Rozprawy doktorskie: „Dielectric Properties - Nanocomposites”

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Ayoob, Raed. "Dielectric properties of hexagonal boron nitride polymer nanocomposites". Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/417272/.

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There is a growing research interest in polymer nanocomposite materials due to their potential in enhancing dielectric properties. However, a considerable amount of variability exists in the literature regarding the electrical performance of polymer nanocomposites, and therefore the underlying mechanisms underpinning their electrical properties are still far from fully understood. Possible reasons for the existing inconsistencies could be due to different material preparation techniques, different nanoparticle dispersion states, unknown filler content, inconsistent sample storage conditions, and unknown water level content in the samples. Determining the principal factors that dominate the electrical behaviour of polymer nanocomposites could allow engineers to tailor the electrical properties of dielectrics for their specific application. As a result, the work reported in this thesis was mainly set out to explore the factors governing the electrical properties of polymer nanocomposites such that the inconsistencies in the literature can be better understood, and consequently eliminated. This thesis investigated the performance of hexagonal boron nitride (hBN) nanocomposites based on two thermoplastic polymers: polystyrene and polyethylene. Prior to producing any nanocomposites, the hBN particles were characterised using different techniques. The characterisation primarily revealed that the boron nitride particles are in the hexagonal form and the surface of hBN contains a scarce amount of hydroxyl groups. Polystyrene nanocomposites were prepared containing identical amounts of hBN dispersed in different solvents in an attempt to obtain different dispersion states, as a result of different hBN/solvent interactions. The effect of solvent processing was negligible on the dispersion state of the hBN in the polystyrene; no observable difference in the dispersion and electrical properties was reported although the presence of hBN resulted in a slight increase in the breakdown strength relative to the unfilled polystyrene. A range of polyethylene nanocomposites were produced containing different amounts of hBN to understand the effect of the dispersion or aggregation state of the hBN on the breakdown strength. The results revealed that the nanocomposites, regardless of the morphology, exhibited a monotonic increase in breakdown strength with increasing hBN content from 2 wt % to 30 wt %, while maintaining the low dielectric losses of the unfilled polyethylene. While the hBN was found to have a strong nucleating effect on the polyethylene, it was determined that the local change in morphology was not the cause of the enhanced breakdown strength as both the polyethylene nanocomposites obtained by rapid crystallisation, where the development of spherulites was suppressed, and the amorphous polystyrene nanocomposites, also exhibited an improved breakdown strength. Further experiments indicated that the polyethylene nanocomposites did not absorb any moisture from the environment in ambient conditions, and absorbed a very small amount of water even in the 30 wt % polyethylene/hBN nanocomposite when completely immersed in water. Dielectric spectroscopy measurements revealed that the surface hydroxyl groups on the hBN are most likely located only on the edge surfaces of the hBN rather than basal surfaces. The water was most likely loosely bound to the hBN particles, where local water clusters formed. It was remarkable that a percolating water network was not formed in a nanocomposite consisting of an already percolating hBN network, which was largely attributed to the surface chemistry of hBN. Despite the presence of water in the system, the hBN nanocomposites continued to exhibit an enhanced breakdown strength in comparison to the unfilled polyethylene. Therefore, this thesis demonstrated that the electrical behaviour of polymer nanocomposites is most likely dominated by the surface state of the nanoparticles and how the particles interact with the charge carriers; any other effects due to local morphological changes or nanoparticle dispersion are considered to be secondary reasons for changes in the electrical properties.

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Xu, Jianwen. "Dielectric Nanocomposites for High Performance Embedded Capacitors in Organic Printed Circuit Boards". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11525.

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Conventionally discrete passive components like capacitors, resistors, and inductors are surface-mounted on top of the printed circuit boards (PCBs). To match the ever increasing demands of miniaturization, cost reduction, and high performance in microelectronic industry, a promising approach is to integrate passive components into the board during PCB manufacture. Because they are embedded inside multilayer PCBs, such components are called embedded passives. This work focuses on the materials design, development and processing of polymer-based dielectric nanocomposites for embedded capacitor applications. The methodology of this approach is to combine the advantages of the polymer and the filler to satisfy the electric, dielectric, mechanical, fabrication, and reliability requirements for embedded capacitors. Restrained by poor adhesion and poor thermal stress reliability at high filler loadings, currently polymer-ceramic composites can only achieve a dielectric constant of less than 50. In order to increase the dielectric constant to above 50, effects of high-k polymer matrix, bimodal fillers, and dispersing agent are systematically investigated. Surface functionalization of nanofiller particles and modification of epoxy matrix with a secondary rubberized epoxy to form sea-island structure are proposed to enhance the dielectric constant, adhesion and high-temperature thermal stress reliability of high-k composites. To obtain photodefinable high-k composites, fundamental understanding of the photopolymerization of the novel epoxy-ceramic composite photoresist is addressed. While the properties of high-k composites largely depend on the polymer matrix, the fillers can also drastically affect the material properties. Carbon black- and carbon nanotubes-filled ultrahigh-k polymer composites are investigated as the candidate materials for embedded capacitors. Dielectric composites based on percolation typically show a high dielectric constant, and a high dielectric loss which is not desirable for high frequency applications. To achieve a reproducible low-loss percolative composite, a novel low-cost core-shell particle filled high-k percolative composite is developed. The nanoscale insulating shells allow the electrons in the metallic core to tunnel through it, and thereby the composites exhibit a high dielectric constant as a percolation system; on the other hand, the insulating oxide layer restricts the electron transfer between filler particles, thus leading to a low loss as in a polymer-ceramic system.

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Comer, Anthony C. "DYNAMIC RELAXATION PROPERTIES OF AROMATIC POLYIMIDES AND POLYMER NANOCOMPOSITES". UKnowledge, 2011. http://uknowledge.uky.edu/cme_etds/1.

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The dynamic relaxation characteristics of Matrimid® (BTDA-DAPI) polyimide and several functionalized aromatic polyimides have been investigated using dynamic mechanical and dielectric methods. The functionalized polyimides were thermally rearranged to generate polybenzoxazole membranes with controlled free volume characteristics. All polyimides have application in membrane separations and exhibit three motional processes with increasing temperature: two sub-glass relaxations (ƴ and β transitions), and the glass-rubber (α) transition. For Matrimid, the low-temperature ƴ transition is purely non-cooperative, while the β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. For the thermally rearranged polyimides, the ƴ transition is a function of the polymer synthesis method, thermal history, and ambient moisture. The β relaxation shows a dual character with increasing thermal rearrangement, the emerging lower-temperature component reflecting motions encompassing a more compact backbone contour. For the glass-rubber (α) transition, dynamic mechanical studies reveal a strong shift in Tα to higher temperatures and a progressive reduction in relaxation intensity with increasing degree of thermal rearrangement. The dynamic relaxation characteristics of poly(ether imide) and poly(methyl methacrylate) nanocomposites were investigated by dynamic mechanical analysis and dielectric spectroscopy. The nanoparticles used were native and surface-modified fumed silicas. The nanocomposites display a dual glass transition behavior encompassing a bulk polymer glass transition, and a second, higher-temperature transition reflecting relaxation of polymer chain segments constrained owing to their proximity to the particle surface. The position and intensity of the higher-temperature transition varies with particle loading and surface chemistry, and reflects the relative populations of segments constrained or immobilized at the particle-polymer interface. Dielectric measurements, which were used to probe the time-temperature response across the local sub-glass relaxations, indicate no variation in relaxation characteristics with particle loading. Nanocomposite studies were also conducted on rubbery poly(ethylene oxide) networks crosslinked in the presence of MgO or SiO2 nanoparticles. The inclusion of nanoparticles led to a systematic increase in rubbery modulus and a modest positive offset in the measured glass transition temperature (Tα) for both systems. The sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in these crosslinked networks.

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Chen, Zou. "The effect of humidity and surface functionalisation on the dielectric properties of nanocomposites". Thesis, University of Leicester, 2007. http://hdl.handle.net/2381/859.

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Work is reported on composites comprising either epoxy resin or crosslinked polyethylene (XLPE) filled with silica nanoparticles (surface functionalisated and unfunctionalisated). Measurements were made of the dielectric spectra, charging and discharging currents under high electric fields, and space charge dynamics using the pulsed electroacoustic (PEA) technique. Considerable studies were made of the effect of humidity on epoxy nanocomposites. It was found that the epoxy composites filled with nanoparticles could absorb up to 60% more water by weight than the unfilled epoxy. For composites filled with microparticles, nearly all the water was absorbed by the resin. The glass transition temperature (Tg) for all epoxy samples, measured by both differential scanning calorimetry (DSC) and dielectric spectroscopy, showed a monotonic reduction with increase of hydration resulting in a 20K decrease for fully hydrated samples. This led to the conclusion that the extra hydration found in the nanocomposites was not in the bulk resin but was likely to be located on the surface of the nanoparticles. This is further supported by measurement of the hydration isotherms at room temperature and the resultant swelling as a function of humidity. A "water shell" model is developed in which there is an inner layer of approximately 5 – 10 bound water molecules on the surface of the nanoparticles, a further layer, approximately 25nm thick, in which water is in sufficient concentration to allow conduction, and an outer layer, approximately 50nm thick, which cannot support true conduction (i.e. the continuous movement of charge carriers.) This model is used to explain the sub-hertz dielectric results (in terms of percolation limited conduction) as well as those at around 1 – 10Hz that indicate the presence of bound or free water.

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Kanbur, Yasin. "Conductive Polymer Nanocomposites Of Polypropylene And Organic Field Effect Transistors With Polyethylene Gate Dielectric". Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613312/index.pdf.

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One of the aim of this study is to prepare conductive polymer nanocomposites of polypropylene to obtain better mechanical and electrical properties. Composite materials based on conductive fillers dispersed within insulating thermoplastic matrices have wide range of application. For this purpose, conductive polymer nanocomposites of polypropylene with nano dimentional conductive fillers like carbon black, carbon nanotube and fullerene were prepared. Their mechanical, electrical and thermal properties were investigated. Polypropylene (PP)/carbon black (CB) composites at different compositions were prepared via melt blending of PP with CB. The effect of CB content on mechanical and electrical properties was studied. Test samples were prepared by injection molding and compression molding techniques. Also, the effect of processing type on mechanical and electrical properties was investigated. Composites become semiconductive with the addition of 2 wt% CB. Polypropylene (PP) / Carbon Nanotube (CNT) and Polypropylene / Fullerene composites were prepared by melt mixing. CNT&rsquo
s and fullerenes were surface functionalized with HNO3 : H2SO4 before composite preparation. The CNT and fullerene content in the composites were varied as 0.5, 1.0, 2.0 and 3.0 % by weight. For the composites which contain surface modified CNT and fullerene four different compatibilizers were used. These were selected as TritonX-100, Poly(ethylene-block-polyethylene glycol), Maleic anhydride grafted Polypropylene and Cetramium Bromide. The effect of surface functionalization and different compatibilizer on mechanical, thermal and electrical properties were investigated. Best value of these properties were observed for the composites which were prepared with maleic anhydride grafted polypropylene and cetramium bromide. Another aim of this study is to built and characterize transistors which have polyethylene as dielectric layers. While doing this, polyethylene layer was deposited on gate electrode using vacuum evaporation system. Fullerene , Pentacene ve Indigo were used as semiconductor layer. Transistors work with low voltage and high on/off ratio were built with Aluminum oxide - PE and PE dielectrics.

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Preda, Ioana. "Modélisation et caractérisation des matériaux nanocomposites par des méthodes diélectriques". Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20013/document.

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"Il ya beaucoup de place vers le bas!", ait déclaré Richard Feynman dans son discours sur les nanotechnologies en 1959, ouvrant un nouveau monde de la science et de la technologie! L'idée d'utiliser des nanoparticules afin d'améliorer les propriétés diélectriques des polymères qui étaient déjà en cours d'utilisation a suscité l'intérêt des chercheurs dans les deux dernières décennies. Nanocharges tels que la silice, l'alumine, l dioxyde de titan, etc, mais aussi des particules plus grosses comme les argiles ou les nanotubes de carbone ont été mélangés avec les polymères «classiques» afin d'améliorer les propriétés du polyéthylène, des résines époxy, de polypropylène, etc.De nos jours, le rendement de conversion d'énergie de générateurs électriques est limitée par des problèmes thermiques et électriques, limitations étant surtout liées à la qualité des rubans isolants appliqués sur les barres en cuivre. En conséquence, des rubans isolants innovants basés sur des de matériaux nanostructurés ont été envisagés pour augmenter le rendement énergétique des alternateurs et le but de ce travail est d'étudier ces matériaux innovants et de comparer leurs propriétés avec celles des matériaux déjà utilisés, afin d'aider à choisir le meilleur matériau composite pour les futurs rubans. Après une brève introduction sur le contexte de ce travail, on a présenté bref état de l'art les propriétés des polymères époxy, avec un débat sur les propriétés électriques de la matrice polymère choisie (résine époxyde), ses propriétés chimiques et thermiques. Ensuite, les nanocharges choisies et leurs propriétés spécifiques sont présentés, en discutant les différentes étapes du procédé de fabrication, aussi qu'un débat sur les phénomènes qui apparaissent à l'échelle nanométrique et leur éventuelle influence sur les propriétés du matériau composite fini.Différents groupes de matériaux composites à base d'époxy remplis de silice nanométrique, argile organique ou de nitrure de bore sont analysés dans ce travail. Afin de caractériser et interpréter leurs propriétés, plusieurs outils ont été utilisés: la microscopie imagerie, la caractérisation thermique ainsi que les méthodes d'investigation à fort ou faible champ électrique. Leur caractéristiques sont ressemblés et différents observations sur des propriétés «générales» ou «spécifiques» des matériaux composites ont été observés et discutés par rapport à l'influence du type de charge utilisée, de son traitement ou de son poids total sont débattues.Enfin, un modèle numérique basé sure une généralisation de la loi des mélanges sera utilisée afin de prédire la réponse diélectrique des matériaux composites ainsi que les paramètres (taille, permittivité) de l'interphase, «l'ingrédient« magique du mélange matrice de remplissage. Le modèle présenté nous a permis de donner un lien entre les différents matériaux et de valider les résultats obtenus expérimentalement. Une approche par éléments finis est utilisée.Ce manuscrit s'achève par des conclusions sur le travail présenté et il laisse entrevoir les perspectives dans l'analyse complexe des polymères nanocomposites
“There's plenty of room of the bottom!” said Richard Feynman in his talk on top-down nanotechnology in 1959, bringing into the spot light a new world of science and technology ! The idea of using nanoparticles in order to improve the dielectric properties of the polymers that were already in use attracted the interest of researchers for the last two decades. Nanofillers such as silica, alumina, titania etc, but also larger particles such as clays or carbon nanotubes were mixed with the “classic” polymers in order to improve the properties of polyethylene, epoxy resins, polypropylene etc. Since nowadays the energy conversion efficiency of electrical generators is restricted by thermal and electrical issues, these limitations can be related to the electrical insulator tapes themselves. Thus, innovative insulating tapes based on nanostructured material scenarios to address the energy saving concern are intended and the purpose of this work is to investigate these innovative materials and to compare their properties with those of the materials already in use, in order to help choosing the best composite material for the future tapes.This works begins with a state of the art regarding the properties of epoxy polymers. Their chemical, thermal and dielectric properties are presented. Afterwards, the chosen fillers and their specific properties are presented. The influence of the chosen fillers as well as different steps of the nanocomposite materials manufacturing process are presented and the discussion ends with a debate on the phenomena appearing at the nanometric scale and their possible influence on the properties of the finite composite material .Different materials groups of epoxy based composites filled with nanometric silica, organoclay or boron nitride are analyzed afterwards. In order to characterize and interpret their properties, several tools were used: imaging microscopy, thermal characterization as well as high and low electric field investigation methods. A debate trying to distinguish between so called “general” or “specific” behavior of the composite materials with respect to the normal, unfilled polymer is also presented. The influence of the type of filler, its treatment or its weight total percentage will be are chosen as comparison criteria. Finally, a numerical model based on Finite Element Method approximation was used in order to predict the dielectric response of the composite materials as well as the specific parameters (size, permittivity) of the interphase, the magic “ingredient” of the matrix-filler mix. The presented model allowed us to give a connection between the different materials and validate the experimentally obtained results. This manuscript ends with conclusions on the presented work and suggests possible future works in the complex analysis of polymer nanocomposites

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Ben, ghzaiel Tayssir. "Synthèse, caractérisation et étude des propriétés magnétiques et diélectriques de nanocomposites Polyaniline/hexaferrite pour l'absorption des micro-ondes". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLN003/document.

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Ces travaux de thèse consistent à élaborer des nanocomposites Polyaniline/hexaferrite pour l’absorption des micro-ondes. L’idée principale est la mise en œuvre de matériaux composites à base de polymères conducteurs intrinsèques telle la Polyaniline que nous avons dopée avec différents types d’acides (HCl, CSA, NSA et TSA…) et l’hexaferrite de baryum de type magnétoplombite (M) stœchiométrique ou substitué. Au niveau de l’hexaferrite de baryum, la substitution du Fe3+ s’est faite par les ions Al3+, Bi3+, Cr3+ et Mn3+.L’hexaferrite de baryum et les hexaferrites substitués par les différents ions cités ci-dessus ont été synthétisés par voie hydrothermale dynamique en faisant varier divers paramètres au cours de la synthèse (pH, température, temps, rapport [OH-]/[NO3-]…).L’élaboration des composites Polyaniline/hexaferrite (pur ou substitués) a été effectuée par polymérisation oxydative en utilisant plusieurs techniques de synthèse : la polymérisation chimique en solution (en tenant compte de la nature de l’acide utilisé) avec ou sans agitation (Aqueous-Based Polymerization with or without stirring) et la polymérisation oxydative par voie solide (Solid-Based Polymerization). L’optimisation de ces différentes techniques de synthèse après caractérisations physicochimiques (DRX, FTIR, ATG, MEB, EDX), diélectriques (ε’, ε’’, σdc) et magnétiques (Mr, Ms, Hc, Tc, µ’, µ’’) des échantillons, a montré que la polymérisation par voie solide se trouve la méthode la plus facile, économique et respectueuse de l’environnement. Elle est aussi adaptée à la production du composite Pani/BaFe12O19 avec de bonnes propriétés structurales, physiques et magnétiques. L’étude de la substitution du Fe3+ dans le BaFe12O19 par Al3+, Bi3+, Cr3+ et Mn3+ a montré une forte dépendance des propriétés structurales et magnétiques avec la distribution de ces ions dans la maille cristalline hexagonale. En effet, les ions Al3+, Cr3+ et Mn3+ ont une tendance à occuper les sites tétraédriques, alors que le Bi3+ occupe les sites octaédriques. Une augmentation de Hc associée à la taille des cristallites a été observée pour les particules substituées avec l'Al et le Cr alors qu’une modification de l'anisotropie magnetocristalline (fort terme d'ordre supérieur) a été mise en évidence pour les substitutions Bi et Mn, dû à leur grand rayon ionique. L’incorporation des hexaferrites substitués dans la Polyaniline pour obtenir des composites Pani/BaMeFe11O19, où Me = Al, Bi, Cr et Mn, révèle une variation des propriétés électromagnétiques dans la gamme de fréquences allant de 1 à 18 GHz. En effet, ces variations sont dues à la formation de dipôles entre l’ion de substitution et les cations O2- dans le ferrite qui sont responsables de la résonance ferromagnétique, de l'anisotropie magnétocristalline et des interactions avec la matrice polymérique. Le composite Pani/BaFe12O19 présente des absorptions dans la bande X qui se déplacent vers la bande Ku avec la substitution du fer confirmant
This thesis deals with the formulation of Polyaniline/hexaferrite nanocomposite for absorbing electromagnetic waves. The main idea is the process of composite materials based on polymers intrinsic conductors such as polyaniline that we doped with different types of acids (HCl, CSA, NSA, and ... TSA) and barium hexaferrite with magnetoplumbite structure with or without substitution according to desired stoichiometries. In the barium hexaferrite, the substitution of Fe 3+ is made by Al3+, Bi3+, Cr3+ and Mn3+ ions.The barium hexaferrite and its substitutions by different ions mentioned above were synthesized dynamic hydrothermal method by varying various parameters during the synthesis (pH, temperature, time, ratio [OH-]/[NO3-] ...).The elaboration of polyaniline/hexaferrite composite (pure or substituted) was carried out by oxidative polymerization using various synthesis techniques: Aqueous-Based Polymerisation with or without agitation (taking into account the nature of the acid used) (ABP) and Solid-Based Polymerization (SBP). The optimization of these various synthesis techniques after physicochemical (XRD, FTIR, TGA, SEM, EDX), dielectric (ε ', ε' ', σdc) and magnetic (Mr, Ms, Hc, Tc, µ', µ'') characterizations of the samples showed that the solid route is the easiest method, economical and environmentally friendly. It is also suitable for the production of composite Pani/BaFe12O19 with good structural, physical and magnetic properties.The study of the substitution of Fe 3+ in the BaFe12O19 by Al3+, Bi3+, Cr3+ and Mn3+ showed a strong dependence of the structural and magnetic properties with the distribution of these ions in the hexagonal crystal lattice. In fact, Al3+, Cr3+ and Mn3+ ions tend to occupy the tetrahedral sites, while the Bi3+ favoured the octahedral sites. An increase in Hc associated with the small crystallite size observed for particles substituted with Al and Cr and the enhancement magnetocristalline anisotropy (strong higher order term) for Bi and Mn due to their high ionic radius.The incorporation of the substituted hexaferrite in the polyaniline to obtain Pani/BaMeFe11O19 composite, where Me = Al, Bi, Cr and Mn, reveals a variation in electromagnetic properties in the frequency range from 1 to 18 GHz. In fact, these variations are due to the formation of dipoles between the substituting ion and surrounding O2- cations in the ferrite which are responsible for the ferromagnetic resonance, the magnetocrystalline anisotropy and the exchange interaction with the polymer. The composite Pani/BaFe12O19 shows absorption bands at the X-band that shift to the Ku-band with the substitution of iron, confirming the potential of these materials for microwave applications

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Kim, Mu Seong. "Design, Synthesis, Processing, and Thermal Analysis of Nanocomposites with Tunable Properties". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4099.

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Polymer composites containing nanosized fillers have generated explosive interest since the early 1980's. Many recent studies have been conducted incorporating nano-fillers into polymer matrices to design and synthesize materials with tunable mechanical, thermal, and optical properties. Conventional filled polymers, where the reinforcement is on the order of microns, have been replaced by composites with discrete nanosized fillers. Gradually, theories that predicted that composite properties are independent of particle size in the micron range were challenged by nanocomposites. Rather, nanocomposite properties are greatly influenced by the surface area of the. All of this is complicated by the fact that nanoparticles are inclined to aggregate or migrate to interfaces. Much effort has been devoted to optimize dispersion of nanofillers in the polymer matrices, as polymer-nanoparticle interactions and adhesion greatly influence performance of the material. A well- dispersed composite system with various noncovalent interactions such as those that arise from hydrogen bonding, electrostatic attractions and π-π interactions between the filler and the matrix, can transfer stress and the interface will stop the development of cracks and impede stress concentrations. Overall, large reinforcement increases are noted at low nanoparticle loadings. Additionally, functional properties such as thermal, electrical conductivity and porosity can be tailored for specific applications. The design of high performance composites requires optimizing dispersion, nanoparticle-polymer noncovalent interactions and the chemistry of the materials. Therefore polymer composites with different types of nanofillers were investigated to prove various noncovalent interaction and to improve the mechanical, thermal and electrical properties in this study. Poly (methyl methacrylate) (PMMA) with BaTiO3 and Bi2O3 composites were fabricated by two different methods; sonication of fillers in PMMA and in situ polymerization. Samples were irradiated in air via a JL Shepherd Mark I cesium-137 source. The dose rate was 985 rads/min and the total dose was 2.0 Mrad. The polymer sonication (PSON) method has a greater effect than in situ polymerization on sample uniformity. With the PSON method there was a slight improvement in rad hardness in the barium titanate composites. This is the case with and without MWNTs and coupling agents. The storage modulus and loss modulus were measured via Dynamic Mechanical Analyzer (DMA) under the tension film mode using a heating rate of 5 °C min-1 from -150 °C to 200 °C and a scanning frequency range of 1-100 Hz. Scanning electron microscopy (SEM) provided images of the polymer-nanocomposites. An aliphatic isocyanate, polyether, polyol thermoplastic polyurethane, Tecoflex® SG-85A, was solution processed with the varying amounts of silica nanowire. A new grade polyurethane, Tecoflex®, was synthesized from the aliphatic 4,4-methylene dicyclohexyl diisocyanate (H12MDI) with polytetramethylene ether glycol. Despite Tecoflex®'s longevity and wide use, this polymer's dielectric behavior has not been widely studied. Therefore, the dielectric response of neat PU, Tecoflex®, and PU composites with silica nanowire from -150 to 150 °C is presented. The mechanism of nanowire growing with diameters ranging from 50 to 500 nm has been established to follow the vapour liquid solid (VLS) model via the PtSi phase acting as the catalyst. Our previous thermal stability study of PU nanowire composites have yielded increased heat stability to 330 °C. In comparison, neat PU only maintains thermal stability in temperatures that range to 250 °C. The onset of decomposition temperature was measured by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) provided images of the polymer-nanocomposites. A series of PMMA-dodecyloxy NB and PHEMA-dodecyloxy NB composites were synthesized in situ and characterized. The dodecyl groups significantly alter the solubility of the nanoballs, imparting hydrophobicity to the surface of the nanoball. A comparison study was made between the PMMA-NB and PHEMA-NB nanocomposites. Structure property relations are discussed in terms of interactions between the polymer matrices and nanoball surfaces and interiors. These OC12 NB and the hydroxyl NB polymer composites are the first studies to date that probe relaxations and conductivity in discrete polyhedral metal-organic polymer composites. A novel ultra-flexible polycarbonate-polyurethane (PCPU) was synthesized with methylene bis(4-cyclohexylisocyanate), 1,4 butanediol as a chain extender and a polycarbonate polyol containing 1,6-hexanediol and 3-methyl-1,5-pentanediol. Through the techniques of water coagulation, the synthesis of self-healing PCPU with various concentrations of SWNT (Single-Walled Nanotubes) is possible. The resulting features of this synthesized rubber-like substance are to be evaluated to determine glass transition temperature. This novel type of polyurethane material targets growing markets for biocompatible polymers. Also, a secondary goal of this project is to obtain information useful to determining whether PCPU-carbon nanotube composites would be good candidates for use as a gel electrolyte in polymer batteries. All nanocomposites were characterized by differential scanning calorimetry (DSC) to determine glass transition temperatures. The dielectric permittivity (ε’) and loss factor (ε”) were also measured via Dielectric Analysis (DEA) in the frequency range 1Hz to 100 kHz and between the proper temperatures in all polymer composite. The electric modulus formalism was used to reveal structural relaxations including conductivity relaxation. The activation energies for the relaxations are presented.

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Jäverberg, Nadejda. "Dielectric properties of poly(ethyelene-co-butyl acrylate) filled with Alumina nanoparticles". Licentiate thesis, KTH, Elektroteknisk teori och konstruktion, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-31407.

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In this work dielectric properties of the poly(ethylene-co-butyl acrylate)filled with alumina nanoparticles are evaluated. These nanocomposite materialswere manufactured at the department of Fibre and Polymer Technology,KTH.This study is limited to the properties of general importance for the AC applications.The dielectric permittivity of the nanocomposite materials wasstudied as a function of filler size, filler content, coating, temperature and airhumidity used for conditioning of the samples. The ultimate goal with thisproject is to describe the influence of material composition, temperature andair humidity on the dielectric properties and model these dependencies.In this thesis the experimental setup for voltage endurance testing of thenanocomposites, namely studying applied voltage frequency dependence ofpartial discharges in electrical trees, with a possibility of following electricaltreeing optically, was developed and described.The dielectric spectroscopy measurements were performed on thoroughly driednanocomposites - so-called dry DS study. It was shown that the experimentaldata can be fitted with Havriliak-Negami approximation, which justifiesthe correctness of the measurement results. It has been shown that addingnanoparticles to the EBA matrix changes the low frequency dispersion significantlyfor the dried samples. It was also indicated that the particle coatingused has very low impact on the resulting permittivity of the thoroughly driedsamples. From the dry DS studies it was suggested that the main cause ofthe scattering in data between the dry samples is most likely the influenceof the material inhomogeneity and possibly the moisture absorption. Thisleads to a possibility of using dielectric spectroscopy as a tool for probing thedispersion of nanoparticles in the polymer matrix.The dielectric spectroscopy measurements were also carried out on the nanocompositesconditioned in the environments with different humidity levels of air inorder to study the influence of absorbed water on the dielectric permittivity- so-called wet DS study. From the wet study it was shown that for the wetsamples the amplitude of the loss peak is defined by the filler size, filler contentand coating used; while its position in frequency domain is determinedby the coating and the humidity level used for conditioning.
QC 20110315

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Briesenick, Daniel [Verfasser]. "Reinforced interphases in PAI-MMT-nanocomposites : synthesis and characterization of effects on thermal, mechanical and dielectric properties / Daniel Briesenick". Paderborn : Universitätsbibliothek, 2015. http://d-nb.info/1073944832/34.

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Jäverberg, Nadejda. "Electrical Insulating Properties of Poly(Ethylene-co-Butyl Acrylate) Filled with Alumina Nanoparticles". Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-116862.

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In this work the electrical insulating properties of the nanocomposite materials based on poly(ethylene-co-butyl acrylate) filled with alumina nanoparticles are studied. The dielectric properties chosen for the evaluation are the dielectric permittivity and loss as well as the breakdown strength and the pre-breakdown currents. The reason for choosing these particular properties is partly due to the importance of these for the general electrical applications and partly due to the uncertainties involved for these particular properties of the nanocomposite materials. The importance of moisture absorption for the dielectric properties is outlined in this work. All measurements were performed in both dry conditions and after conditioning of the materials in humid environment until saturation. The data for moisture absorption was taken from the water absorption study performed at the Department of Fibre and Polymer Technology, KTH. The dielectric spectroscopy in frequency domain was employed for measuring dielectric permittivity and loss. Havriliak-Negami approximation was used for characterization of the measurement data and at the same time ensuring the fulfillment of the Kramers-Kronig relations. Results from the dielectric spectroscopy study in dry conditions suggest that dielectric spectroscopy can be used for evaluating nanoparticle dispersion in the host matrix, based on correlation between the morphology data obtained from SEM investigation and the scatter in the dielectric loss. The dielectric spectroscopy study performed on the nanocomposites after conditioning in humid environment showed that absorbed moisture has a distinct impact on the dielectric loss. Especially pronounced is its’ influence on the frequency behavior, when the dielectric loss peaks are shifted towards higher frequencies with increased moisture content. The nanocomposite materials characterized by higher specific surface area generally exhibit higher dielectric losses. Surface functionalization of the nanoparticles does not seem to have much influence on the dielectric loss in dry conditions. After conditioning in humid environment, however, the surface modification was shown to have a significant impact. Temperature is another significant factor for the frequency behavior of the dielectric loss: it was found that the studied nanocomposites can be characterized by Arrhenius activation. The breakdown strength and pre-breakdown currents study outlined the influence of moisture as well. The study indicated that surface treatment of the nanoparticles can enhance properties of the nanocomposite materials, namely aminopropyltriethoxy silane was an especially successful choice: • The highest breakdown strength was determined by the study for NDA6 material formulation in dry conditions. • After conditioning in humid environment the NDA6 material continued showing the best breakdown strength among the nanocomposite mate rials, as well as this value was close to the breakdown strength of the reference unfilled material. This study confirms the existence of the optimal nanofiller content or rather optimal specific surface area of the dispersed nanoparticles in the host matrix. The latter is supported by the comparison between the nanocomposites based on nanoparticles with two different specific surface areas, which shows that the dielectric properties worsen, i.e. the dielectric losses increase and the influence of absorbed moisture on the breakdown strength becomes more pronounced, for nanomaterials with larger specific surface area. The pre-breakdown currents were found to follow space-charge limited conduction mechanism reasonably well. The following conduction regimes were identified: constant region (likely due to measurement difficulties at low field strengths), Ohm’s regime, trap-filled-limit regime and trapfree dielectric regime. The breakdown usually occurred either during the trap-filled-limit regime, when the current increased dramatically for the small change in electric field, or during the trapfree dielectric regime. The threshold values between different conduction regimes seem to correlate well with the oxidation induction times (OIT), which in turn depend on the total specific surface area. The pre-breakdown currents tend to be highest for the materials filled with the untreated nanoparticles. Increased absorbed moisture content causes higher pre-breakdown currents for the nanocomposite materials, while for the reference unfilled material the pre-breakdown currents do not show such tendency. Generally it can be said that the repeatability in the measured data is higher for the nanocomposite materials in comparison to the unfilled host material, as was demonstrated by both dielectric spectroscopy and breakdown studies.

QC 20130207

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Mahadevegowda, Amoghavarsha. "Processing, microstructure and properties of polymer-based nano-composite dielectrics for capacitor applications". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:fb974b13-2ec5-4104-9f80-45d1cb97eb48.

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The processing and properties of novel polymer-based nano-composite (PNC) dielectrics for capacitor applications has been studied. PNCs were fabricated via a vacuum based deposition technique and their micro/nano-structure, chemical and dielectric properties investigated. After process development and optimisation, co-deposited Al and nylon-6 PNCs had a dielectric constant k∼7 at an approximate Al volume fraction of 0.3 that agreed with analytical predictions if it was assumed that the Al transformed to an oxide in-situ and/or after deposition. The significant effect of absorbed water vapour and temperature on PNC dielectric properties was revealed using different types of post-deposition heat treatment. Alternately-deposited PNCs consisting of Al or Ag 2-20 nm layers sandwiched between nylon-6 layers were fabricated in which the overall PNC Al or Ag volume fraction was controlled by varying the nominal Al or Ag layer thickness. Ag layers comprised of discrete nano-islands that produced a nano-capacitor network effect that increased k to ∼11. In the case of Al layers, when the layer thickness was ≥ 5 nm, corresponding to a nominal volume fraction of 0.1, Al (core)-oxide (shell) nanoparticles were formed and the PNC dielectric constant increased to ∼19. The detailed nano-structure of the core-shell particles was studied using various types of transmission electron microscopy (TEM), and the elevations in dielectric constant ascribed to multiple-interface polarisation effects dependent on the formation of the core-shell structure. PNCs based on alternate deposition of Ti sandwiched in nylon-6, and then both Ti and Ag in nylon-6 were also fabricated, with k reaching ∼73 for Ag+Ti/nylon-6 PNCs. As well as Ti-based core (metal)-shell (oxide) particles, the Ag volume fraction was sufficiently high in the 10 nm nylon-6 layers to again form a nano-capacitor network that contributed to the overall device capacitance and effective dielectric constant. Again, various types of high magnification TEM were critical in resolving the Ti-based core-shell structure and its role in high-k behaviour. The vacuum-based alternate deposition technique has been developed to offer ease of operation, reliability, flexibility and applicability to chemically different filler and matrix systems in the fabrication of high-k PNC based capacitors, in which high-k performance relies critically on the formation of core (metal)-shell (oxide) particles in both Al and Ti based systems.

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Bouharras, Fatima Ezzahra. "Développement de nanocomposites BaTiO3 @ polymères fluorés pour les matériaux diélectriques et comme liant de cathode dans les batteries lithium Core shell structured Poly(Vinylidene Fluoride) -grafted- BaTiO3 nanocomposites prepared via Reversible Addition-fragmentation chain transfer (RAFT) polymerization of VDF for high energy storage capacitors Recent Progress on Core-Shell Structured BaTiO3/Fluorinated Polymers Nanocomposites for High Energy Storage: Synthesis, Dielectric properties and Applications". Thesis, Montpellier, Ecole nationale supérieure de chimie, 2020. http://www.theses.fr/2020ENCM0002.

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Les matériaux nanocomposites présentent des propriétés physico-chimiques uniques qui ne peuvent être obtenues en utilisant un seul composant. Ainsi, l'amélioration des propriétés de ces matériaux a suscité un intérêt majeur dans différents domaines. Les matériaux nanocomposites diélectriques à haute densité d'énergie présentent des performances prometteuses pour les applications de stockage d'énergie. Des efforts importants ont été menés pour combiner la constante diélectrique élevée de la céramique avec la flexibilité et la facilité de mise en œuvre des polymères. Ainsi, cette thèse porte sur le développement et la caractérisation de nanocomposites à base de céramique BaTiO3 et de polymères fluorés. Dans un premier temps, la synthèse de PVDF-g-BaTiO3 a été réalisée en utilisant la polymérisation RAFT du VDF à partir de la surface des nanoparticules fonctionnalisées, en utilisant différentes concentrations en BaTiO3, et l'effet de ce pourcentage sur les propriétés finales a été étudié. Les résultats ont montré que le greffage du PVDF a été réalisé avec succès, conduisant à des nanocomposites avec une stabilité thermique améliorée. De plus, le succès du greffage du PVDF a été principalement prouvé par la spectroscopie RMN HRMAS, qui a été utilisée pour la première fois pour caractériser les nanocomposites préparés. Les propriétés diélectriques de ces matériaux ont été étudiés et révèlent l'existence de trois relaxations : la première a été attribué à la relaxation secondaire β dans le PVDF, la seconde a été liée à la fraction cristalline dans le polymère, tandis que la troisième relaxation a été attribué à la polarisation interfaciale résultant de la présence de charges et d'impuretés dans le système. Cependant, la relaxation liée à la température de transition vitreuse n'a pas pu être observé en raison de la cristallinité élevée du polymère. Le procédé de mélange en solution a été également utilisé pour préparer des matériaux nanocomposites constitués de PVDF-g-BaTiO3/P(VDF-co-HFP) et les films préparés ont été entièrement caractérisés. La dispersion uniforme des nanocomposites PVDF-g-BaTiO3 dans la matrice de copolymère a conduit à des performances mécaniques améliorées. Ensuite, pour fournir une application pour les nanocomposites PVDF-g-BaTiO3 préparés, ces derniers ont été utilisés comme liant pour préparer un matériau de cathode pour les batteries. La procédure de calandrage a été utilisée pour préparer les films d'électrode et a permis d'obtenir une structure uniforme et des performances de cyclage améliorées
Nanocomposite materials present unique physic-chemical properties that cannot be obtained using one component. Thus, the improvement in the properties of such materials have resulted in major interest for versatile fields. Dielectric nanocomposite materials with high energy density exhibit promising performances for energy storage applications. Major efforts have been conducted to combine the efficient properties and high dielectric constant of ceramics with the flexibility and easy processing of polymers. Thus, this thesis focuses on the development and characterizations of nanocomposites based on BaTiO3 ceramic and fluoropolymers. First, the synthesis of PVDF-g-BaTiO3 was realized using RAFT polymerization of VDF from the surface of functionalized nanoparticles, using different BaTiO3 concentrations, and the effect of such percentage on the final properties was studied. Results showed the successful grafting of PVDF leading to nanocomposites with enhanced thermal stability. Furthermore, the successful grafting of PVDF onto the functionalized nanoparticles was mainly proved by HRMAS NMR spectroscopy, which was used for the first time to characterize the prepared nanocomposites. The dielectric properties of such materials were investigated, and reveals the existence of three relaxations: the first one was attributed to the well-known β secondary relaxation in PVDF, the second one was assigned to the crystalline fraction in the polymer, while the third relaxation was assigned to interfacial polarization arising from the presence of fillers and impurities in the system. However, the relaxation related to glass transition temperature could not be observed due to the high crystallinity of the polymer. Solution blending strategy was also used to prepare nanocomposite materials consisting of PVDF-g-BaTiO3/P(VDF-co-HFP) and the prepared films were fully characterized. The uniform distribution of PVDF-g-BaTiO3 nanocomposites in the copolymer matrix leads to enhanced mechanical performances resulting in increased Young’s modulus. Then, to supply an application for the prepared PVDF-g-BaTiO3 nanocomposites, those later were used as binder to prepare cathode material for batteries. Calendering procedure was used to prepare the electrode films and enabled to obtain uniform structure and enhanced cycling performances

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Houssat, Mohammed. "Nanocomposite electrical insulation : multiscale characterization and local phenomena comprehension". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30211.

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Dans le domaine de l'isolation électrique, il a été démontré que les matériaux hybrides organiques/inorganiques nanocomposites (NC) assurent une nette amélioration de leur fonctionnement à haute température/haute tension et permettent aux systèmes d'isolation électrique de renforcer leurs propriétés diélectriques. Récemment, il a été démontré que certaines modifications des propriétés électriques telles que la permittivité, la rupture diélectrique, la résistance aux décharges partielles ou la durée de vie étaient souvent attribuées à l'interphase nanoparticule/matrice, une région où la présence des nanoparticules modifie les propriétés de la matrice. De plus, des études récentes montrent qu'une fonctionnalisation de la surface des nanoparticules permet une meilleure dispersion dans la matrice hôte. Cette meilleure dispersion affecte la zone d'interphase et joue également un rôle majeur dans l'amélioration des propriétés des nanocomposites. Cependant, le rôle de l'interphase reste théorique et peu de résultats expérimentaux existent pour décrire ce phénomène. Par conséquent, en raison de l'échelle nanométrique de l'interphase, une caractérisation de ses propriétés demeure un défi. Au cours de cette thèse, deux études principales sont menées afin de mieux comprendre la relation structure-propriété dans les polymères nanocomposites. Tout d'abord, la microscopie à force atomique (AFM) est utilisée pour effectuer simultanément des mesures qualitatives et quantitatives de ces zones d'interaction dans le nanocomposite polyimide/nitrure de silicium (PI/Si3N4). Le mode Peak Force Quantitative Nano Mechanical (PF QNM) dérivé de l'AFM révèle la présence de l'interphase en mesurant les propriétés mécaniques (module de Young, déformation ou adhérence). Le mode microscopie à force électrostatique (EFM) est utilisé pour détecter et mesurer la permittivité locale de la matrice et de l'interphases. Par ailleurs, l'objectif de ce travail est de présenter l'effet de la fonctionnalisation de surface des nanoparticules de nitrure de silicium (Si3N4) sur les régions d'interphase. Ces résultats quantitatifs, à la fois mécaniques et électriques, permettent de comparer la dimension et les propriétés des interphase autour des nanoparticules traitées et non traitées. Par conséquent, cette nouvelle approche de caractérisation de cette zone confronte les résultats expérimentaux à des modèles théoriques. Un nouveau modèle basé sur les résultats expérimentaux obtenus est proposé. De plus, la deuxième partie de cette étude présente une caractérisation macroscopique des propriétés et de la rigidité diélectrique des films de polyimide pur, du nanocomposite avec des particules traitées et non traités. Les résultats révèlent le rôle de l'interphase sur la réduction du phénomène de polarisation de l'électrode (PE) dû aux mouvements ioniques surtout à haute température. Pour les nanoparticules non traitées, ces effets sont moins importants en raison de la formation d'agrégats. En revanche, une diminution nette de la PE est obtenue en fonctionnalisant la surface des nanoparticules avec le silane comme agent de couplage. Enfin, la rigidité diélectrique de l'ensemble des échantillons est mesurée et montre une augmentation considérable de la performance diélectrique des nanocomposites à haute température par rapport au PI pur
In the electrical insulation field, it was demonstrated that nanocomposite (NC) organic/inorganic hybrid materials assure a distinct improvement of their high temperature/high voltage functioning and allow the electrical insulation to strengthen its dielectric properties. Recently, it was shown that some modifications of the electrical properties such as permittivity, dielectric breakdown, partial discharges resistance or lifetime are often awarded to the nanoparticle/matrix interphase, a region where the presence of the nanoparticle changes the matrix properties. Moreover, recent studies show that the nanoparticle surface functionalization allows a better dispersion of the particles within the host matrix. This better dispersion affects the interphase zone and plays a major role in the nanocomposite properties improvement as well. However, the role of the interphase remains theoretical and few experimental results exist to describe this phenomenon. Accordingly, because of its nanometer scale, the interphase properties characterization remains a challenge. Two main studies are carried out, during this thesis work, that can provide a better understanding of structure-properties relationships in polymer nanocomposite. First, Atomic Force Microscopy (AFM) is employed to make at the same time qualitative and quantitative measurements of these interaction zones within Polyimide/Silicon Nitride (PI/Si3N4) nanocomposite. The Peak Force Quantitative Nano Mechanical (PF QNM) AFM mode reveals the presence of the interphase by measuring mechanical properties (Young modulus, deformation or adhesion). Electrostatic force microscope (EFM) mode is used in order to detect and measure the matrix and interphase local permittivity. Moreover, the aim of this work is to present the effect of the surface functionalization of silicon nitride (Si3N4) nanoparticles on the interphase regions. Mechanical and electrical quantitative results permit comparing the interphase dimension and properties between treated and untreated Si3N4 nanoparticles. As a result, this new approach to characterize the nanocomposite interphase zone using local measurements confronts experimental results with theoretical models. A new model based on the obtained experimental results is proposed. In addition, the second part of this study presents a macroscopic investigation on the dielectric properties and breakdown strength of neat polyimide, untreated and treated nanocomposite films. Results reveal the interphase role on the reduction of the electrode polarization (EP) phenomenon due to ionic movements especially at high temperatures. For untreated nanoparticles, these effects are less important due to the aggregate formation. In contrast, an EP drastic decrease is obtained by functionalizing the nanofiller surface with a silane coupling agent. Finally, the high temperature breakdown strength for all samples is investigated and shows a considerable increase of nanocomposites dielectric performance at high temperature compared to neat PI

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Pirondelli, Andrea. "Production and Electrical Characterization of Low Density Polyethylene-based Micro- and Nano-dielectrics containing Graphene Oxide, Functionalized Graphene and Carbon Black additives". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.

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Oggigiorno la ricerca di nuovi materiali per gradatori di campo da impiegarsi in accessori di cavi ha iniziato a studiare alcuni materiali nano dielettrici con proprietà elettriche non lineari con la tensione ed aventi proprietà migliorate rispetto al materiale base. Per questo motivo in questo elaborato si sono studiati materiali nanostrutturati a base di polietilene a bassa densità (LDPE) contenenti nano polveri di grafene funzionalizzato (G*), ossido di grafene (GO) e carbon black (CB). Il primo obiettivo è stato quello di selezionare e ottimizzare i metodi di fabbricazione dei provini. La procedura di produzione è suddivisa in due parti. Nella prima parte è stata utilizzatala tecnica del ball-milling, mentre nella seconda un pressa termica (thermal pressing). Mediante la spettroscopia dielettrica a banda larga (BDS) si sono misurate le componenti reali e immaginarie della permettività e il modulo della conducibilità del materiale, in tensione alternata. Il miglioramento delle proprietà rispetto al provino di base composto dal solo polietilene si sono ottenute quando il quantitativo delle nanopolveri era maggiore. Le misure sono state effettuate sia a 3 V che a 1 kV. Attraverso misurazioni di termogravimetria (TGA) si è osservato l’aumento della resistenza termica di tutti i provini, soprattutto nel caso quando la % di nanopolveri è maggiore. Per i provini LDPE + 0.3 wt% GO e LDPE + 0.3 wt% G* si è misurata la resistenza alle scariche parziali attraverso la valutazione dell’erosione superficiale dei provini. Per il provino contenente G* è stato registrato una diminuzione del 22% del volume eroso, rispetto al materiale base, mentre per quello contenente GO non vi sono state variazioni significative. Infine si è ricercata la resistenza al breakdown di questi ultimi tre provini sopra citati. Per la caratterizzazione si è fatto uso della distribuzione di Weibull. Lo scale parameter α risulta aumentare solo per il provino LDPE + 0.3 wt% G*.

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Hinchcliffe, Claire. "Processing and properties of nanocomposite dielectric films". Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437011.

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Kurimoto, M., H. Watanabe, K. Kato, M. Hanai, Y. Hoshina, M. Takei i H. Okubo. "Dielectric Properties of Epoxy/Alumina Nanocomposite Influenced by Particle Dispersibility". IEEE, 2008. http://hdl.handle.net/2237/12131.

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Somani, Vikas. "ALUMINA-ALUMINUM TITANATE-TITANIA NANOCOMPOSITE: SYNTHESIS, SINTERING STUDIES, ASSESSMENT OF BIOACTIVITY AND ITS MECHANICAL AND". Master's thesis, University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2489.

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This thesis reports the development, synthesis and characterization of a ceramic-ceramic nanocomposite system for its possible application as structural and electronic biomaterial in the biomedical industry. The study selected and synthesized alumina-aluminum titanate-titania (Al2O3-Al2TiO5-TiO2) nanoceramic composite using a simple Sol-Gel technique, which can be easily reproduced. Aluminum propoxide and titanium propoxide were used as precursor chemicals. Propanol and 2- methoxy ethanol were used as solvent and stabilizer, respectively. Thermal analyses were performed for a systematic understanding of phase evolution from the synthesized gel. X-Ray diffraction technique was used to confirm the phase evolution, phase purity, crystallite size and crystal structure(s) of the phase(s). Calcination of the powder at low temperatures (700°C) leads to formation of Al2O3-TiO2 nanocomposite and at higher temperatures into Al2O3-Al2TiO5-TiO2 nanocomposite confirmed by XRD analysis. Electron microscopic techniques were used to investigate powder morphology, crystallite size and inter-planner spacing. High Resolution Transmission Electron Microscopy images of the calcined powder showed agglomerates of powder particles with particle size in 15-20 nm range. As-synthesized powder was uniaxially pressed into cylindrical pellets and sintered at elevated temperatures (1000-1400oC) to study the sintering behavior, densification characteristics, and measurement of mechanical and electrical properties and assessment of bioactivity. Phase transformation induced by the sintering process was analyzed by X-ray powder diffraction technique. The effects of nanosize of powder particles and multi-phases on densification, and mechanical and electrical properties were investigated. Vickers hardness and biaxial flexural strength tests were used to determine mechanical properties. Bioactivity of the nanocomposite was assessed in Simulated Body Fluid (SBF), which has the same ionic concentration as that of human plasma. Effects of biodegradation and change in mechanical properties of the composite when kept in SBF and maintained in a static condition were studied in terms of weight loss, change in the pH of the acellular solution and change in mechanical properties (hardness and biaxial strength). Scanning Electron Microscopy was used to observe the formation of apatite crystals on the surface of the nanocomposite specimens soaked in SBF. The results obtained throw light on biocompatibility and bioactivity of Al2TiO5 phase, which has not been reported so far in the literature to the best of our knowledge. Dielectric constant and dissipation factor of the sintered nanocomposite pellets were measured using HP 4284A impedance-capacitance-resistance meter and 16451 B dielectric test fixture at 1 MHz frequency. The effects of sintering time, temperature and phases present on the electrical properties were studied and are reported in the thesis.
M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering

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Hayakawa, Naoki, Masafumi Takei, Yoshikazu Hoshina, Masahiro Hanai, Katsumi Kato, Hitoshi Okubo i Muneaki Kurimoto. "Dielectric Properties of Epoxy/Alumina Nanocomposite Influenced by Control of Micrometric Agglomerates". IEEE, 2010. http://hdl.handle.net/2237/14530.

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Marashdeh, Wajeeh. "Relaxation Behavior and Electrical Properties of Polyimide/Graphene Nanocomposite". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595850361812632.

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Pugliara, Alessandro. "Elaboration of nanocomposites based on Ag nanoparticles embedded in dielectrics for controlled bactericide properties". Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30324/document.

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Les nanoparticules (NPs) d'Ag sont très utilisées dans le secteur de la santé, dans l'industrie alimentaire et dans les produits de consommation pour leurs propriétés antimicrobiennes. Le grand rapport surface sur volume des NPs d'Ag permet une augmentation importante du relargage d'Ag comparé au matériau massif et donc une toxicité accrue vis à vis des micro-organismes sensibles à cet élément. Ce travail de thèse présente une évaluation des propriétés antimicrobiennes de petites NPs d'Ag (<20 nm) enrobées dans des matrices de silice sur la photosynthèse d'algues vertes. Deux techniques d'élaboration par voie physique ont été utilisées pour fabriquer ces nanocomposites: (i) l'implantation ionique à basse énergie et (ii) la pulvérisation d'Ag couplée avec la polymérisation plasma. Les propriétés structurales et optiques de ces nanostructures ont été étudiées par microscopie électronique à transmission, réflectivité et ellipsométrie. Cette dernière technique, couplée à un modèle basé sur l'approximation quasi-statique de type Maxwell-Garnett, a permis la détection de petites variations dans la taille et la densité des NPs d'Ag. Le relargage d'argent de ces NPs d'Ag enrobées dans des diélectriques a été mesuré par spectrométrie de masse après immersion dans de l'eau tamponnée. La toxicité à court terme de l'Ag sur la photosynthèse d'algues vertes, Chlamydomonas reinhardtii, a été évaluée par fluorométrie. L'enrobage des nanoparticules dans un diélectrique réduit leur interaction avec l'environnement, et les protège d'une oxydation rapide. La libération d'Ag bio-disponible (impactant sur la photosynthèse des algues) est contrôlée par la profondeur à laquelle se trouvent les NPs d'Ag dans la matrice hôte de silice. Cette étude permet d'envisager le design de revêtements à effet biocide contrôlé. En couplant les propriétés antimicrobiennes de ces NPs d'Ag enrobées à leur qualité d'antenne plasmonique, ces nanocomposites peuvent être utilisés pour détecter et prévenir les premières étapes de la formation de biofilms sur des surfaces. Ainsi, une dernière partie de ce travail est dédiée à l'étude de la stabilité et de l'adsorption de protéines fluorescentes Discosoma rouges recombinantes (DsRed) sur ces surfaces diélectriques avec la perspective du développement de dispositifs SERS
Silver nanoparticles (AgNPs) because of their strong biocide activity are widely used in health-care sector, food industry and various consumer products. Their huge surface-volume ratio enhances the silver release compared to the bulk material, leading to an increased toxicity for microorganisms sensitive to this element. This work presents an assessment of the biocide properties on algal photosynthesis of small (<20 nm) AgNPs embedded in silica layers. Two physical approaches were used to elaborate these nanocomposites: (i) low energy ion beam synthesis and (ii) combined silver sputtering and plasma polymerization. These techniques allow elaboration of a single layer of AgNPs embedded in silica films at defined nanometer distances (from 0 to 7 nm) beneath the free surface. The structural and optical properties of the nanocomposites were studied by transmission electron microscopy, reflectance spectroscopy and ellipsometry. This last technique, coupled to modelling based on the quasi-static approximation of the classical Maxwell-Garnett formalism, allowed detection of small variations over the size and density of the embedded AgNPs. The silver release from the nanostructures after immersion in buffered water was measured by inductively coupled plasma mass spectrometry. The short-term toxicity of Ag to the photosynthesis of green algae, Chlamydomonas reinhardtii, was assessed by fluorometry. Embedding AgNPs reduces their interactions with the buffered water, protecting the AgNPs from fast oxidation. The release of bio-available silver (impacting on the algal photosynthesis) is controlled by the depth at which AgNPs are located for the given host silica matrix. This provides a procedure to tailor the biocide effect of nanocomposites containing AgNPs. By coupling the controlled antimicrobial properties of the embedded AgNPs and their quality as plasmonic antenna, these coatings can be used to detect and prevent the first stages of biofilm formation. Hence, the last part of this work is dedicated to a study of the structural stability and adsorption properties of Discosoma recombinant red (DsRed) fluorescent proteins deposited on these dielectric surfaces with perspectives of development of SERS devices

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Benhadjala, Warda. "Fiabilité et miniaturisation des condensateurs pour l'aéronautique : de l'évaluation de composants céramique de puissance à l'étude de nanoparticules hybrides céramique / polymère pour technologies enterrées". Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR15271/document.

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L’amélioration des systèmes électroniques pour le déploiement de l'avion tout électrique dépend de la capacité des composants passifs, tels que les condensateurs, à réduire leur volume, leur masse et leur coût, et augmenter leurs performances et leur fiabilité, particulièrement dans l’environnement aéronautique. Dans ce contexte, cette thèse a eu pour objectif l’étude et le développement de nouvelles technologies de condensateurs pour des applications avioniques. Dans la première partie des travaux, nous abordons l’évaluation de condensateurs céramique de puissance. La technologie céramique constitue, en effet, l’une des rares solutions matures capables de répondre aux exigences des équipementiers. La caractérisation, l’analyse des mécanismes de défaillance, de leurs effets et de leur criticité (AMDEC) ainsi que l’étude de fiabilité et de robustesse de composants commerciaux présentant des architectures originales (condensateurs multi-chips) ont été réalisées. Ces résultats ont été complétés par une étude plus amont sur la caractérisation de céramiques frittées par frittage flash (SPS). Les permittivités colossales de ces matériaux permettraient d’accroitre la fiabilité et la miniaturisation des condensateurs tout en conservant de fortes valeurs de capacité et de tension nominale. La seconde partie, plus fondamentale, a été consacrée au développement de nanoparticules céramique/polymère coeur-écorce pour des applications de condensateurs enterrés, opérant aux radiofréquences. La synthèse et les caractérisations physico-chimiques des nanocomposites ainsi que les procédés de fabrication de condensateurs en couches épaisses sont, en premier lieu, décrits. Une méthode de caractérisation électrique large bande a été mise au point pour permettre l’analyse des propriétés diélectriques et des mécanismes de conduction des nanoparticules. Les performances des dispositifs ont été recherchées en fonction de la température et des procédés de mise en forme. En outre, la durabilité en température de ces derniers a été évaluée
The improvement of electronic systems for the deployment of all-electric aircrafts depends on the ability of passive components, such as capacitors, to reduce their volume, weight and cost, and to increase their performance and reliability, particularly in the aeronautical environment. In this context, the objective of this thesis was to study and develop novel capacitor technologies for avionics. In the first part of this work, the evaluation of power ceramic capacitors has been discussed. Indeed, the ceramic technology appeared to be one of the few mature solutions meeting the requirements of OEMs. The characterization, the failure mode, effects and criticality analysis (FMECA) and reliability and robustness assessment of commercial components using original architectures (multi-chip capacitors) have been performed. These results have been completed by a more advanced study on the characterization of new ceramics sintered by spark plasma sintering (SPS). The colossal permittivity of these materials could allow to increase reliability and miniaturization of capacitors while maintaining high values of capacitance and voltage rating. The second part, more fundamental, is devoted to the development of core-shell ceramic/polymer nanoparticles for embedded capacitors operating at radiofrequencies. The synthesis and the physicochemical characterization of the nanocomposites as well as the manufacturing processes of the thick film capacitors are first described. A new broadband electrical characterization methodology has been developed to analyze the dielectric properties and the conduction mechanisms of the nanoparticles. The effects of the temperature and the manufacturing process on the device performance have been investigated. In addition, the durability was evaluated

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23

Badard, Mathieu. "Optimisation et contrôle de la transition dynamique de percolation au sein de matériaux nonostructurés : expérience et modélisation". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI093.

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L'émergence des nanotubes de carbone a ouvert de nouveaux champs d'application dans le domaine des matériaux polymères. L'ajout de ces charges carbonées au sein de polymères permet la mise en œuvre de composites aux propriétés électriques optimisées. La conductivité de ces matériaux dépend en grande partie de l'organisation des charges dans la matrice, notamment de la présence de réseaux percolants. L'objectif du présent travail de thèse est de comprendre les mécanismes de structuration des nanotubes de carbone au sein de différents milieux. L'architecture de ces réseaux de charges a principalement été révélée par le biais de mesures électriques et diélectriques. L'originalité de nos travaux réside dans l'utilisation de matrices liquides, notamment des huiles de silicone, afin de s'affranchir des contraintes présentes dans les plastiques d'une part, et de simplifier les processus de mise en œuvre d'autre part. Le manuscrit de thèse est articulé autour de six chapitres. Une première partie bibliographique aborde les propriétés des nanotubes de carbone ainsi que les phénomènes que sont la percolation et la percolation dynamique. Le second chapitre, matériel & méthode, présente les matériaux employés ainsi que les différentes techniques de caractérisation utilisées au cours de la thèse. Le troisième chapitre de la thèse aborde, à travers des mesures de conductivité, la percolation dynamique des nanotubes de carbone sein d'huiles de silicone. Le chapitre 4 propose une modification la loi de puissance de Kirkpatrick, afin de décrire la conductivité en fonction du temps et du taux de charge. L'exposant critique de percolation, caractérisant la transition isolant conducteur, se révèle être un indicateur de l'état de dispersion des nanotubes à travers la matrice. Le chapitre 5 démontre la possibilité de contrôler l'organisation des charges par l'application d'un champ électrique. L'application d'un champ élevé permet une augmentation de plusieurs ordres de grandeur de la conductivité ainsi qu'une diminution des charges nécessaire à la formation d'un réseau percolant. Nous avons notamment déterminé des seuils de percolation de l'ordre de 0.005% massique en nanotube de carbone. Enfin, l'influence des propriétés intrinsèques de la matrice, telles la viscosité et la tension de surface, est étudié dans le chapitre 6. La dispersion des nanotubes de carbone s'avère être favorisée au sein de liquides ayant des tensions de surface proches de celle des tubes. Au contraire, une agrégation de charge est rapidement observée dans le cas ou la différence de tension de surface charge-matrice est importante. Nous avons également observé que la percolation des nanotubes est défavorisée au sein de milieux visqueux
The rise of carbon nanotube has open possibility for composites polymers. Mixing this carbonaceous filler with polymer medias leads to an optimization of the electrical properties. Then, conductivity mainly depends of the filler architecture, especially the presence of percolating networks. The objective of this work is to understand the percolation mechanisms of the carbon nanotubes in different media. During this study, filler network has been revealed by the mean of electrical and dielectrical measurements. The originality of our work lies in the use of liquid matrices, such as silicone oils, in order to overcome the stresses in the plastic on the one hand, and to simplify the processing in other hand. This thesis is organized around six chapters. The first bibliographic part discusses the carbon nanotubes properties as well as percolation and dynamic percolation phenomena. The second chapter, matériel & méthode, presents the materials used and the different characterization techniques employed. The third chapter of the thesis talks about dynamic percolation of carbon nanotubes in silicone oil, probed by conductivity measurements. Chapter 4 provides a change of the power law Kirkpatrick to describe the conductivity as a function of time and filler content. The critical exponent of percolation is proving to be an indicator of the dispersion state of nanotubes throughout the matrix. In the Chapter 5, electric field is depicted as a tool to control the organization of fillers. The application of a high field increases the conductivity of several orders of magnitude and decreases the percolation threshold. Percolation thresholds close to 0.005 wt % have been determined. At last, the influence of the intrinsic properties of the matrix, such as viscosity and surface tension, is discussed in Chapter 6. Carbon nanotubes dispersion appears to be favored if the difference of surface tension between filler and liquid is low. In contrast, a filler aggregation is rapidly observed in the case where the difference in surface tension is important. We also observed that the percolation of the nanotubes is favored in viscous media

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Chang, Chia-Hao, i 張家豪. "Dielectric Properties of Polyaniline／Silver Nanocomposites". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/63424323859831872735.

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碩士
中原大學
物理研究所
99
Abstract In this study, we mixed dedoped polyaniline powder (average diameter of 150 nm) with silver nanoparticles (~ 150nm) in various ratios uniformly. These nanocomposite mixtures were compressed into pellets and their electrical properties were analyzed. We found that when the volume-volume percentage (v/v%) of silver particles was over 6%, percolation effect occurred, and the percolation threshold was much less than that (~16v/v%) of the classical percolation theory. This phenomenon might be due to the aggregation of silver particles in the mixing process. The conductivity of the percolated nanocomposite sample was 1.94×10-2 S/cm, which was much higher than that of pure polyaniline (2.63×10-8 S/cm). In the analysis of the dielectrical properties of the samples, the relative dielectric constant was found to be negative when the percolation effect occurred. It could be explained by referring the electron gas model. The results of our AC conductivity measurements also showed that the percolation threshold of our experiment is different from that of the classical theory. The pressure of the sample compress process also affected the DC conductivity of the nanocomposites. The conductivity increased with increasing pressure. After annealing treatment, we found that the DC conductivity of the sample compressed by lower pressure decreased obviously, and the AC conductivity had a similar behavior. The relative dielectric constant increased with increasing pressure, and decreased with increasing frequency. Finally, the polyaniline/Ag nanocomposites were investigated through variable temperature electrical measurements, and the I-V curves of the nanocomposites were analyzed at low temperature.

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25

Singha, Santanu. "Studies On The Dielectric And Electrical Insulation Properties Of Polymer Nanocomposites". Thesis, 2008. https://etd.iisc.ac.in/handle/2005/842.

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Today, nanotechnology has added a new dimension to materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials and even though they show tremendous promise for dielectric/electrical insulation applications (“nanodielectrics” being the buzzword), the understanding related to these systems is very premature. Considering the desired research needs with respect to some of the dielectric properties of polymer nanocomposites, this study attempts to generate an understanding on some of the existing issues through a systematic and detailed experimental investigation coupled with a critical analysis of the data. An epoxy based nanocomposite system is chosen for this study along with four different choices of nano-fillers, viz. TiO2, Al2O3, ZnO and SiO2. The focus of this study is on the properties of nanocomposites at low filler loadings in the range of 0.1 - 5% by weight and the properties under investigation are the permittivity/tan delta behaviors, DC volume resistivity, AC dielectric strength and electrical discharge resistant characteristics. Significant efforts have also been directed towards addressing the interface interaction phenomena in epoxy nanocomposites and their subsequent influence on the dielectric properties of the material. The accurate characterization of the dielectric properties for polymer nanocomposites depends on the dispersion of nanoparticles in the polymer matrix and to achieve a good dispersion of nanoparticles in the epoxy matrix for the present study, a systematic design of experiments (DOE) is carried out involving two different processing methods. Consequently, a laboratory based epoxy nanocomposite processing methodology is proposed in this thesis and this process is found to be successful in dispersing nanoparticles effectively in the epoxy matrix, especially at filler concentrations lower than 5% by weight. Nanocomposite samples for the study are prepared using this method and a rigorous conditioning is performed before the dielectric measurements. The dielectric properties of epoxy nanocomposites obtained in the present study show interesting and intriguing characteristics when compared to those of unfilled epoxy and microcomposite systems and few of the results are unique and advantageous. In an unexpected observation, the addition of nanoparticles to epoxy is found to reduce the value of nanocomposite real permittivity below that of unfilled epoxy over a wide range of frequencies. Similarly, it has been observed that irrespective of the filler type, tan delta values in the case of nanocomposites are either same or lower than the value of unfilled epoxy up to a filler loading of 5% by weight, depending on the frequency and filler concentration. In fact, the nanocomposite real permittivities and tan delta values are also observed to be lower as compared to the corresponding microcomposites of the same constituent materials at the same filler loading. In another significant result, enhancements in the electrical discharge resistant characteristics of epoxy nanocomposites (with SiO2/Al2O3 nanoparticles) are observed when compared to unfilled epoxy, especially at longer durations of discharge exposures. Contrary to these encouragements observed for few of the dielectric properties, the trends of DC volume resistivity and AC dielectric breakdown strength characteristics in epoxy nanocomposites are found to be different. Irrespective of the type of filler in the epoxy matrix, it has been observed that the values of both AC dielectric strengths and DC volume resistivities are lower than that of unfilled epoxy for the filler loadings investigated. The results mentioned above seem to suggest that there has to be an interaction between the nanoparticles and the epoxy chains in the nanocomposite and therefore, glass transition temperature (Tg) measurements are performed to characterize the interaction phenomena, if any. The results of Tg for all the investigated nanocomposites also show interesting trends and they are observed to be lower than that of unfilled epoxy up to certain nanoparticle loadings. This lowering of the Tg in epoxy nanocomposites was not observed in the case of unfilled and microcomposite systems thereby strongly confirming the fact that there exists an interaction between the epoxy chains and nanoparticles in the nanocomposite. Considering the variations obtained for the nanocomposite real permittivity and Tg with respect to filler loading, a dual nanolayer interface model is utilized to explain the interaction dynamics and according to the model, interactions between epoxy chains and nanoparticles lead to the formation of two epoxy nanolayers around the nanoparticle. Analysis shows that the characteristics of the interface region have a strong influence on the dielectric behaviors of the nanocomposites and the suggested interface model seems to fit the characteristics obtained for the different dielectric/electrical insulation properties rather well. Further investigations are performed to understand the nature of interaction between nanoparticles and epoxy chains through FTIR studies and results show that there is probably an occurrence of hydrogen bonding between the epoxide groups of the epoxy resin and the free hydroxyl (OH) groups present on the nanoparticle surfaces. The results obtained for the dielectric properties of epoxy nanocomposites in this study have widened the scope of applications of these functional materials in the electrical sector. The occurrence of lower values of real permittivity for nanocomposites is definitely unique and unexpected and this result has huge potential in electronic component packaging applications. Further, the advantages related to tan delta and electrical discharge resistance for these materials carry lot of significance since, electrical insulating materials with enhanced electrical aging properties can be designed using nanocomposite technology. Although the characteristics of AC dielectric strengths and DC volume resistivities are not found to be strictly advantageous for epoxy nanocomposites at the investigated filler loadings, these properties can be optimized when designing insulation systems for practical applications. In spite of all these advantages, serious and systematic research efforts are still desired before these materials can be successfully utilized in electrical equipment.

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26

Singha, Santanu. "Studies On The Dielectric And Electrical Insulation Properties Of Polymer Nanocomposites". Thesis, 2008. http://hdl.handle.net/2005/842.

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Today, nanotechnology has added a new dimension to materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials and even though they show tremendous promise for dielectric/electrical insulation applications (“nanodielectrics” being the buzzword), the understanding related to these systems is very premature. Considering the desired research needs with respect to some of the dielectric properties of polymer nanocomposites, this study attempts to generate an understanding on some of the existing issues through a systematic and detailed experimental investigation coupled with a critical analysis of the data. An epoxy based nanocomposite system is chosen for this study along with four different choices of nano-fillers, viz. TiO2, Al2O3, ZnO and SiO2. The focus of this study is on the properties of nanocomposites at low filler loadings in the range of 0.1 - 5% by weight and the properties under investigation are the permittivity/tan delta behaviors, DC volume resistivity, AC dielectric strength and electrical discharge resistant characteristics. Significant efforts have also been directed towards addressing the interface interaction phenomena in epoxy nanocomposites and their subsequent influence on the dielectric properties of the material. The accurate characterization of the dielectric properties for polymer nanocomposites depends on the dispersion of nanoparticles in the polymer matrix and to achieve a good dispersion of nanoparticles in the epoxy matrix for the present study, a systematic design of experiments (DOE) is carried out involving two different processing methods. Consequently, a laboratory based epoxy nanocomposite processing methodology is proposed in this thesis and this process is found to be successful in dispersing nanoparticles effectively in the epoxy matrix, especially at filler concentrations lower than 5% by weight. Nanocomposite samples for the study are prepared using this method and a rigorous conditioning is performed before the dielectric measurements. The dielectric properties of epoxy nanocomposites obtained in the present study show interesting and intriguing characteristics when compared to those of unfilled epoxy and microcomposite systems and few of the results are unique and advantageous. In an unexpected observation, the addition of nanoparticles to epoxy is found to reduce the value of nanocomposite real permittivity below that of unfilled epoxy over a wide range of frequencies. Similarly, it has been observed that irrespective of the filler type, tan delta values in the case of nanocomposites are either same or lower than the value of unfilled epoxy up to a filler loading of 5% by weight, depending on the frequency and filler concentration. In fact, the nanocomposite real permittivities and tan delta values are also observed to be lower as compared to the corresponding microcomposites of the same constituent materials at the same filler loading. In another significant result, enhancements in the electrical discharge resistant characteristics of epoxy nanocomposites (with SiO2/Al2O3 nanoparticles) are observed when compared to unfilled epoxy, especially at longer durations of discharge exposures. Contrary to these encouragements observed for few of the dielectric properties, the trends of DC volume resistivity and AC dielectric breakdown strength characteristics in epoxy nanocomposites are found to be different. Irrespective of the type of filler in the epoxy matrix, it has been observed that the values of both AC dielectric strengths and DC volume resistivities are lower than that of unfilled epoxy for the filler loadings investigated. The results mentioned above seem to suggest that there has to be an interaction between the nanoparticles and the epoxy chains in the nanocomposite and therefore, glass transition temperature (Tg) measurements are performed to characterize the interaction phenomena, if any. The results of Tg for all the investigated nanocomposites also show interesting trends and they are observed to be lower than that of unfilled epoxy up to certain nanoparticle loadings. This lowering of the Tg in epoxy nanocomposites was not observed in the case of unfilled and microcomposite systems thereby strongly confirming the fact that there exists an interaction between the epoxy chains and nanoparticles in the nanocomposite. Considering the variations obtained for the nanocomposite real permittivity and Tg with respect to filler loading, a dual nanolayer interface model is utilized to explain the interaction dynamics and according to the model, interactions between epoxy chains and nanoparticles lead to the formation of two epoxy nanolayers around the nanoparticle. Analysis shows that the characteristics of the interface region have a strong influence on the dielectric behaviors of the nanocomposites and the suggested interface model seems to fit the characteristics obtained for the different dielectric/electrical insulation properties rather well. Further investigations are performed to understand the nature of interaction between nanoparticles and epoxy chains through FTIR studies and results show that there is probably an occurrence of hydrogen bonding between the epoxide groups of the epoxy resin and the free hydroxyl (OH) groups present on the nanoparticle surfaces. The results obtained for the dielectric properties of epoxy nanocomposites in this study have widened the scope of applications of these functional materials in the electrical sector. The occurrence of lower values of real permittivity for nanocomposites is definitely unique and unexpected and this result has huge potential in electronic component packaging applications. Further, the advantages related to tan delta and electrical discharge resistance for these materials carry lot of significance since, electrical insulating materials with enhanced electrical aging properties can be designed using nanocomposite technology. Although the characteristics of AC dielectric strengths and DC volume resistivities are not found to be strictly advantageous for epoxy nanocomposites at the investigated filler loadings, these properties can be optimized when designing insulation systems for practical applications. In spite of all these advantages, serious and systematic research efforts are still desired before these materials can be successfully utilized in electrical equipment.

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27

Tseng, Min-Chi, i 曾敏琪. "Preparation and Properties of Low-Dielectric Polybenzoxazine Nanocomposites". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/31143411325424912818.

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碩士
中原大學
化學工程研究所
97
In this study , two novel benzoxazine monomers containing furan groups：one monomer is monofunctional benzoxazine(Ph-FBz) , the other is bifunctional benzoxazine(BPA-FBz) , they have been synthesized from phenol or bisphenol-A with furfurylamine and formaldehyde. Furthermore , a high molecular weight polymer (BPA-BMI) possessing reactive benzoxazine groups in the mainchain was prepared through the Diels-Alder reaction using BPA-FBz and a bismale-imide (BMI) as monomers. The chemical structures of these novel benzoxazine were confirmed by FT-IR. And then blending benzoxazine monomers (Ph-FBz、BPA-FBz and BPA-BMI) with Methacryl POSS in various weight ratios , respectively. As we know , the existence of silica can resist heat and avoid further oxidation of char to effect of flame retardant. SO blending silica into benzoxazine can enhance thermal stability and comfirmed by Thermal Gravimetric Analysis. In general, to improve benzoxazine hard and brittle nature ,introduction of Si-O-Si soft bond in POSS into benzoxazine structure can also increase the toughness of polymers and can comfirmed by Instron. POSS itself as a result of non-polar molecule and contains uniform nano-holes, and the air dielectric constant value of 1, the structure of POSS into benzoxazine, free volume can be increased, reduce the effective dielectric constant materials.

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28

Lu, Shau Tai, i 呂紹臺. "Synthesis and Dielectric Properties of Polymer/Clay Nanocomposites". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/68903325029069911684.

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碩士
中原大學
化學研究所
91
Abstract We prepare a series of nanocomposites materials which were :polyaniline、poly methyl methacrylate and polyimide hybrid with clay. The three polymer matrixs were first introduce into the interlayer regions of organophilic clay hosts and followed by oxidation polymerization、radical polymerization and condensation polymerization. The as-synthesized Polymer/Clay nanocomposites materials were characterized by infrared spectroscopy、Wide-angle powder X-ray diffraction、Transmission electron microscopy, and Thermogravimetic analysis. The dielectric properties include: dielectric constant and dielectric loss. We find that the dielectric properties of these nanocomposites were: (1) The dielectric constant of polyaniline/clay nanocomposites increases due to the addition space charge polarization caused by intervalation and exfoliation of clay. (2) Dielectric constant and dielectric loss of PMMA and PI decreased due to the suppression of local dynamics caused by the intercalation and exfoliation of clay.

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29

Kalidindi, Sanjay Varma. "Electric Field Alignment of Cellulose Based-Polymer Nanocomposites". Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-05-11216.

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Cellulose whiskers (CWs) obtained from naturally occuring cellulose are nano-inclusions which show a lot of promise as mechanical reinforcements in polymers. Typically, a relatively high content is added to realize improvement in effective mechanical behavior. This enhancement in modulus is usually followed by a modest increase in strength but generally the ductility and toughness decrease. Our approach is to use small concentrations of CWs so as not to detrimentally affect processability, toughness and ductility. By aligning the small concentrations, we target the same kind of improvement in modulus and strength as reported in the literature, but at much smaller volume contents. In this work, we investigate the effect of AC electric field on the alignment of dispersed nanoscale CW in a polymer. Polyvinyl acetate (PVAc) is used as the model polymer because of the good interaction between CWs and PVAc. A low concentration of 0.4wt% was used for the study. Two dispersion methods, namely basic and modified, were developed. The basic method led to micron scale dispersion. Using the modified method, CWs were individually dispersed in PVAc with average lengths and diameters of 260 nm and 8 nm respectively yielding an aspect ratio of approximately 30. The behavior of CWs (alignment and chain formation) under an applied electric field was found to be a function of applied electric field magnitude, frequency and duration. Following alignment, the CW/PVAc nanocomposites are thermally dried in the presence of electric field to maintain the aligned microstructure. Improvements in dielectric constant and mechanical properties were observed for the aligned cases as compared to random case and pure PVAc. The optimal electric field magnitude, frequency and duration for the alignment and chain formation were found to be 200Vpp/mm, 50 KHz for duration of 20 minutes for the microcomposite and 250Vpp/mm, 10KHz for a duration of 1hr for the nanocomposite. At 0.4wt% concentration, 21% increase in dielectric constant for the optimal nanocomposite case. Above Tg, a 680% improvement in elastic modulus at 0.4wt% concentration for the optimal nanocomposite case. The reason for the significant reinforcement is attributed to alignment (rotation and chain formation) and chain-chain interaction (3D network formation and hydrogen bonding).

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30

Yu, Liping. "First principles studies of interface dielectric properties of polymer/metal-oxide nanocomposites". 2009. http://www.lib.ncsu.edu/theses/available/etd-07272009-164521/unrestricted/etd.pdf.

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31

Han, Wei-Hsuan, i 韓瑋軒. "Piezoelectric and Dielectric Properties of Lead Zirconate Titanate/Polyvinylidene Fluoride/Silver Piezoelectric Nanocomposites". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/eb62qk.

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碩士
中原大學
物理研究所
98
In this thesis, the dielectric and piezoelectric properties of lead zirconate titanate/polyvinylidene fluoride/silver (PZT/PVDF/Ag) nanocomposites were investigated. After polarization and annealing treatment, the nanocomposites were characterized by scanning electron microscope (SEM) and x-ray diffraction (XRD). The results are discussed and compared with the electrical characteristics of the composites. The PZT/PVDF composites without Ag content have maximum dielectric constant and piezoelectric coefficient when the composites have 80 wt% PZT and were annealed at 400°C. In the case of that Ag nanoparticles were added into the specimens to form PZT/PVDF/Ag nanocomposites, the dielectric constant and piezoelectric coefficient of the nanocomposites increase with increasing Ag content. This effect is possibly due to the enhanced space charge polarization and the formation of conductive network by the Ag content. After the specimen with 23 wt% Ag was polarized and annealed at 400°C (the mean particle size of the Ag powder is about 150 nm and 100 nm), its dielectric constant is above 5.5 and 6.8 times higher than the original value, and its transverse piezoelectric coefficient is up to -934 and -984 pm/V. However, when the Ag content reaches 28 wt%, a percolation transition occurs in the specimens, the electrical properties of composites would be a significant change in this range. Additionally, the dielectric and piezoelectric properties of the PZT/PVDF/Ag nanocomposites not only increase significantly with increasing Ag content, but also increases the dielectric dissipation factor significantly, causing a large energy loss. Finally, the PZT/PVDF/Ag nanocomposites were i nvestigated through variable temperature electrical measurements, and observed the change of the I-V curve at low temperature.

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32

Fang, Wen-Hui, i 方文輝. "Preparation of Epoxy/BaTiO3 Nanocomposites with High Dielectric Constants and High Performance Properties". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/69kkm5.

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碩士
中國文化大學
化學工程與材料工程學系奈米材料碩士班
105
This project object is to research the unsaturated high dielectric constant and high performance of the phenolic resin / barium titanate nanocomposites and determine properties about physical, mechanical properties,electrical properties,optical properties and dynamic mechanical properties. In this study, using 3-Aminopropyltrimethoxysilane (APTMS) grafted nano barium titanate surface modification. For unsaturated Epoxy Add prepared BaTiO3 and APTMS-m-BaTiO3 Nanocomposites with a different number of grams of composition (per 100 grams of resin contained in the composition of the number of grams). Explore the different components of the number of grams of BaTiO3 and APTMS-m-BaTiO3 nanometer morphology of unsaturated Epoxy composites (FT-IR, SEM), physical properties (density, porosity), mechanical properties (hardness, abrasion index, flexural strength, tensile strength and impact strength), thermal properties (TGA, HDT and VST), electrical properties (dielectric constant)and the optical properties (transmittance). The experimental results that, by TGA, FT-IR and XPS testing can prove the success of silane coupling agent grafted via at particle size analysis, to retain the size of the reinforcing material in nano levels. Unsaturated Epoxy / barium titanate adding BaTiO3 and APTMS-m-BaTiO3 part of the composite material, structure and morphology in SEM image that the addition of BaTiO3 and APTMS-m-BaTiO3 allows more surface structures from the original hole into a smoother surface; a test of physical properties, effectively increasing; in mechanical properties test results, hardness and abrasion index, are all rising. The bending and tensile test, adding BaTiO3 or APTMS-m-BaTiO3, its strength is rised; thermal properties, heat resistance improving effect is more significant; in terms of electrical properties, with BaTiO3 and APTMS-m-BaTiO3 Add permittivity have to enhance the effect; transmittance affect optical properties, add more content BaTiO3 and APTMS-m-BaTiO3, and will make it light transmission decreased, whereas the absorbance of a good promotion effect.

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33

Lin, Jhih-Cian, i 林志謙. "Preparation of Phenolic/BaTiO3 Nanocomposites with High Dielectric Constants and High Performance Properties". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/73408337962344807217.

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碩士
中國文化大學
化學工程與材料工程學系奈米材料碩士班
104
This project object is to research the unsaturated high dielectric constant and high performance of the phenolic resin / barium titanate nanocomposites and determine properties about physical, mechanical properties,electrical properties,optical properties and dynamic mechanical properties. In this study, using 3- (Trimethoxysilyl) propyl methacrylate (MPS) grafted nano barium titanate surface modification. For unsaturated phenolic resin (PF) Add prepared BaTiO3 and MPS-m-BaTiO3 Nanocomposites with a different number of grams of composition (per 100 grams of resin contained in the composition of the number of grams). Explore the different components of the number of grams of BaTiO3 and MPS-m-BaTiO3 nanometer morphology of unsaturated phenolic resin composites (FT-IR, SEM, TEM and XRD), physical properties (density, porosity), mechanical properties (hardness, abrasion index, flexural strength, tensile strength and impact strength), thermal properties (TGA, CTE, HDT and VST), electrical properties (dielectric constant)and the optical properties (transmittance). The experimental results that, by TGA, FT-IR, XRD and XPS testing can prove the success of silane coupling agent grafted via at particle size analysis, to retain the size of the reinforcing material in nano levels. Unsaturated phenolic resin / barium titanate adding BaTiO3 and MPS-m-BaTiO3 part of the composite material, structure and morphology in SEM image that the addition of BaTiO3 and MPS-m-BaTiO3 allows more surface structures from the original hole into a smoother surface; a test of physical properties, effectively increasing; in mechanical properties test results, hardness and abrasion index, are all rising. The bending and tensile test, adding BaTiO3 or MPS-m-BaTiO3, its strength is rised; thermal properties, heat resistance improving effect is more significant; in terms of electrical properties, with BaTiO3 and MPS-m-BaTiO3 Add permittivity have to enhance the effect; transmittance affect optical properties, add more content BaTiO3 and MPS-m-BaTiO3, and will make it light transmission decreased, whereas the absorbance of a good promotion effect.

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34

Lin, X., J. W. Tian, P. H. Hu, Rohan Ambardekar, Glen P. Thompson, Z. M. Dang i Philip D. Coates. "Improved dielectric performance of polypropylene/multiwalled carbon nanotube nanocomposites by solid-phase orientation". 2015. http://hdl.handle.net/10454/16941.

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Yes
By means of die drawing technique at rubber-state, effect of the orientation of microstructure on dielectric properties of polypropylene/multi-walled carbon nanotubes nanocomposites (PP/MWCNTs) was emphasized in this work. Viscoelasticity behavior of PP/MWCNTs with MWCNTs weight loadings from 0.25 to 5 wt% and dielectric performance of the stretched PP/MWCNTs under different drawing speeds and drawing ratios were studied for seeking an insight of the influences of dispersion and orientation state of MWCNTs and matrix molecular chains. A viscosity decrease (ca. 30%) of the PP/MWCNTs-0.25wt% melt was obviously observed owing to the free volume effect. Differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) were adopted to detect the orientation structure and the variation of crystal morphology of PP/MWCNTs. Melting plateau regions, which indicated the mixed crystallization morphology for the stretched samples, were found in the DSC patterns instead of a single-peak for the unstretched samples. It was found that the uniaxial stretching process broke the conductive MWCNTs networks and consequently increased the orientation of MWCNTs as well as molecular chains along the tensile force direction, leading to an improvement of the dielectric performance.

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35

Barhoumi, Ep Meddeb Amira. "Optimization of Polymer-based Nanocomposites for High Energy Density Applications". Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-05-11225.

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Monolithic materials are not meeting the increasing demand for flexible, lightweight and compact high energy density dielectrics. This limitation in performance is due to the trade-off between dielectric constant and dielectric breakdown. Insulating polymers are of interest owing to their high inherent electrical resistance, low dielectric loss, flexibility, light weight, and low cost; however, capacitors produced with dielectric polymers are limited to an energy density of ~1-2 J/cc. Polymer nanocomposites, i.e., high dielectric particles embedded into a high dielectric breakdown polymer, are promising candidates to overcome the limitations of monolithic materials for energy storage applications. The main objective of this dissertation is to simultaneously increase the dielectric permittivity and dielectric breakdown without increasing the loss, resulting in a significant enhancement in the energy density over the unmodified polymer. The key is maintaining a low volume content to ensure a high inter-particle distance, effectively minimizing the effect of local field on the composite's dielectric breakdown. The first step is studying the particle size and aspect ratio effects on the dielectric properties to ensure a judicious choice in order to obtain the highest enhancement. The best results, as a combination of dielectric constant, loss and dielectric breakdown, were with the particles with the highest aspect ratio. Further improvement in the dielectric behavior is observed when the nanoparticles surface is chemically tailored to tune transport properties. The particles treatment leads to better dispersion, planar distribution and stronger interaction with the polymer matrix. The planar distribution of the high aspect ratio particles is essential to limit the enhancement of local fields, where minimum local fields result in higher dielectric breakdown in the composite. The most significant improvement in the dielectric properties is achieved with chemically-treated nano TiO2 with an aspect ratio of 14 at a low 4.6 vol% loading, where the energy density increased by 500% compared to pure PVDF. At this loading, simultaneous enhancement in the dielectric constant and dielectric breakdown occurs while the dielectric loss remains in the same range as that of the pristine polymer.

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36

Shetty, Hitha D. "Dielectric, Mechanical, Magnetic and Electromagnetic Shielding properties of Carbon nanomaterial embedded Polydimethylsiloxane composites". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/4631.

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Composites are the advanced engineering materials invented by men with exceptional properties over traditional materials. These attractive and delightful materials are the result of developments in the area of engineering and materials science. Composites are heterogeneous materials, obtained by combining two or more components known as matrix and fillers. The matrix may be metallic, ceramic or polymeric in nature. It decides the shape, surface quality, environmental tolerance and durability of the composite while the filler, change or improve the mechanical and physical properties of matrix. Hence, the composites are wonderful materials with a combination of most desirable properties of matrix and filler, suppressing their unwanted properties. Since the last few decades, developments in the field of nanotechnology has been inspired by the discovery of various carbon structures in nanoscale. The era of carbon nanostructures started and gathered massive attention from researchers, with the finding of fullerene in 1985 and has continued till today. Outstanding work by Andre Geim and Konstantin Novoselov on carbon flake of just 1-atom thickness or graphene fetching them the Nobel prize in the year 2010, opened another new chapter in the history of carbon nanostructures. Even a small variation in the orbital or macroscopic structures of carbon, can give rise to variety of new and fascinating properties. Thus, carbon nanomaterials such as carbon nanotubes, graphene, bucky balls, carbon nanofibers and many more are the supreme filler materials in the growth of nanotechnology. The area of research based on carbon nanomaterials is extraordinary, motivated by exceptional and ground-breaking findings evolving both science and technology. This has encouraged the birth of research journals dedicated to research findings exclusively in the field of carbon nanotechnology. The study of composites with these superior filler materials over the last decade, have given birth to polymer nanocomposites with enhanced electrical, thermal and mechanical properties in addition to lower density and ease of processability. Here we are reporting about polymer composites with polydimethylsiloxane (PDMS) as matrix which has distinctive properties such as optical transparency, flexibility, biocompatibility and ease of moulding. PDMS composites with carbon nanostructures make them ideal candidates for various applications. In this thesis, dielectric, electrical, mechanical and electromagnetic shielding properties of various PDMS-carbon nanostructure composites are compared and discussed to understand the effect of macroscopic structural forms of carbon on PDMS. The thesis is divided into eight chapters to put forward the understanding of PDMS composites with variety of carbon-based fillers from different aspects.

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37

Kumar, Vivek. "Development of modifified bamboo fiber reinforced plastic nanocomposites and study of their dielectric, mechanical and thermal properties". Thesis, 2012. http://localhost:8080/xmlui/handle/12345678/4563.

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38

Patra, Ananya. "Exploring one and two-channel Kondo effect and investigating dielectric properties in ferrimagentic nanocomposites of LaNiO3 and CoFe2O4". Thesis, 2019. https://etd.iisc.ac.in/handle/2005/5039.

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The Kondo effect is a well-known and intensely studied phenomenon in condensed matter physics. After the theoretical prediction of Zawadowski and Noizères about the two-channel Kondo (2CK) effect, several successful attempts have been made to experimentally realize the 2CK effect. Usually the 2CK fixed point is not stable in the presence of magnetism as it can break the channel symmetry. But Zhu et al. have recently reported the coexistence of ferromagnetism and 2CK effect in thin films of L10- MnGa and L10- MnAl. The small spin polarization due to the disorder-induced antiparallel aligned between Mn–Mn atoms results in weak channel asymmetry and hence coexistence of 2CK with ferromagnetism. In order to get new insights about the simultaneous presence of magnetism and the 2CK effect, the low temperature magneto-transport properties of the composites containing LaNiO3 (LNO) and CoFe2O4 (CFO) [(1−x)LNO + xCFO; x = 0, 0.10, 0.15, 0.20, 0.25] are studied extensively. For composite with lower percentage of CFO (x = 0.10), spin one channel Kondo effect dominates at low temperature. However, in case of x ≥ 0.15 resistivity below the upturn is governed by orbital 2CK effect which originates from the scattering of conduction electrons with the structural disorders created at the interfaces between the two phases (LNO and CFO). The magnetoresistance and anomalous Hall effect (AHE) are studied in the two composites with x = 0.15 and 0.20 to understand the origin of AHE in systems with structural defects and to unravel the correlation between AHE and 2CK physics. The AHE shows two important phenomena, one is the AHE of the composites with 15 % and 20 % CFO follow scaling behaviour with longitudinal resistivity at high temperature, but shows a deviation around Kondo temperature (TK) and a sudden jump in the temperature variation of anomalous Hall coefficient near TK. These two observations suggest the AHE is strongly influenced by the presence of orbital 2CK effect. The complex impedance spectroscopy (CIS) is a useful tool to correlate the electrical properties with the microstructure and to determine various polarization process present in grain, grain boundaries and electrode-interfaces of polycrystalline materials. In the second part of my thesis, the same compounds (LNO and CFO) are used with changing the composition in such a way that CFO acts as insulating matrix and LNO plays the role of conductive filler [xLNO + (1-x)CFO; x = 0, 0.05, 0.10, 0.15]. The physics of transport and dielectric properties are investigated in detail applying the CIS technique. Adding LNO affects the grain boundary transport in the composites enabling short range hopping of the ions across it

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39

Chang, Kung-Chin, i 張光欽. "Synthesis and Dielectric Properties of Polymer-Clay Nanocomposite Materials". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/eck7sq.

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碩士
中原大學
化學研究所
92
Abstract Clay-dispersed polystyrene (PS)、poly(styrene-co-acrylonitrile) (PSA) and polyimide (PI) nanocomposties were synthesized by intercalation and in-situ polymerization processes. By using the wide angle X-ray diffraction, FTIR spectroscopy and TEM technique, it is confirmed that polystyrene (PS)、poly(styrene-co-acrylonitrile) (PSA) and polyimide (PI) were inserted between the interlayer of montmorillonite (MMT) clay. The enhanced thermal and mechanical properties of PsCN、PSAN and PiCN with the addition of clay was studied by the TGA、DSC and DMA. The reduced moisture absorption of PiCN was found to be related with the addition of clay. The dielectric properties of PsCN、PSAN and PiCN were measured under different frequencies and temperatures. It is firstly understood that the nanocomposites may exist a lower dielectric constants and losses due to the intercalation and exfoliation of nano-clay.

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40

Li, Shih-ming, i 李世銘. "Preparation of Polyimide/Clay Nanocomposite and Its Dielectric Properties Investigation". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/78wcqv.

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碩士
中原大學
化學研究所
92
This thesis focused on polyimide/Clay nanocmposities.At first, inorganic Motmorilltonite was made into organophilic Motmorilltonite by ion-exchange method. Monomers of Polyimide are mixed with clay in different ratio in order to synthesize polyimide/Clay nanocomposites. TGA/DSC , TEM , XRD Were employed to investigate the structure and characteristics of synthesized polyimide/Clay nanocomposites. Dielectric properties of these nanocomposites were measured by LCR meter from 30℃ to 150℃ at frequencies of 1KHz to 1MHz. It was found that dielectric constant decreased at higt temperature and high clay content.

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Tsai, Li-Yu, i 蔡立瑜. "Preparation and the Dielectric Properties of Polyimide/BaTiO3 Nanocomposite Films". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/rcp393.

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碩士
中原大學
化學研究所
91
Reactive powder of nano-BaTiO3 powder is prepared by the hydrothermal method.Two serises of the monoers of polyimide have been used for the prepartion of polyimide/BaTiO3 composite films. Polyimide/BaTiO3 composite films were obtained by three methods: mixing method, sol-gel mothed and mixing with dispersant. Dielectric constant and morphology of polyimide/BaTiO3 composite films were investigated as a fuction of the BaTiO3 powder content. TEM show that mixing with disperant is an effective way to synthesize polyimide/BaTiO3 nano-dispersed composites. We have found that the thermal stability of composite films decrease and dielectric constants increase slightly as the BaTiO3 powder content increases. However, dielectric constant varies when BaTiO3 particles are not well dispersed. The best properties obtained is derived from the serises of the BSAA of polyimide/BaTiO3 composite films (III). Their all fabricated polyimide/BaTiO3 composites films exhibit low dielectric loss (<0.05) dielectric constants increase from 3.6 to 5.3 and dielectric losses are mostly less than 0.03.

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42

Panda, Bandana. "Studies on Magnetic, Electric and Dielectric Properties of Ferrite Modified LCMO Nanocomposite Systems". Thesis, 2020. http://ethesis.nitrkl.ac.in/10170/2/2020_MTR_BPanda_616PH6001_Studies.pdf.

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The evolution of new composite materials for multi-purpose applications turns into a trend in today’s research.The present study comprises the study of unique manganite La0.7Ca0.3MnO3and its ferrite modified nanocomposites synthesized via. sol-gel self-sustaining combustion method. The structural, optical, magnetic, electric, and dielectric properties of these synthesized products have been evaluated in the present study. These properties are found to be enhanced on enhanced incorporation of ferrites in the La0.7Ca0.3MnO3system. These enhanced properties of manganite-ferrite nanocomposites have been illustrated on the basis of cation distribution among various sites and internal structure modification. The important findings show CoFe2O4incorporated system has the more reasonable magnetic property as compared to NiFe2O4incorporated system. Whereas, NiFe2O4incorporated system shows the more reasonable dielectric property. These enhanced properties are valuable for the possible use of the nanocomposites in magnetic storage devices and nanocapacitor applications. The detailed study has been specified orderly in six different chapters. Chapter I describes an introduction to rare-earth manganites, specifically lanthanum calcium manganite and its physical properties, spinel ferrites, specifically semi-hard cobalt ferrite and soft nickel ferrite, their physical properties and application scope of manganite-ferrite nanocomposites. Chapter II describes the synthesis procedure and characterization of manganite nanoparticles and its ferrite incorporated nanocomposites synthesized by sol-gel auto combustion method. Chapter III describes the structural, optical, magnetic, electric, and dielectric properties of La0.7Ca0.3MnO3 nanograins. Chapter IV describes the structural, optical, magnetic, electric, and dielectric properties of (1-x) La0.7Ca0.3MnO3/x CoFe2O4 (x = 0, 0.1, 0.2, 0.3) nanocomposites. Chapter V describes the structural, optical, magnetic, electric, and dielectric properties of (1-x) La0.7Ca0.3MnO3/x NiFe2O4 (x = 0, 0.1, 0.2, 0.3) nanocomposites. Chapter VI focuses on important findings and comparative study of the thesis work and its future scope.

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43

Κουφάκης, Ελευθέριος. "Ανάπτυξη, χαρακτηρισμός και λειτουργική συμπεριφορά σύνθετων συστημάτων πολυμερικής μήτρας - νανοσωματιδίων τιτανικού ψευδάργυρου (ZnTiO3) και τιτανικού βαρίου (BaTiO3)". Thesis, 2012. http://hdl.handle.net/10889/6599.

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Τα Νανοσύνθετα συστήματα πολυμερικής μήτρας – σιδηροηλεκτρικών ή πιεζοηλεκτρικών σωματιδίων (κεραμικά εγκλείσματα) αναμένεται να αποτελέσουν μια νέα γενιά υψηλού τεχνολογικού ενδιαφέροντος που θα επιδεικνύουν λειτουργικές ιδιότητες λόγω της ποικίλης πόλωσης των κεραμικών νανοσωματιδίων. Η διασπορά κεραμικών εγκλεισμάτων στο εσωτερικό πολυμερικής μήτρας προσδίδει στα σύνθετα συστήματα βελτιωμένη μηχανική και ηλεκτρική συμπεριφορά. Τέτοιου τύπου συστήματα υλικών, που έχουν υψηλή ηλεκτρική διαπερατότητα (high-Κ materials) χρησιμοποιούνται σε ηλεκτρονικές εφαρμογές, καθώς μειώνουν τα ρεύματα διαρροής και παράλληλα λειτουργούν ως ενσωματωμένοι νανο-πυκνωτές και αισθητήρες ακουστικών εκπομπών. Η ηλεκτρική απόκριση τους, εκφράζεται κυρίως μέσω της ηλεκτρικής διαπερατότητας και μπορεί να ρυθμιστεί, ελέγχοντας τον τύπο, το μέγεθος και την ποσότητα της κεραμικής ενίσχυσης. Η ενσωμάτωση σιδηροηλεκτρικών ή πιεζοηλεκτρικών κρυστάλλων, που επιδεικνύουν υψηλή πόλωση, σε μια πολυμερική μήτρα, όπως η εποξειδική ρητίνη – που εν γένει είναι ηλεκτρικός μονωτής- με χαμηλή ηλεκτρική διαπερατότητα και υψηλή διηλεκτρική αντοχή μπορεί να οδηγήσει στην ανάπτυξη ενός ευφυούς συστήματος. Σκοπός αυτής της εργασίας είναι η παρασκευή και ο χαρακτηρισμός σύνθετων πολυμερικών συστημάτων εποξειδικής ρητίνης – νανοσωματιδίων τιτανικού ψευδάργυρου (ZnTiO3) καθώς και σύνθετων υβριδικών συστημάτων εποξειδικής ρητίνης - νανοσωματιδίων τιτανικού ψευδάργυρου (ZnTiO3) και τιτανικού βαρίου (BaTiO3) ώστε να οδηγηθούμε σε ένα σύστημα υλικών με βέλτιστη συμπεριφορά. Στο θεωρητικό κομμάτι αυτής της εργασίας συζητούνται βασικές έννοιες και θεωρίες που αφορούν τα σύνθετα υλικά, τη θεωρία των διηλεκτρικών και ενεργών διηλεκτρικών, την ηλεκτρική συμπεριφορά σύνθετων υλικών με πολυμερική μήτρα καθώς και πειραματικές τεχνικές χαρακτηρισμού. Στο πειραματικό μέρος, νανοσύνθετα πολυμερικά συστήματα παρασκευάστηκαν από εποξειδική ρητίνη και νανοσωματίδια ZnTiO3 και BaTiO3. Η μέση διάμετρος σωματιδίων βάσει των προδιαγραφών του προμηθευτή ήταν λιγότερο από 100nm για το ZnTiO3 και στην περιοχή των 30 - 50nm για το BaTiO3. Στη συνέχεια τα νανοσύνθετα υποβλήθηκαν σε μορφολογικό, θερμικό και ηλεκτρικό χαρακτηρισμό. Η μορφολογία των δειγμάτων εξετάστηκε για τυχούσα παρουσία κενών (voids) και συσσωματωμάτων (clusters) μέσω του Ηλεκτρονικού Μικροσκοπίου Σάρωσης (SEM) και η θερμική τους απόκριση μέσω της Διαφορικής Θερμιδομετρίας Σάρωσης (DSC). Η διασπορά των κεραμικών εγκλεισμάτων θεωρήθηκε ικανοποιητική, παρόλο που συνυπάρχουν οι νανοδιασπορές με συσσωματώματα. Οι διηλεκτρικές ιδιότητες και τα σχετιζόμενα φαινόμενα διεργασιών χαλάρωσης μελετήθηκαν με χρήση της Διηλεκτρικής Φασματοσκοπίας Ευρέως Φάσματος (BDS) στο εύρος θερμοκρασιών -100 oC έως 160 oC και στο διάστημα συχνοτήτων 10-1 Hz έως 106 Hz. Η ανάλυση των πειραματικών αποτελεσμάτων διεξήχθη με τη χρήση των φορμαλισμών της ηλεκτρικής διαπερατότητας και του ηλεκτρικού μέτρου. Από τα πειραματικά αποτελέσματα προκύπτει πως παρατηρούνται διηλεκτρικές χαλαρώσεις που οφείλονται τόσο στην πολυμερική μήτρα, όσο και στην ενισχυτική φάση. Τα φάσματα των υβριδικών συστημάτων καταγράφουν τουλάχιστον τέσσερεις διακριτούς τρόπους χαλάρωσης. Αυτά αποδίδονται στη διεπιφανειακή πόλωση (Interfacial Polarization ή φαινόμενο MWS) μήτρας/εγκλεισμάτων, στην α- χαλάρωση λόγω υαλώδους μετάβασης του πολυμερούς και στην β- και γ- χαλάρωση εξαιτίας της κίνησης πλευρικών πολικών ομάδων και τοπικής κίνησης μικρών τμημάτων της πολυμερικής αλυσίδας. Η λειτουργικότητα των νανοσύνθετων σχετίζεται με την μεταβολή της πόλωσης, που σχετίζεται ευθέως με το πραγματικό μέρος της ηλεκτρικής διαπερατότητας, την εξάρτηση της ειδικής αγωγιμότητας από την θερμοκρασία και την περιεκτικότητα σε ενισχυτικό μέσο και την δυνατότητα αποθήκευσης ενέργειας.
Nanocomposite systems, which include ferroelectric or piezoelectric particles represent a novel class of materials which are expected to exhibit functional properties because of the varying polarization of the ceramic particles. Dispersing ceramic inclusions within a polymer matrix, results in enhanced mechanical and electrical behavior. Such material systems exhibiting enhanced electrical response are used in electronic applications, for the reduction of leakage currents, as integrated nano- capacitors and as acoustic emission sensors. The electrical response of these composites, namely dielectric permittivity and conductivity can be tailored, by controlling the type, the size and the amount of ceramic inclusions. The ceramic filler could be ferroelectric and/or piezoelectric crystal particles. Their high level of polarization can be combined with a polymer host, like an epoxy resin – which is, in general, electrical insulator – with low dielectric permittivity and high dielectric breakdown strength. This combination could lead in the development of a smart materials’ system. The aims of this work are the preparation and characterization of epoxy resin nanocomposites with embedded zinc titanate (ZnTiO3) and nanoparticles and in tandem hybrid system of epoxy resin– zinc titanate (ZnTiO3) and barium titanate (BaTiO3) nanoparticles. In the first part of this work basic aspects concerning composite materials, dielectric theory, electrical behaviour and characterization techniques of polymer matrix composites are presented. In the experimental part of this study, nanocomposites were prepared by employing commercially available materials such as epoxy resin, ceramic ZnTiO3 and BaTiO3 nanopowder. The mean particle diameter, as indicated by the supplier, was less than 100nm for ZnTiO3 and 30-50nm for BaTiO3 particles. Furthermore, morphology, thermal and electrical response of the produced specimens was examined. The morphology of the specimens was checked for voids and clusters, by means of Scanning Electron Microscopy and the thermal response via Differential Scanning Calorimetry (DSC). Ceramic particles distribution is considered as satisfactory, although clusters co-exist with nanodispersions in all the examined systems. The dielectric properties and the related relaxation phenomena were studied by means of Broadband Dielectric Spectroscopy (BDS) in the temperature range from -100 oC to 160 oC and frequency range from 10-1 Hz to 10-6 Hz. Experimental data analysis was conducted by means of dielectric permittivity and electric modulus formalisms. Based on the conducted analysis, the recorded relaxation phenomena include contributions from both the polymeric matrix and the reinforcing phase. In the spectra of hybrid nanocomposites at least four relaxation processes can be detected. They were attributed to Interfacial Polarization phenomenon (MWS effect), α-mode due to glass/rubber transition of the polymer and β- , γ- modes resulting from the motion of polar side groups and local motion of small segments of the polymer chain. The functionality of the nanocomposite systems is related to the variation of polarization, which is directly connected to the real part of dielectric permittivity, the dependence of conductivity on the temperature and the filler content, and the energy storage efficiency expressed by the density of energy.

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