic Particles." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499911.

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Brown, A. B. D. "Order in concentrated colloidal dispersions of anisotropic particles under shear." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597000.

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The properties of colloidal dispersions, particularly under flow, are important in many areas of life, and yet present many fascinating and profound scientific problems. This dissertation presents an investigation of the positional and orientational order found in stable dispersions of anisotropic colloidal particles under shear. In order to understand the reasons behind the order present, it is necessary to study simple systems. To keep the dispersions simple, an emphasis is placed upon knowing and controlling the shape, size distribution and interactions of the particles investigated. A number of dispersions of anisotropic particles were prepared and stabilised to give an approximation to 'hard' particles. A technique was developed to measure the orientation distribution using the diffraction from mono-crystalline colloidal particles. The positional order was measured using small angle scattering. New shear geometries were designed and tested for shearing samples in a neutron beam. Two dispersions of plate shaped particles were studied. Plates with an aspect ratio of 5 and a polydispersity of 13 % (nickel (II) hydroxide) displayed an equilibrium phase transition to a columnar phase. Under low shear an aligned columnar phase was observed with columns oriented near the flow direction, and plate normals in the compressional quadrant at 20 degrees to the flow direction. As the shear rate was increased a 'phase transition' was observed to a smectic structure, with layers and particles normal to the gradient direction. Upon ceasing shear the structure returned to the columnar phase without the particles reorienting. Plates with a higher aspect ratio and a broader size distribution (kaolinite) were observed to align with normals in the compressional quadrant, moving towards the gradient direction at higher shear rates. At volume fractions below 0.13 the orientational order increased with concentration, while at higher concentrations the orientational order decreased with increasing concentration.

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Al-Shehri, Hamza Saeed A. "Wettability of anisotropic and porous particles adsorbed to fluid interfaces." Thesis, University of Hull, 2015. http://hydra.hull.ac.uk/resources/hull:15376.

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The wettability of particles and the way they attach to liquid interfaces is important for many technologies where powders are mixed with liquids or used as emulsifiers. Most such powders are highly agglomerated into larger aggregates that are highly porous. The attachment of such porous particles to liquid–fluid interfaces has not been studied in detail, especially in cases where the porous particles are impregnated with another fluid phase. The overall aim of the thesis is to study the behaviour of particles at the liquid–fluid interface with an emphasis on non– spherical and porous solid particles. We study the orientation of anisotropic microparticles and measure the contact angle of smooth and porous microparticles with the gel–trapping technique (GTT) to find the wettability of microparticles adsorbed in fluid interfaces. This technique allows us to obtain micrographs by scanning electron microscopy (SEM) for particles resting on polydimethylsiloxane (PDMS), which replicates the non–polar phase and allows for measuring the particle contact angle. We show the results of the typical attachment and orientation of needle–like (aragonite), rhombohedra–like (calcite) microcrystals and ethyl cellulose micro–rods, as well as highly porous hydrophilic and hydrophobic silica microparticles at these liquid interfaces. The importance of these results is in gaining an understanding of the adsorption behaviour and demonstrating actual information on anisotropic particles which have potential applications in industrial formulations and products. We also investigate how carboxylate modified latex (CML) microparticles adsorb at liquid surfaces and the preferred type of emulsion they can stabilise depending on the particle size and the surface density of carboxylic groups. We also study, both theoretically and experimentally, the effect of salt in the aqueous phase on the contact angle of such microparticles. The main finding is that the wettability of CML microparticles is governed by the carboxylic group density on the particle surface rather than their ionisation. We demonstrate that the type of Pickering emulsions is governed by the wettability of microparticles at the oil–water interface. We study the effect of the initial impregnation of porous particles with polar or non–polar phases on their attachment at liquid interfaces both theoretically and experimentally. Model supra–particles have been prepared by using building blocks of smaller colloid particles packed in a spherical aggregate. The particles were produced by drying latex particle suspensions of various particle volume fractions and concentrations, followed by partial fusion of the particles achieved by thermal annealing. We have studied the particle surface morphology and porosity and showed how the annealing temperature, the initial particle volume fraction of sulphate latex suspension and the evaporation temperature can be used to control the supra–particle final structure and porosity. Furthermore, we have investigated the link between the wettability of the porous supra–particle building blocks, i.e. sulphate latex particles, and the macroscopic (apparent) contact angle of the porous supra–particle when attached to liquid surfaces. The contact angles of porous supra–particles infused with water at the oil–water interface were found to be much bigger than those at the air–water interface as expected. We also show how the type of liquid filling the pores of the supra–particle affects its macroscopic contact angle at the oil–water interface.

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Butterworth, Sean. "Shape and chemical anisotropic particles in low dielectric constant media." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/shape-and-chemical-anisotropic-particles-in-low-dielectric-constant-media(d8ace7a1-8993-4a6b-a50d-2a2ea71c10f8).html.

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Electrophoretic displays (EDPs) are an attractive low power technology for small to large area displays. Such display technology has seen a surge of research interest with the launch of successful e-readers in the market place, owing to their lower power consumption and paper-like quality. This work aims to look at the influence of shape on the electrophoretic mobility of particles for such devices. Crosslinked poly(methyl methacrylate) (PMMA) precursor particles with a narrow size distribution were produced by non aqueous dispersion polymerisation utilising a pump-feed method. To produce shape anisotropic particles an adapted version of the dynamic swelling method for polar media was chosen. Suitable monomers were screened by the use of Hansen solubility theory to find monomers which interact with PMMA but not the solvent. It was found that 2- hydroxyethyl methacrylate (HEMA) and N-hydroxyethyl acrylamide (HEAm) were two such suitable monomers, methyl methacrylate (MMA) was also used as a control series.It was found that cluster-like particle morphologies could be produced by the MMA system by the inclusion of small quantities of crosslinking monomer. This was due to precipitation of higher molecular weight polymer segments to the seed particle surface. The cluster-like morphology could be enhanced by use of a polar crosslinking monomer and by sequential reactions. For the polar system, it was found that the reactions with pure monomer were unclean, due to the solubility mismatch of the monomer and the solvent system. This was overcome by a copolymerisation with MMA. The system showed different particle morphologies could be produced by varying the polar monomer content. In one case a sample of pure dumbbell-like particles could be produced. These dumbbell-like particles are thought to be chemical as well as shape anisotropic owing to monomer composition. EPD evaluation for the particles was undertaken and showed that all particles can become highly charged in low dielectric constant media, but that the shape anisotropic particles are prone to adsorption to the cell walls and electrodes.The work outlined in this thesis shows the first reporting of shape anisotropic polymeric particles produced in low dielectric constant solvents system.

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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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Tigges, Thomas Verfasser], Martin [Akademischer Betreuer] [Möller, and Andreas [Akademischer Betreuer] Walther. "Anisotropic particles for colloidal self-assembly / Thomas Tigges ; Martin Möller, Andreas Walther." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162498412/34.

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Tigges, Thomas [Verfasser], Martin [Akademischer Betreuer] Möller, and Andreas [Akademischer Betreuer] Walther. "Anisotropic particles for colloidal self-assembly / Thomas Tigges ; Martin Möller, Andreas Walther." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162498412/34.

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Newton, Bethany Jade. "Using external fields to control the behaviour of anisotropic particles at liquid interfaces." Thesis, University of Hull, 2016. http://hydra.hull.ac.uk/resources/hull:15426.

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In this thesis we use analytical theory and high resolution finite element simulations (using the program ‘Surface Evolver’) to consider the influence of an external magnetic field on the orientation and self-assembly of rod-like magnetic particles. Firstly, we calculate the equilibrium tilt angle with respect to the undeformed interface and the meniscus shape around an ellipsoidal particle when a magnetic field is applied perpendicular to the interface. As we increase field strength, the particle undergoes a discontinuous transition to the ‘perpendicular’ orientation. We show that it is necessary to include meniscus deformations in our calculations in order to accurately model this transition. We also show for the first time that the tilt angle vs. magnetic field curve exhibits hysteresis behaviour. Secondly, we study the orientation of magnetic cylindrical particles. For cylindrical particles at a liquid interface, orientational transitions induced by an external field remain when the external field is removed i.e. the switching effect is non-volatile. By tuning both the aspect ratio and contact angle, we show that it is possible to engineer cylindrical particles that have multiple locally stable orientations and hence obtain extremely rich magnetic responses to an external field. We show that such systems provide a facile platform for creating switchable functional materials. Finally, we investigate the interactions between, and self-assembly of, multiple ellipsoidal particles. For two ellipsoidal particles, the only stable configuration was found to be the side-to-side configuration. However, for three ellipsoidal particles, the tip-to-tip configuration was also found to be locally stable. There is good qualitative agreement between our finite element simulations and a linearised analytical theory and we attribute quantitative discrepancies between the two to non-linear and many-body effects.

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Bouville, Florian. "Self-assembly of anisotropic particles driven by ice growth : Mechanisms, applications and bioinspiration." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0155/document.

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Les phénomènes d'auto-assemblage sont au premier plan de la recherche en sciences des matériaux car ils comblent le vide laissé entre les procédés d'assemblage à l'échelle macroscopique et nanoscopique. L'auto-assemblage est basé sur l'organisation spontanée de composants individuels en motifs et structures. Contrôler l’agencement de la matière peut accroître les propriétés de matériaux en introduisant une certaine anisotropie. Cet agencement, comme de nombreux matériaux naturels le prouvent, peut même sous certaines conditions faire émerger de nouvelles caractéristiques. Au cours de ces trois années, nous avons utilisé l’ « ice templating » (texturation à la glace) pour déclencher l’alignement de plaquettes de dimensions microniques, le but final étant de répliquer la microstructure de la nacre. Cette technique induit la ségrégation des constituants d’une suspension à l’échelle du micron tout en obtenant des échantillons de quelques centimètres cubes. Ce procédé a permis la création de matériaux inorganique avec une microstructure semblable à la nacre, en additionnant trois niveaux de contrôles successifs : l’alignement local des plaquettes, l’alignement à longue distance des cristaux de glaces et enfin le contrôle de l’interface entre ces-mêmes plaquettes. L’utilisation d’une modélisation par éléments discrets nous a permis d’étudier la dynamique de l’auto-assemblage des particules anisotropes. Ce modèle, parce qu’il tient compte de la dynamique du procédé, nous a révélé comment l’organisation de ces particules se produit. La tomographie par rayon X a permis de visualiser les structures finales des échantillons et d’attester de la pertinence du modèle. L’alignement local des plaquettes dans les parois générées par la solidification de la glace peuvent accroître les propriétés fonctionnelles et structurales de composites. Dans ce cadres deux applications ont été étudiées : la conduction thermique dans des composites nitrure de bore hexagonal / silicone et les propriétés mécaniques d’alumine macroporeuses. Une adaptation du procédé a permis d’obtenir l’alignement à longue distance (quelques centimètres) des cristaux de glaces. Différents outils ont été développés pour caractériser la réponse fonctionnelle de ce type de composite en fonction de leurs architectures aux deux échelles considérées (celles des macropores et parois). Enfin, après la mise en place de ces deux niveaux de contrôle sur la structure, l’addition d’une phase vitreuse inorganique et de nanoparticules aux joints de grains des plaquettes a introduit, de façon similaire à la nacre, des interfaces pouvant dévier et arrêter la propagation de fissures
Self-assembly phenomena are of prime interest in materials science, because they fill the gap between assembly of macrostructure and processing of nanomaterials. Self-assembly is based on the spontaneous organization of individual small constituents into patterns and structures. Controlling the spatial arrangement can possibly improve materials properties by maximizing its response in a given direction. Furthermore, particular types of spatial arrangement, such as found in natural structures, can even induce new properties. During the past three years, we have used ice templating process to trigger the assembly of platelet-shaped particles to replicate the hierarchical structure of nacre. Control over this technique allowed structural customization at different length-scales: local orientation of the platelets, ice crystal long range order, and the control if the interfaces between the platelets. This hierarchical process has set the ground for the creation of a new fully mineral nacre-like alumina. The local platelet self-assembly triggered by ice growth was investigated by Discrete Element Modelling which provided new insight into the dynamic phenomenon responsible for the particles alignment. Synchrotron X-ray tomography was used to validated the model results. The different architecture observed in the final samples are not the result of a percolation threshold, as one could expect, but is instead a consequence of the delicate balance between pushing and engulfment at the solidification front. The local alignment of platelets can be beneficial for the functional and structural characteristics of composites and relevant aspects for two potential applications were investigated: the thermal properties of the hexagonal boron nitride/silicon rubber composites and the mechanical properties of macroporous alumina. Further adaptation of the process allowed for long range ordering of the ice crystals (up to the centimeter scale). Different tools have also been developed in order to characterize the response of composites as a function of the architecture at the level of the macropores and particle organisation. Once those two levels of alignment were achieved, the addition of a glassy phase and nanoparticles to the grain boundaries of the platelets introduces, just like in nacre, interfaces capable of deflect and even stopping crack propagation

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Steinbach, Gabi. "Ferromagnetic colloidal particles with anisotropic magnetization distribution: self-assembly and response to magnetic fields." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-207403.

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Systems of interacting colloidal particles are ideal tools for studies of pattern formation and collective non-equilibrium dynamics on the mesoscopic scale. These processes are governed by the interaction between the particles, which can be tuned by sophisticated fabrication. In this thesis, self-assembly of artificially designed magnetic spheres dispersed in water has been studied via video microscopy. The particles are based on silica microspheres with hemispherical ferromagnetic coating of [Co/Pd] multilayers with perpendicular magnetic anisotropy. These particles are exceptional in that they exhibit an off-centered net magnetic moment and yet obey rotational and mirror symmetry. It has been demonstrated how these magnetic properties provide innovative flexibility in pattern formation and collective dynamics based on magnetostatic interactions on the mesoscopic scale. The results are supported by analytical and numerical calculations of interacting spheres with radially shifted point dipoles (sd-particles). In two dimensions, the particles spontaneously self-assemble into branched structures as a result of a bistable assembly behavior where neighboring particles exhibit a non-collinear magnetic orientation. It has been shown that these features, which are atypical for homogeneous systems of magnetic particles, can be reproduced by simulation. It employs a theoretical model of a sphere that contains a distribution of three radially shifted point dipoles in analogy to the magnetization distribution in the coated particles. The stability of the assembly has been examined further by external manipulation using optical tweezers and homogeneous magnetic fields. A rich variety of stable structures with diverse spatial and magnetic ordering has been found. Particularly, the collective alignment of the specially designed particles in external fields opens completely new possibilities for the remote control over reversible pattern formation on the micrometer scale. In time-dependent fields, the collective dynamics of the anisotropic particles has revealed a novel approach for magnetically actuated translation. The variety of stable structures particularly enables control over this motion
Kolloidale Suspensionen sind geeignete Systeme zur Untersuchung von Strukturbildung und kollektiver Nichtgleichgewichtsdynamik in mesoskopischen Größenskalen. Diese Vorgänge werden durch die Wechselwirkung zwischen den Teilchen bestimmt, welche durch geeignete Partikelherstellung angepasst werden kann. In der vorliegenden Arbeit wird ein System von künstlich hergestellten magnetischen Partikelsuspensionen mittels Videomikroskopie untersucht. Quarzglas-Mikrokugeln wurden halbseitig mit einer ferromagnetischen Dünnschicht aus [Co/Pd] Multilagen mit senkrechter Anisotropie beschichtet. Solche Partikel sind ausgezeichnet durch ein resultierendes magnetisches Moment mit Rotations- und Spiegelsymmterie, welches zusätzlich vom Mittelpunkt der Kugel verschoben ist. Die vorliegende Arbeit zeigt, dass diese Besonderheit zu einer bisher unbekannten Flexibilität bei der mesoskopischen Strukturbildung und der kollektiven Dynamik auf der Basis magnetostatischer Wechselwirkung führt. Die vorgestellten Ergebnisse werden durch analytische und numerische Berechnungen unterstützt, denen ein Modell einer idealen Kugel mit verschobenem Dipol zugrunde liegt. Die zweidimensionale Selbstanordnung der Partikel zeigt experimentell zwei stabile Formen der Verknüpfung, welche zu verzweigten Strukturen mit unterschiedlich magnetischer Ausrichtung benachbarter Partikel führen. Diese für ein homogenenes System magnetischer Partikel außergewöhnlichen Eigenschaften konnten in Simulationen durch ein Modellsystem aus Kugeln mit drei verschobenen Punktdipolen reproduziert werden. Darüber hinaus wurde die spontante Anordnung unter externer Manipulation mittels optischer Pinzette und magnetischen Feldern untersucht. Es konnte eine Vielfalt an stabilen Strukturen mit verschiedenen magnetischen und strukturellen Anordnungen gefunden werden. Insbesondere die kollektive Ausrichtung dieser Partikel in externen Feldern eröffnet neuartige Möglichkeiten, kontrolliert und reversibel Mikrostrukturen zu erzeugen. In zeitabhängigen Feldern zeigen die anisotropen Partikel zusätzlich eine kollektive Dynamik welche eine neue Möglichkeit zum magnetischen Antrieb von Partikelagglomeraten eröffnet. Die Vielfalt der möglichen stabilen Strukturen erlaubt es in besonderer Weise diese Bewegung zu steuern

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Häring, Johannes Maria [Verfasser]. "Microscopically founded elasticity theory for defect-rich systems of anisotropic particles / Johannes Maria Häring." Konstanz : KOPS Universität Konstanz, 2020. http://d-nb.info/1233967290/34.

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Klement, Marco [Verfasser], Michael [Akademischer Betreuer] Schmiedeberg, Michael [Akademischer Betreuer] Engel, and Michael [Gutachter] Schmiedeberg. "Computational Studies of Anisotropic Particles / Marco Klement ; Gutachter: Michael Schmiedeberg ; Michael Schmiedeberg, Michael Engel." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2021. http://d-nb.info/1235224945/34.

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Campbell, Andrew Lee. "Fabrication of novel functional anisotropic micro-particles for foam stabilisation and structuring in food formulations." Thesis, University of Hull, 2009. http://hydra.hull.ac.uk/resources/hull:2488.

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This thesis is concerned with the fabrication of novel food-grade anisotropic solid particles for foam stabilisation and applications in food formulations. Two main techniques were employed for the fabrication of these particles. Acidic hydrolysis of Nata de Coco bacterial cellulose was used to form cellulose nano-rods which were applied as a foam scaffolding material. Characterisation and modification of Nata de Coco nano-rods was also carried out. It was found that cellulose nano-rods modified with a surface layer of ethyl cellulose exhibited good foamability.Secondly, a combination of in-shear-flow dispersion and solvent attrition techniques were employed to form micro-rods from the edible polymeric materials shellac, ethyl cellulose and zein. Characterisation of the properties of shellac, ethyl cellulose and zein micro-rods was carried out, together with assessments of their foam stabilisation ability. Stable aqueous foams were produced using shellac, ethyl cellulose and zein micro-rods as stabilisers, and ethyl cellulose micro-rods were also used to form water-in-oil emulsions.An extension of this technique was used in the fabrication of novel functional anisotropic food-grade micro-rods with micro-particle inclusions giving altered morphology. Enhanced foamability and drainage retardation was achieved using lumpy yeast-shellac micro-rods to stabilise aqueous foams. The method was extended to the production of aqueous dispersions of ballooned micro-rods, formed by two different protocols.This procedure also allowed the formation of novel, dual-function micro-rod capsules or ‘micro-ampules’ for stabilisation and encapsulation by inclusion of oils into the dispersed phase prior to micro-rod fabrication. The oils became trapped within the micro-rods resulting in micro-ampules with a range of morphologies which were characterised by fluorescence doping and microscopy.

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Letessier, Dylan. "Chute en régime inertiel de cylindres isolés ou en groupes dans une cellule mince." Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP030.

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Afin d'améliorer notre compréhension du comportement de corps solides anisotropes en mouvement dans un liquide en régime inertiel, nous avons étudié la chute d'un groupe de cylindres de taille finie évoluant en milieu confiné. L'utilisation d'une cellule de faible entrefer, qui laisse trois degrés de liberté aux cylindres, permet de suivre par imagerie rapide leur comportement. Dans ce but, un dispositif expérimental pré-existant a été amélioré, afin de permettre notamment d'introduire un contre-écoulement, ainsi qu'un système permettant la libération coordonnée de cylindres en groupe. En complément, les champs de vitesses dans le liquide, intégrés sur l’épaisseur de la cellule, peuvent être obtenus par PIV ombroscopique. En variant les longueurs et masses volumiques des cylindres toujours dans de l'eau, nous avons analysé l'impact des rapports de forme, des rapports de densité et du nombre d'Archimède sur la cinématique observée. Dans un premier temps, nous avons analysé l'influence de ces paramètres sur les caractéristiques du comportement d'un cylindre seul, isolé en milieu confiné. Ceci nous a conduit à une modélisation approfondie des forces en jeu et de leur interaction avec le fluide environnant. Cette modélisation s'est appuyée sur le formalisme des équations généralisées de Kelvin-Kirchhoff auxquelles nous avons ajouté des forces de traînée et de portance, mais également une force d'histoire qui permet de fermer le modèle sur une large gamme de paramètres. Nous montrons que les larges amplitudes des fluctuations conduisent à une contribution moyenne de la force inertielle couplant les translation et rotation du cylindre qui impacte sa vitesse moyenne de chute. Ceci nous a également permis d'avoir une prédiction de la fréquence d'oscillation. La présence d'un contre-écoulement ascendant, n'affecte pas sensiblement la vitesse relative par rapport au fluide et la fréquence d'oscillation du corps. Cependant, elle peut conduire à une re-stabilisation des trajectoires, dans certaines gammes de paramètres. Dans un second temps, notre attention s'est portée vers le comportement collectif d'un groupe de cylindres en chute libre en régime inertiel. Les conditions de lâchers étaient similaires d'un essai à l'autre, incluant le temps de lâcher et l'arrangement initial ; seul le nombre de cylindres, la masse volumique des cylindres et leur rapport de forme étaient variables. En observant ces groupes suffisamment loin du point d'injection, nous avons montré qu'ils évoluaient avec des vitesses verticales de chute constantes, occupaient une surface constante et présentaient des structures internes complexes fortement dépendantes des paramètres de contrôle. La structure est constituée d'objets regroupant plusieurs cylindres, qui interagissent, coalescent ou se fragmentent. Nous avons aussi mis en évidence la présence d’hétérogénéités importantes au sein du groupe, avec l’apparition de zones plus concentrées comprenant un plus grand nombre d'objets, plongeant plus vite dans le liquide, que nous avons appelé "coulées". L'analyse détaillée des vitesses des différents objets nous a permis de montrer que ceux-ci présentent des distributions statistiques comparables. Un modèle simple équilibrant traînée et flottabilité considérant le groupe comme un objet unique homogénéisé nous a permis d'obtenir une prédiction de la vitesse de chute du groupe, une fois son rayon équivalent connu. L'analyse des écarts-types des fluctuations de vitesse des objets au sein du groupe nous a permis de fournir des lois d'échelle prédictives basées sur deux ingrédients différents dans les directions horizontales et verticales, respectivement : la mobilité propre du corps isolé, caractérisée par sa fréquence d'oscillation et de lâcher tourbillonnaire, et les entraînements par les sillages et les coulées, moteur des fluctuations verticales, pris en compte par une concentration caractéristique du nuage
In order to improve our understanding of the behavior of anisotropic solid bodies in motion within a liquid under inertial conditions, we investigated the fall of a group of finite-sized cylinders in a confined environment. The use of a thin-gap cell, reducing the motion of the cylinders to three degrees of freedom, allowed us to track their behavior through high-speed imaging. To achieve this, an existing experimental setup was improved, by introducing in particular a counterflow and a system enabling the coordinated release of cylinders in a group. In addition to high-resolution cameras, seeding of the liquid was performed to enable the determination of the liquid velocity field, integrated across the thickness of the cell, using PIV shadowgraphy. By varying the lengths and densities of the cylinders, released in water, we analyzed the impact of the aspect ratios, the density ratio, and the Archimedes number of the cylinders on the observed kinematics. Initially, we examined the influence of these parameters on the behavior characteristics of a single cylinder, isolated in a confined medium. This led to a comprehensive modeling of the forces at play and their interaction with the surrounding fluid. The modeling relied on the Kelvin-Kirchhoff generalized equations, to which we added drag and lift forces, as well as a history force to close the model over a wide range of parameters. We demonstrated that the large amplitudes of fluctuations contribute to an average inertial force coupling the translation and rotation of the cylinder, affecting its mean fall velocity. This also allowed us to predict the oscillation frequency of the fluttering motion. The presence of an upward counterflow does not significantly affect the cylinder velocity relative to the fluid and the oscillation frequency. However, it may lead to trajectory restabilization under certain parameter ranges. In a second phase, we focus our attention to the collective behavior of a group of freely falling cylinders under inertial conditions. Release conditions were consistent across experiments, including release time and initial packing; only the number of cylinders, cylinder density, and aspect ratio varied. Observing these groups sufficiently far from the injection point, we demonstrated that the groups evolved with constant vertical falling velocities, occupied a constant surface, and featured complex internal structures highly dependent on control parameters. These structures consisted of objects grouping several cylinders, interacting, coalescing, or fragmenting. We also highlighted significant heterogeneities within the group, with the emergence of more concentrated areas containing a greater number of objects, plunging faster into the liquid, which we referred to as "streams". Detailed analysis of the velocities displayed by the different objects allowed us to show that they presented comparable statistical distributions. A simple model balancing drag and buoyancy, considering the group as a homogenized single object, allowed us to predict the group's fall velocity once its equivalent radius was known. The analysis of the standard deviations of velocity fluctuations of objects within the group allowed us to provide predictive scaling laws based on two different ingredients in the horizontal and vertical directions, respectively: the proper mobility of the isolated body, characterized by its frequency of oscillation and of vortex shedding, and the entrainment by the wakes and streams, driving the vertical fluctuations, accounted for by a characteristic concentration for the group

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Eriksson, Kristofer. "Development and Applications of Surface-Confined Transition Metal Complexes : Heterogeneous Catalysis and Anisotropic Particle Surfaces." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-88215.

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The main focus of this thesis has been directed towards developing novel surface-confined transition metal complexes for applications in heterogeneous catalysis and for the preparation of anisotropic particle surfaces. The first part describes the heterogenization of a homogeneous transition metal-based catalyst tetraphenyl cobalt porphyrin (CoTPP) on silicon wafers and on silica particles. The activity in hydroquinone oxidation for the silica particle-immobilized CoTPPs was found to be increased 100-fold compared to its homogeneous congener whereas the silicon wafer-immobilized CoTPPs achieved lower activity due to the formation of clusters of catalyst molecules on the support surface as detected with atomic force microscopy (AFM). The second part of this thesis describes the development and characterization of anisotropic particle-surfaces by electrochemical site-specific oxidation of surface-confined thiols. Reactive patches or gold gradients could be obtained on the particle surfaces depending on the type of working electrode used and on the electrolyte composition. The particle surface functionalities were characterized with X-ray photoelectron spectroscopy (XPS) and the particle-surface-confined patches and gradients were conjugated with proteins to obtain fluorescence for investigation using fluorescence microscopy. Gold-functionalized siliceous mesocellular foams were further demonstrated to be highly efficient and selective catalysts in the cycloisomerization of 4-alkynoic acids to lactones. The final part of this thesis describes the preparation and characterization of palladium nanoparticles heterogenized in the pores of siliceous mesocellular foam. The nanoparticles were analyzed with transmission electron microscopy (TEM) and found to have a size of 1-2 nm. Primary- and secondary benzylic- and allylic alcohols were oxidized by the heterogeneous palladium nanoparticles in high to excellent yields using air atmosphere as the oxygen source. The nanopalladium catalyst was used up to five times without any decrease in activity and the size of the nanoparticles was retained according to TEM.

At the time of doctoral defence the following paper were unpublished and had a status as follows: Paper1: Manuscript; Paper 4: Manuscript

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Cerrón-Infantes, Alonso, and Miriam M. Unterlass. "High-Performance polyimide particles with angular shape." Revista de Química, 2016. http://repositorio.pucp.edu.pe/index/handle/123456789/99080.

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Los polímeros de alto rendimiento (HPP) desempeñan un rol importante en la actualidad. El desarrollo de métodos más económicos para sintetizar estos polímeros minimizando el impacto tanto en la salud como en el medio ambiente es una prioridad. Las poliimidas (PI) pertenecen al grupo de los HPP y presentan características excepcionales como una gran estabilidad ante elevadas temperaturas, alta resistencia a los productos químicos agresivos y a la radiación, así como propiedades de aislamiento. Sin embargo, la síntesis de las PI presenta aún retos importantes. En este artículo presentamos un enfoque alternativo para sintetizar PI de forma y tamaño impresionante.
High-performance polymers (HPPs) play an important role in modern technology. Many efforts aim to develop cost-effective pathways to synthesize polymers without causing any harm to health and the environment. Polyimides (PIs) belong to the class of HPPs and they show outstanding features e.g. high-temperature stability, resistance to aggressive chemicals and radiation, as well as insulating properties. PI synthesis, however, present yet major challenges. We herein present an alternative approach to PIs of intriguing shape and of impressive size.

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Wittkowski, Raphael [Verfasser], Hartmut [Akademischer Betreuer] Löwen, Helmut [Akademischer Betreuer] Brand, and 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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Novak, Sanja [Verfasser], Jan K. G. [Akademischer Betreuer] Dhont, and Stefan U. [Gutachter] Egelhaaf. "Self-assembly of anisotropic DNA-based patchy particles / Sanja Novak ; Gutachter: Stefan U. Egelhaaf ; Betreuer: Jan K. G. Dhont." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2019. http://d-nb.info/1196870713/34.

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26

He, Kunyun. "Vers la production de 'patchy particles' à base de cristaux liquides." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLET002.

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L'un des objectifs majeurs de la recherche contemporaine en science des matériaux est la production d'architectures tridimensionnelles complexes grâce à l'auto-assemblage de briques élémentaires colloïdales. De ce point de vue, le développement de méthodes permettant la production de particules colloïdales capables d'interagir entre elles de façon complexe est donc crucial. Cette thèse décrit une nouvelle stratégie pour produire des particules anisotropes à l’aide de cristaux liquides. Il s’agit de doubles émulsions, où un cristal liquide nématique est confiné à l’intérieur d’une coque sphérique, et dont la géométrie impose la présence de défauts topologiques. Le nombre et la position des défauts déterminent la valence des particules ainsi que la directionalité des futures liaisons entre celles-ci. Dans cette étude, nous fabriquons de telles coques de cristaux liquides de façon contrôlée à la fois vis-à-vis de leur taille et des configurations de défauts. Nous décrivons les méthodes microfluidiques traditionnelles qui permettent de produire des coques de cristaux liquides, et nous en testons les limites de fonctionnement. Nous montrons que ces techniques ne permettent pas de réduire la taille du système à l’échelle colloïdale. Nous présentons un setup microfluidique amélioré, qui nous permet de produire des coques avec une grande distribution de taille et à haute fréquence. En combinant résultats expérimentaux et simulations numériques, nous étudions la possibilité d’induire des transitions entre différentes configurations de défauts, grâce à une modification continue de la géométrie de la coque. Enfin, nous nous intéressons à un cristal liquide chromonique doté d’une grande anisotropie élastique en phase nématique. Nous étudions la manière dont ce nématique exotique répond à l’influence du confinement et de la courbure, et nous explorons les nouvelles symétries qui en émergent
One main goal of modern material science is to produce complex three-dimensional architectures from the self-assembly of pre-designed colloidal building blocks. Developing methods to produce colloidal particles capable to interact in complex ways is crucial in this perspective. This thesis describes a new strategy in which liquid crystals are used for producing anisotropic colloidal particles. These new particles are double emulsions where a nematic liquid crystal is confined to a spherical shell, the geometry of which imposes the presence of topological defects. The number and position of the defects set the valence of the particles as well as the directionality of the eventual bonds between them. Our study aims at fabricating such liquid crystal shells in a controlled way, both in terms of size and defect structure. We describe the standard microfluidic methods used to produce liquid crystal shells and test their operational limits. We show that the standard microfluidic techniques do not allow for scaling the system down to the colloidal scale. We then present a new microfluidic set-up which improves our capability of producing shells in a large range of sizes at high frequencies. Combining experiments and numerical simulations, we study the possibility of inducing transitions between different valence states through a continuous variation of the shell geometry. Finally, we study a lyotropic chromonic liquid crystal, which exhibits a large elastic anisotropy in the nematic phase. We study how this exotic nematic liquid crystal responds to confinement and curvature and investigate the new emerging symmetries

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Michel, Antoine. "Simulation du comportement d'ellipsoïdes en écoulement turbulent confiné." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0188.

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En utilisant la simulation numérique directe (DNS), la dynamique de particules non sphériques inertielles dans un écoulement turbulent de canal a été étudiée numériquement. Un suivi lagrangien de particules, qui sont supposées ponctuelles et modélisées par des ellipsoïdes de révolution allongés, est utilisé pour étudier l’influence du rapport d’aspect et du temps de relaxation des particules sur leur interaction avec l’écoulement. La simulation numérique directe de l’écoulement permet d’obtenir une information précise sur les caractéristiques du fluide à la position des particules, qui sont nécessaire pour calculer les actions hydrodynamiques auxquelles elles sont soumises. Deux méthodes de calculs des actions hydrodynamiques ont été définies afin d’analyser leur influence sur la dynamique des particules. La première est basée sur des modèles théoriques, qui sont valides sous l’hypothèse d’un écoulement rampant à l’échelle de la particule et sont très utilisés dans la littérature. La seconde est basée sur l’utilisation de corrélations semi-empiriques, valides pour des valeurs du nombre de Reynolds particulaire modérées. Les simulations ont été réalisées jusqu’à ce que la distribution des particules atteigne un état stationnaire, afin d’obtenir une comparaison non biaisée de l’influence de la forme et de l’inertie. Quelle que soit la modélisation, les statistiques de la vitesse de translation ne dépendent pas significativement de l’allongement des particules. Il y a par contre des différences quantitatives importantes entre les statistiques de translation obtenues avec ces deux méthodes de modélisation pour les particules d’inertie élevée. Les statistiques de rotation sont affectées de façon majeure par la modélisation des actions hydrodynamiques, quelle que soit la position dans le canal. Ces observations concernant l’influence de la modélisation restent valides pour des valeurs plus élevées du nombre de Reynolds. L’augmentation de la valeur de ce paramètre cause néanmoins une uniformisation de la distribution des particules et une augmentation de l’intensité des fluctuations de la vitesse et de la vitesse angulaire de l’écoulement vu par les particules. Ces fluctuations plus intenses modifient l’orientation préférentielle des ellipsoïdes, indépendamment de leurs caractéristiques et du modèle utilisé pour calculer les actions hydrodynamiques. La comparaison des résultats obtenus par simulation avec des données expérimentales indique que les formulations bas Reynolds permettent une représentation correcte de la dynamique de particules très allongées et non inertielles
Using direct numerical simulation (DNS), the dynamics of inertial, non-spherical particles carried by the turbulent flow in a channel has been studied numerically. Under the hypothesis of pointwise particles, modelled as prolate ellipsoids, Lagrangian particles tracking is used to study the influence of the particle aspect ratio and inertia on their interaction with the flow. Direct numerical simulation of the flow allows to obtain an accurate information about the properties of the fluid at the particle position, which are required to compute the hydrodynamic actions that they undergo. The hydrodynamic actions have been computed using two different methods to study the influence of their modelling on the particle dynamics. The first model is based on theoretical formulas which are valid under the assumption that there is a creeping flow motion at the particle scale and are widely used in the literature. The second model relies on correlations, which are valid at moderate values of the particle Reynolds number. Simulations have been carried until the particle distribution reaches a steady state in order to obtain an unbiased comparison of the influence the particle shape and inertia. For both modelling of the hydrodynamic actions, translation velocity statistics do not significantly depend on the particle shape. There are however important quantitative differences between the translation statistics obtained using each model. Angular velocity statistics are strongly influenced by the hydrodynamic actions modelling, everywhere in the channel. These observations about the influence of the modelling remain valid for higher values of the flow Reynolds number. Increasing the value of this parameter nonetheless causes an uniformization of the particle distribution and increases the magnitude of the fluctuations of the velocity and angular velocity of the fluid seen by the particles. These stronger fluctuations modify the preferential orientation of the ellipsoids, regardless of their characteristics and of the model used to compute the hydrodynamic actions. The comparison of the simulation results with experimental data indicates that the model valid under the creeping flow assumption allows to simulate the dynamics of very long and weakly inertial ellipsoids realistically

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Wu, Liang. "Modelling liquid crystalline ordering in anisotropic and inhomogeneous fluids : from simple models of rod- and disc-like particles to polypeptides." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/14620.

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A liquid crystal (LC) is a substance that exhibits phases intermediate between a crystal and a disordered liquid state. LCs have attracted longstanding research interest because of their potential commercial applications in opto-electronics, pharmaceuticals and surfactants but also because ordered soft matter is prevalent in bio-molecular systems such as DNA and lipid cell membranes. In liquid-crystalline systems, both molecular shape and asymmetric attractive interactions contribute to the formation and ultimate stability of anisotropic phases. The research outlined in this thesis provides a fundamental understanding of these systems by developing theoretical models and undertaking detailed molecular simulation studies. In the first part of this thesis, prototype oblate models for LCs are studied: cut spheres and cylindrical discs. Coupled with a scaled Onsager approach, a general equation of state (EoS) for hard-core discotic LCs is developed that allows for an accurate description of the isotropic and nematic phases of oblate discs by introducing a correction to incorporate the negative contributions from high-order virial coefficients. Combining the above mentioned approach with an extended cell approach, the isotropic-nematic-columnar phase diagram of cut spheres is determined. The accuracy of the EoS is assessed by comparison with the more traditional Parsons-Lee description and existing simulation data. Although the anisotropic athermal hard-body fluid is a reasonable representation of lyotropic or colloidal LCs, for thermotropic LC systems temperature plays a key role. In the second part of this thesis a model of hard-core particles incorporating additional anisotropic attractive interactions is proposed to describe thermotropic LCs. Based on a perturbation theory and the Onsager-Parsons-Lee approach, a van der Waals-type (meanfield level) theory of attractive hard-core particles is formulated in a compact algebraic form. The phase diagrams of model attractive prolate (spherocylinder) and oblate (cylindrical disc) molecules are calculated in order to examine the separate effects of molecular shape and anisotropic attractive interactions. As a practical example, a coarse-grained model comprising an attractive spherocylinder is employed to describe phase behaviour of solutions of the polypeptide poly-(γ-benzyl-L-glutamate) (PBLG) in dimethylformamide (DMF). Quantitative agreement between the results obtained from the EoS and experimental data is obtained. In the final part of the thesis, a detailed Monte Carlo (MC) simulation study of athermal mixtures of hard spherocylinders and hard spheres between two well separated parallel hard walls is performed. A combination of constant volume (canonical ensemble) and constant (normal) pressure (isobaric-isothermal ensemble) simulations are carried out. With these simulations, the bulk phase behaviour as well as surface-induced LC ordering are explored. The phase diagram of binary mixtures of hard spherocylinders and hard spheres is presented and is compared with the predictions of the one-fluid Parsons-Lee and many-fluid theories. Rich phase behaviour is exhibited on the surface of the walls: drying (de-wetting), isotropic wetting, and nematic wetting are all observed. A previously unreported entropy-driven transition from a bulk nematic state to a homeotropic smectic surface ordering (with particles arranged in a perpendicular orientation relative to the surface plane) is seen in for both the pure hard rod system and the mixture of hard rods and hard spheres as the density is increased (high pressure states).

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Mondiot, Frédéric. "Comportement de particules colloïdales dans des solvants nématiques : influence de la forme et de la taille." Phd thesis, Bordeaux 1, 2011. http://tel.archives-ouvertes.fr/tel-00657747.

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Ces travaux de thèse ont pour but d'étudier l'état de dispersion de particules colloïdales dans des cristaux liquides nématiques lyotropes. Ces solvants organisés sont constitués de micelles nanométriques anisotropes. Dans un premier temps, nous montrons qu'il est possible de réaliser des suspensions cinétiquement stables en jouant notamment sur la forme des inclusions micrométriques. Un modèle, développé dans le cadre de cette étude, permet de rendre compte de nos observations. Dans un second temps, nous nous intéressons à l'influence de la diminution de taille de particules sur l'état de dispersion du système. A l'échelle nanométrique, le mouvement brownien, anisotrope dans ce type de milieu, semble gouverner les phénomènes observés.

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Pal, Santosh Kumar. "Anisotropic hard magnetic nanoparticles and nanoflakes obtained by surfactant-assisted ball milling." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-193165.

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The research work in this thesis has been devoted to understand the formation mechanism of single-crystalline and textured polycrystalline nanoparticles and nanoflakes of SmCo5 and Nd2Fe14B prepared by surfactant-assisted (SA) ball milling and to study their microstructural and magnetic properties. The nanoparticles and nanoflakes are promising candidates to be used as hard magnetic phase for the fabrication of high-energy-density exchange-coupled nanocomposite magnets. The influence of a range of different surfactants, solvents and milling parameters on the characteristics of ball-milled powder has been systematically investigated. Small fraction (~10 wt.%) of SmCo5 nanoparticles of average diameter 15 nm along with textured polycrystalline nanoflakes of average diameter 1 µm and average thickness of 100 nm were obtained after SA – ball milling of SmCo5 powder. Isolated single-crystalline particles (200-500 nm) and textured polycrystalline flakes (0.2-1.0 µm) of Nd2Fe14B have been prepared in bulk amount (tens of grams), after SA – ball milling of dynamic-hydrogen-disproportionation-desorption-recombination (d-HDDR) processed Nd2Fe14B powder. These single-crystalline Nd2Fe14B particles are promising for their microstructure for the fabrication of exchange-coupled nanocomposite permanent magnets. The SmCo5 and Nd2Fe14B flakes and particles were well aligned in magnetic field: the former showed [001] out-of-plane orientation while the latter showed [001] in-plane orientation. A maximum degree of texture values of 93 % and 88 % have been obtained for the magnetically-oriented SmCo5 flakes and Nd2Fe14B single-crystalline particles, respectively. SA – ball milling resulted in an increase of coercivity of SmCo5 particles from 0.45 T for un-milled powder to a maximum value of 2.3 T after 1 h of milling, further milling resulted in a decrease of the coercivity. The coercivity of SA – ball-milled Nd2Fe14B particles decreased drastically from 1.4 T for un-milled d-HDDR powder to 0.44 T after 0.5 h of milling, isolated single-crystalline particles (200-500 nm size) obtained after 4 h of SA – ball milling showed a coercivity of 0.34 T. The drastic decrease in coercivity of ball-milled Nd2Fe14B particles is attributed to the morphological change because the demagnetization in Nd2Fe14B magnets is governed by nucleation mechanism. A remarkable enhancement in coercivity from 0.26 T to 0.70 T for ethanol-milled sample and from 0.51 T to 0.71 T for oleic-acid-milled samples has been obtained after an optimum heat-treatment at 400 0C. An increase of α-Fe and Nd2O3 phase contents and a sharp change of lattice parameter c of Nd2Fe14B was observed when heat-treating above 400 0C. The change in lattice parameter at higher temperature is thought to be due to partial substitution of carbon atoms present in the surfactant or solvent, for boron atoms
Das Ziel dieser Arbeit ist es, den Mechanismus der Herstellung von einkristallinen und texturierten polykristallinen Nanopartikeln und Nanoflakes aus SmCo5 und Nd2Fe14B durch Tensid-gestütztes Kugelmahlen zu verstehen. Des Weiteren soll deren Gefüge und magnetische Eigenschaften untersucht werden. Die Nanopartikel sind vielversprechende Kandidaten zur Verwendung als hartmagnetische Phase in hochentwickelten, austauschgekoppelten Nanokomposit-Magneten. Der Einfluß der Art der verwendeten Tensid, Lösungsmittel sowie Mahlparameter auf die Eigenschaften der kugelgemahlenen Pulver wurde systematisch untersucht. Ein kleiner Anteil (~10 m.%) von SmCo5 Nanopartikeln mit mittlerem Durchmesser von 15 nm zusammen mit texturierten polykristallinen Plättchen mit mittlerem Durchmesser von 1 µm und mittlerer Dicke von 100 nm wurden nach Tensid-gestütztes Kugelmahlen erzeugt. Alleinstehende einkristalline Partikel (200-500 nm) und texturierte polykristalline Plättchen (0,2-1,0 µm) aus Nd2Fe14B wurden in größeren Mengen (einige 10 g) hergestellt. Das verwendete Ausgangspulver wurde hierbei durch dynamisches-Hydrierung-Disproportionierung-Desorption-Rekombination (d-HDDR) hergestellt und anschließend Tensid-gestütztes Kugelmahlen. Die genannten einkristallinen Nd2Fe14B Partikel sind ebenfalls vielversprechend als hartmagnetischer Bestandteil von austauschgekoppelten Nanokomposit-Magneten. Die SmCo5- und Nd2Fe14B-Plättchen und -Partikel wurden alle in einem Magnetfeld ausgerichtet: erstere zeigten aus der Ebende herauszeigende und letztere in der Ebene liegende [001]-Orientierung. Ein maximaler Texturgrad von 93% wurde für im Magnetfeld ausgerichtete SmCo5 flakes bzw. 88% für einkristalline Nd2Fe14B Partikel erzielt. Tensid-gestütztes Kugelmahlen führte zu einem Anstieg der Koerzitivfeldstärke von SmCo5 Partikeln von 0,45 T für ungemahlenes Pulver auf 2,3 T nach einer Mahldauer von 1 h. Weiteres Mahlen führte zu einem Abfall der Koerzitivfeldstärke. Die Koerzitivfeldstärke von Tensid-gestütztes Kugelmahlen Nd2Fe14B Partikeln verringerte sich stark von 1,4 T von ungemahlenem d-HDDR Pulver auf 0,44 T nach 0,5 h Mahlen. Freistehende einkristalline Partikel (200-500 nm groß), welche nach 4 h Tensid-gestütztes Kugelmahlen erhalten wurden, zeigten eine Koerzitivfeldstärke von 0,34 T. Der starke Abfall der Koerzitivfeldstärke von gemahlenen Nd2Fe14B Partikeln wird die morphologischen Veränderungen zurückgeführt, da die Ummagnetisierung nukleationsgesteuert ist. Ein bemerkenswerter Anstieg der Koerzitivfeldstärke von 0,26 T auf 0,70 T wurde für eine in Ethanol gemahlene Probe verzeichnet, sowie ein Anstieg von 0,51 auf 0,71 T für eine Probe, welche mit einer Zugabe von Oleinsäure gemahlen wurde. Beide Proben wurden einer optimierten Wärmebehandlung bei 400°C unterzogen. Bei höheren Temperaturen wurde für Nd2Fe14B ein Anstieg der Menge an α-Fe und Nd2O3 gefunden und eine sprungartige Veränderung des Gitterparameters c der Nd2Fe14B Phase. Die Veränderung des Gitterparameters wird auf die partielle Substitution von Kohlenstoffatomen des Tensid oder Lösungsmittels gegen Boratome zurückgeführt

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Wüstner, Cornell. "Selbstorganisierte Strukturen mit Saturn-Partikeln." Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-157631.

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Die vorliegende Arbeit beschreibt Herstellungsmöglichkeiten für sogenannte Saturn-Partikel. Es handelt sich dabei um Partikel, die auf ihrer Oberfläche drei Bereiche mit unterschiedlichen Eigenschaften aufweisen. Zwei Kappen mit gleichen Eigenschaften sind durch einen Gürtel getrennt, der sich stark von den Kappen unterscheidet. Im Speziellen geht es hier um die unterschiedliche Benetzbarkeit der Bereiche. Die Herstellung von Saturn-Partikeln mit einem hohen Benetzungskontrast wurde auf zwei verschiedenen Wegen realisiert. Als Ausgangspunkt dienten Mikroglaskugeln, die zunächst zur Hydrophobierung ihrer Oberfläche mit einem Silan behandelt wurden. Eine Art der Saturn-Partikel wurde durch das Ätzen eines Gürtels rund um die Partikel mit Flusssäure in einer im Rahmen dieser Arbeit entwickelten Spülzelle erzeugt. Auf diese Weise konnten Partikel mit zwei hydrophoben Kappen und einem hydrophilen Gürtel erhalten werden. Eine weitere Art dieser Partikel wurde durch das Abschleifen der Partikelkappen nach vorheriger Einbettung in Polymerfilme erhalten, wodurch die hydrophobe Beschichtung abgetragen und das ursprünglich hydrophile Glas freigelegt wurde. Die so erhaltenen Partikel wiesen zwei parallele, hydrophile Bereiche auf, die durch einen hydrophoben Gürtel voneinander getrennt waren. Es wird gezeigt, dass Saturn-Partikel in Systemen mit Wasser und Öl beim Mischen von unterschiedlichen Anteilen der drei Phasen durch Selbstorganisationsprozesse verschiedene Strukturen wie Ketten oder Schichten ausbilden können. Des Weiteren sind sie in der Lage in einem System mit Wasser und Luft besondere Schäume auszubilden, die eine sehr hohe Stabilität aufweisen. Die Partikel stabilisieren darin Flüssigkeitsfilme zwischen den Luftblasen, wobei der hydrophile Gürtel im Wasserfilm und die hydrophoben Kappen in der Luft liegen.

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Effenberger, Frederic [Verfasser], Horst [Gutachter] Fichtner, and Hans Jörg [Gutachter] Fahr. "Anisotropic diffusion of energetic particles in galactic and heliospheric magnetic fields / Frederic Effenberger ; Gutachter: Horst Fichtner, Hans Jörg Fahr ; Fakultät für Physik und Astronomie." Bochum : Ruhr-Universität Bochum, 2013. http://d-nb.info/1191479730/34.

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Steinbach, Gabi [Verfasser], Artur [Akademischer Betreuer] Erbe, Artur [Gutachter] Erbe, Sibylle [Akademischer Betreuer] Gemming, and Michael [Gutachter] Schreiber. "Ferromagnetic colloidal particles with anisotropic magnetization distribution: self-assembly and response to magnetic fields / Gabi Steinbach ; Gutachter: Artur Erbe, Michael Schreiber ; Artur Erbe, Sibylle Gemming." Chemnitz : Universitätsbibliothek Chemnitz, 2016. http://d-nb.info/1214305008/34.

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MORADI, KAMRAN. "Acoustic Manipulation and Alignment of Particles for Applications in Separation, Micro-Templating, and Device Fabrication." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/1753.

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This dissertation studies the manipulation of particles using acoustic stimulation for applications in microfluidics and templating of devices. The term particle is used here to denote any solid, liquid or gaseous material that has properties, which are distinct from the fluid in which it is suspended. Manipulation means to take over the movements of the particles and to position them in specified locations. Using devices, microfabricated out of silicon, the behavior of particles under the acoustic stimulation was studied with the main purpose of aligning the particles at either low-pressure zones, known as the nodes or high-pressure zones, known as anti-nodes. By aligning particles at the nodes in a flow system, these particles can be focused at the center or walls of a microchannel in order to ultimately separate them. These separations are of high scientific importance, especially in the biomedical domain, since acoustopheresis provides a unique approach to separate based on density and compressibility, unparalleled by other techniques. The study of controlling and aligning the particles in various geometries and configurations was successfully achieved by controlling the acoustic waves. Apart from their use in flow systems, a stationary suspended-particle device was developed to provide controllable light transmittance based on acoustic stimuli. Using a glass compartment and a carbon-particle suspension in an organic solvent, the device responded to acoustic stimulation by aligning the particles. The alignment of light-absorbing carbon particles afforded an increase in visible light transmittance as high as 84.5%, and it was controlled by adjusting the frequency and amplitude of the acoustic wave. The device also demonstrated alignment memory rendering it energy-efficient. A similar device for suspended-particles in a monomer enabled the development of electrically conductive films. These films were based on networks of conductive particles. Elastomers doped with conductive metal particles were rendered surface conductive at particle loadings as low as 1% by weight using acoustic focusing. The resulting films were flexible and had transparencies exceeding 80% in the visible spectrum (400-800 nm) These films had electrical bulk conductivities exceeding 50 S/cm.

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Campana, Lorenzo. "Modélisation stochastique de particules non sphériques en turbulence." Thesis, Université Côte d'Azur, 2022. http://www.theses.fr/2022COAZ4019.

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Le mouvement de petites particules non-sphériques en suspension dans un écoulement turbulent a lieu dans une grande variété d’applications naturelles et industrielles. Par exemple, ces phénomènes impactent la dynamique des aérosols dans l’atmosphère et dans les voies respiratoires, le mouvement des globules rouges dans le sang, la dynamique du plancton dans l’océan, la glace dans les nuages ou bien la combustion. Les particules anisotropes réagissent aux écoulements turbulents de manière complexe. Leur dynamique dépend ainsi d’un large éventail de para- mètres (forme, inertie, cisaillement du fluide). Les particules sans inertie, dont la taille est inférieure à la longueur de Kolmogorov, suivent le mouvement du fluide avec une orientation généralement gouvernée par le gradient local de vitesse turbulente. Cette thèse est axée sur la dynamique de tels objets en turbulence en ayant recours à des méthodes Lagrangienes stochastiques. Le développement d’un modèle qui peut être utilisé comme outil prédictif dans le cadre de la dynamique de fluides numérique (CFD) au niveau industriel est d’un grand intérêt pour les applications concrètes en ingénierie. Par ailleurs, pour progresser dans le domaine de la médecine, de l’environnement et des procédés industriels, il est nécessaire que ces modèles atteignent un compromis acceptable entre simplicité et précision. La formulation d’un modèle stochastique pour l’orientation de telles particules est tout d’abord présentée dans le cadre d’un écoulement turbulent bidimensionnel avec un cisaillement homogène. Des simulations numériques directes (DNS) sont produites pour guider et évaluer la proposition de modèle. Les questions abordés dans ce travail portent sur la représentation de formes analytiques du modèle, sur les effets des anisotropies inclues dans le modèle, et sur l’extension de la notion de dynamique rotationnelle dans le cadre de cette approche stochastique. Les résultats obtenus avec le modèle, comparés avec la DNS, produisent une réponse qualitative acceptable, même si ce modèle diffusif n’est pas conçu pour reproduire les caractéristiques non-gaussiennes des expériences numériques (DNS). L’extension au cas tridimensionnel du modèle d’orientation pose le problème de son implé- mentation numérique efficace. Dans ce travail, un schéma numérique capable de simuler la dynamique d’orientation de telles particules, à un coût de calcul raisonnable, est introduit. La convergence de ce schéma est également analysée. Pour ce faire, un schéma fondé sur la décomposition de la dynamique a été développé pour résoudre les équations différen- tielles stochastiques (EDS) de rotation de ces particules. Cette décomposition permet de surmonter les problèmes d’instabilité typiques de la méthode Euler–Maruyama; on a ainsi obtenu une convergence en norme L2 d’ordre 1/2 et une convergence faible d’ordre 1, comme classiquement attendu. Enfin, le schéma numérique a été implémenté dans un code CFD industriel (Code_Saturne). Ce modèle a ensuite été utilisé pour étudier l’orientation et la rotation de particules anisotropes sans inertie dans le cas d’un écoulement turbulent inhomogène, à savoir un écoulement de canal plan turbulent. Cette application dans un cas pratique a permis de mettre en evidence deux difficultés liées au modèle : d’abord, l’implémentation numérique dans un code industriel, ensuite la capacité du modèle à reproduire les expériences numériques obtenues par DNS. Ainsi, le modèle stochastique Lagrangien pour l’orientation de sphéroïdes implémenté dans Code_Saturne permet de reproduire, avec certaines limites, les statistiques d’orientation et de rotation de sphéroïdes mesurées dans la DNS
The motion of small non- spherical particles suspended in a turbulent flow is relevant for a large variety of natural and industrial applications such as aerosol dynamics in respiration, red blood cells motion, plankton dynamics, ice in clouds, combustion, to name a few. Anisotropic particles react on turbulent flows in complex ways, which depend on a wide range of parameters (shape, inertia, fluid shear). Inertia-free particles, with size smaller than the Kolmogorov length, follow the fluid motion with an orientation generally defined by the local turbulent velocity gradient. Therefore, this thesis is focused on the dynamics of these objects in turbulence exploiting stochastic Lagrangian methods. The development of a model that can be used as predictive tool in industrial computational fluid dynamics (CFD) is highly valuable for practical applications in engineering. Models that reach an acceptable compromise between simplicity and accuracy are needed for progressing in the field of medical, environmental and industrial processes. The formulation of a stochastic orientation model is studied in two-dimensional turbulent flow with homogeneous shear, where results are compared with direct numerical simulations (DNS). Finding analytical results, scrutinising the effect of the anisotropies when they are included in the model, and extending the notion of rotational dynamics in the stochastic framework, are subjects addressed in our work. Analytical results give a reasonable qualitative response, even if the diffusion model is not designed to reproduce the non-Gaussian features of the DNS experiments. The extension to the three-dimensional case showed that the implementation of efficient numerical schemes in 3D models is far from straightforward. The introduction of a numerical scheme with the capability to preserve the dynamics at reasonable computational costs has been devised and the convergence analysed. A scheme of splitting decomposition of the stochastic differential equations (SDE) has been developed to overcome the typical instability problems of the Euler–Maruyama method, obtaining a mean-square convergence of order 1/2 and a weakly convergence of order 1, as expected. Finally, model and numerical scheme have been implemented in an industrial CFD code (Code_Saturne) and used to study the orientational and rotational behaviour of anisotropic inertia-free particles in an applicative prototype of inhomogeneous turbulence, i.e. a turbulent channel flow. This real application has faced two issues of the modelling: the numerical implementation in an industrial code, and whether and to which extent the model is able to reproduce the DNS experiments. The stochastic Lagrangian model for the orientation in the CFD code reproduces with some limits the orientation and rotation statistics of the DNS. The results of this study allows to predict the orientation and rotation of aspherical particles, giving new insight into the prediction of large scale motions both, in two-dimensional space, of interest for geophysical flows, and in three-dimensional industrial applications

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Prabhu, Achutha. "Agrégation irréversible par patchs de particules colloïdales : une étude par simulation numérique." Phd thesis, Université du Maine, 2012. http://tel.archives-ouvertes.fr/tel-00795636.

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La variété des structures colloïdales auto assemblées est principalement due à la présence d'interactions anisotropes. Nous présentons ici une méthode numérique pour étudier l'agrégation irréversible par patches de particules sphériques. Il s'agit d'une amélioration de la dynamique d'amas browniens prenant en compte les interactions par patches et les mouvements de rotation. Nous limitons notre étude aux particules à deux patches opposés de taille variable. Une interaction isotrope, faible, est également ajoutée pour modéliser une polymérisation par étape dans diverses conditions de solvant. Cet algorithme a été testé sur des chaînes isolées et nous avons retrouvé les propriétés statiques et dynamiques attendues. En jouant sur la balance entre la qualité du solvant et la taille des patches diverses morphologies hors-équilibres sont obtenues. Même dans la limite diluée, les collisions corrélées jouent un rôle important et une description de type Smoluchowski échoue.

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Huck, Peter Dearborn. "Particle dynamics in turbulence : from the role of inhomogeneity and anisotropy to collective effects." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN073/document.

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La turbulence est connue pour sa capacité à disperser efficacement de la matière, que ce soit des polluantes dans les océans ou du carburant dans les moteurs à combustion. Deux considérations essentielles s’imposent lorsqu’on considère de telles situations. Primo, l’écoulement sous-jacente pourrait avoir une influence non-négligeable sur le comportement des particules. Secundo, la concentration locale de la matière pourrait empêcher le transport ou l’augmenter. Pour répondre à ces deux problématiques distinctes, deux dispositifs expérimentaux ont été étudiés au cours de cette thèse. Un premier dispositif a été mis en place pour étudier l’écoulement de von Kàrmàn, qui consiste en une enceinte fermé avec de l’eau forcé par deux disques en contra-rotation. Cette écoulement est connu pour être très turbulent, inhomogène, et anisotrope. Deux caméras rapides ont facilité le suivi Lagrangien des particules isodenses avec l’eau et petites par rapport aux échelles de la turbulence. Ceci a permis une étude du bilan d’énergie cinétique turbulente qui est directement relié aux propriétés de transport. Des particules plus lourdes que l’eau ont aussi été étudiées et montrent le rôle de l’anisotropie de l’écoulement dans la dispersion des particules inertielles. Un deuxième dispositif, un écoulement de soufflerie ensemencé avec des gouttelettes d’eau micrométriques a permis une étude de l’effet de la concentration locale de l’eau sur la vitesse de chute des gouttelettes grâce à une montage préexistant. Un modèle basé sur des méthodes théorique d'écoulements multiphasiques a été élaboré enfin de prendre en compte les effets collectifs de ces particules sedimentant dans un écoulement turbulent. Les résultats théoriques et expérimentaux mettent en évidence le rôle de la polydispersité et du couplage entre les deux phases dans l’augmentation de la sédimentation des gouttelettes
Turbulence is well known for its ability to efficiently disperse matter, whether it be atmospheric pollutants or gasoline in combustion motors. Two considerations are fundamental when considering such situations. First, the underlying flow may have a strong influence of the behavior of the dispersed particles. Second, the local concentration of particles may enhance or impede the transport properties of turbulence. This dissertation addresses these points separately through the experimental study of two different turbulent flows. The first experimental device used is the so-called von K\'arm\'an flow which consists of an enclosed vessel filled with water that is forced by two counter rotating disks creating a strongly inhomogeneous and anisotropic turbulence. Two high-speed cameras permitted the creation a trajectory data base particles that were both isodense and heavier than water but were smaller than the smallest turbulent scales. The trajectories of this data base permitted a study of the turbulent kinetic energy budget which was shown to directly related to the transport properties of the turbulent flow. The heavy particles illustrate the role of flow anisotropy in the dispersive dynamics of particles dominated by effects related to their inertia. The second flow studied was a wind tunnel seeded with micrometer sized water droplets which was used to study the effects of local concentration of the settling velocities of these particles. A model based on theoretical multi-phase methods was developed in order to take into account the role of collective effects on sedimentation in a turbulent flow. The theoretical results emphasize the role of coupling between the underlying flow and the dispersed phase

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Cadiou, Corentin. "L’impact des grandes structures de l’Univers sur la formation des halos de matière noire et des galaxies How does the cosmic web impact assembly bias? Accurate tracer particles of baryon dynamics in the adaptive mesh refinement code Ramses Galaxy evolution in the metric of the cosmic web Galaxies flowing in the oriented saddle frame of the cosmic web." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS508.

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À grande échelle, la distribution anisotrope de la matière forme un large réseau de vides délimités par des murs qui, avec les filaments présents à leurs intersections, tissent la toile cosmique. La matière qui doit former plus tard les halos de matière noire et leurs galaxies afflue vers les nœuds compacts se situant à l’intersection des filaments et garde dans ce processus une empreinte de la toile cosmique. Dans cette thèse, je développe une extension contrainte de la théorie de l’excursion qui, à l'aide d'un modèle de filament, me permet de montrer que l'environnement anisotrope a un effet sur l'histoire de formation des halos de matière noire. La toile cosmique a donc un rôle dans la formation des halos et de leurs galaxies. Dans un second temps, je construis un modèle qui décrit l'évolution de la toile cosmique (fusion de halos, mais aussi de filaments et de murs) afin de mieux contraindre les modèles de formation de galaxies. Le modèle prédit un excès d'accrétion anisotrope dans les filaments par rapports aux nœuds, biaisant ainsi la formation des galaxies. L'effet de l'accrétion anisotrope sur la formation des galaxies est ensuite étudié à l'aide de simulations hydrodynamiques et d'une nouvelle méthode permettant le suivi précis de l'histoire d'accrétion du gaz. J'y montre que le moment angulaire est transporté efficacement des grandes échelles de la toile cosmique jusque dans les zones internes du halo, où les couples gravitationnels le redistribue au disque de la galaxies et au halo interne
The anisotropic large-scale distribution of matter is made of an extended network of voids delimited by sheets, with filaments at their intersection which together form the cosmic web. Matter that will later form dark matter halos and their galaxies flows towards compact nodes at filaments' intersections and in the process, retains the imprint of the cosmic web. In this thesis, I develop a conditional version of the excursion set theory which, using a model of a large-scale filament, enables me to show that anisotropic environment have an impact on the formation history of dark matter halos. The cosmic web then has a role in the formation of halos and their galaxies. I then build a model that is able to capture the evolution of the cosmic web (halo mergers, but also filament and wall mergers) that can be used to better constrain galaxy formation models. The model predicts that an excess of anisotropic accretion is expected in filaments compared to nodes, so that the formation history of galaxies is biased. The effect of anisotropic accretion on galaxy formation is then studied using hydrodynamical simulations and a novel numerical method tailored to accurately follow the accretion history of the gas. I show that the angular momentum is transported efficiently from the cosmic web down to the inner halo, where gravitational torques redistribute it to the disk and the inner halo

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de, Leon Al Caimol. "Development, Fabrication, and Application of Hierarchically-Structured Polymer Systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1448375702.

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Silva, Rafael Caetano Jardim Pinto da. "Síntese e caracterização de nanocompósitos do tipo polímero/silicatos lamelares com propriedades anisotrópicas via polimerização RAFT em emulsão." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/97/97136/tde-01022016-143552/.

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Nos últimos anos, a incorporação de partículas inorgânicas em uma matriz polimérica com a finalidade de se obter sistemas híbridos orgânico/inorgânico utilizando diferentes técnicas de polimerização tem recebido grande atenção. Neste sentido, preservar e controlar as propriedades físico-químicas das partículas inorgânicas torna-se essencial para manter a integridade destas em nanoescala, bem como para obtenção de dispersões uniformes, magnificando os efeitos de reforço e demais ganhos de propriedades desejadas para a matriz polimérica. Quando se utiliza partículas inorgânicas anisotrópicas tais como a montmorilonita, silicato lamelar mais utilizado para obtenção de nanocompósitos do tipo polímero/silicato lamelar, este controle apresenta-se como um problema particularmente desafiador. Nesse contexto, a polimerização radicalar controlada (PRC) vem se destacando como uma importante via para atingir os objetivos mencionados acima, encontrando-se na literatura diversas estratégias de síntese em meio a solventes orgânicos na qual a efetiva nanoencapsulação de partículas inorgânicas dá-se por meio do crescimento de cadeias poliméricas na superfície destas estruturas inorgânicas. Entretanto, poucos trabalhos são encontrados envolvendo rota de obtenção semelhante em meio aquoso, tais como suspensão, emulsão e miniemulsão, processos estes que possuem grande interesse industrial, ambiental e viabilidade real de ampliação de escala quanto à produção.Desta forma, o objetivo deste projeto de pesquisa concentra-se na síntese e na caracterização de nanocompósitos do tipo polímero/silicato lamelar via polimerização radicalar controlada em emulsão. As polimerizações radicalares controladas de estireno em emulsão, via mecanismo de transferência reversível de cadeia por adição-fragmentação (RAFT), foram conduzidas na presença de argila montmorilonita (MMT) e mediadas por dois macroagentes de transferência de cadeia com grupo funcional tri-tioéster, sendo o primeiro constituído de cadeia polimérica não iônica de monoetil éter de poli(etilenoglicol) (MPEG-CPP) e outro derivado do MPEG-CPP contendo adicionalmente um bloco ionizável de poli(ácido metacrílico) incorporado à cadeia polimérica (MPEG-b-PMAA-CPP). Foram avaliados inicialmente os parâmetros de adsorção dos macroagentes MPEG-CPP e MPEG-b-PMAA-CPP na superfície da MMT bem como a influência das variáveis do processo de polimerização na adsorção dos macroagentes na MMT e na estabilidade coloidal dos complexos macroagente RAFT / MMT formados. Posteriormente foram avaliados os efeitos do pH, das concentrações dos macroagente RAFT e de MMT, bem como do tipo de iniciador na cinética de polimerização em emulsão \"ab-initio\" de estireno, conduzidas na ausência de surfatantes. As técnicas utilizadas nos estudos de adsorção e para a caracterização das argilas, dos látices híbridos e dos materiais nanocompósitos incluem: espectroscopia de UV-vis, espalhamento dinâmico de luz (DLS), espalhamento eletroforético de luz (ELS), cromatografia de permeação em gel (GPC), análise termogravimétrica (TGA), calorimetria diferencial de varredura (DSC) e microscopia eletrônica de transmissão (TEM).
In recent years, the incorporation of inorganic particles in a polymer matrix in order to obtain hybrid organic/inorganic systems using different polymerization techniques have received great attention. In this sense, preserve and manage the physical and chemical properties of inorganic particles is essential to maintain its integrity at the nanoscale, as well as to obtain uniform dispersions of them, magnifying the effects of reinforcement and other desired properties into the polymer matrix. When using anisotropic inorganic nanoobjects such as montmorillonite, the most used layered silicate to obtain polymer / layered silicate nanocomposites, this control is presented as a particularly challenging problem. In this context, the controlled radical polymerization (CRP) has been highlighted as an important way to achieve the goals mentioned above, several strategies of organic solvent-borne synthesis can be found in literature in which the effective nanoencapsulation of inorganic particles is given by through the growth of polymer chains on the surface of these inorganic structures. However, few works are found involving obtaining similar route in water-borne, such as suspension, emulsion, miniemulsion, these procedures have great interest in industrial, environmental and actual feasibility of expanding scale in manufacture. Thus, the objective of this research project focuses on the synthesis and characterization of nanocomposite-type polymer / layered silicate via controlled radical polymerization in emulsion media. The controlled radical polymerizations in emulsion, via transfer mechanism for the reversible addition-fragmentation chain (RAFT) have been conducted in the presence of montmorillonite clay (MMT) and mediated by two macroRAFT agents with functional tri-thioesters groups, being the first one constituted by a nonionic poly(ethylene glycol) methyl ether polymeric chain (MPEG-CPP) and the second on being MPEG-CPP derived but containing additionally an ionizable block of poly(methacrylic acid) inserted to its polymeric chain. The parameters of adsorption of MPEG-CPP and MPEG-b-PMAA-CPP agent on the surface of MMT as well as the influence of the polymerization process variables on the adsorption of PEO-RAFT in MMT and colloidal stability of the complex formed macroRAFT agents / MMT were firstly evaluated. Subsequently, the influence of pH, macroRAFT agents and MMT concentrations as well as the type of initiator on the kinetics of RAFT emulsion polymerization were equally evaluated. The techniques used the for adsorption studies and characterization of clays, latexes of hybrid materials and nanocomposites include: UV-vis spectroscopy, dynamic light scattering (DLS), electrophoretic light scattering (ELS), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), dynamic scanning calorimetry (DSC) and transmission electron microscopy (TEM).

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41

Krouppa, Brandon. "Quarkonium suppression using 3+1d anisotropic hydrodynamics." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1532523360257784.

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Takae, Kyohei. "Phase Transitions and Glassy Behaviours in Anisotropic Particle Systems." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/175107.

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Williams, Dennis Andrew. "A study of anisotropic particle emission from oriented nuclei." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363998.

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44

Ouari, Bachir. "Dynamique de l'aimantation des particules superparamagnétique avec anisotropie triaxiale." Perpignan, 2006. http://www.theses.fr/2006PERP0739.

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Dans ce travail, nous avons effectué des études théoriques sur le processus de relaxation de l’aimantation des nanoparticules superparamagnétiques avec une anisotropie triaxiale (orthorhombique). Dans le contexte du modèle de Néel-Brown, nous avons obtenu les solutions numériques et analytiques de l’équation de Fokker-Planck-Brown qui décrit la dynamique de l’aimantation de la particule monodomaine. Le processus de relaxation magnétique est caractérisé par le temps de relaxation de l’aimantation le plus long, les temps intégraux et effectifs. Dans le domaine des fréquences, il est caractérisé par les composantes longitudinale et transversales du tenseur de la susceptibilité magnétique. Les résultats des calculs numériques nous ont donnés la possibilité d’évaluer ces grandeurs importantes avec beaucoup d’habilités pour les valeurs typiques de la constante de dissipation α, de la température T, des constantes d’anisotropie et la pulsation  en absence ou en présence d’un champ magnétique uniforme extérieur H0. En utilisant l’approche de Kramers-Brown-Coffey, nous avons déduit les équations analytiques pour les temps de relaxation de l’aimantation et pour les composantes longitudinale et transversale de la susceptibilité magnétique. Ces équations sont en accord complet avec les résultats du calcul numérique. Elles ont des formes simples et nous permettent de comprendre le comportement qualitatif des temps de relaxation de l’aimantation et des spectres de la susceptibilité magnétiques dans toute la gamme de variation des paramètres physiques (température, pulsation, champ extérieur, et constante de dissipation)
In this thesis, a theoretical study of the dynamics of the magnetization of superparamagnetic nanoparticles with triaxial (orthorhombic) anisotropy has been carried out using the Néel-Brown model. Numerical and analytical solutions of the Fokker-Planck equation given by Brown, which describes the relaxation of the magnetization in the nanoparticles, have been obtained in order to facilitate this study. The process of relaxation of the magnetization is characterized by the longest relaxation time, integral relaxation time, and, in the frequency domain, by the longitudinal and transverse components of the magnetic susceptibility tensor. The numerical solutions allows us to evaluate these characteristics for typical values of the dissipation constant α, temperature T, anisotropy constants with and without a uniform external magnetic field H0. By using the approach of Kramers-Brown-Coffey, analytical equations for the magnetization relaxation times and for the longitudinal and transversals components of the magnetic susceptibility have been deduced. These analytical equations are in complete agreement with the results of our numerical calculations. They have simple analytical forms and allow one to quantify the dependence of the relaxation times and the magnetic susceptibility on the temperature T, angular frequency , strength of the external field H, and dissipation constant α. Moreover they can be used to estimate the relaxation times and the magnetic susceptibility in wide ranges of variation of T,, H, and α. The results obtained may be considered as a complete solution of the problem of relaxation of the magnetization in nano particles with triaxial anisotropy

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Abdul, Latiff Hawa Alima Binti. "Magnetic anisotropy and coercivity of tetragonally distorted spinel ferrite particles via the Jahn-Teller distortion and the magnetoelastic coupling." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY005.

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Cette étude propose l'idée des aimants dits de ferrite tétragonale en rendant la symétrie cristalline des ferrites de spinelle cubique afin d'améliorer l'anisotropie magnétique (et donc, d'améliorer la coercivité). Pour concrétiser cette idée, nous avons synthétisé des particules (Cu, Co) -ferrite à distorsion tétragonale et caractérisé systématiquement les propriétés magnétiques en conséquence avec leurs distorsions de réseau. Les facteurs intrinsèques et extrinsèques contribuant à la coercivité ont été étudiés. Pour élucider l'anisotropie magnétique, nous avons démontré un modèle de couplage physique de l'effet Jahn-Teller (JT) et de l'effet magnétoélastique (ME) au sein de la théorie phénoménologique. Ensuite, nous avons effectué une analyse de coercivité dans deux modèles généraux de coercivité afin de clarifier les paramètres de la microstructure contribuant au mécanisme d'inversion de la magnétisation. À partir de l'analyse du modèle magnétoélastique, nous avons démontré l'expression linéaire de l'anisotropie magnétique en utilisant le paramètre tétragonal obtenu à partir de la distorsion JT. Les valeurs du coefficient magnétoélastique pour Cu (B1Cu = 2 MJ / m3) et Co (B1Co = 40 MJ / m3) déduites de la courbe expérimentale étaient acceptables avec la valeur calculée pour le ferrite de cuivre en vrac (B1Cu en vrac = 4 MJ / m3) et le cobalt. ferrite (masse B1Co = 55 MJ / m3). Les résultats suggèrent que l’anisotropie magnétique peut être attribuée au couplage de la distorsion JT avec l’effet magnétoélastique de Co. Au lieu d’une augmentation indéfinie avec x, l’anisotropie magnétique Ku tend à atteindre une valeur de saturation en raison de la concurrence entre les effet magnétoélastique de Co et le JT de Cu. Entre le x tétragonal x = 0,1 et le x cubique = 0,2, les valeurs de Ku constantes d'anisotropie magnétique intrinsèque ne varient pas de manière aussi significative que la différence entre les champs de coercivité et d'anisotropie. La réduction des champs d'anisotropie supérieurs à x = 0,1 peut alors être attribuée à l'augmentation de l'aimantation spontanée. L'analyse de la coercivité au sein du modèle micromagnétique a révélé une contribution importante à la coercivité de la microstructure et de l'effet démagnétisant local. Le paramètre de microstructure αMM = 0,25 obtenu était une valeur classique de l'analyse micromagnétique, suggérant le départ du champ d'anisotropie avec ce facteur de réduction. Les facteurs démagnétisants locaux effectifs NeffMM d’environ 1,4 obtenus étaient plutôt importants, ce qui suggère un effet démagnétisant significatif. Dans l'analyse du modèle global (GM), les valeurs de NeffGM obtenues étaient were 0,38 pour l'échantillon x = 0,1. La valeur négative suggère la présence d'une interaction d'échange agissant efficacement en opposition à l'interaction dipolaire. En deçà de 100 K, une différence dans le modèle suggère l’idée d’un réchauffement local consécutif à l’activation thermique due au changement d’énergie Zeeman et à une dissipation de chaleur inefficace. Cet événement peut avoir conduit à la réduction du champ coercitif à une température suffisamment basse dans l'échantillon x = 0.1 en supposant que les grains sont fortement couplés en échange
This study proposes the idea of the so-called tetragonal ferrite magnets by rendering the crystal symmetry of the cubic spinel ferrites to enhance the magnetic anisotropy (and hence, enhance the coercivity). To realize this idea, we synthesized tetragonally distorted (Cu,Co)-ferrite particles and systematically characterized the magnetic properties accordingly with their lattice distortions. The intrinsic and extrinsic factors contributing to coercivity were investigated. To elucidate the magnetic anisotropy, we demonstrated a physical coupling model of the Jahn-Teller (JT) effect and the magnetoelastic (ME) effect within the phenomenological theory. Then, we performed coercivity analysis within two general models of coercivity to clarify the microstructure parameters contributing to the magnetization reversal mechanism. From the magnetoelastic model analysis, we demonstrated the linear expression of the magnetic anisotropy using the tetragonal parameter obtained from the JT distortion. The magnetoelastic coefficient values for Cu (B1Cu = 2 MJ/m3) and Co (B1Co = 40 MJ/m3) deduced from the experimental curve were agreeable with the value calculated for bulk copper ferrite (B1Cu bulk= 4 MJ/m3) and cobalt ferrite (B1Co bulk= 55 MJ/m3). The results suggests that the source of magnetic anisotropy can be attributed to the coupling of the JT distortion with the magnetoelastic effect of Co. Instead of an indefinite increase with x, the magnetic anisotropy Ku tends to reach a saturation value due to the competition between the magnetoelastic effect of Co and the JT effect of Cu. Between the tetragonal x = 0.1 and the cubic x = 0.2 samples, the intrinsic magnetic anisotropy constant Ku values do not vary as significantly compared to the difference in the coercivity and the anisotropy fields. The reduction of anisotropy fields above x = 0.1 then can be attributed to the increase in the spontaneous magnetization.The coercivity analysis within the micromagnetic model revealed significant contribution to the coercivity by the microstructure and the local demagnetizing effect. The microstructure parameter αMM = 0.25 obtained was a classical value in the micromagnetic analysis, suggesting the departure of anisotropy field with this reduction factor. The effective local demagnetizing factor NeffMM of about 1.4 obtained were rather large suggesting a significant demagnetizing effect. Within the global model (GM) analysis, the values of NeffGM obtained were －0.38 for the x = 0.1 sample. The negative value suggests the presence of an exchange interaction acting effectively in opposition to the dipolar interaction. Below 100 K, discrepancy in the GM suggests the idea of a local heating event following the thermal activation due to the change in Zeeman energy and ineffective heat dissipation. This event may have led to the reduction of coercive field at sufficiently low temperature in the x = 0.1 sample assuming the grains are strongly exchange-coupled

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46

Alani, Mahdi Ahmed 1954. "Neutral particle Green's function in an infinite medium with anisotropic scattering." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/282874.

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The linear Boltzmann equation for the transport of neutral particles is investigated with the objective of generating benchmark-quality calculations for homogeneous infinite media. In all cases, the problems are stationary, of one energy group, and the scattering is both isotropic and anisotropic. In the transport problems considered, the Green's function is generally the quantity of interest. The solution is obtained through the use of the Fourier transform method. The numerical inversions use standard numerical techniques, such as Gauss-Legendre quadrature, summation of infinite series, and Euler-Knopp acceleration. The most basic source of neutral particles is the point-beam source, or Green's function source. The Green's function in an infinite medium with isotropic scattering is treated as explained in chapter two. The Green's function in an infinite medium with anisotropic scattering is treated using two different mathematical methods as explained in chapters three and four. The results for both cases is shown in chapter 5.

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47

Kirillova, Alina, Georgi Stoychev, and Alla Synytska. "Programmed assembly of oppositely charged homogeneously decorated and Janus particles." Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A36153.

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The exploitation of colloidal building blocks with morphological and functional anisotropy facilitates the generation of complex structures with unique properties, which are not exhibited by isotropic particle assemblies. Herein, we demonstrate an easy and scalable bottom-up approach for the programmed assembly of hairy oppositely charged homogeneously decorated and Janus particles based on electrostatic interactions mediated by polyelectrolytes grafted onto their surface. Two different assembly routes are proposed depending on the target structures: raspberry-like/half-raspberry-like or dumbbell-like micro-clusters. Ultimately, stable symmetric and asymmetric microstructures could be obtained in a well-controlled manner for the homogeneous–homogeneous and homogeneous–Janus particle assemblies, respectively. The spatially separated functionalities of the asymmetric Janus particle-based micro-clusters allow their further assembly into complex hierarchical constructs, which may potentially lead to the design of materials with tailored plasmonics and optical properties.

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48

Metzger, Bloen. "Sédimentation de particules et instabilités à bas nombre de Reynolds." Aix-Marseille 1, 2006. http://theses.univ-amu.fr.lama.univ-amu.fr/2006AIX11031.pdf.

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Dabat, Thomas. "Anisotropie des milieux poreux argileux et implication sur la diffusion de l'eau." Thesis, Poitiers, 2019. http://www.theses.fr/2019POIT2277/document.

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Les minéraux argileux sont omniprésents à la surface de la Terre. Leur forme plaquettaire et leur taille le plus souvent (sub)micrométrique en font des composants influençant, entre autres, la perméabilité et la capacité d’échange ionique des sols et des roches. L’étude des milieux poreux argileux est ainsi d’importance notamment pour l’exploitation et la préservation de ressources naturelles, le suivi de polluants ou encore le stockage de CO2. Si les propriétés physico-chimiques des surfaces argileuses contrôlent les processus d’adsorption-désorption de l’eau et des ions, la porosité et l’anisotropie du réseau poral gouvernent les processus de diffusion au sein des milieux poreux argileux. Dans ce contexte, le travail présenté dans ce mémoire de thèse se focalise sur la caractérisation de l’orientation des particules argileuses, et son influence sur l’anisotropie des propriétés de diffusion de l’eau dans le réseau poral. Une première partie de ce manuscrit regroupe des analyses systématiques de l’organisation des particules argileuses dans des milieux poreux modèles et naturels variés. Tout d’abord, une étude de milieux poreux modèles simulés et expérimentaux composés de disques sédimentés, monodisperses en taille, a mis en évidence une relation simple entre l’anisotropie d’orientation des particules et l’anisotropie de la phase porale. Puis, une étude de l’orientation préférentielle des particules argileuses dans des milieux poreux expérimentaux composés de minéraux argileux purs a été réalisée pour des compositions minéralogiques et des modes de dépôt variés. Une généralisation de la description des fonctions de distribution d’orientation des particules argileuses a été proposée et appliquée avec succès à trois milieux poreux naturels. Ces résultats visent ainsi à faciliter la prise en compte de l’orientation préférentielle des particules argileuses dans la description géométrique des milieux poreux argileux. La seconde partie de ce mémoire de thèse tente de faire le lien entre l’anisotropie de la phase solide, telle que décrite précédemment par l’orientation préférentielle des particules, et les prédictions de diffusion de l’eau dans ces milieux poreux argileux. Une première étude couplant des simulations numériques et des mesures expérimentales a été réalisée pour des milieux de kaolinite ayant des anisotropies contrastées, tout autre paramètre égal par ailleurs (porosité du milieu, taille et forme des particules). Les résultats montrent une évolution d’un facteur 2 du coefficient de diffusion de l’eau dans la direction longitudinale par rapport à l’axe de compaction et une évolution de l’anisotropie de diffusion d’une valeur de 1 (isotrope) à environ 5 (le plus anisotrope mesuré). Des mesures complémentaires ont ensuite permis d’établir une loi d’Archie modifiée prédisant le coefficient de diffusion de l’eau à partir du couple porosité/orientation des particules pour une gamme de porosité de 30 à 60%. Ces résultats visent à faciliter la prise en compte de l’orientation des particules argileuses dans les modèles de diffusion macroscopique de l’eau. En parallèle, l’influence d’un gradient de salinité et les rôles des porosités interfoliaire et interparticulaire sur la dynamique de l’eau et des ions Na+ et Cl- au sein de milieux de vermiculites (milieu chargé à double porosité) ont été analysés pour des organisations de particules connues
Clay minerals are ubiquitous at the surface of the Earth and can influence, among other properties, the permeability and the ionic exchange properties of soils and rocks due to their platy shape and their most often (sub)micrometric size. Thus, studying clay porous media is of prime importance for different research fields such as: the exploitation and conservation of natural resources, the tracking of pollutants or CO2 storage. While the physicochemical properties of the surface of clay minerals control the adsorption-desorption mechanisms of water and ions, it is the porosity and the anisotropy of the poral network that govern diffusion phenomenon within clay porous media. In this respect, the work presented in the following doctoral thesis focuses on the characterization of clay particle orientation and its influence on anisotropic diffusion properties of water in the associated pores. A first part of this manuscript gathers systematic structural analyses of various model and natural samples. One study presents the analyze of experimental and simulated stackings made from sedimented discs with a unique particle size. Results underlined a simple correlation between the particle orientation anisotropy and the poral network anisotropy. Then, an other study was performed on experimental media made of pure clay minerals for various mineralogical compositions and various preparation methods. Based on this data, a reference function was proposed to describe the experimental orientation distribution functions and was successfully applied to three natural porous media. These results aim to facilitate and improve the description of the preferential orientation of clay particles as part of a geometrical characterization of clay porous media. A second part of this manuscript try to describe the link between the anisotropy of the solid phase, previously characterize by the particle orientation, and the prediction of water diffusion coefficients in these clay porous media. A study using both simulated and experimental media was performed on kaolinite porous media presenting contrasted anisotropy and with all other parameters held equal (porosity of the medium, size and shape of particles). Results show a variation of water diffusion coefficients with a factor 2 in the longitudinal direction, compared to the compaction axis, and an anisotropic diffusive ratio varying from 1 (isotropic) to almost 5 (most anisotropic medium analyzed). Then, complementary measures allowed establishing a modified version of Archie’s law that predicts water diffusion coefficients from the porosity/particle orientation couple for a range of porosity of 30-60%. These results aim to improve the description of the orientational anisotropy of clay particles in macroscopic diffusion models of water. Simultaneously, the influence of a salinity gradient and the roles of interparticular and interfoliar porosities are discussed for the diffusion of water, Na+, and Cl- within vermiculite media (charged media with double porosity) for known structural organizations

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50

Ballard, Nicholas. "Anisotropic colloids in soft matter environments : particle synthesis and interaction with interfaces." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/54360/.

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We have shown new applications and synthetic routes for polymer colloids in the field of home and personal care products by controlling polymer and/or colloidal architectures. Our initial aim was to develop functional particles that imparted beneficial properties to fibrous substrates and as such our first goal was to develop a method for depositing particles onto such surfaces. Chapter 2 describes the method by which we achieved this goal, namely adding a small amount of a low glass transition polymer to an otherwise non-adhesive polymer to enhance colloidal deposition. Following on from this work we looked into ways in which to impart desirable characteristics from the particles onto fibres. In Chapter 3 we describe how the use of a hydrazide functional monomer in polymer gels can provide a continuing slow release of fragrance molecules that reacts to the environment it is held in such that if the local fragrance concentration is low then more is released. In Chapter 4 we describe the synthesis of highly porous particles with controlled pore sizes and the use of such particles in oil absorption for applications in water-free cleaning systems. The particles are capable of carrying many times their own weight in oil and are shown to be reusable. In Chapter 5 we describe a computational model that predicts the ability of a particle to stabilize emulsions. The model is highly adaptable and can be used to predict the surface activity of almost any particle morphology. Chapter 6 builds on this work and described the synthesis of highly anisotropic polymer particles by templating preexisting structures and explains their surface activity, or lack thereof.

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Dissertations / Theses on the topic 'Anisotropic particles'

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