Dissertations / Theses: 'Magnetics of ferrofluids'

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Davies, P. "The magnetic and microwave properties of ferrofluid composites." Thesis, Bangor University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380797.

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Daffé, Niéli. "Anisotropies and Magnetic Couplings of Texturable Ferrofluids." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066640/document.

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Les ferrofluides sont des suspensions colloïdales de nanoparticules magnétiques dispersées dans un liquide porteur. La possibilité de moduler les propriétés des ferrofluides in situ en appliquant un champ magnétique externe leur procure un fort potentiel d’étude, à la fois d’un point de vue fondamental ou pour des applications industrielles variées. En particulier, les nanospinels de ferrite ferrimagnétiques MFe2O4 (M = Fe2+, Co2+, Mn2+…) sont largement étudiés pour leurs propriétés électriques et magnétiques. Plus spécifiquement, une forte énergie d’anisotropie de ces matériaux à l’échelle nanométrique est requise pour des applications dans le stockage de l’information ou l’hyperthermie pour lesquels ils sont considérés. Une connaissance fine des mécanismes régissant ces propriétés d’anisotropies magnétiques est ainsi primordiale pour la création de nouveaux objets aux propriétés magnétiques contrôlées à l’échelle nanométrique. L’originalité de notre approche consiste à utiliser une technique fine du magnétisme, le dichroïsme magnétique circulaire des rayons X (XMCD) à l’étude des anisotropies et couplages magnétiques des nanospinels composants les ferrofluides. Au cours de cette thèse, nous nous sommes intéressés à différentes stratégies possibles pour induire une forte énergie d’anisotropie aux nanospinels de ferrite par l’utilisation de cobalt. Des nanoparticules de tailles et compositions variées ont été obtenues par différentes voies de synthèse, et nous démontrons que l’anisotropie magnétique de ces systèmes est fortement gouvernée par la symétrie de site du Co2+ en structure spinel qui peut être directement corrélé au processus de synthèse utilisé. Nous nous sommes aussi intéressés à l’ordre et au couplage magnétique de ferrite spinels structurés en coeur-coquille, dont le cœur et la coquille sont réalisés à partir de matériaux aux propriétés magnétiques intrinsèques différentes. Nous montrons ainsi que pour des nanospinels MnFe2O4@CoFe2O4, la très fine coquille formée de CoFe2O4 impose une forte anisotropie magnétique au cœur doux de MnFe2O4. Enfin, nous nous sommes intéressés à une troisième classe de ferrofluide à base de nanospinels, les ferrofluides binaires, constitué d’un mélange physique de ferrofluides aux propriétés magnétiques intrinsèques différentes. Pour de tels systèmes, il est essentiel de préserver le liquide porteur du ferrofluide pour ne pas dénaturer les interactions entre particules existantes. L’un des objectifs de cette thèse fut donc d’étendre la technique du XMCD à l’étude d’échantillons de ferrofluides in situ, dans leur phase liquide ou gelée. Nous avons débuté la conception d’une cellule liquide compatible avec les rayons X mous et un environnement ultra-vide sur la ligne de lumière DEIMOS (SOLEIL) qui est toujours en développement Ferrofluids are colloidal suspensions of magnetic nanoparticles dispersed in a carrier liquid. The intimate interaction between the magnetic nanoparticles and the liquid provides a unique system, from both fundamental and industrial application point of views, whose flow and properties can be precisely controlled using an external magnetic field. Magnetic nanoparticles of spinel ferrites MFe2O4 (M = Fe2+, Co2+, Mn2+…) are of particular scientific interest and have been extensively studied for their electrical and magnetic properties. Spinel ferrites find potential applications, notably in storage devices, for computers, or hyperthermia, for cancer treatment, where high magnetic anisotropy energies are required at the nanoscale. However, deeper knowledges of the fine mechanisms playing a significant role on the magnetic anisotropies existing in the nanospinels are necessary to help the creation of rationalized materials with controlled magnetic anisotropies for the requirement of the system. In this thesis, we have used X-ray Magnetic Circular Dichroism (XMCD) as an original approach for probing the magnetic anisotropies and magnetic couplings of nanospinels obtained in ferrofluids. The nanoparticles are iron bearing spinels for which cobalt ions have been introduced in the spinel structure of the nanoparticles as a true makers of magnetic anisotropy. First, magnetic nanospinels have been synthesized by tuning their size and composition and using different synthesis processes. XMCD investigations revealed that the coercive field of the nanospinels is governed by the concentration of Co2+ ions sitting in octahedral sites of the spinel structure, and this can be directly linked to some synthesis parameters. Then, we have investigated core@shell nanoparticles, which can be synthesized with an appropriate choice of magnetic anisotropies for the core and the shell in order to tailor optimal magnetic properties. In the case of MnFe2O4@CoFe2O4, our findings reveal that the very thin CoFe2O4 shell imposes a strong magnetic anisotropy to the otherwise very soft MnFe2O4 core. The other class of ferrofluids that has been investigated during this thesis are binary ferrofluids that are constituted of two different types of magnetic nanoparticles. For such systems, the carrier liquid must be preserved to understand the magnetic interactions in the ferrofluid as they are. Another motivation of this thesis was thus to extend XMCD to the in situ investigation of the nanospinels dispersed in ferrofluids. We have been started a liquid cell development in the DEIMOS beamline at SOLEIL. The setup is still in progress and is aimed at being compatible with soft X-Rays short penetration depth and ultra-high vacuum environment. Hard X-ray photon-in/photon-out spectroscopy coupled to XMCD (1s2p RIXS-MCD) can be a very valuable alternative to soft X-ray XMCD at K-edge of 3d elements when liquid cell sample environment is required. The instrumental development of a liquid cell used with 1s2p RIXS-MCD spectroscopy allowed us to investigate the nanoparticles directly in the ferrofluids revealing interparticles magnetic couplings in binary ferrofluids

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Ezzaier, Hinda. "Agrégation et séparation magnétique des nanoclusters magnétiques." Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4107/document.

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Depuis deux dernières décennies, la séparation magnétique revient sur le tapis grâce aux applications biomédicales émergentes à la séparation de cellules ou de protéines et aux tests immunologiques. Cette thèse porte sur l’exploration détaillée de la séparation magnétique de nanoparticules à l’échelle microfluidique, amplifiée par la séparation de phase induite par le champ. Dans ce but, nous synthétisons des nanoclusters superparamagnétiques d’oxyde de fer de taille 40-70 nm, composés de nanoparticules de taille 7-9 nm. Nous faisons une étude détaillée de la cinétique de la séparation de phase de ces nanoclusters induite par le champ ainsi que de leur séparation magnétique dans des canaux microfluidiques munis de réseaux ordonnés de micropiliers magnétisables. Le taux d’agrégation de nanoclusters est principalement régi par le paramètre du couplage dipolaire et par la fraction volumique de nanoclusters, tandis que l’efficacité de capture – par le nombre de Mason. Les couches de molécules adsorbées sur la surface de nanoclusters d’habitude affaiblissent les interactions magnétiques et diminuent l’efficacité de capture, cependant, dans certains cas, elles peuvent induire des interactions colloïdales attractives et augmenter l’efficacité de capture. Les résultats de ce travail peuvent être utiles pour le développement des tests immunologiques magnéto-microfluidiques Magnetic separation has been gaining a new interest during two last decades thanks to emerging biomedical applications to cell or protein separation and immunoassays. This thesis is aimed at detailed exploration of magnetic nanoparticle separation in microfluidic scale enhanced by field-induce phase separation of nanoparticles. To this purpose, we synthesize superparamagnetic iron oxide nanoclusters of a size of 40-70 nm composed of numerous nanoparticles of a size 7-9 nm. We perform a detailed study of the kinetics of the field-induced phase separation of these nanoclusters as well as of their magnetic separation in microfluidic channels equipped with ordered arrays of magnetizable micropillars. The nanocluster aggregation rate is mostly governed by the dipolar coupling parameter and the nanocluster volume fraction, while the capture efficiency – by the Mason number. Molecular layers adsorbed on the nanocluster surface usually weaken magnetic interactions and decrease the capture efficiency, however, in some casesthey may induce attractive colloidal interactions and enhance the capture efficiency. The results of this work could be useful for development of magnetomicrofluidic immunoassays

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Sakhnini, Lama Issam. "The microwave, optical and magnetic properties of magnetic fluids." Thesis, Bangor University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385796.

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Lopes, Filomeno Cleber. "Dispersions de nanoparticules magnétiques de type coeur-coquille MFe2O4@g-Fe2O3 dans des solvants polaires : réactivité électrochimique et rôle de l'interface oxyde/solution sur les propriétés colloïdales." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066673/document.

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Les dispersions de nanoparticules magnétiques (NPs) dans les solvants polaires sont utilisées dans de nombreuses applications dans des domaines variés, du biomédical à l'environnement ou à l'énergie. Aussi appelés ferrofluides (FFs), ces systèmes sont des dispersions de ferrites spinelle magnétiques pouvant être stabilisées par des répulsions électrostatiques. Cela nécessite une bonne compréhension de l'interface NPs/solvant porteur, qui contrôle les interactions entre NPs, la nanostructure et de nombreuses autres propriétés. Nous étudions ici en milieu aqueux la réactivité électrochimique de particules c¿ur/couronne de type MFe2O4@ Fe2O3 (M = Fe,Co,Mn,Cu,Zn), espèces électroactives non conventionnelles. La voltammétrie à signaux carrés et la coulométrie à potentiel contrôlé permettent d'étudier la coquille de maghémite ( Fe2O3), dont le rôle est la protection de l'oxyde mixte du c¿ur en milieu acide. D'autre part, un nouveau procédé d'élaboration de dispersions dans les solvants polaires, testé dans l'eau, est appliqué au diméthylsulfoxide (DMSO). A partir du point de charge nulle des NPs, un ajout connu d'acide ou de base permet de contrôler la charge des NPs, la nature des contreions et la quantité d'électrolyte libre. Des dispersions stabilisées par des répulsions électrostatiques sont obtenues dans le DMSO. La diffusion de rayons X aux petits angles et la diffusion dynamique de la lumière sont utilisées pour comprendre la nanostructure et quantifier les interactions entre particules. De forts effets spécifiques liés aux ions sont mis en évidence ainsi que le rôle de l'interface solide liquide, en particulier sur les propriétés de thermodiffusion Dispersions of magnetic nanoparticles (NPs) in polar solvents have been inspiring many applications, to cite a few, biomedical, industrial and thermoelectrical ones. Also called ferrofluids (FFs), they are usually colloidal dispersions of magnetic spinel ferrite NPs, which can be stabilized thanks to electrostatic repulsion. A good understanding of the interface between NPs and the carrier solvent is thus a key point, which governs the interparticle interactions, the nanostructure and many other applicative properties. We study here the electrochemical reactivity of core-shell ferrite MFe2O4@ Fe2O3 (M=Fe,Co,Mn,Cu,Zn) NPs in aqueous medium. Square-wave voltammetry and potential controlled coulometry techniques are used on these non-conventional electroactive systems in order to evidence the shell of maghemite ( Fe2O3), the main function of which is to ensure the thermodynamical stability of NPs in acidic medium. We also present a new process for the elaboration of maghemite based FF in polar solvents, tested in water and applied to dimethyl sulfoxide (DMSO). Departing from the point of zero charge, the NPs are charged in a controlled way by adding acid or base, which enables us to better control the charge and the counter-ions nature, as well as the amount of free electrolyte in the dispersion. Stable dispersions are obtained thanks to electrostatic repulsion, also in DMSO. Small Angle X-ray scattering and Dynamic Light Scattering are used to understand the nanostructure and quantify the interparticle interactions. Specific ionic effects are evidenced as well as the strong influence of the solid/liquid interface on the migration of the NPs in a thermal gradient

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Schumacher, Kristopher Ray. "Direct numerical simulation of ferrofluid turbulence in magnetic fields /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9892.

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Williams, Alicia M. "The Hydrodynamics of Ferrofluid Aggregates." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/29446.

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Ferrofluids are comprised of subdomain particles of magnetite or iron oxide material that can become magnetized in the presence of a magnetic field. These unique liquids are being incorporated into many new applications due to the ability to control them at a distance using magnetic fields. However, although our understanding of the dynamics of ferrofluids has evolved, many aspects of ferrohydrodynamics remain largely unexplored, especially experimentally. This study is the first to characterize the stability and internal dynamics of accumulating or dispersing ferrofluid aggregates spanning the stable, low Reynolds number behavior to unstable, higher Reynolds numbers. The dynamics of ferrofluid aggregates are governed by the interaction between the bulk flow shear stresses acting to wash away the aggregate and magnetic body forces acting to retain them at the magnet location. This interaction results in different aggregate dynamics, including the stretching and coagulation of the aggregate to Kelvin-Helmholtz shedding from the aggregate interface as identified by focused shadowgraphs. Using TRDPIV, the first time-resolved flow field measurements conducted in ferrofluids reveal the presence of a three-stage process by which the ferrofluid interacts with a pulsatile bulk flow. An expanded parametric study of the effect of Reynolds number, magnetic field strength, and flow unsteadiness reveals that the increased field results can result in the lifting and wash away of the aggregate by means of vortex strengthening. In pulsatile flow, different forms of the three-stage interaction occur based on magnetic field, flow rate, and Reynolds number. Ph. D.

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Shirzadfar, Hamidreza. "Conception et réalisation d'un biocapteur à GMR pour la caractérisation de milieux biologiques." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0045/document.

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L'objectif de cette thèse est de développer des bio-capteurs à base de magnétorésistance géante (GMR), ainsi que l'électronique de conditionnement associée, en vue de caractériser magnétiquement des ferrofluides biologiques. Ce travail a été réalisé en collaboration avec le Pr Sotoshi YAMADA de l'Institut « Nature and Environmental Technology» de l'Université de Kanazawa. La première partie porte sur l'état de l'art et les méthodes de mesures des propriétés magnétiques des ferrofluides et la physique de l'effet GMR. La deuxième partie concerne la mise en place d'un dispositif de mesure pour déterminer et caractériser la valeur de la sensibilité de chaque capteur. Cette sensibilité est une caractéristique cruciale pour toute application biomédicale. Sa connaissance et son optimisation permettent d'envisager des mesures précises et justes des propriétés magnétiques des ferrofluides notamment à bas niveau de signal. La troisième partie, également expérimentale, décrit les mesures de la perméabilité relative (µr) et de la susceptibilité (X) de fluides magnétiques (ferrofluides) par des capteurs GMR I, II. En outre, afin de confirmer les résultats expérimentaux obtenus avec ces capteurs, nous les avons comparés à ceux obtenus avec d'autres méthodes comme la magnétométrie à échantillon vibrant (VSM) ou à des calculs théoriques. Le quatrième et dernier chapitre présente les résultats expérimentaux de la perméabilité relative et de la susceptibilité d'un marqueur magnétique permettant la détection de la bactérie pathogène Escherichia coli O157: H7 The intent of this thesis is to develop bio-sensors based on giant magnetoresistance (GMR) and the associated conditioning electronics, to characterize magnetically organic ferrofluids. This work was done in collaboration with Pr Sotoshi YAMADA of the Institute "Nature and Environmental Technology" at the University of Kanazawa. The first part focuses on the state of the art and the methods for magnetic properties measurements of ferrofluids and the description of the GMR effect. The second part concerns the introduction of a measuring device to determine and characterize the value of the sensitivity of each sensor. This sensitivity is a crucial parameter for any biomedical application. Its knowledge allows optimization of sensors ability to measure very low magnetic parameters of ferrofluids very precisely. The third experimental part describes measurements of relative permeability (µr) and susceptibility (X) of magnetic ferrofluids with GMR sensors I, II. In addition, to confirm the experimental results obtained with these sensors, we have compared them to those obtained with other methods such as vibrating sample magnetometer (VSM) or by theoretical calculations. The fourth and last chapter presents the experimental results of the relative permeability and susceptibility of a magnetic marker used to detect pathogenic bacteria (Escherichia coli O157: H7)

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Rosenthal, Adam D. (Adam David) 1978. "Ferrofluid flow and torque measurements in rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16857.

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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002. Includes bibliographical references (leaves 117-121). This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. The purpose of this research is to provide data from ferrofluid flow and torque measurements in uniform and nonuniform rotating magnetic fields that can be compared to theoretical analyses in order to fully understand observed paradoxical ferrofluid behavior. In the presence of rotating magnetic fields, ferrofluid particles will rotate to try to align their magnetic moment with the field but because of the fluid viscosity, magnetization M will lag behind the rotating H field, thereby resulting in a body torque on the ferrofluid. The viscous torque from this fluid flow is measured using a Couette viscometer as a function of magnetic field amplitude, frequency, and direction of rotation. The first three sets of experiments measure this torque on the outer wall of a Lexan spindle that is attached to a viscometer, functioning as a torque meter. The spindle is immersed in a beaker of ferrofluid centered inside a 2-pole or 4-pole motor stator winding, creating uniform or nonuniform rotating magnetic fields, respectively. The spindle rotates at a constant speed up to 100 rpm or is stationary in these measurements. Anomalous behaviors such as zero and negative magnetoviscosity are demonstrated and discussed. The next set of experiments measure the magnetic torque on the inner wall of a hollow spindle attached to the torque meter and filled completely with ferrofluid so that there is no free surface. The spindle is centered inside the motor stator windings and exposed to clockwise (CW) or counterclockwise (CCW) rotating magnetic fields. The last set of experiments measures the surface spin rate of a small floating plastic ball placed on the ferrofluid surface at a fixed location as a function of magnetic field parameters and radial position on the surface. When the rotating magnetic fields induce ferrofluid flows, the ball spins in the opposite direction to magnetic field rotation and this spin rate is determined using frame-by-frame video analysis. by Adam D. Rosenthal. M.Eng.

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Salvador, Daniel. "Estudo de filmes magnéticos nanoestruturados produzidos com ferrofluidos." Florianópolis, SC, 2011. http://repositorio.ufsc.br/xmlui/handle/123456789/94983.

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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Física Made available in DSpace on 2012-10-25T18:53:12Z (GMT). No. of bitstreams: 1 295969.pdf: 1516842 bytes, checksum: d6455002ebf9d5ca9a1d2e87f14da09b (MD5) Apresentamos nesta dissertação a produção e caracterização de filmes automontados utilizando ferrofluidos (FFs) surfactados (catiônicos e aniônicos). FFs são uma classe muito interessante de materiais, pois apresentam tanto características magnéticas quanto fluidas. Por esse motivo apresentam grande interesse tecnológico, podem ser manipulados com o uso de campos magnéticos sem contato mecânico. Filmes automontados foram produzidos pela técnica de LBL utilizando-se o policátion poli(alilamina hidroclorada) (PAH) com um FF aniônico e o poliânion poli(vinil sulfonato, sais de sódio) (PVS) com um FF catiônico. As amostras foram produzidas variando-se o tempo de imersão, o pH das soluções poliméricas e o número de bicamadas. O crescimento dos filmes foi caracterizado por espectroscopia UV-Vis e a morfologia e espessura por medidas de AFM. Em algumas amostras fizemos ainda caracterização com um magnetômetro de amostra vibrante (VSM), a fim de verificar a dependência da resposta magnética ao pH utilizado na sua produção. Nós investigamos a dependência do crescimento dos filmes com os parâmetros de produção, onde fizemos uso de teoria de leis de escala com o objetivo de correlacionar o regime de crescimento dos filmes LBL com o FF utilizando. A partir deste trabalho foi possível estabelecer os parâmetros mais adequados para obtenção de filmes nanoestruturados de FFs bastante homogêneos, com espessura e rugosidade controladas. A partir das leis de escala obtivemos uma caracterização completa dos padrões de crescimento dos filmes. Portanto, este trabalho contribui para o estabelecimento desta técnica como ferramenta promissora na obtenção de filmes finos magnéticos controlados

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Cabuil, Valérie. "Ferrofluides a base de maghemite : synthese, proprietes physicochimiques et magneto-optiques." Paris 6, 1987. http://www.theses.fr/1987PA066001.

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Les ferrofluides etudies sont constitues de particules de maghemite solubilisees en milieu aqueux (ferrofluides ioniques) ou non aqueux (ferrofluides surfactes). Le mode de synthese permet de controler les caracteristiques des grains (taille et densite superficielle de charge)

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Morales, Marienette B. "Magnetization Dynamics and Interparticle Interactions in Ferrofluids and Nanostructures." Scholar Commons, 2009. http://scholarcommons.usf.edu/etd/3913.

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Nanoparticle assemblies are of current interest as they are used in a wide variety of industrial and biomedical applications. This work presents two studies aimed at understanding the magnetization dynamics and interparticle interactions in nanoparticle assemblies and various types of ferrofluids. First, we studied the influence of varying strengths of dipolar interaction on the static and dynamic magnetic properties of surfactant-coated monodispersed manganese-zinc ferrite nanoparticles using reversible transverse susceptibility. We tracked the evolution of the anisotropy peaks with varying magnetic field, temperature, and interaction strength. The anisotropy peaks of weakly interacting particles appears as non-symmetric peaks and at lower fields in a unipolar transverse susceptibility scan. On the other hand, a strongly interacting particle system exhibits symmetric anisotropy peaks situated at higher field values. In the second study, we successfully synthesized stable ferrofluids out of high quality Fe 3O4 and CoFe2O4 nanoparticles. Such ferrofluids are excellent systems for the investigation of physics of relaxation phenomena in magnetic nanoparticles. Motivated by the need to understand their peculiar magnetic response, a comparative study on Fe 3O4 - and CoFe 2O4 -based ferrofluids was performed. We investigated cases in which particle blocking and carrier fluid freezing temperatures were close and far apart from each other. Our experimental results reveal the true origin of the glass-like relaxation peaks that have been widely observed in ferrofluids by many groups but remained largely unexplained. Contrary to the speculation of previous literature, we argue that the formation of the magnetic anomaly is due not only to the particle blocking but also to its correlation with the the carrier fluid freezing effects. It is also shown that the nature of these peaks is strongly affected by varying particle size and carrier fluid medium. Quantitative fits of the frequency dependent AC susceptibility to the Vogel-Fulcher scaling law clearly indicate that the blocking of magnetic nanoparticles in the frozen state significantly affects the interparticle dipole-dipole interaction, causing characteristic spin-glass-like dynamics. A clear correlation between the blocking and freezing temperatures emerges from our studies for the first time.

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Elborai, Shihab M. (Shihab Mahmoud) 1977. "Ferrofluid surface and volume flows in uniform rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37846.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006. 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. 255-260). Ferrofluid surface and volume effects in uniform dc and rotating magnetic fields are studied. Theory and corroborating measurements are presented for meniscus shapes and resulting surface driven flows, spin-up flows, and Hele-Shaw cell flows and instabilities. To characterize the water-based and oil-based ferrofluids used in experiments, measurements were made of the magnetization curve, surface tension, viscosity, density, and the speed of sound. Extensive measurements of the height and shape of ferrofluid menisci in applied uniform dc magnetic fields show that the height of the meniscus increases for vertical applied magnetic fields, whereas horizontal magnetic fields decrease meniscus height. An approximate energy minimization analysis agrees with the observed trends in ferrofluid meniscus height. The effects of ferrofluid meniscus curvature on spin-up flow were modeled under simplified assumptions. Analytical solutions were derived for two dimensional low Reynolds number flows and extended results were obtained numerically using COMSOL's Multiphysics finite element software package (FEMLAB) to solve for three dimensional recirculating flows at higher Reynolds numbers. (cont.) Familiar magnetostatic energy expressions in linear magnetic media were extended to non-linear magnetization relations. These energy expressions were applied to study the effects of linear and non-linear magnetization on flows and instabilities in Hele-Shaw cells with simultaneously applied in-plane rotating and dc axial magnetic fields. Ultrasound velocimetry of the spin-up flow in the bulk region of water-based ferrofluids conclusively demonstrates the co-rotation of the bulk of the ferrofluid with the applied rotating magnetic field with and without a free surface. Careful ultrasound investigation of flow profiles at different heights in uncovered ferrofluid cylinders showed flow direction reversal between the counter-rotating top free surface and the co-rotating bulk region of the ferrofluid. A framework for a numerical solution of the coupled governing equations of conservation of linear and angular momentum in magnetic spin-up flows that considers all the terms in the first Shliomis magnetization relaxation equation was formulated and solved. Previous solutions in the literature which decouple the magnetic and fluid mechanical dynamics by neglecting the linear and spin velocities in the magnetization relaxation equations result in no spin-up flow in uniform magnetic fields in the absence of spin diffusion effects. (cont.) Contrary to the commonly held view in the literature, spin-up flows develop in rotating uniform magnetic fields even in the absence of spin diffusion effects. Including the linear and spin velocity terms in the magnetization relaxation equation results in non-zero spin-up flow. Numerical solutions using FEMLAB software are shown for flow profiles with zero and non-zero spin viscosity. Fitting numerical simulations to velocity profile ultrasound measurements allows the estimation of the magnetization relaxation time and the spin viscosity for Ferrotec Corp.'s MSG Wll and EMG705 water-based ferrofluids. by Shihab Mahmoud Elborai. Ph.D.

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Dozier, Kahlil A. "Characterizing ferrofluid spin-up flow in rotating uniform magnetic fields." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91442.

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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014. 6 Cataloged from PDF version of thesis. Includes bibliographical references (page 85). A ferrofluid is a collection of nanoscale ferromagnetic particles with a stabilizing surfactant in a liquid to form a colloid. The dynamic behavior of ferrofluids in the presence of magnetic fields has long been an area of research interest. A particular area of interest deals with the "spin-up" mechanisms of ferrofluids, which describe how a container of ferrofluid comes to a steady state of bulk flow when subjected to a uniform rotating external magnetic field. There are two prevailing theories that attempt to explain the spin-up mechanisms of ferrofluids: spin diffusion theory, and the presence of non-uniformities in the magnetic field, due to "demagnetizing factors" introduced by the shape of the container. This research attempts to confirm previous measurements indicating that non-uniformities in the magnetic field are the primary cause of ferrofluid bulk flow. Partial spheres and cylindrical containers of different volumes -- and thus different demagnetizing factors -- were filled with Ferrotec EFH1 oil-based ferrofluid and subjected to an external uniform rotating magnetic field for various parameters of rotation direction and magnetic field. Ferrofluid bulk flow was measured using ultrasound velocimetry, and the magnitudes and shapes of the velocity profiles were compared. Despite the complicated flows observed within the containers, enough of a trend was established to safely conclude that demagnetizing factors are often the primary cause of ferrofluid bulk flow. by Kahlil A. Dozier. M. Eng.

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Canaday, Tyrone Carwell 1976. "Ferrofluid duct flow in alternating and travelling wave magnetic fields." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80056.

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Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999. Includes bibliographical references (leaf 86). by Tyrone Carwell Canaday. S.B.and M.Eng.

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Strömberg, Mattias. "Molecular Diagnostics Using Volume-Amplified Magnetic Nanobeads : Towards the Development of a Novel Biosensor System." Doctoral thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9542.

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Micro- or nanometer sized magnetic particles (beads) currently have a vast range of life science applications in, for example, bioseparation techniques, cancer therapy, development of contrast agents and biosensing techniques. In the latter field, magnetic beads offer several unique advantages, including minimal background signals, physical and chemical stability and low manufacturing costs. Because of these properties, magnetic biosensing techniques are potential candidates for low-cost, easy-to-use molecular diagnostic devices. This doctoral thesis focuses mainly on the proof of principle and further development of a new magnetic biosensor platform for detection of DNA targets, a potential candidate for a new generation of low-cost, easy-to-use diagnostic devices: the Volume-Amplified Magnetic Nanobead Detection Assay (VAM-NDA). The VAM-NDA principle combines target recognition by padlock probe ligation followed by rolling circle amplification (RCA) of the reacted probes with changes in Brownian relaxation behaviour of magnetic nanobeads (typically ~100 nm in diameter) induced by a change in hydrodynamic bead volume. More specifically, the RCA products (coils, typically ~1 μm in diameter) are detected magnetically by adding magnetic beads tagged with detection probes complementary to part of the repeating RCA-coil sequence. Thus, depending on the target concentration, a certain quantity of beads binds to the coils by base-pair hybridisation (bead immobilisation), resulting in a dramatic bead volume increase, which is then detected by measuring the complex magnetisation spectrum. Use of a commercial SQUID magnetometer for measuring complex magnetisation resulted in a detection limit in the low pM range for DNA targets with excellent quantification accuracy. Simultaneous multiplexing was also evaluated. The stability and aging of typical commercial ferrofluids (suspensions of magnetic beads) were investigated by measuring the complex magnetisation of and interbead interactions in oligonucleotide-functionalised ferrofluids. In summary, the bead surface characteristics were found to have a strong impact on the measured dynamic magnetic properties.

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Walker, Mathew William. "Improved techniques for isolation of pure cellular organelles with magnetic ferrofluid." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/70620/.

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Lysosomes are essential cellular organelles known to be the main site for the breakdown and recycling of endocytosed macromolecules within cells. However, our knowledge of lysosomal function has changed considerably over the last decade with the lysosome now being a recognized Ca2+ signaling organelle with additional roles in plasma membrane repair, clearance of defective organelles and mediating cell death as well as established roles in clearing infection. Our ability to study these unique organelles has however been stymied by a dearth of good techniques for the purification of functional lysosomes not contaminated by other organelles.

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Khushrushahi, Shahriar Rohinton. "Ferrofluid spin-up flows from uniform and non-uniform rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60150.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010. Cataloged from PDF version of thesis. Includes bibliographical references. When ferrofluid in a cylindrical container is subjected to a rotating azimuthally directed magnetic field, the fluid "spins up" into an almost rigid-body rotation where ferrofluid nanoparticles have both a linear and an angular "spin" velocity. Flow observations are often limited to the ferrofluid free surface due to the opaque nature of the ferrofluid and the surface flow can spin-up in the same or opposite directions to the direction of the rotating field. The mechanisms governing this flow have been attributed to surface driven flows that depend on the shape of the meniscus formed by the free surface. However, bulk flow experiments using ultrasound velocimetry show that even in the presence of a stationary cover, bulk ferrofluid flows would result when a rotating magnetic field was applied. The mechanisms explaining the bulk flows have been attributed by some authors to being a result of spin diffusion theory while others believe that non-uniform magnetic properties drive the flow, with both theories being rigorously explored in this thesis. This thesis applies ferrohydrodynamic analysis to extended fluid flow equations driven by magnetization forces and torques on the ferrofluid, Maxwell's equations relating magnetization, magnetic field and ferrofluid flow, and a Langevin magnetization relaxation constitutive law including the effects of fluid linear and spin velocities. Some key concepts investigated in this analysis are: (1) Ferrofluid filled cylindrical vessels of finite height placed within a uniform magnetic field result in non-uniform magnetic fields inside the ferrofluid due to demagnetization effects that can drive the flow; (2) A spherical vessel of ferrofluid in a uniform magnetic field has a resulting uniform magnetic field unless there is a spatial variation of magnetic properties, induced in this thesis by an external source of non-uniform magnetic field from a current carrying coil or a permanent magnet; and (3) COMSOL Multiphysics spin-diffusion modeling shows that spin viscosity can also initiate a flow due to spin-velocity boundary conditions which can hinder magnetic nanoparticle rotation near a wall or allow particles to roll along a wall due to flow vorticity. Ferrofluid spin-up flows were investigated that take into account demagnetizing effects associated with the shape of the container. The experiments conducted in this thesis involve using a sphere of ferrofluid in a uniform rotating field since a sphere has uniform and equal demagnetizing factors in all three Cartesian directions. The uniform rotating magnetic field is generated by two orthogonally placed spherical coils, known as "fluxballs" that generate a uniform magnetic field in the horizontal and vertical directions inside the fluxballs and a dipole field outside. By driving the coils with sinusoidal signals that are out of phase in time by 90 degrees a uniform rotating field is generated inside the test chamber containing the sphere of ferrofluid. The test sphere of ferrofluid is placed at the center of the larger surrounding "fluxball" machine. Negligible flows are measured within the ferrofluid filled sphere using ultrasound velocimetry in the "fluxball" machine with a uniform rotating magnetic field. COMSOL simulations using non-zero values of spin-viscosity, with a zero spin-velocity boundary condition at the outer wall, predict measurable flow while simulations setting spin-viscosity to zero result in negligible flow. Previously published values of spin-viscosity measured in cylindrical vessels are much larger than values allowed by kinetic theory because the flows, from which they were determined, are actually due to the demagnetizing field effects and not due to spin-diffusion. Experiments were also performed by partially filling the test sphere with ferrofluid but only 2/3 full, resulting in significant flows due to non-uniform magnetic fields from spatially dependent demagnetizing factors and possibly free surface effects. Ultrasound velocimetry measurements were also performed with a small permanent magnet or a DC/AC excited small coil on top of the ferrofluid filled test sphere, causing a nonuniform DC or AC magnetic field within the ferrofluid filled test sphere in addition to the uniform rotating magnetic field imposed by the fluxball coils. With an imposed non-uniform magnetic field component from magnet or coil, complex measurable flows with strong vortices are obtained. Formation of vortices is also confirmed in COMSOL simulations of an infinitely long cylinder subjected to a uniform rotating field and the field from an infinitely long permanent magnet. These measurements demonstrate that a non-uniform magnetic field or a non-uniform distribution of magnetic properties drive the flow. The spin-up ferrofluid flow in a rotating uniform externally applied field is highly dependent on the shape of the container due to demagnetizing effects. These demagnetizing effects in a finite-height ferrofluid filled cylindrical container create a non-uniform field inside the ferrofluid that drives the flow and is the cause for previously observed flows in the classic cylindrical spin-up flow experiments. COMSOL Multiphysics simulations applied to a cylinder of infinite height filled with ferrofluid show that spin-diffusion theory cannot be the dominant mechanism for spin-up flows as fitting the COMSOL analysis to measurements result in unphysically large values of spin viscosity. The unphysically large values of spin viscosity are obtained by attributing spin-up flow to be due to spin-diffusion alone rather than the correct non-uniform magnetic field effects. In conclusion, this thesis, through experimental results and numerical simulations, proves that non-uniform magnetic properties within the ferrofluid and not spin-diffusion theory is the driving mechanism for the measured flow. by Shahriar Rohinton Khushrushahi. Ph.D.

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RODRIGUES, KATIA C. "Caracterizacao cristalina e magnetica de precipitados de magnetita obtidos na preparacao do ferrofluido Fe sub(3) O sub(4) + D sub(2)O." reponame:Repositório Institucional do IPEN, 1994. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10386.

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Made available in DSpace on 2014-10-09T12:38:05Z (GMT). No. of bitstreams: 0 Made available in DSpace on 2014-10-09T14:05:08Z (GMT). No. of bitstreams: 1 05584.pdf: 5406312 bytes, checksum: cdcdc9731d40e83f10b28b342361bb34 (MD5) Dissertacao (Mestrado) IPEN/D Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Pop, Loredana. "Investigation of the microstructure of ferrofluids under the influence of a magnetic field and shear flow /." Düsseldorf : VDI-Verl, 2006. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=015009943&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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Judge, Andy. "Air Gap Elimination in Permanent Magnet Machines." Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-dissertations/123.

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In traditional Permanent Magnet Machines, such as electric motors and generators, power is transmitted by magnetic flux passing through an air gap, which has a very low magnetic permeability, limiting performance. However, reducing the air gap through traditional means carries risks in manufacturing, with tight tolerances and associated costs, and reliability, with thermal and dynamic effects requiring adequate clearance. Using a magnetically permeable, high dielectric strength material has the potential to improve magnetic performance, while at the same time offering performance advantages in heat transfer. Ferrofluids were studied as a method for improved permeability in the rotor / stator gap with a combined experimental and computational approach. Results show promise for the ferrofluid technique. An off-the-shelf motor system showed improved performance with ferrofluids vs. fluids of equivalent viscosity, and improved performance vs. an air gap at low RPM. New generator designs showed design dependent performance gains, although some potential for negative performance effects. A proof of concept generator was built and tested, with increased voltage vs. RPM predicted through virtual prototyping, and validated through experimentation, showing ~10% improvement on voltage vs. RPM at the <600 RPM range. More repeatable engineering tests demonstrated a ~30% increase in the voltage / RPM relationship for designs with an isolated stator chamber and a large stator - rotor gap. However, the effects were negative for a similar system with a small stator-rotor gap due to leakage flux effects. New contributions to the body of knowledge in this area include: Ã¢â‚¬Â¢ Application of the ferrofluid technique to axial flux designs. Ã¢â‚¬Â¢ Development of a virtual prototype, including variations in the fluid viscosity due to ferrohydrodynamic effects. Ã¢â‚¬Â¢ Consideration of negative effects of ferrofluid immersion, such as shear losses and increases in leakage flux. Ã¢â‚¬Â¢ Optimization of the design to eliminate increased viscous losses. The improved design has been designed, built, and tested, featuring isolation of the ferrofluid from the rotating region. This offers all of the performance gain of improved magnetic permeability, while minimizing the offsetting losses from increased shear effects.

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Vargas, Maycol Marcondes. "Effect of transient gas-phase on ferrofluid droplet vaporization: under large magnetic power regime." Instituto Nacional de Pesquisas Espaciais (INPE), 2014. http://urlib.net/sid.inpe.br/mtc-m21b/2014/01.23.11.02.

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In this work the influence of transient processes of the gas phase on the vaporization of isolated ferrofluid droplet with spherical symmetry under the influence of an external alternating magnetic field is investigated. Dispersed magnetic nanoparticles inside the droplet act as a heat source. The nanoparticle dipole reacts to the alternating magnetic field rotating the nanoparticle. The friction between the rotating nanoparticle and the surrounding liquid produces heat (viscous dissipation). Brownian motion of the liquid molecules is responsible for the nanoparticle dipoles misalignment when the magnetic field amplitude is null. Therefore, in each cycle of the magnetic field the nanoparticle rotates, generating heating in the core of the liquid. Applying this process on droplets is possible to reduce the droplet heating time. The conditions addressed in this problem leads to the magnetic power to be much larger than the thermal power, provided by the heat flux from the gas phase. The characteristic of this problem is a thermal boundary layer established close to the droplet surface in the liquid side. The magneto relaxation source is found to be dependent on initial conditions. In addition, because of the dependency of the magneto relaxation heating on temperature, a local maximum of temperature is found inside the thermal boundary layer. In the current model it is also observed the increasing of the droplet vaporization with pressure. Neste trabalho é estudado a influência dos processos transientes da fase gasosa na vaporização de uma gota isolada de ferrofluido com simetria esférica e sob influência de um campo magnético externo alternado. Nanopartículas magnéticas homogeneamente dispersas no fluido agem como uma fonte de calor. Os dipolos das nanopartículas respondem ao campo magnético alternado fazendo a nanopartícula rotacionar. O atrito entre a nanopartícula e o líquido nos arredores da partícula produz calor (dissipação viscosa). O movimento Browniano das moléculas do líquido é responsável pelo desalinhamento dos dipolos na ausência do campo magnético. Desse modo em cada ciclo do campo magnético as nanopartículas rotacionam, gerando calor dentro da gota. Aplicando esse processo em gotas é possivel reduzir o tempo de aquecimento. As condições assumidas neste problema resultam em uma potência magnética muito maior do que a potência térmica, dada pelo fluxo de calor da fase gasosa. A característica desse problema consiste em uma camada limite térmica estabelecida bem próximo à superfície no lado líquido da gota. O fonte magnética é dependente das condições iniciais do problema. Além disso, devido à dependência da fonte magnética com a temperatura, uma temperatura máxima local dentro da camada limite térmica é encontrada. O modelo atual observa o aumento da taxa de vaporização da gota com a pressão.

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Liangruksa, Monrudee. "Nanoscale thermal transport for biological and physical applications." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/29770.

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Nanotechnology has made it possible to create materials with unique properties. This development offers new opportunities and overcomes challenges for many thermal transport applications. Yet, it requires a more fundamental scientific understanding of nanoscale transport. This thesis emphasizes how simulation, mathematical, and numerical methods can lead to more grounded studies of nanoscale thermal transport for biological and physical applications. For instance, magnetic fluid hyperthermia (MFH), an emerging cancer treatment, is a noninvasive method to selectively destroy a tumor by heating a ferrofluid-impregnated malignant tissue with minimal damage to the surrounding healthy tissue. We model the problem by considering an idealized spherical tumor that is surrounded by healthy tissue. The dispersed magnetic nanoparticles in the tumor are excited by an AC magnetic field to generate heat. The temperature distribution during MFH is investigated through a bioheat transfer relation which indicates that the P\'eclet, Joule, and Fourier numbers are the more influential parameters that determine the heating during such a thermotherapy. Thus, we show that a fundamental parametric investigation of the heating of soft materials can provide pathways for optimal MFH design. Since ferrofluid materials themselves play a key role in heating, we examine six materials that are being considered as candidates for MFH use. These are simulated to investigate the heating of ferrofluid-loaded tumors. We show that iron-platinum, magnetite, and maghemite are viable MFH candidates since they are able to provide the desired heating of a tumor which will destroy it while keeping the surrounding healthy tissues at a relatively safe temperature. Recent advances in the synthesis and nanofabrication of electron devices have lead to diminishing feature sizes. This has in turn increased the power dissipation per unit area that is required to cool the devices, leading to a serious thermal management challenge. The phonon thermal conductivity is an important material property because of its role in thermal energy transport in semiconductors. A higher thermal conductivity material is capable of removing more heat since higher frequency phonons are able to travel through it. In this thesis, the effects of surface stress on the lattice thermal conductivity are presented for a silicon nanowire. Based on a continuum approach, a phonon dispersion relation is derived for a nanowire that is under surface stress and the phonon relaxation time is employed to subsequently determine its thermal conductivity. The surface stress is found to significantly influence the phonon dispersion and thus the Debye temperature. Consequently, the phonon thermal conductivity decreases with increasing surface stress. Different magnitudes of surface stress could arise from various material coatings and through different nanofabrication processes, effects of which are generally unclear and not considered. Our results show how such variations in surface stress can be gainfully used in phonon engineering and to manipulate the thermal conductivity of a nanomaterial. The thermal transport during thermoelectric cooling is also an important property since thermoelectric devices are compact, reliable, easy to control, use no refrigerants and require lower maintenance than do more traditional refrigeration devices. We focus on the Thomson effect that occurs when there is a current flow in the presence of a temperature gradient in the material, and investigate its influence on an intrinsic silicon nanowire cooler. The temperature dependence of the Thomson effect has a significant influence on the cooling temperature. We also consider thermal nonequilibrium between electrons and phonons over the carrier cooling length in the nanowire. The results show that a strong energy exchange between electrons and phonons lowers the cooling performance, suggesting useful strategies for thermoelectric device design. Ph. D.

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Espinosa, Daniel Humberto Garcia. "Estudo das propriedades ópticas não lineares de ferrofluidos e filmes finos de magnetita na escala de tempo de femtosegundos." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-10052017-152839/.

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As propriedades ópticas não lineares refrativas e absortivas de ferrofluidos, formados por nanopartículas de magnetita dispersas em óleo ou em água, e de filmes finos feitos a partir dos ferrofluidos são estudadas através da técnica experimental de varredura-z. Um feixe laser Gaussiano pulsado, com cerca de 200 femtosegundos de largura de pulsos e comprimento de onda de 800 nm, é utilizado para a medida do índice de refração não linear n2 e do coeficiente de absorção de dois fótons . Apresentamos toda a caracterização do feixe necessária para tais medidas, assim como as caracterizações ópticas e estruturais das amostras. Em particular, os diâmetros das nanopartículas são obtidos pelas técnicas de difratometria de raios X, espalhamentos de raios X a baixos ângulos e microscopia eletrônica de transmissão. Os efeitos ópticos não lineares provenientes do aquecimento da amostra pelo laser são evitados com o emprego, em conjunto, de um obturador eletromecânico e de um modulador eletro-óptico. n2 e são medidos em função do diâmetro médio das nanopartículas, e como resultado diminui com a diminuição do diâmetro médio das nanopartículas. Além disso, a comparação de para amostras de diferentes concentrações permite a obtenção da seção de choque de absorção de dois fótons 2PA da magnetita. As absorções e refrações não lineares também são estudadas em função da aplicação de um campo magnético externo sobre os filmes finos e ferrofluidos. Para esses últimos, os valores de aumentam com a aplicação de campo magnético na mesma direção da polarização da luz, e diminuem com a aplicação de campo perpendicular à polarização. Os possíveis motivos de tal comportamento são discutidos e a determinação de elementos do tensor susceptibilidade óptica de terceira ordem são obtidos a partir desses resultados. The refractive and absorptive nonlinear optical properties of ferrofluids, made with magnetite nanoparticles in water or oil, and of thin films made from the ferrofluids, are investigated by z-scan technique. A Gaussian pulsed laser beam, with pulse width of ~ 200 femtoseconds and wavelength of 800 nm is used in the nonlinear refractive index n2 and two-photon absorption coefficient measurements. The beam characterization is detailed, as well as the samples optical and structural characterization. The nanoparticles mean diameters, especially, are achieved by X-ray diffractometry, small angle X-ray scattering and transmission electron microscopy. An electro-optical modulator and an electromechanical shutter are applied in the setup to avoid the thermal nonlinear optical effects, that could be present due to the sample heating by the beam. n2 and are measured as a function of the mean nanoparticles diameters, and as a result, values decrease when the diameters decrease. Besides, the values comparison for samples with different concentrations allows the determination of the magnetite two-photon absorption cross section 2PA. The nonlinear absorption and refraction are also studied as a function of an external magnetic field applied in the thin films and ferrofluids. For the last, values increase with the field when its direction is parallel to the light polarization, and decrease with field when its direction is perpendicular to the polarization. The possible reasons are discussed, and some elements of the third-order optical susceptibility are obtained from these results.

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Hay, Henri. "Organisation of magnetic microparticles in a ferrofluid : a computational approach to a self-assembly process." Thesis, Uppsala universitet, Materialfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-176898.

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Orji, Uzoma A. "Ferrofluid dynamics in a Hele-Shaw cell simultaneously stressed by DC and rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41666.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007. Includes bibliographical references (p. 81). Earlier experiments have been repeated to evaluate magnetic fluid behavior in DC, AC and rotating magnetic fields. Understanding these behaviors are essential to the ferrohydrodynamic applications of ferrofluids in biomedicine. Careful measurements in Hele-Shaw cells with simultaneous perpendicular DC and in-plane rotating magnetic fields have shown that ferrofluid drop spiral patterns rotate in the same direction as the rotating magnetic field, independent of the polarity of the perpendicular DC magnetic field. This corrects inconsistencies in previously reported measurements. The large and heavy electromagnet and power supply used in earlier work were also replaced by a small permanent magnet assembly from MagswitchTM to still produce ferrofluid spirals and spontaneous self-assembling ferrofluid dot patterns. by Uzoma A. Orji. M.Eng.

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Snively, Michael John. "Effects of demagnetizing factors on transient motion of ferrofluid in a uniform rotating magnetic field." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68699.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. Cataloged from student submitted PDF version of thesis. Includes bibliographical references (p. 105). The mechanisms that lead to bulk flow within a ferrofluid-filled container subjected to a rotating uniform magnetic field are experimentally studied. There are two prevailing theories: spin diffusion theory and flow due to non-uniformities in magnetic field within the ferrofluid due to nonuniform demagnetizing factors. This research sought to confirm previous measurements that indicated demagnetizing factors are the primary cause of bulk ferrofluid flow. Flattened spherical containers of various volumes, and thus different demagnetizing factors, were filled with EFH1 oil-based ferrofluid and subjected to a uniform rotating magnetic field of varying conditions (rotation direction and field strength). The shapes and magnitudes of the velocity profiles measured by an ultrasound velocimeter system differed between containers, indicating that demagnetizing factors did affect flow. The complicated flows within the flattened spheres that affected both the shape and magnitude of the flow velocity prevented a direct magnitude comparison between profiles but the flows differed enough to safely conclude that spatial non-uniformities within the fluid likely caused the bulk flow of fluid in the uniform rotating magnetic field. by Michael John Snively. S.B.

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Panth, Mohan. "USING SURFACE TENSION GRADIENTS AND MAGNETIC FIELD TO INFLUENCE FERROFLUID AND WATER DROPLET BEHAVIOR ON METAL SURFACES." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1470164188.

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Ramírez, Ríos Liliana Patricia. "Superpara- and paramagnetic polymer colloids by miniemulsion processes." Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/137/.

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Polymerverkapselte magnetische Nanopartikel versprechen, in der Zukunft sehr erfolgreich bei Anwendungen in der Biologie und der Medizin eingesetzt werden zu können z. B. in der Krebstherapie und als Kontrastmittel bei der magnetischen Kernspinresonanztomographie. Diese Arbeit zeigt, dass durch die interdisziplinäre Kombination verschiedener Techniken Herstellungsverfahren und Eigenschaften solcher Partikel verbessert werden können. Unter Miniemulsionen versteht man wässrige Dispersionen relativ stabiler Öltröpfchen, zwischen 30 und 50 nm Größe. Ein Nanometer (nm) ist der 1.000.000.000ste Teil eines Meters. Ein Haar ist ungefähr 60.000 Nanometer breit. Hergestellt werden Miniemulsionen durch Scherung eines Systems bestehend aus Öl, Wasser, Tensid (Seife) und einer weiteren Komponente, dem Hydrophob, das die Tröpfchen stabilisieren soll. Die Polymerisation von Miniemulsionen ermöglicht die Verkapselung anorganischer Materialen z. B. magnetischer Teilchen oder Gadolinium-haltiger Komponenten. Zu Optimierung des Verkapselung, ist es notwendig, die richtige Menge eines geeigneten Tensids zu finden. Die magnetischen polymerverkapselten Nanopartikel, die in einer wässrigen Trägerflüssigkeit dispergiert sind, zeigen in Abhängigkeit von Partikelgröße, Zusammensetzung, elektronischer Beschaffenheit, etc. ein sogenanntes superpara- oder paramagnetisches Verhalten. Superpara- oder paramagnetisches Verhalten bedeutet, dass die Flüssigkeiten in Anwesenheit äußerer Magnetfeldern ihre Fließfähigkeit beibehalten. Wenn das Magnetfeld entfernt wird, haben sie keine Erinnerung mehr daran, unter dem Einfluss eines Magnetfeldes gestanden zu haben, d. h., dass sie nach Abschalten des Magnetfeldes selbst nicht mehr magnetisch sind. Die Vorteile des Miniemulsionsverfahrens sind der hohe Gehalt und die homogene Verteilung magnetischer Teilchen in den einzelnen Nanopartikeln. Außerdem ermöglicht dieses Verfahren nanostrukturierte Kompositpartikel herzustellen, wie z. B polymerverkapselte Nanopartikel mit Nanoschichten bestehend aus magnetischen Molekülen. Combining the magnetic properties of a given material with the tremendous advantages of colloids can exponentially increase the advantages of both systems. This thesis deals with the field of magnetic nanotechnology. Thus, the design and characterization of new magnetic colloids with fascinating properties compared with the bulk materials is presented. Ferrofluids are referred to either as water or organic stable dispersions of superparamagnetic nanoparticles which respond to the application of an external magnetic field but lose their magnetization in the absence of a magnetic field. In the first part of this thesis, a three-step synthesis for the fabrication of a novel water-based ferrofluid is presented. The encapsulation of high amounts of magnetite into polystyrene particles can efficiently be achieved by a new process including two miniemulsion processes. The ferrofluids consist of novel magnetite polystyrene nanoparticles dispersed in water which are obtained by three-step process including coprecipitation of magnetite, its hydrophobization and further surfactant coating to enable the redispersion in water and the posterior encapsulation into polystyrene by miniemulsion polymerization. It is a desire to take advantage of a potential thermodynamic control for the design of nanoparticles, and the concept of "nanoreactors" where the essential ingredients for the formation of the nanoparticles are already in the beginning. The formulation and application of polymer particles and hybrid particles composed of polymeric and magnetic material is of high interest for biomedical applications. Ferrofluids can for instance be used in medicine for cancer therapy and magnetic resonance imaging. Superparamagnetic or paramagnetic colloids containing iron or gadolinium are also used as magnetic resonance imaging contrast agent, for example as a important tool in the diagnosis of cancer, since they enhance the relaxation of the water of the neighbouring zones. New nanostructured composites by the thermal decomposition of iron pentacarbonyl in the monomer phase and thereafter the formation of paramagnetic nanocomposites by miniemulsion polymerization are discussed in the second part of this thesis. In order to obtain the confined paramagnetic nanocomposites a two-step process was used. In the first step, the thermal decomposition of the iron pentacarbonyl was obtained in the monomer phase using oleic acid as stabilizer. In the second step, this iron-containing monomer dispersion was used for making a miniemulsion polymerization thereof. The addition of lanthanide complexes to ester-containing monomers such as butyl acrylate and subsequent polymerization leading to the spontaneous formation of highly organized layered nanocomposites is presented in the final part of this thesis. By an one-step miniemulsion process, the formation of a lamellar structure within the polymer nanoparticles is achieved. The magnetization and the NMR relaxation measurements have shown these new layered nanocomposites to be very apt for application as contrast agent in magnetic resonance imaging.

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Kavaliou, Klim [Verfasser], and Lutz [Akademischer Betreuer] Tobiska. "Mathematical modeling of the diffusion of magnetic particles in a ferrofluid seal under magnetic and centrifugal forces / Klim Kavaliou ; Betreuer: Lutz Tobiska." Magdeburg : Universitätsbibliothek, 2016. http://d-nb.info/111482027X/34.

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Magnet, Cécilia. "Mécanismes de capture de nanoparticules magnétiques : application à la purification de l'eau." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00932715.

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La séparation magnétique est utilisée dans le domaine de la purification de l'eau. Des nanoparticules magnétiques fonctionnalisées ou nues sont en charge de capter un polluant ciblé puis sont enlevées de l'eau par l'application d'un champ magnétique. Nous avons montré que l'utilisation d'un ferrofluide aqueux classique constitué de nanoparticules d'oxyde de fer recouvertes par une double couche de surfactant d'acide oléique permet une adsorption efficace des cations métalliques (ion nickel Ni2+) puis leur enlèvement en utilisant des microparticules magnétiques. Nous avons montré que des interactions magnétiques suffisamment fortes entre les nanoparticules induisent une transition de phase colloïdale. Il existe trois régimes de captage qui dépendent de deux paramètres, le premier paramètre est lié à l'intensité du champ magnétique et le second est la concentration en nanoparticules. En présence de l'écoulement de la suspension des nanoparticules, le captage des nanoparticules est toujours régi par la concentration en nanoparticules et également par le nombre de Mason. Nous avons mené une expérience de captage des nanoparticules par un milieu poreux. L'efficacité de filtration est liée à la compétition entre les forces hydrodynamiques et magnétiques ainsi que de la séparation de phase au sein de la suspension. Les théories développées lors de ce travail sont en accord raisonnable avec les résultats expérimentaux et montrent l'augmentation de l'efficacité de captage des nanoparticules avec l'augmentation de l'intensité du champ magnétique et de la concentration en nanoparticules ainsi que la diminution de l'efficacité de captage avec l'augmentation du nombre de Mason.

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Edalatpour, Mojtaba. "FERROFLUID DROPLET BEHAVIOR ON PATTERNED AND NON-PATTERNED SURFACES IN THE PRESENCE OF EXTERNAL UNIFORM MAGNETIC FIELDS." Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami1543455437727546.

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Cherief, Wahid. "Etude des ferrofluides et de leurs applications à l'intensification des transferts de chaleur par convection forcée." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT102/document.

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Cette thèse a pour objectif d’étudier les performances thermiques et rhéologiques des ferrofluides sous champ magnétique pour des applications de refroidissement. L’approche adoptée dans cette thèse est de nature macroscopique, et est basée sur plusieurs études expérimentales. Cette caractérisation des performances des ferrofluides est focalisée sur trois aspects : i) étude de la rhéologie ii) étude de la convection forcée iii) étude la conductivité thermique. Différents outils de caractérisation correspondant à chaque domaine d’étude ont été développés. Dans le domaine de la rhéologie, une cellule magnétique a été construite et adaptée à un rhéomètre afin d’étudier le comportement rhéologique du ferrofluide sous un champ magnétique allant jusqu’à 0,8 T. Cette démarche met en évidence l’influence du champ magnétique et de son intensité sur les forces de cisaillement. Dans le domaine des transferts de chaleur, une boucle thermohydraulique pour l’étude de l’échange de chaleur en convection forcée avec une paroi à flux imposée sous champ magnétique a été mise au point. Ce type de dispositif permet l’étude de plusieurs paramètres liés à la configuration spatiale du champ magnétique appliqué, à l’effet de l’uniformité du champ sur l’intensification des échanges de chaleur. La compréhension et l’analyse de ces résultats sont consolidées par l’étude de la conductivité thermique du ferrofluide sous champ magnétique. Un banc a été mis en place et a permis de mettre en évidence l’influence de la température ainsi que de l’intensité du champ magnétique sur cette grandeur. Á l’issue de ces caractérisations, l’application des ferrofluides pour le refroidissement de composants électroniques de puissance est discutée par une mise en œuvre expérimentale. Ces essais ouvrent la voie pour de nouvelles recherches et permettent de mener des réflexions relatives aux domaines d’application des ferrofluides This thesis aims to study the thermal and rheological performances of ferrofluids under magnetic field for an application in cooling systems. The approach consists on macroscopic analysis based on experimental studies. Our approach is focused on three aspects: i) rheology ii) internal forced convection iii) thermal conductivity. We developed different characterization benches. For rheological studies, a magnetic circuit is developed and integrated into rheometer to create magnetic fields reaching 0,8 T. This approach demonstrates the influence of magnetic flux density on the shear forces. Concerning heat transfers, we carried out experimental tests based on the use of a closed loop flow system to study forced convection of ferrofluids with imposed wall flux under magnetic field. This test bench allows us to understand the impact of several parameters related to the configuration of the applied magnetic field on the enhancement of convective heat transfers. To analyze why convective heat transfers are better under magnetic field, we carried out a system for measuring the thermal conductivity. This bench tests allows us to show the effect of temperature and magnetic flux density on this physical property. All these tests are paving the way for new research activities and to the ferrofluids applications in cooling systems

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Petit, Pierre-Antoine. "Structures macro-organisées et processus irréversibles : modulations de surface d'un film ferrofluide, états de paroi dans les mémoires à linges de Bloch." Grenoble 1, 1993. http://www.theses.fr/1993GRE10087.

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Le contenu de cette these repose sur l'etude de structures spatiales macroscopiques creees a la suite de processus irreversibles. Cette etude tres generale a ete realisee tres specifiquement sur deux materiaux magnetiques respectivement liquide et solide: le ferrofluide et le grenat. La premiere partie de cette these est consacree a l'etude statique des patterns qui apparaissent a la surface des films de ferrofluide, en presence d'un champ magnetique normal a sa surface. Ces patterns sont des reseaux de modulation d'epaisseur du film, et leur etude a ete realisee par traitement d'images. Nous presentons la structure et la forme de ces differents patterns, ainsi que les grandeurs caracteristiques qui les decrivent. Nous avons determine experimentalement et par un modele, les energies (de surface, de gravite et dipolaire. . . ) et leur evolution dans ce systeme. La deuxieme partie est consacree aux differents etats de parois qui apparaissent lors de coupe locale de domaines magnetiques dans un grenat epitaxie a anisotropie perpendiculaire. Cette etude est realisee dans le but de determiner des parametres de fonctionnement pour l'operation de lecture dans les memoires magnetiques a lignes de bloch. Nous avons determine les conditions satisfaisant cette operation, et nous avons interprete les effets de champs plans sur les mecanismes de nucleation de lignes qui interviennent lors de ce processus de coupe

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Lira, Sérgio Henrique Albuquerque. "Viscous Fingering In Complex Magnetic Fluids: Weakly Nonlinear Analysis, Stationary Solutions And Phase-field Models." Universidade Federal de Pernambuco, 2014. https://repositorio.ufpe.br/handle/123456789/12734.

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Submitted by Daniella Sodre (daniella.sodre@ufpe.br) on 2015-04-08T13:19:43Z No. of bitstreams: 2 TESE Sérgio Henrique Lira.pdf: 10473188 bytes, checksum: ad39baf570ad4b641f94987468e9d1d0 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Made available in DSpace on 2015-04-08T13:19:43Z (GMT). No. of bitstreams: 2 TESE Sérgio Henrique Lira.pdf: 10473188 bytes, checksum: ad39baf570ad4b641f94987468e9d1d0 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2014-02-21 CNPq; INCT-FCx. Nesta Tese são empregadas técnicas analíticas e numéricas para investigar o fenômeno de formação de dedos viscosos entre fluidos imiscíveis confinados quando um destes fluidos é um fluido magnético complexo. Diferentes tipos de esquemas geométricos efetivamente bidimensionais foram investigados. Duas situações distintas são tomadas com relação à natureza da amostra de fluido magnético: um fluido newtoniano usual, e um fluido magneto-reológico que apresenta um yield stress dependente da intensidade do campo magnético. Equações governantes adequadas são derivadas para cada um dos casos. Para obter um entendimento analítico dos estágios iniciais da evolução temporal da interface foi empregada uma análise fracamente não-linear de modos acoplados. Este tipo de análise acessa a estabilidade de uma interface inicialmente perturbada e também revela a morfologia dos dedos emergentes. Em algumas circunstâncias soluções estacionárias podem ser encontradas mesmo na ordem não-linear mais baixa. Nesta situação é feita uma comparação de algumas destas soluções com soluções estáticas totalmente não-lineares obtidas através de um formalismo de vortex-sheet na condição de equilíbrio. Em seguida foi desenvolvido um modelo de phase-field aplicado a fluidos magnéticos que é capaz de simular numericamente a dinâmica totalmente não-linear do sistema. O modelo consiste em introduzir uma função auxiliar que reproduz uma interface difusa de espessura finita. Utilizando esta ferramenta também é possível estudar um complexo problema de dedos viscosos de origem biológica: o fluxo de actina como um fluido ativo dentro de um fragmento lamelar.

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36

Moening, Andrew. "Post-Consumer Plastic Particle Sortation by Plastic Type with the Use of Magnetic Fields and Ferrofluids for the Recycling Industry: A Proof of Concept Study." University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1384548911.

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37

Marie, Hélène. "Magnétoliposomes pour le diagnostic et le traitement du glioblastome par vectorisation magnétique et hyperthermie." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA114834.

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L’ensemble de l’étude in vivo réalisée sur souris porteuses de glioblastome U87 démontre la faisabilité du ciblage magnétique pour accumuler les magnétoliposomes superparamagnétiques, ou MFLs, au niveau du glioblastome, tout en préservant le reste du tissu cérébral sain. L’étude révèle que le bénéfice apporté par l’action d’un gradient de champ magnétique produit par un aimant extracorporel repose sur un effet EPR (« enhanced permeation and retention » effect) amplifié. Les résultats sont étayés par la combinaison de plusieurs techniques (IRM, RPE, microscopie confocale de fluorescence, microscopie électronique). Concernant les mécanismes de transport empruntés par les magnétoliposomes pour atteindre les cellules tumorales, la voie d’endocytose non spécifique s’apparentant à un processus de macropinocytose est pressentie. Dans l’optique d’une application thérapeutique par hyperthermie, la capacité d’échauffement des magnétoliposomes a été pour la première fois explorée. Les résultats prouvent un comportement thermique des magnétoliposomes compatible avec les conditions d’un traitement par hyperthermie. Enfin, dans le cadre d’une étude portant sur le développement de cancers mécano-induits, l’application des magnétoliposomes a été élargie un autre organe non étudié à ce jour, le côlon. Ces travaux illustrent la problématique de la vectorisation magnétique au sein d’un organe situé dans une région interne de l’organisme First, the in vivo study on U87-glioblastoma bearing mice demonstrates the ability of magnetic targeting to accumulate magnetic-fluid-loaded liposomes (MFLs) into glioblastoma while sparing the rest of the healthy brain tissue. The enhancement of liposome local concentration by applying a magnetic field gradient produced by an external magnet is based on an amplified EPR effect (“enhanced permeation and retention” effect). The results were supported by combining several techniques (MRI, ESR, confocal fluorescence microscopy, electron microscopy). The investigations concerning the mechanisms of transport of the magnetoliposomes to reach the tumor cells suggest a non-specific endocytose pathway, presumably macropinocytosis. Secondly, in the context of a therapeutic application by hyperthermia the heat capacity of MFLs was explored. The results showed that the thermal behaviour of the magnetoliposomes depends on the containment state of the iron oxide nanocrystals and is compatible with the conditions of hyperthermia treatment. Finally, as part of a study concerning the development of mechanically induced cancers, application of MFLs was extended to target another organ not yet studied: the colon. This work especially illustrates the potential and related limits of magnetic targeting towards an organ located in an inner region of the body

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38

Tourinho, Francisco. "Ferrofluides a base de ferrite de cobalt et de ferrite de manganese : elaboration, comportement physicochimique et magnetique." Paris 6, 1988. http://www.theses.fr/1988PA066570.

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Oliveira, Liliam Gleicy de Souza. "Estudo da suspensão do óleo de copaíba Multijulga com Nanopartículas de magnetitas substituídas." Universidade Federal do Amazonas, 2015. http://tede.ufam.edu.br/handle/tede/4712.

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Submitted by Geyciane Santos (geyciane_thamires@hotmail.com) on 2015-11-25T20:31:11Z No. of bitstreams: 1 Tese - Liliam Gleicy de souza Oliveira.pdf: 1737358 bytes, checksum: 0abd9d5d0e82ee6d0303d74ebab41689 (MD5) Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-11-27T18:46:54Z (GMT) No. of bitstreams: 1 Tese - Liliam Gleicy de souza Oliveira.pdf: 1737358 bytes, checksum: 0abd9d5d0e82ee6d0303d74ebab41689 (MD5) Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-11-27T18:56:45Z (GMT) No. of bitstreams: 1 Tese - Liliam Gleicy de souza Oliveira.pdf: 1737358 bytes, checksum: 0abd9d5d0e82ee6d0303d74ebab41689 (MD5) Made available in DSpace on 2015-11-27T18:56:45Z (GMT). No. of bitstreams: 1 Tese - Liliam Gleicy de souza Oliveira.pdf: 1737358 bytes, checksum: 0abd9d5d0e82ee6d0303d74ebab41689 (MD5) Previous issue date: 2015-09-03 Não informada Nanotechnology excels in many areas of expertise, for example, magnetic nanoparticles of iron oxides contribute to the therapy and diagnosis of cancer. Nanoparticles from iron oxides (NM) and magnetite (Fe3O4) and maghemite (γ-Fe2O3) assist in early detection of tumors by nuclear magnetic resonance and permeate into cancer cells for the eradication of tumors by hyperthermia. However, the application of magnetic iron oxides depends on the synthetic route of the magnetic namomaterial and their incorporation in cancer cells. Thus, a series of NM, replaced by Ni and Co, was synthesized by co-precipitation in this work to incorporate them into Copaiba oil Copaifera multijuga as a way to produce nanomaterials able to interact with cancer cells. Six NM replaced by Ni (Ni 1 Ni 2, Ni 3) and Co (Co1, Co 2, Co 3) were chosen using the exploratory techniques HCA and PCA with the R software (ChemoSpec packet) applied to spectra ray diffraction X. Selected NM were studied by XRD, FT-NIR, SEM-EDS and Mössbauer spectroscopy on samples embedded in C. oil multijuga and not incorporated. The results of XRD, SEM and FT-NIR showed a mixture of magnetite / maghemite particles distributed in small average particle size, or even amorphous. This suggests that the synthesis process generated the formation of NM with different morphologies. The Mössbauer spectra suggest different behavior as it increases the isomorphic substitution, so the higher is the substitution is superparamagnetic NM synthesized. A nanotecnologia destaca-se em muitas áreas do conhecimento, por exemplo, nanopartículas magnéticas de óxidos de ferro contribuem na terapia e diagnóstico do câncer. Nanopartículas dos óxidos de ferro magnéticos (NM) como magnetita (Fe3O4) e maghemita (γ-Fe2O3) auxiliam na detecção precoce de tumores por ressonância magnética nuclear e impregnam-se em células cancerígenas para a erradicação dos tumores por hipertermia. Todavia, a aplicação dos óxidos de ferro magnéticos depende da rota sintética do namomaterial magnético e sua incorporação nas células cancerígenas. Sendo assim, uma série de NM, substituídas por Ni e Co, foi sintetizada por coprecipitação neste trabalho a fim de incorporá-las em óleo de copaíba da espécie Copaifera multijuga como forma de produzir nanomateriais capazes de interagir com células cancerígenas. Seis NM substituídas por Ni (Ni 1, Ni 2, Ni 3) e Co (Co1,Co 2, Co 3) foram escolhidas usando as técnicas exploratórias de HCA e PCA com o programa R (pacote ChemoSpec) aplicadas a espectros de difração de raios X. As NM selecionadas foram estudadas por DRX, FT-NIR, MEV-EDS e Espectroscopia Mössbauer em amostras incorporadas em óleo de C. multijuga e não incorporadas. Os resultados de DRX, FT-NIR e MEV mostraram uma mistura de magnetita/maghemita distribuída em particulas pequeno tamanho médio de partículas ou mesmo amorfas. Esse fato sugere que o processo de síntese gerou a formação de NM com morfologias diferentes. Os espectros Mössbauer sugerem comportamentos diferentes à medida que aumenta a substituição isomórfica, ou seja, quanto maior é a substituição mais superparamagnética é a NM sintetizada

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40

Donatini, Fabrice. "Étude de l'anisotropie optique circulaire magneto-induite des ferrofluides dans le domaine spectral visible-proche infrarouge : applications." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0091.

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Les liquides magnetiques (ou ferrofluides) sont des suspensions colloidales, stables et homogenes, de particules nanometriques d'un materiau magnetique dans un liquide. Ordinairement isotropes, ces milieux composites acquierent une certaine anisotropie optique lorsqu'ils sont soumis a l'influence d'un champ magnetique. Cette anisotropie est circulaire dans la configuration longitudinale de faraday (ou la direction du champ magnetique applique est colineaire au vecteur d'onde). Les effets magneto-optiques longitudinaux observes sont non reciproques, ce sont les birefringence et dichroisme circulaires, respectivement proportionnels a la rotation faraday et a l'ellipticite faraday. Une etude systematique (statique et dynamique) de ces effets, pour divers ferrofluides (differents ferrites dans differents liquides porteurs), et en fonction de l'evolution de nombreux parametres (intensite et frequence du champ magnetique applique, longueur d'onde de la lumiere dans le domaine spectral visible-proche infrarouge, temperature et concentration volumique en materiau magnetique) a permis de mettre en evidence leurs comportements tres interessants au plan scientifique. Ainsi, un melange judicieux de ferrofluides peut conduire (a certaines longueurs d'onde) a l'annulation du dichroisme circulaire et a l'obtention de valeurs de rotation faraday tres importantes (les constantes de verdet peuvent etre plusieurs centaines de fois plus grandes que celles des meilleurs verres a ions paramagnetiques ou diamagnetiques). Ces nouveaux liquides magnetiques se comportent alors comme de purs rotateurs de polarisation dont l'utilisation est ideale pour la conception de modulateurs de polarisation ou d'isolateurs optiques miniatures

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41

Zierold, Robert [Verfasser], and Kornelius [Akademischer Betreuer] Nielsch. "Magnetite Nanotubes and Nickel Nanorods of Low Aspect Ratios : From Synthesis to Application in Ferrofluidic Suspensions / Robert Zierold. Betreuer: Kornelius Nielsch." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/104744030X/34.

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42

Sprenger, Lisa. "Beeinflussung der thermomagnetischen Konvektion in Ferrofluidschichten durch den magnetischen Soret-Effekt." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-127792.

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Diese Arbeit stützt sich auf die theoretische und experimentelle Untersuchung der Thermodiffusion im Magnetfeld. Bei magnetischen Flüssigkeiten als kolloidalen Suspensionen versteht man unter der Thermodiffusion einen durch einen Temperaturgradienten angestoßenen unidirektionalen Partikeltransport, der zur Separation des Fluids führt. Beschrieben wird die Thermodiffusion theoretisch über das Konzentrationsprofil der Partikel in Abhängigkeit von Zeit und Ort in einer Fluidschicht. Die Experimente detektieren die Separation des Fluids über die Konzentrationsdifferenz zwischen zwei Fluidkammern. Die Bestimmung des Soret-Koeffizienten erfolgt über einen Datenfit zwischen experimentellen und theoretischen Daten. Für das kerosinbasierte Ferrofluid EMG905 wurden zwei Effekte festgestellt. Bei kleinen Magnetfeldstärken wandern die Partikel zum kalten Rand der Schicht (ST>0), bei steigenden Feldstärken kehrt sich diese Richtung um (ST<0). Die Ergebnisse der Untersuchungen zur Thermodiffusion gehen dann in eine lineare Stabilitätsanalyse einer Ferrofluidschicht bei anliegendem Temperaturgradienten und Magnetfeld ein. Dabei wird festgestellt, dass die kritische Rayleigh-Zahl als charakteristische Größe zum Einsetzen von Konvektion von dem Soret-Koeffizienten abhängt. Ist letzterer positiv, wird das Einsetzen von Konvektion begünstigt, ist er wiederum negativ, so kann Konvektion vollständig unterdrückt werden.

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43

Diedhiou, Daouda Lamine. "Étude de dispositifs hyperfréquences accordables en technologie microfluidique." Phd thesis, Université de Bretagne occidentale - Brest, 2012. http://tel.archives-ouvertes.fr/tel-00857484.

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La multiplication des besoins des utilisateurs dans le domaine des télécommunications a conduit à une surexploitation du spectre de fréquence. Ceci a engendré la raréfaction des bandes de fréquence conduisant à une nécessité de gestion rationnelle des fréquences. Des contraintes ont été rajoutées aux systèmes d'émission / réception et en particulier sur les filtres pour éviter la saturation des services. Dans cette thèse, les travaux s'orientent surtout vers la conception de résonateurs, de filtres planaires et volumiques (3D) accordables dans le domaine des fréquences millimétriques (>= 30 GHz) en utilisant une nouvelle technique d'accordabilité basée sur des principes microfluidiques. Il s'agit d'une nouvelle approche d'agilité qui consiste à faire circuler de la matière (liquides conducteur, diélectrique ou magnétique) dans un substrat diélectrique par le biais de micro canaux. Le substrat diélectrique utilisé, est une résine SU-8 qui offre une souplesse dans la réalisation des micros canaux et des structures volumiques grâce à son bon facteur de forme (≈ 50%). La circulation de liquides dans le substrat, permet de modifier localement les propriétés électromagnétiques du milieu, ce qui conduit à une modification de la fréquence de résonance du dispositif.

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Lin, Gungun. "Multifunctional Droplet-based Micro-magnetofluidic Devices." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-208797.

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Confronted with the global demographic changes and the increasing pressure on modern healthcare system, there has been a surge of developing new technology platforms in the past decades. Droplet microfluidics is a prominent example of such technology platforms, which offers an efficient format for massively parallelized screening of a large number of samples and holds great promise to boost the throughput and reduce the costs of modern biomedical activities. Despite recent achievements, the realization of a compact and generic screening system which is suited for resource-limited settings and point-of-care applications remains elusive. To address the above challenges, the dissertation focuses on the development of a compact multifunctional droplet micro-magnetofluidic system by exploring the advantages of magnetic in-flow detection principles. The methodologies behind a novel technique for biomedical applications, namely, magnetic in-flow cytometry have been put forth, which encompass magnetic indexing schemes, quantitative multiparametric analytics and magnetically-activated sorting. A magnetic indexing scheme is introduced and intrinsic to the magnetofluidic system. Two parameters characteristic of the magnetic signal when detecting magnetically functionalized objects, i.e. signal amplitude and peak width, providing information which is necessary to perform quantitative analysis in the spirit of optical cytometry has been proposed and realized. Magnetically-activated sorting is demonstrated to actively select individual droplets or to purify a population of droplets of interest. Together with the magnetic indexing scheme and multiparametric analytic technique, this functionality synergistically enables controlled synthesis, quality administration and screening of encoded magnetic microcarriers, which is crucial for the practical realization of magnetic suspension arrays technologies. Furthermore, to satisfy the needs of cost-efficient fabrication and high-volume delivery, an approach to fabricate magnetofluidic devices on flexible foils is demonstrated. The resultant device retains high performance of its rigid counterpart and exhibits excellent mechanical properties, which promises long-term stability in practical applications.

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45

Rahn, Helene. "Semi-quantitative röntgentomographische Untersuchungen zur Biodistribution von magnetischen Nanopartikeln in biologischem Gewebe." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-83592.

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Im Rahmen der vorliegenden Dissertationsschrift „Semi-quantitative röntgentomographische Untersuchungen zur Biodistribution von magnetischen Nanopartikeln in biologischem Gewebe“ wurden tomographische Untersuchungen an biologischen Objekten durchgeführt. Bei diesen Objekten handelt es sich um Gewebeproben nach minimal-invasiven Krebstherapien wie zum Beispiel magnetischem Drug Targeting und magnetischer Wärmebehandlung. Der Erfolg dieser Therapien ist sowohl abhängig von der korrekten Verteilung der magnetischen Nanopartikel als auch von der Tatsache, dass diese in der Zielregion in einer ausreichenden Menge vorhanden sind. Das Vorliegen dieser beiden Voraussetzungen ist in der vorliegenden Arbeit untersucht worden. Dabei lag der Schwerpunkt der Arbeit auf der Quantifizierung von magnetischem Material in unterschiedlichen biologischen Gewebeproben mittels Röntgenmikrocomputertomographie (XµCT). Für diesen Zweck wurde ein Kalibrationssystem mit speziellen Phantomen entwickelt, mit dessen Hilfe eine Nanopartikelkonzentration einem Grauwert voxelweise zugewiesen werden kann. Mit Hilfe der Kalibration kann der Nanopartikelgehalt sowohl in monochromatischen als auch in polychromatischen tomographischen Daten im Vergleich zu magnetorelaxometrischen Ergebnissen mit wenigen Prozent Abweichung ermittelt werden. Trotz Polychromasie und damit einhergehenden Artefakten können 3-dimensionale röntgentomographische Datensätze mit einer geringfügigen Konzentrationsabweichung im Vergleich zur quantitativen Messmethode Magnetorelaxometrie semi-quantitativ ausgewertet werden The success of the minimal invasive cancer therapies, called magnetic drug targeting and magnetic heating treatment, depends strongly on the correct distribution of the magnetic nanoparticles on one side. On the other side it depends on the fact that a sufficient amount of magnetic nanoparticles carrying drugs is accumulated in the target region. To study whether these two requirements are fulfilled motivates this PhD thesis „Semi-quantitative X-ray-tomography examinations of biodistribution of magnetic nanoparticles in biological tissues“. The analysis of the distribution of the magnetic nanoparticles in tumours and other tissue examples is realized by means of X-ray-micro computer tomography (XμCT). The work focuses on the quantification of the magnetic nanoparticles in different biological tissue samples by means of XµCT. A calibration of the tomographic devices with adequate phantoms, developed in the frame of this work, opens now the possibility to analyze tomographic data in a semi-quantitative manner. Thus, the nanoparticle concentration can be allocated voxel-wise to the grey values of the three-dimensional tomographic data. With the help of calibration of the tomography equipments used, polychromatic as well as monochromatic three-dimensional representations of objects can be analyzed with regard to the biodistribution of magnetic nanoparticles as well as with regard to their quantity. The semi-quantitative results have been compared with results obtained with a quantitative measurement method magnetorelaxometry (MRX). Thereby a good agreement of the semi-quantitative and quantitative data has been figured out

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Nasri, Ridha. "Conception et réalisation d'un adaptateur haute impédance programmable : epplication à la caractérisation de liquides magnétiques." Saint-Etienne, 1994. http://www.theses.fr/1994STET4014.

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Ce travail s'inscrit dans le cadre de la recherche sur les ferrofluides ou liquides magnétiques. Les évolutions, qui peuvent être rapides, des propriétés diélectriques de ces matériaux telles que les changements de phase du liquide porteur, la perte d'homogénéité par formation d'agrégats ou de multicouches nécessitent l'automatisation complète de l'acquisition des mesures. Pour cela, nous avons développé autour d'un analyseur vectoriel, un adaptateur haute impédance programmable en mode shunt fonctionnant dans la gamme 1mhz-10khz. Cette réalisation fait appel à l'électronique haute impédance : résistances de fortes valeurs allant jusqu'à iteraohm et condensateurs à faibles fuites ; ces composants sont commutés par des relais de résistance d'isolement supérieure à 1000teraohms commandes par le bus VXI. Ce spectromètre automatique nous a permis de caractériser, entre 50c et -200c, un ferrofluide ionique composé de particules nanométriques de ferrite de manganèse (Fe2Mno4) dispersées dans le tétrachlorure de carbone (CCL4) utilisé comme liquide porteur. Nous avons ainsi mis en évidence les différentes phases du tétrachlorure de carbone pur à pression atmosphérique (liquide, plastique, solide). Les résultats obtenus sur le ferrofluide, à plusieurs concentrations, ont été analysés selon diverses lois de mélanges théoriques utilisant les constantes diélectriques des deux constituants. Nous avons pu montrer, dans nos conditions expérimentales, la perte de stabilité de ce ferrofluide à basse température et forte concentration

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Vatta, Laura Lisa. "Manufacture of ferrofluid : basic aspects and the influence of key parameters on the process." Diss., 2003. http://hdl.handle.net/2263/24792.

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Yang, Po-Wen, and 楊伯文. "Synthesis,Characterization of Magnetite Nanoparticles and Ferrofluid." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/ep38e8.

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碩士 國立臺北科技大學 有機高分子研究所 97 In this study, both of Fe3O4 and CoFe2O4 nanopartilces with 3 different sizes were synthesized by varying the reaction temperature and concentration of surfactant during the thermal decomposition reaction of metal complex and high boiling point solvent.One kind of the synthesized Fe3O4 nanopartilces was surface modified by adsorbing a molecular linker which had a alkyl bromide group to act as an initiator for growing polystyrene via atom transfer radical polymerization (ATRP). To form PS@Fe3O4 core-shell like nanoparicles.The thus-prepared magnetite nanparicles were characterized by TEM，GPC，FT-IR. Mix the magnetite nanoparticles with silicone oil to synthesize 7 kinds of ferrofluids and find their magneto rheology characteristics. In this way ,we understanded how magnetite nanoparticles effect the magneto rheology characteristics of ferrofluids.

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盧俊溢. "Dynamic of Ferrofluid Drops in a Rotational Magnetic Field." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/722634.

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碩士 國立交通大學 機械工程系所 105 There are two-part in my study. First, the stretched length of a droplet decrease when we increase the frequency of the extend field. Because there is a lag theta between the extend field and the direction of the drop. This lag theta can divide into parallel and vertical part of the drop. When we increase the frequency, the lag theta also increase. The vertical part becomes smaller so it leads to the stretched length shorter. In the second case of two droplets, different initial diameters and initial drops distances showed that there are three different situation: self-spin, dual rotation, rigid rotation. Self-spin is the longest initial drops distance. Rigid rotation is bigger radial velocity than dual rotation.

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Peng, Wen-Zhi, and 彭文志. "Motion of Ferrofluid Drops in a Rotational Magnetic Field." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/es76wa.

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碩士 國立交通大學 機械工程系所 108 This study investigates how the initial diameter between two droplets in immiscible fluids affects the rotation type. The experiment put magnetic fluid together with non-magnetic fluid, and use plane revolving magnetic field to create tensile effect on the droplets. As the magnetic field was added, the shape of the droplet changes from circle into ellipse. This study changes the initial diameter and distance between two magnetic droplets, and there are four types of motion being observed: self-spin, dual rotation, rigid rotation and coalescence. Self-spin possesses the longest initial distance, and the angular acceleration of rigid rotation is higher than dual rotation. In this study, the initial diameter and distance between two droplets, angular velocity and angular acceleration and radial velocity are combined to get dimensionless parameters such as Weber number, Capillary number, Bond number, Laplace number and DL, and are plotted into a dimensionless diagram. Since droplet motion cannot be discriminated from the dimensionless plot, so in order to find the diagram able to differentiate the four motions, diagram between angular acceleration and D/L were plotted for further study.

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Dissertations / Theses on the topic 'Magnetics of ferrofluids'

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