Dissertations / Theses on the topic 'Magnetic Nano Composite'

Les dispositifs photoniques magnéto-optiques (MO) sont l’objet d’une attention particulière pour leur capacité à améliorer la sensibilité des biocapteurs ou leur sensibilité au champ magnétique. Les effets MO, pouvant se manifester par une rotation de polarisation ou une modification d'intensité de la lumière sous champ magnétique, sont cependant plutôt faibles lors d’interactions simples (réflexion ou transmission) avec les films magnétiques classiques. Le dispositif proposé dans le cadre de ce travail permet d’exalter les effets MO. C’est une structure diélectrique planaire simple formée par un réseau 1D de résine photosensible (PR) déposé à la surface d’un film MO lui-même déposé sur un substrat de verre. Selon les conditions de couplage imposées par le réseau, des modes guidés (TE et TM) sont excités dans le film MO par la lumière incidente, augmentant ainsi l'interaction lumière-matière. Un tel couplage produit ainsi une résonance étroite qui se traduit par un creux (pic) dans le spectre de la transmittance (réflectance). Le film MO est un composite formé par des nanoparticules magnétiques (CoFe2 04) insérés dans une matrice de silice par un procédé sol-gel. Ce composite nano-structurable peut être facilement déposé sur des substrats classiques à faible température de recuit (90°C), ce qui n'est pas le cas de la plupart des matériaux MO utilisés dans les plates-formes d’optiques intégrées. Des exaltations importantes des différents effets de rotation de polarisation (Faraday et Kerr longitudinal) ont été atteintes par les mesures et les simulations grâce à cette structure résonnante toute diélectrique. Les principaux résultats de ce travail concernent cependant l'effet Kerr MO transverse (TMOKE). Cet effet induit un décalage spectral non réciproque de la résonance de transmittance (réflectance) lors de l'inversion de l'aimantation, résultant en une modulation d'intensité. Des valeurs de TMOKE atteignant 9,5% et 18,5% ont été mesurées respectivement en transmission avec T = 80%, et en réflexion avec R = 5%. Ces valeurs très significatives de TMOKE sont principalement dues au facteur de qualité élevé des résonances de transmittance (réflectance) du mode TM. La valeur de TMOKE pour un film MO sans réseau étant d'environ 0,01%, une exaltation de trois ordres de grandeur a ainsi été obtenue grâce à la structure fabriquée. Les valeurs mesurées de TMOKE sont bien positionnées par rapport à la littérature où, à notre connaissance, des valeurs maximales de 1,5% et 15% ont été démontrées expérimentalement par des structures respectivement diélectriques et magnéto-plasmoniques. De plus, des effets magnétiques réciproques inattendus ont été démontrés expérimentalement. Enfin, la structure proposée est un dispositif à faible coût, qui peut être fabriqué sur des substrats à grande échelle, est capable d'exalter tous les effets MO. Cela en fait une structure à fort potentiel pour des applications comme le contrôle non destructif, les capteurs de champ magnétique et même les biocapteurs
Magneto-optical (MO) photonic devices are currently highly desirable because of their ability to improve the sensitivity of biosensors or their sensitivity to the magnetic field. However, MO effects being rather small through classical magnetic films, it is relevant to find ways to enhance such effects which can manifest as light polarization rotation or intensity modification under magnetic field. The proposed device in this work to enhance MO effects is an all-dielectric planar structure formed by a 1D photoresist (PR) grating deposited on top of a MO film itself deposited on a glass substrate. Under coupling conditions through the grating, guided-modes (TE and TM) with narrow resonances are excited in the MO film by the incident light, increasing hence the light-matter interaction. Such coupling results as a dip (peak) in the transmittance (reflectance) spectrum. The MO film is a composite formed by magnetic nanoparticles (CoFe2 04) embedded in a silica matrix and obtained through sol-gel process. This nano-structurable composite can be easily deposited on common substrates with low annealing temperature (90°C), which is not the case of the most MO materials used within integrated optics platforms. Large enhancements of the different non-reciprocal polarization rotation effects (such as Faraday and longitudinal MO Kerr) were achieved experimentally and numerically through the all-dielectric resonant structure. The main results of this work concern the transverse MO Kerr effect (TMOKE). This effect induces a non-reciprocal spectral shift of the transmittance (reflectance) resonance upon magnetization reversal, resulting in an intensity modulation effect. TMOKE values up to 9.5% and 18.5% were measured respectively in transmission with T = 80% and in reflection with R = 5%. These large TMOKE values are mainly due to the high quality factor of TM transmittance (reflectance) resonances. The TMOKE signal for a single MO film is around 0.01%, hence an enhancement with three orders of magnitude was achieved through the fabricated structure. The reached measured TMOKE values are highly competitive with the literature where, to our knowledge, maximum values of 1.5% and 15% were experimentally demonstrated respectively through all-dielectric and magneto-plasmonic structures. Moreover, unexpected reciprocal magnetic effects were experimentally evidenced. Finally, the proposed all-dielectric structure is a low-cost device, which can be fabricated on large scale substrate, and able to enhance all the MO effects. Hence, it is a promising structure for non-destructive testing, magnetic field sensing and even biosensing

The transmission and effective magnetic properties of a metamaterial consisting of silver nanowires that we call a "silver nanoforest" was investigated using finite element numerical simulations in the optical regime. The variation of these properties with the arrangement and size of the nanowires was also investigated along with resilience to fabrication disorder. The silver nanoforest metamaterial exhibited low loss diamagnetism associated with Fabry Perot interference. In addition to diamagnetism both negative pelmeability and negative refractive index were obtained, but not simultaneously at same' wavelength and geometry. Both negative permeability and negative index experienced significant loss and therefore low transmission due to the plasmonic Origins of these effects. Magnetic responses of the silver nanoforest metamaterial were dampened but not inhibited by disorder, with diamagnetic response being the most resilient magnetic response to disorder.

Composites with magnetic properties have been successfully synthesized by means of the deposition of manganese oxide, Mn3O4, precipitated by using O2 (an ecofriendly oxidant), onto magnetite particles. The magnetite particles in the composites (~40m2.g-1) form agglomerates with Mn3O4 particles. Solid-liquid separation by means of the application of a magnetic field is possible. The application of the magnetic composite in the oxidative adsorption of As3+ was evaluated. The arsenic sorption isotherm fits return values of b>1 for the Langmuirconstant, demonstrating high affinity of the composites for As(III), which is desired for the removal of trace and sub-trace contaminants from water. The maximum adsorption capacity is ~14mgAs.gsolid -1 (0.0048mmolAs.m-2 solid). During the As oxidation-adsorption process, iron is not released and part of the Mn(II) released to solution is being adsorbed or precipitated, or both, which implies in a less contaminants release to solution. XANES of the As-loaded composites show thatthe arsenic adsorbed is in the oxidized arsenic form, As(V), emonstrating that As(III) is successfully oxidized by Mn3O4. Raman and IR spectral data of Asloaded (5.0 to 16mg.g-1) samples suggest the presence of As-O bands referring to the formation of inner-sphere monodentate and bidentate complexes, elucidating arsenic surface complexes on the composite. The magnetic Mn3O4 composite was also applied to oxidize and remove methylene blue (MB) from water. UV-vis results show that Mn3O4 composite is capable of oxidizing MB forming its partially and fully demethylated derivatives. Decolorization of 85% is achieved in 60min, atpH 3. For pH>3, oxidation does not occur and only 50% of the MB is adsorbed. Desorption by methanol of the organic compounds adsorbed in the composite have shown that the fully demethylated MB derivative, thionine, is the only adsorbed compound. Therefore, the present work simplifies the synthesis of a manganese oxide composite to be applied in environmental systems as both an oxidant and an adsorbent. Moreover, the work improves the knowledge about the mode of Asinteractions with Mn3O4 by using vibrational spectroscopic techniques.
Compósitos com propriedades magnéticas foram sintetizados com sucesso por meio da deposição de óxido de manganês, Mn3O4, sobre partículas de magnetita. O óxido de manganês é obtido por precipitação usando O2 como oxidante. As partículas de magnetita nos compósitos (~40m2.g-1) formam aglomerados com as partículas de Mn3O4. A separação sólido-líquido é possível, por meio da aplicação de um campo magnético. A aplicação do compósito magnético na adsorção oxidativa de As(III) foi avaliada. Os ajustes das isotermas de sorção retornam valores de b>1 para a constante de Langmuir, demonstrando elevada afinidade dos compósitos por As(III), o que é desejado na remoção de contaminantes traços e sub-traços. A capacidade de adsorção máxima é 14mgAs.g-1 sólido (0,0048mmolAs.m-2 sólido). Durante o processo de adsorção e oxidação, o ferro não é liberado e parte do Mn2+ liberado para a solução, é adsorvido ou precipitado, ou ambos, o que implica em poucos contaminantes liberados e portanto, uma solução mais limpa. O espectro XANES dos compósitos carregados com As mostram que o arsênio adsorvido está na formaoxidada, As(V), demonstrando que o As(III) é oxidado com sucesso pelo Mn3O4. Dados espectrais de Raman e infravermelho das amostras carregadas com As (5,0 a 16mg.g-1) sugerem a presença de bandas As-O referindo-se à formação de complexos monodentados e bidentados, elucidando a adsorção de arsênio na superfície do compósito. O compósito magnético de Mn3O4 foi também aplicadopara oxidar e remover azul de metileno (MB) de soluções aquosas. Resultados de UV-vis mostram que o compósito de Mn3O4 é capaz de oxidar MB formando seus derivados parcial e totalmente desmetilados. A descoloração de 85% é alcançado em 60min, em pH 3. Para pH>3, a oxidação não ocorre, e apenas 50% do MB é adsorvido. Dessorção por metanol dos compostos orgânicos adsorvidos no compósito mostra que o derivado de MB totalmente desmetilado, a tionina, é o único composto adsorvido. Portanto, o presente trabalho simplifica a síntese de umcompósito magnético de óxido de manganês para ser aplicado em sistemas ambientais, tanto como oxidante, quanto como adsorvente. Além disso, o trabalho acrescenta conhecimento sobre o modo das interações de As com Mn3O4 usando técnicas espectroscópicas vibracionais.

Les matériaux multiferroïques présentent plusieurs ordres ferroïques, i.e. ferromagnétiques, ferroélectriques et/ou ferroélastiques. Le couplage entre ses ordres ferroïques permet de contrôler les propriétés magnétiques en appliquant un champ électrique et vice versa. Afin d’utiliser leur multifonctionnalités dans des nouvelles applications, ce couplage doit être efficace à température ambiante. Cette thèse étudie les systèmes couplant artificiellement ensemble une phase ferromagnétique / magnétostrictive à une phase ferroélectrique / piézoélectrique. Le couplage entre ces deux phases est appelée magnétoélectrique (ME). Le premier chapitre décrit l’état de l’art de ce couplage ME dans différentes structures composites multiferroïques. Tandis que les techniques de caractérisation et les outils de simulation micromagnétiques utilisées sont présentées dans le deuxième chapitre. Dans le troisième chapitre, une hétéro-structure type film magnétostrictif/substrat flexible/actuateur piézoélectrique (FeCuNbSiB/Kapton/PE) a été étudiée. Les domaines magnétiques du FeCuNbSiB ainsi que leur orientation sont contrôlées en appliquant un champ électrique et étudiées par microscopie locale (MFM). Le quatrième chapitre étudie un composite incluant des nanoparticules magnétostrictives dans une matrice piézoélectrique flexible (polymère PVDF). L’effet des inclusions (nanoparticules) sur la réponse piézoélectrique locale du PVDF est étudiée par microscopie de piézoréponse (PFM). Symétriquement, l’influence de la matrice piézoélectrique sur les propriétés magnétiques des nanoparticules est analysée. Dans le dernier chapitre, l’optimisation des propriétés magnétiques statiques d’un ensemble de nanoparticules anisotropes (nanofils de cobalt) est étudiées sous l’influence de leur structure, de leur forme et de leurs interactions. Cette étude expérimentale est corroborée par les simulations et vise des nouveaux composites incluant ces nanoparticules anisotropes dans une matrice piézoélectrique flexible
Multiferroic materials present several ferroic orders, i.e. ferromagnetic, ferroelectric and/or ferroelastic. The coupling between these ferroic orders allow the control of the magnetic properties by applying an electric field and vice versa. In order to use their multifunctionality in new applications, this coupling must be efficient at room temperature. This thesis concentrates on materials artificially coupling together a ferromagnetic/ magnetostrictive phase with a ferroelectric/piezoelectric one. The coupling between these two phases is called magnetoelectric (ME). The first chapter describes the state of the art of this ME coupling for different multiferroic composite structures. Characterization techniques and micromagnetic simulation tools are presented in the second chapter. In the third chapter, a hetero-structure given by a magnetostrictive film/flexible substrate/piezoelectric actuator (FeCuNbSiB/Kapton/PE) is studied. The magnetic domains of FeCuNbSiB as well as their orientation are controlled by applying an electric field and studied by local microscopy (MFM). The fourth chapter focuses on a nanocomposite material including magnetostrictive nanoparticles in a flexible piezoelectric matrix (PVDF polymer). The effect of these inclusions (nanoparticles) on the local piezoelectric response of the PVDF is studied by piezoeponse microscopy (PFM). Symmetrically, the influence of the piezoelectric matrix on the static magnetic properties of the nanoparticles is analyzed. In the last chapter, the optimization of the magnetic properties of a set of anisotropic nanoparticles (cobalt nanowires) is studied as fonction of their structure, shape and mutual interactions. This experimental study is corroborated by simulations and targets new composites ME materials including the anisotropic nanoparticles in a flexible piezoelectric matrix

Synthesis and characterization studies of promising nano-sized hydrogel composites based on nisopropylacrylamide and magnetite have been studied. N-isopropylacrylamide (NIPA) gel component was used as a carrier of various drugs, magnetite was used as a magneto-responsive component. Presence of magnetite it was proved by EPR method. Composite nanoparticles were characterized by electron microscopy (TEM) and by dynamyc light scattering (DLS) method. It was shown that the average size of nanoparticles is 50 or 100 nm, depending on the method of preparation. The hydrogel is characterized by clear phase transition between swollen and collapsed state upon heating above 32⁰C. Rapid release of the incorporated drug (as a model was used the photosensibilizer -Methylene Blue) observed during thermoresponsive nanocomposite gels heating in the physiologically acceptable range, but still above phase transition temperature (up to 40–50 ⁰C), allows application of the discussed drug delivery systems in medical hyperthermia.

This thesis describes the preparation and characterization of core-shell noble metal-magnetite hybrid hollow nanocomposites utilizing hierarchical architecture. The hollow magnetite (hFe3O4) nanoparticles were prepared by hydrothermal method, forming the cavity via Oswald ripening. Further surface modifications involved both inorganic and organic coatings, conferring the intracellular drug delivery ability and the catalytic enhancement. In the first part, a series of hierarchical core-shell nanostructures flower-like hFe3O4@AlOOH was synthesized through solvothermal method and sol-gel process. The formation of cavity accessible hFe3O4@γ-AlOOH was achieved using silica-templated solvothermal treatment where the Kirkendall effect was observed. The morphologies of the as-prepared nanocomposites were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR). Then, the nano-encapsulation of platinum drug using hollow magnetite and its derivatives, has been developed with improved loading efficiency via co-solvent system. A dimethylformamide/water co-solvent system was found to be the most efficient system to encapsulate water-insoluble cisplatin. The platinum content was further quantitatively and qualitatively analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and FTIR spectroscopy. The enhancement of loading efficiency could be driven by emulsification due to the diffusion of hydrophobic cisplatin into the hollow cavity of iron oxide nanoparticles. By incorporating water, the loading efficiency of hFe3O4 and hFe3O4@γ-AlOOH increased from 1-2% to 27% and from 6% to 54%, respectively. The grafting of cisplatin on AlOOH nanoflakes might account for the high loading efficiency of flower-like hFe3O4@AlOOH. As a complement to naked hFe3O4, a cell-penetrating poly(disulfide)s (CPD)-decorated hollow iron oxide nanoparticle was synthesized by immobilizing both cysteine and MPTMS as an initiator, followed by in situ polymerization to form hFe3O4-Cys-CPD-CONH2 and hFe3O4-MPS-CPD-CONH2. The morphologies were characterized by TEM/energy-dispersive X-ray spectroscopy (TEM/EDX) and the compositions of the as-prepared iron oxide nanocomposites were characterized by TGA, FTIR and X-ray photoelectron spectroscopy (XPS) and ICP-MS. The CPD coating not only serve as a protective layer, but also prevent the encapsulated cisplatin from a premature release. The hFe3O4-MPS-CPD-CONH2 exhibit promising features for the intracellular delivery of cisplatin, demonstrating a glutathione (GSH)-responsive drug release. Comparing with other hFe3O4 nanoparticles, an enhancement of cellular uptake of hFe3O4-MPS-CPD-CONH2 could be observed by optical microscope, showing rapid accumulation of the hFe3O4-MPS-CPD-CONH2 nanocomposites in the primary human renal proximal tubular epithelial cells (HRPTEpiCs) cell in 2 h. At 24 h, hFe3O4 (F), hFe3O4-MPS (FS) and hFe3O4-MPS-CPD-CONH2 (FSC) together with cisplatin treatment did not cause any significant cytotoxicity to the cells when the particle concentration is less than 10 µg/mL. Interestingly, FSCC showed a certain extent of toxicity with increasing Fe and Pt concentration along with the treated time. It may suggest that the hFe3O4-MPS-CPD-CONH2 nanoparticle, as a cisplatin carrier, could enhance the drug efficiency by increasing cellular uptake of the nanoparticles in HRPTEpiCs together with the boosted cytotoxicity. Based on these data, cisplatin- hFe3O4-MPS-CPD-CONH2 (FSCC) treatments with the concentration less than 20 µg/mL and duration no more than 24 h could maintain around 70% of the cell viability of the HRPTEpiCs. The hypothesis, at which CPD serves as an efficient carrier for intracellular cisplatin delivery, could be confirmed by both microscopic images and the cell viability test. In the second part, a series of Au/Fe3O4 hybrid nanocomposites was prepared to investigate their catalytic efficiencies using 4-nitrophenol reduction as a model system. The flower-like hFe3O4@γ-AlOOH@SiO2-NH2@Au was prepared by using protonated ammonium on hFe3O4@γ-AlOOH@SiO2-NH2 to entangle gold nanoparticles (AuNPs) via electrostatic attraction. In comparison to numerous of catalytic studies, the turnover frequency (TOF) of hFe3O4@γ-AlOOH@SiO2-NH2@Au shows a superior conversion rate up to 7.57 min-1 (4-nitrophenol per Au per min) for the 4-nitrophenol using sodium borohydride as a reductant. A rapid conversion of 4-nitrohpenol was observed using flower like composites that converted the 4-nitrophenol within 2 min. Our result suggests that silica residue hinders the reduction rate of the 4-nitrophenol. A significant deviation from pseudo first order was observed for densely AuNPs-functionalized nanoflower system, hFe3O4@γ-AlOOH@SiO2-NH2@Au2X, which is different from most of the 4-nitrophenol reductions reported in literature. The hFe3O4@γ-AlOOH@SiO2-NH2@Au also demonstrates catalytic activity when heated up to 800 °C before reduction. The recyclability was examined using magnetically recycled hFe3O4@γ-AlOOH@SiO2-NH2@Au, which showed insignificant decrease in the catalytic efficiency. To prove the concept, platinum nanoparticles (PtNPs) immobilized hFe3O4@γ-AlOOH@SiO2-NH2@Pt and hFe3O4@γ-AlOOH@SiO2-NH2@Pt/Au were also prepared via electrostatic attraction to verify the feasibility of endowing modular functionality via post modification.

Le domaine de nanocomposites polymères conducteurs a fait l’objet de nombreux travaux et recherches, vu que ces matériaux présentent un fort potentiel pour de nombreuses applications concernant différents secteurs. Toutefois, malgré les progrès et les résultats obtenus pour l’instant, les performances de ce type des matériaux restent insuffisantes pour certaines applications qui peuvent requérir l’association de diverses propriétés (électriques, thermiques, blindage électromagnétique…). Dans cette thèse, on détaille l’élaboration et la caractérisation de nanocomposites polymères conducteurs. Deux types de nanocharges conductrices (nanotubes de carbone (MWCNTs) et nanoparticules d’argent (Ag-NPs)) ont été dispersées soit dans un polymère thermoplastique (polyéthylène PE), soit dans une matrice thermodurcissable (résine époxy amine). Les nanocomposites polymères conducteurs obtenus ont présenté de bonnes propriétés électriques et thermiques ainsi qu’une bonne tenue mécanique favorisée par des taux de charges relativement faibles. La thèse a non seulement étudié des propriétés fondamentales d’un point de vue expérimental mais aussi plus théorique avec de la modélisation. Entre autres, on a pu analyser les mécanismes de conduction à très basses température dans ce type de composites. Les propriétés en termes de conductivité thermique se sont révélées cohérentes avec celles obtenues en conductivité électrique. Des propriétés de blindage électromagnétique de nos composites à base de PE ont été mis en évidence par résonance magnétique nucléaire (RMN)
Conductive polymer nanocomposites have been the object of intense researches and investigations recently. In fact, these materials have shown a great potential to be useful for many applications including different sectors. However, despite the promising results reported at the moment in this area, there is still a lack in the performance which can be improved by synchronization of their properties. In this PhD work, we present the preparation and full characterization of conductive polymer nanocomposites. Two kinds of conductive nanofillers (carbon nanotubes (MWCNTs) and silver nanoparticles (Ag-NPs)) have been dispersed either in a thermoplastic polymer (polyethylene PE), or in a thermoset matrix (epoxy amine). The conductive polymer nanocomposites obtained exhibit good electrical and/or thermal properties with conserving the mechanical properties ensured by low fillers fraction. The study was not only based on experimental characterizations but also on modulation to analyze the charge carrier transport at very low temperature in these systems to provide successful understanding to some basic properties which are still actually not fully investigated. Electrical properties are in good agreement with thermal properties. Electromagnetic shielding of our PE based nanocomposites have been studied by Nuclear Magnetic Resonance (NMR)

Magnetic nano-particles dispersed in a non-magnetic matrix is promising for storage technology. Additionally, such magnetic nano composite (MNC) materials have potential applications in the field of telecommunication, nano-capacitors, high frequency filters and bio-medical domains. Conventionally, Nano composite (NC) material comprises of sub 100 nm particles randomly distributed in a matrix material. The shape, size and distribution of the particles play an important role in determining the physical properties. The aim of this work is to develop ordered and aligned magnetic nanocomposite and explain composite behaviors in terms of behaviors of single nanowire. Hence, ordered and aligned ferromagnetic Nickel nanophase homogeneously dispersed in alumina matrix is developed. The matrix phase separates the magnetic nanophase and modifies the magnetic interaction, electrical transport and mechanical strength. Anodization of aluminum is used to fabricate nano-porous alumina matrix. Under certain controlled electrochemical conditions, anodization of aluminum results in a highly ordered hexagonal porous structure. Nickel is electrochemically deposited into these pores resulting in uniformly distributed magnetic nanowires of high aspect ratio. This ordered MNC is characterized for its mechanical, electrical, magnetic and tribological properties to explore the possibility of using for various possible applications with the focus to study the feasibility for magnetic storage application. Ordered porous alumina is formed by a two-step anodization process. By optimizing the anodization conditions, the thickness and the pore size of the porous alumina layer is controlled. The interface between the porous structure and aluminum substrate comprise of thick and non-conducting barrier oxide layer. However, to deposit metal into the pores using electrodeposition technique, a conducting path should be established through this barrier layer. Hence, the barrier layer is thinned by reducing the anodizing voltage in steps and subsequent chemical etching. The pores are filled with Ni by pulsed electro-deposition. Uniform deposition is achieved by optimizing the pulse duty cycle. From electrical resistance measurements, the resistance of single nanowire is found to vary between 400 Ω to 700 Ω. Whereas, the composite resistance is measured to be about few ohms. The resistivity of the Ni within composite is 2.9 × 10-7 Ω-m, which is two orders higher than the bulk Ni, confirming larger scattering events at smaller scale. Electrical resistivity further gave information on structural details of the as developed MNC. It is found that during low frequency measurements only a fraction of nanowires take part in conduction. Rest of the nanowires are not conducting as a capacitive barrier layer separates Ni nanowire from base aluminum. Also, magneto-capacitance response at high carrier frequency is observed. Magnetic response of the nanocomposite is measured using magnetic force microscopy and magnetoresistance measurement. It is found that neighboring magnetic domains are dipole coupled which makes it difficult to change magnetization state of the composite compared to single Ni nanowire. This has important implication for magnetic storage application. Mechanical hardness and elastic modulus of the single suspended nanostructure are characterized using atomic force microscopy (AFM) based indentation technique. Using nanoindentation it is found that for the MNC, inclusion of ductile metal improves the hardness of the brittle matrix by 40%. Finally, a macro scale experiment is designed to mimic magnetic read / write operation by allowing electrical current to flow from probe to sample under static load and dynamic load conditions. These experiments helped us to understand the effect of static and frictional force on the electrical response. Static and reciprocating electrical contact resistance measurement tool is developed. Monitoring contact resistance helps to understand, evolution of the real contact area, which affects both the electrical and tribological behaviors. It is observed that, the high electrical field increases wear rate of the composite. Subsequent chemical etching. The pores are filled with Ni by pulsed electro-deposition. Uniform deposition is achieved by optimizing the pulse duty cycle. From electrical resistance measurements, the resistance of single nanowire is found to vary between 400 Ω to 700 Ω. Whereas, the composite resistance is measured to be about few ohms. The resistivity of the Ni within composite is 2.9 × 10-7 Ω-m, which is two orders higher than the bulk Ni, confirming larger scattering events at smaller scale. Electrical resistivity further gave information on structural details of the as developed MNC. It is found that during low frequency measurements only a fraction of nanowires take part in conduction. Rest of the nanowires are not conducting as a capacitive barrier layer separates Ni nanowire from base aluminum. Also, magneto-capacitance response at high carrier frequency is observed. Magnetic response of the nanocomposite is measured using magnetic force microscopy and magnetoresistance measurement. It is found that neighboring magnetic domains are dipole coupled which makes it difficult to change magnetization state of the composite compared to single Ni nanowire. This has important implication for magnetic storage application. Mechanical hardness and elastic modulus of the single suspended nanostructure are characterized using atomic force microscopy (AFM) based indentation technique. Using nanoindentation it is found that for the MNC, inclusion of ductile metal improves the hardness of the brittle matrix by 40%. Finally, a macro scale experiment is designed to mimic magnetic read / write operation by allowing electrical current to flow from probe to sample under static load and dynamic load conditions. These experiments helped us to understand the effect of static and frictional force on the electrical response. Static and reciprocating electrical contact resistance measurement tool is developed. Monitoring contact resistance helps to understand, evolution of the real contact area, which affects both the electrical and tribological behavior. It is observed that, the high electrical field increases wear rate of the composite.

碩士
國立中興大學
化學工程學系
93
Nano-technology has been regarded as one of the important science and technology in this century. It’s application includes photo-electric, material science, mechanics, and biotechnology. Recently, it is found that nano-magnetic composite material can produce the ferromagnetic resonance effect due to absorbing microwave in the wide frequency. This investigation aims to use the oleic acid (9wt%) and nano-cobalt particles (30wt%) for fabricating nano-magnetic dispersion in heptane solution, and dry it to become composite powders and blend with epoxy resin for nano-magnetic composite material. Additionally, the free space reflection method is utilized to measure microwave absorption of nano-magnetic composite material with the incidence source of 3.5GHz to 17.5GHz microwave in the different thickness. As shown in the result from TGA test, the cobalt particle can be protected with the oleic acid from oxidation. In addition, in the range of 4GHz to 10GHz, the permeability absolute value of nano magnetic composite materials is -0.03 and less than -0.83 of sneok’s limit for attenuate rate. It is worth mentioned that the refection loss of microwave is over 20dB ranging from 4 to 9GHz and reach 73dB at 4.4GHz in matching thickness 4.5mm of magnetic composite material with 46.2wt.% nano-cobalt particles. In summary, the microwave absorber of nano-magnetic composites materials with low cobalt content has been successfully manufactured to reduce matching thickness and develop semiconductor microwave filter component, antenna materials, and radar absorber in the wide range of frequency in this study.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science WITS University, Johannesburg, 2013
Occurring parallel to the developments in imprinting technology are magnetic materials which are being applied increasingly in environmental remediation, medicine, biotechnology and many other fields. Combining the imprinting effects of the polymer and nano magnetic particles yields composite materials which are both selective to the template and magneto responsive for easy polymer removal from aqueous solutions. In this study, magnetic ion imprinted polymers with high recognition for uranyl ion (UO2 2+) in the presence of competing ions were synthesized by bulk and precipitation polymerizations. The uranyl template was removed from the magnetic polymer matric by 1M HCl and 1M NaHCO3 leachants to form cavities which were complimentary in shape and size to the template. Full characterization of the magnetite and magnetic polymers was achieved by use of the following characterization techniques: Raman spectroscopy (RS), Transmission electron microscopy (TEM), Energy dispersive spectrometry (EDS), Powder X-ray diffraction (PXRD) analysis, Brunauer, Emmett and Teller (BET) analysis, Ultraviolet visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), Thermo-gravimetric analysis (TGA), Carbon, hydrogen, nitrogen and sulphur (CHNS) analysis, Diffuse reflectance spectroscopy (DRS) and Atomic force microscopy (AFM). Parameters which were optimized included sample pH, which gave an optimum value of 4. Magnetic IIP and NIP amounts which gave maximum adsorption capacities were found to be 50 mg for both of these adsorbents. The optimum contact time was found to be 45 minutes. The performance of all magnetic ion imprinted polymers (IIPs) was expectedly superior to that of the corresponding non imprinted polymers (NIPs) in all adsorption studies. The first rate constant (k1) and correlation coefficient (R2) values evaluated for the pseudo first order were found to be between 0.048-0.093 min-1 and 0.602-0.991 min-1, respectively. For the pseudo second order, second rate constant (k2) and correlation coefficient (R2) were found to be between 0.273- 0.678 and 0.9811-0.9992, respectively. The selectivity order observed was as follows: UO2 2+ > Fe3+ > Pb2+ > Ni2+ > Mg2+. The magnetic polymers selective to Cr(VI) were also synthesized and were leached with HCl to remove the template. The synthesized Cr(VI) magnetic polymers, the optimum pH obtained was 4 for both the magnetic IIP and the corresponding NIP. The amount of the adsorbent which gave the maximum adsorption was determined to be 20 and 65 mg for the magnetic IIP and NIP, respectively. A Cr(VI) concentration which was adsorbed maximally was from 5 mg L-1 which was therefore taken as the optimum. The maximum adsorption capacities for the magnetic polymers were 6.20 and 1.87 mg g-1 for the magnetic IIP and NIP, respectively. The optimum time for the adsorption of the Cr(VI) analyte was determined as 40 minutes. Investigation of the order of selectivity of anions followed the trend: Cr2O7 2- SO4 2- F- NO3- -.

Bone cancer treatment usually originates bone defects with residual tumour cells that can proliferate during bone regeneration. Therefore, a scaffold for bone regeneration that simultaneously kill residual tumour cells is needed. This project aims at producing a composite system composed of a bioactive glass (BAG) and magnetic nanoparticles (MNPs). This system is highly bioactive and reabsorbable due to the bioactive glass which leads to formation of a hydroxyapatite (HA) layer that bonds to bone. The system is biodegradable at an adequate rate for bone regeneration. Magnetic nanoparticles act as thermoseeds generating clinically relevant heat under an applied alternating magnetic field to kill or sensitize tumour cells. In combination with release of an anticancer drug, this composite system will effectively kill bone tumour cells whilst providing a base for bone regeneration. BAG was produced by a simple sol-gel technique assisted by EISA (Evaporation Induced Self-Assembly). Ball milling equipment was used to decrease the BAG particle size and increase its dispersibility. The powders were characterized by SEM (scanning electron microscopy), EDS (energy dispersive x-ray spectroscopy), and FTIR (Fourier Transform Infrared Spectroscopy). IONPs were produced through chemical co-precipitation and coated with oleic acid to avoid aggregation and loss of superparamagnetic properties over time. First, PVP/BAG composite membranes were produced by electrospinning and the parameters were optimized to produce smaller fibres as it translates into higher surface area and higher bioactivity. IONPs were then incorporated in the solution. The electrospun membranes were crosslinked due to the PVP water-soluble characteristic. UV and thermal crosslinking were employed, but only thermal crosslinking proved to be successful. For this to be successful TGA/DSC was helpful to find the crosslinking temperature and provided information about the thermal stability of the membranes. Water-insoluble membranes were tested for magnetic hyperthermia application and cytotoxicity assays were also performed. The IONPs proved to have superparamagnetic properties and a small temperature variation was achieved for a 10 mg membrane sample, which proved the potential of composite membranes for this application.

碩士
國立高雄師範大學
物理學系
94
This aim of this thesis is to study the magnetic properties of composite material made of soft magnetic ferrites and hard magnetic NdFeB. In this study, the nano-sized ferrites were synthesized by combustion method, and then were mixed with micro-sized NdFeB. The ferrites/NdFeB composites were pressed into pellet for measuring the behavior of magnetization versus applied field (M-H) by a Vibration Samples Measurements. The M-H behavior has displayed a ferromagnetic hysteresis loop with a wasp-waisted shape, which constricted in the middle section, while wider at above and below section. Further, various amount (1, 3, 5%)of NdFeB were mixed with Ni-Zn ferrites. The M-H behavior has shown markedly different coercivity and wasp-waisted hystsresis. Our works discuss the magnetic characteristics of wasp-waisted hysteresis loops and outline a rationale for this type of behavior by superposition of hard and soft magnetic phases. Because of the absence of magnetic interactions between particles, in measurement procedure, we could sum the magnetization mathematically of the isolated particles at each field value to create a composite hysteresis loops. These data show the disagreement between the curves is shown and it's small. The result may provide a understanding of interactions between particles could give rise to significant nonadditivity.

碩士
長庚大學
化工與材料工程研究所
92
The purpose of this study is to use FeCl3 to synthesize magnetic polyaniline nano-composites (PAn/Magnetite/CDs) in -cyclodextrin (-CD) and to investigate their structure, physical properties and applications on the absorption of microwave. These nano-composites consist of PAn, -CD and Fe3O4 as confirmed by Ultraviolet-Visible spectroscopy (UV-Vis), Infrared spectroscopy (IR), and X-ray diffractometer (XRD). The hydrogen bonding was formed between polyaniline and cyclodextrin as measured by FT-IR. For the Brunauer-Emmett-Teller (BET) analysis, the surface area of PAn/Fe3O4/CDs nano-composites increased 2.5 times and the particles diameter decreased from 681 nm to 85 nm when the concentration of the -CD increased 10 times, indicating that the growth of magnetic polyaniline particles was inhibited by -CD. It is found that the magnetite is the source of magnetic properties as measured by Superconducting Quantum Interference Device Magnetometer (SQUID). The conductivity of nano-composites increased one order after doping chemically with FeCl3/CHCl3 solution as measured by four-point probe. The free electron spin density increased with doping and the orientation of magnetic moment became more regular. The saturated magnetization (Ms) of nano-composites increased from 10 to 39 emu/g after doping. The maximum microwave absorptions of the magnetic PAn particles about 3 mm thickness and doped with FeCl3/CHCl3 solution for 3 and 6 hrs were -15 dB at 10 GHz and -30 dB at 12 GHz, respectively. It indicated that the doping of magnetic polyaniline nano-composites with FeCl3 have the potential applications on the absorption of microwave.

碩士
國立臺中教育大學
科學教育與應用學系科學教育碩士班
103
The mixing and heating method and the hydrothermal method are applied to synthesizing two visible-light-driven (VLD) photocatalysts, SrFeO3-x/g-C3N4 and BiOBr/PbBiO2Br, respectively. X-ray diffractometer, Field Emission-Scanning Electron Microscopy-Energy Dispersive Spectroscopy, Field Emission-Transmission Electron Microscopy-Energy Dispersive Spectroscopy, Fourier Transform Infrared Spectroscopy, UV-vis diffuse reflectance spectra, Surface Area and Porosity Analyzer, and Ultraviolet Photoelectron Spectroscopy are utilized for distinguishing the synthesized samples. SrFeO3-x/g-C3N4 and BiOBr/PbBiO2Br degraded crystal violet dye and chloramphenicol solution are used for simulating the environmental target pollutants. From the reaction rate constant of the degraded crystal violet dye solution, the 4wt.% SrFeO3-x is added g-C3N4 for the calcination at 500℃ for 2 hours. The acquired SrFeO3-x/g-C3N4 0.0997h-1 is higher than g-C3N4 0.0209h-1 and SrFeO3-x 0.0014h-1, and the degradation efficiency constant of BiOBr/PbBiO2Br appears 0.0601h-1 which apparently enhances the photocatalytic efficiency in comparison to BiOBr 0.0207h-1 and PbBiO2Br 0.0017h-1. The distinguishing with reactive species and Electron Paramagnetic Resonance shows the important roles of free radicals, ․OH and․O2— , in the photocatalytic reaction. In order to understand the pathway of the crystal violet dye and chloramphenicol degradation, the reactive intermediate in the HPLC-PDA-ESI-MS separation process is used for predicting the possible photocatalytic degradation mechanism for the research basis of crystal violet dye and chloramphenicol degradation.