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Su, Xing. "Polymer/montmorillonite nanocomposites : polyamide 6 nanocomposites and polyacrylamide nanocomposite hydrogels." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18366/.
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Polymer/clay nanocomposites have attracted great attention of researchers for two decades because they are light in weight, easy to be fabricated, and have some unique properties such as thermal barrier and corrosion resistant. Montmorillonite (MMT) is frequently chosen as the clay filler for polymer/clay nanocomposites because of its abundance, high functionality and high cation exchange capacity. This project aims to prepare novel polymer/MMT nanocomposites with adjustable microstructure, good mechanical properties and unique stimuli-sensitive properties. As the control over the clay intercalation/exfoliation ratio is difficult for the polymer/clay nanocomposites, the effect on clay exfoliation of polyamide 6/MMT nanocomposites by using a chemical blowing agent (CBA), citric acid, during extrusion was studied. X-ray diffraction confirmed that the decomposition of CBA did improve clay exfoliation. As many surfactants used for treating clay surface are likely to degrade during the melt processing of polymer/MMT nanocomposites, a novel thermally stable surfactant was used. Polyamide 6/MMT nanocomposites were prepared by either twice or triple extrusion. And the effect on the mechanical properties and thermal stability were studied. The incorporation of clays increased Young’s modulus but decreased strain at break. There was no significant improvement on the thermal stability by the incorporation of clays and/or CBA. Polymer nanocomposite hydrogels often showed high hysteresis when subject to cyclic tension, and their mechanical properties were hardly tested at the fully swollen state. Therefore a novel polyacrylamide (PAM)/polysaccharide-treated MMT nanocomposite hydrogel with low cyclic tensile hysteresis was successfully prepared by in situ polymerisation. This was shown to be stretchable, tough and highly compression-resistant at the fully swollen state. An interpenetrating nanocomposite hydrogel using PAM, MMT, alginate and Ca2+ was proposed in the same chapter. At the fully swollen state, apart from the good mechanical properties such as stretchability, toughness and resilience, it displayed significantly pH-dependant shape changes. As for the current alginate/MMT nanocomposites in the literature, only the mechanical properties under the dry state were studied. The mechanical properties of the fully swollen alginate/MMT/Ca2+ nanocomposite were investigated. The nanocomposite films turned out to be stiff, strong and transparent. Also some of the nanocomposite films were ultraviolet light-proof or sensitive to acetone. Based on the above findings, it is concluded that: firstly, there was a large amount of residual citric acid in the extruded materials, which reduced the mechanical properties and thermal stability of polyamide 6/MMT nanocomposites. Secondly, the thermally stable polymeric surfactant has the potential of enhancing the toughness and thermal stability of polyamide 6/MMT nanocomposites. Thirdly, it was likely to achieve low cyclic-tensile hysteresis, high strength, high toughness and stimuli-responsivity by the polymer/clay nanocomposite hydrogels at the fully swollen state. Those nanocomposite hydrogels can be used in a variety of applications including artificial tissues, medicine, agriculture, skin care and other aquatic uses.
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Coelho, Caio Parra Dantas. "Obtenção e caracterização de nanocompósitos de poliestireno e argilas esmectíticas." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-05082009-165838/.
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Neste trabalho foram preparados nanocompósitos de Poliestireno (PS) e argilas organofílicas. As argilas, inicialmente hidrofílicas, foram modificadas organicamente utilizando três sais quaternários de amônio diferentes: Cloreto de hexadecil trimetil amônio (CTAC), Cloreto de alquil dimetil benzil amônio (Dodigen) e Cloreto de dimetil dioctadecil amônio (Praepagen). A argila organofílica Cloisite 20A foi também utilizada neste estudo. Os nanocompósitos foram preparados por intercalação no polímero fundido por três técnicas diferentes: adição de argila em suspensão de álcool etílico por uma bomba dosadora de líquidos durante a extrusão, adição de argila em pó por um alimentador mecânico durante a extrusão e adição de suspensão de argila em álcool etílico durante obtenção por batelada. Os materiais obtidos foram caracterizados por difração de raios-X (DRX), microscopia óptica (MO) e microscopia eletrônica de transmissão (MET) e ensaios reológicos de Cisalhamento Oscilatório de Pequenas Amplitudes (COPA). As propriedades térmicas foram analisadas por análise termogravimétrica (TG) e as propriedades mecânicas foram analisadas por ensaios de tração e impacto Izod. As três técnicas se mostraram eficazes na preparação dos nanocompósitos, e seus resultados apresentaram uma similaridade muito grande. Os resultados de DRX e microscopia mostraram que a maioria dos nanocompósitos apresentou estruturas compostas de fases intercaladas e esfoliadas. As análises térmicas mostraram que a adição de argila ao PS o tornou mais estável termicamente, suportando maiores temperaturas antes de iniciar o processo de degradação. Os ensaios reológicos de COPA e ensaios mecânicos dos nanocompósitos obtidos não apresentaram grandes variações em relação ao PS puro.In this work nanocomposites of polystyrene (PS) and organophilic clays were prepared. The clays were organically modified using three different ammonium quaternary salts: cetyltrimethyl ammonium chloride (commercial name: CTAC), alquildimethyl benzyl ammonium chloride (commercial name: Dodigen) and distearyl dimethyl ammonium chloride (commercial name: Praepagen). The organoclay Cloisite 20 A was also used in this work. The nanocomposites were prepared by melt intercalation using three different techniques: adding the organoclay as a diluted organic solvent supension to the extruder using a motor-driven metering pump, adding the organoclay as powder to the extruder using a mechanical feeder and adding the organoclay as a diluted organic solvent suspension to the mixer. The materials obtained were characterized by X-ray diffraction (XRD), optical microscopy (OM), transmission electron microscopy (TEM) and by rheological studies through small amplitude oscillatory shear tests (SAOS). The thermal properties were studied by thermogravimetrical analyses (TG) and the mechanical properties were studied by tensile and impact Izod strength tests. The three techniques were efficient to prepare nanocomposites, and their results were very similar. The DRX and microscopy results showed that the most nanocomposites presented structures composed by intercalated and exfoliated phases. The thermal analyses showed that the addition of organoclay turned PS more thermally stable, increasing their degradation temperatures. The results of rheological studies (SAOS) and the mechanical tests did not present significant variations compared to the neat PS.
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Tong, Wan. "Characterisation of PA/clay nanocomposite and glass fibre filled PA/clay nanocomposites." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439857.
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Karabulut, Metin. "Production And Characterization Of Nanocomposite Materials From Recycled Thermoplastics." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1255728/index.pdf.
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Nanocomposites are a new class of mineral-field plastics that contain relatively small amounts (<10%) of nanometer-sized clay particles. The particles, due to their extremely high aspect ratios (about 100-15000), and high surface area (in excess of 750-800 m2/g) promise to improve structural, mechanical, flame retardant, thermal and barrier properties without substantially increasing the density or reducing the light transmission properties of the base polymer. Production of thermoplastic based nanocomposites involves melt mixing the base polymer and layered silicate powders that have been modified with hydroxyl terminated quaternary ammonium salt. During mixing, polymer chains diffuse from the bulk polymer into the van der Waals galleries between the silicate layers. In this study, new nanocomposite materials were produced from the components of recycled thermoplastic as the matrix and montmorillonite as the filler by using a co-rotating twin screw extruder. During the study, recycled poly(ethylene terepthalate), R-PET, was mixed with organically modified quaternary alkylammonium montmorillonite in the contents of 1, 2, and 5 weight %. Three types of clays were evaluated during the studies. For comparison, 2 weight % clay containing samples were prepared with three different clay types, Cloisite 15A, 25A, 30B. The nanocomposites were prepared at three different screw speeds, 150, 350, 500 rpm, in order to observe the property changes with the screw speed. Mechanical tests, scanning electron microscopy and melt flow index measurements were used to characterize the nanocomposites. The clay type of 25A having long alkyl sidegroups gave the best results in general. Owing to its branched nature, in nanocomposites with 25A mixing characteristics were enhanced leading to better dispersion of clay platelets. This effect was observed in the SEM micrographs as higher degrees of clay exfoliation. Nearly all the mechanical properties were found to increase with the processing speed of 350 rpm. In the studies, it was seen that the highest processing speed of 500 rpm does not give the material performance enhancements due to higher shear intensity which causes defect points in the structure. Also the residence time is smaller at high screw speeds, thus there is not enough time for exfoliation. In general, the MFI values showed minimum, thus the viscosity showed a maximum at the intermediate speed of 350 rpm. At this processing speed, maximum exfoliation took place giving rise to maximum viscosity. Also, the clay type of 25A produced the lowest MFI value at this speed, indicating the highest degree of exfoliation, highest viscosity, and best mechanical properties.
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Bera, Chandan. "Thermo electric properties of nanocomposite materials." Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00576360.
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Cette thèse présente une étude théorique du transport de chaleur dans les matériaux composites nano poreux et nano fils ainsi qu'une étude théorique des propriétés thermoélectriques de l'alliage Si0:8Ge0:2 confrontée à des mesures expérimentales réalisées pour une partie, dans le cadre de l'étude.La première étude démontre que les alliages poreux affichent des réductions de conductivité thermique à des dimensions de pores beaucoup plus grandes que les matériaux poreux non alliés de même porosité nominale. Si on considère une taille de pores de 1000nm, la conductivité thermique de l'alliage Si0:5Ge0:5 avec 0:1 de porosité est deux fois plus faible que la conductivité thermique d'un matériau non poreux, alors que les pores plus petits que 100 nm sont nécessaires pour obtenir la même réduction relative dans le Si ou Ge pur. Nos résultats indiquent que les alliages nano poreux devraient être avantageux devant les matériaux nano poreux non alliés, et ceux pour les applications nécessitant une faible conductivité thermique, tels que les nouveaux matériaux thermoélectriques.La deuxième étude théorique sur la conductance thermique de nano fils révèle l'effet de la structure sur le transport des phonons. Avec un modèle théorique qui considère la dépendance en fréquence du transport des phonons, nous sommes en mesure quantitativement de rendre compte des résultats expérimentaux sur des nano fils droits et coudés dans la gamme de température qui montre qu'un double coude sur un fil réduit sa conductance thermique de 40% à la température de 5K. Enfin, nous avons procédé à une approche théorique des propriétés thermoélectriques des alliages SiGe frittés, en les comparant aux mesures expérimentales nouvelles et antérieures, tout en évaluant leur potentiel d'amélioration. L'approche théorique a été validée par comparaison de la mobilité prévue et la conductivité thermique prévues, en faisant varier la quantité de Ge et les concentrations de dopage, dans une gamme de température comprise entre 300 et 1000K. Nos calculs suggèrent qu'une optimisation par rapport à l'état de l'art actuel est possible pour le matériau de type n et type p, conduisant potentiellement à une augmentation de 6% (5%) du ZT _a 1000K et 25% (4%) _a température ambiante. Même des améliorations plus grandes devraient être possibles si la probabilité de diffusion des phonons aux joints de grains pouvait être augmentée au-delà de sa valeur actuelle de 10%.
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Sengezer, Engin Cem. "Multifunctional Nanocomposites and Particulate Composites with Nanocomposite Binders for Deformation and Damage Sensing." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78782.
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At present, structural health monitoring efforts focus primarily on the sensors and sensing systems for detecting instances and locations of damage through techniques such as X-ray, micro CT, acoustic emission, infrared thermography, lamb wave etc., which only detect cracks at relatively large length scales and rely heavily on sensors and sensing systems which are external to the material system. As an alternative to conventional commercially available SHM techniques, the current work explores processing-structure-property relationships starting from carbon nanotube (CNT) based nanocomposites to particulate composites with nanocomposite binder/matrix materials, i.e. hybrid particulate composites to investigate deformation and damage sensing capabilities of inherently sensing materials and structures through their piezoresistive (coupled electro-mechanical) response. Initial efforts focused on controlling the dispersion of CNTs and orientation of CNT filaments within nanocomposites under dielectrophoresis to guide design and fabrication process of nanocomposites by tuning CNT concentration, applied AC electric field intensity, frequency and exposure time. It is observed that a combination of exposure time to AC electric field and the AC field frequency are the key drivers of filament width and spacing and that the network for filament formation is much more efficient for pristine CNTs than for acid treated functionalized CNTs. With the knowledge obtained from controlling the morphological features, AC field-induced long range alignment of CNTs within bulk nanocomposites was scaled up to form structural test coupons. The morphology, electrical and mechanical properties of the coupons were investigated. The anisotropic piezoresistive response both for parallel and transverse to CNT alignment direction within bulk composite coupons under various loading conditions was obtained. It is observed that control of the CNT network allows for the establishment of percolation paths and piezoresistive response well below the nominal percolation threshold observed for random, so called well-dispersed CNT network distributions. The potential for use of such bulk nanocomposites in SHM applications to detect strain and microdamage accumulation is further demonstrated, underscoring the importance of microscale CNT distribution/orientation and network formation/disruption in governing the piezoresistive sensitivities. Finally, what may be the first experimental study in the literature is conducted for real-time embedded microscale strain and damage sensing in energetic materials by distributing the CNT sensing network throughout the binder phase of inert and mock energetic composites through piezoresistive response for SHM in energetic materials. The incorporation of CNTs into inert and mock energetic composites revealed promising self-diagnostic functionalities for in situ real-time SHM applications under quasi-static and low velocity impact loading for solid rocket propellants, detonators and munitions to reduce the stochastic nature of safety characterization and help in designing insult tolerant energetic materials.Ph. D.
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Smith, Jon Anthony. "Polyaniline Gold Nanocomposites." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4900.
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Polyaniline/Gold Nanocomposites
J. Anthony Smith
141 Pages
Directed by Dr. Ji and #345;?anata
The expectation that it is possible to create a range of new materials from two basic components, polyaniline fibers and gold particles is explored. Three synthetic methods were employed each of which created different materials and required different investigation techniques. The methods are: chemical, one step aniline oxidation / AuCl4- reduction; electrochemical/chemical, a two-step composite growth achieved by electrochemical polyaniline thin film growth followed by film immersion in AuCl4- solution and spontaneous reduction to gold particles; electrochemical, resulting in freestanding polyaniline thin film/Au nanoparticles carried out by electrochemical stripping of a polyaniline thin film grown over a sacrificial gold layer in the presence halide solutions. The incorporation of particles was shown to affect film morphology and electrical properties in all synthetic methods. The changes are in large part attributed to the development of a contact potential between the polyaniline and the gold particles. Applications for the composites include use as chemically sensitive layers, corrosion inhibition materials, and use as probes to evaluate nanoparticle substrate interactions.
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Mohaddes, pour Ahmad. "Granular polymer nanocomposites." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117135.
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Contrary to classical theories, nanoparticle dispersion in polymer melt has been shown to decrease the bulk viscosity, and to increase the membrane permeability and selectivity when incorporated into certain amorphous polymer glasses. However, the effects of particle concentration, particle size, and polymer configuration at particle interfaces are not well understood. To elucidate how the particle size, chain length, and mixture composition influence polymer-chain packing and, thus, free volume---which is known to primarily influence rheological and permeation properties of polymer nanocomposites---the volume of acrylic spheres (representing nanoparticles) mixed with aluminum ball chains (representing polymer chains) was measured, and the partial molar sphere volume at small but finite sphere volume fractions was calculated. The results show that the sphere radius with respect to the minimum chain loop size is the primary dimensionless parameter that affects mixture free volume. Moreover, free volume is maximal---up to twice the intrinsic inclusion volume per particle---when the sphere radius and the minimum chain loop size are comparable, which is because of the increase in sphere-chain interactions, whereas sphere-sphere interactions decrease the mixture free volume when particles are large. It was further determined that, in the presence of nanoparticles, free volume and polymer chain architecture play a determinative role in influencing the glass transition temperature of polymer nanocomposites. The reason for the decrease in the glass transition temperature of polymer nanocomposites is known to be the repulsive chain-nanoparticle interactions. However, in the absence of enthalpic interactions, it is still elusive how and why the glass transition temperature declines with nanoparticle loading. To examine the nanoparticle influence on chain relaxation dynamics and, thus, nanocomposite glass transition temperature, the relaxation time (the time to reach the close-packed, jammed state) of granular chain-sphere mixtures was measured by systematically changing the sphere size, chain length, and mixture composition. Measuring the compaction dynamics reveals that spherical inclusions profoundly influence the chain relaxation time when the characteristic nanoparticle separation and nanoparticle size are comparable to the chain loop size. This study can shed light on polymer architecture in the presence of nanoparticles, especially when chains are very long and, thus, beyond the capability of current computer simulations. This macroscopic, granular model can also be used to optimize the design of polymer nanocomposites by a judicious choice of nanoparticle size, chain length, and mixture composition for industrial and biomedical applications.Contrairement aux théories classiques, les nanoparticules ont été utilisées pour diminuerla viscosité de volume lorsqu'elles sont dispersées dans un mélange de polymère, et pour augmenter la perméabilité de la membrane et la sélectivité lorsqu'elles sont incorporées dans certains verres polymères amorphes. Cependant, les effets sur la concentration des particules, sur la taille des particules et sur la configuration des polymères à particules inter faciales ne sont pas bien compris. Afin de comprendre comment la taille des particules, la longueur de la chaîne, et les différentes compositions influencent l'assemblage des chaines de polymères et, par conséquent, le volume libre — qui est connu principalement pour agir sur les propriétés rhéologiques et d'infiltration despolymères nanocomposites—le volume de sphères acryliques (représentant les nanoparticules) couplé avec les chaînes de billes d'aluminium (ce qui représente des chaînes de polymère) a été mesurée, et le volume molaire partiel des sphères a été calculée à partir depetit volume fini . Les résultats montrent que le rayon de la sphère par rapport à la taille dela boucle de la chaîne minimum est le paramètre qui affecte principalement la dimensiondu volume de mélange libre. De plus, le volume libre est maximale—jusqu'à deux fois levolume de l'inclusion intrinsèque par particule—lorsque le rayon de la sphère et la taille minimum de la boucle de la chaîne sont comparables, ce qui est d à l'augmentation des interactions dans la chaîne de la sphère, alors que les interactions sphère-sphère diminuent le volume du mélange libre lorsque les particules sont grandes. Il a également été déterminé que, en présence de nanoparticules, le volume libre et l'architecture de la chaîne du polymère jouent un rôle déterminant en influençant la température de transition vitreuse des polymères nano composites. La raison ostensible pour la diminution dela température de transition vitreuse des polymères nano composites est connue pour tre la répulsion entre les chaînes des nanoparticules. Toutefois, en l'absence d'interactions enthalpiques, c'est encore élusif de comment et pourquoi la température de transition vitreuse baisse avec le chargement des nanoparticules. Pour étudier l'influence des nanoparticules sur la dynamique de relaxation de la chaîne et, par conséquent, la température de transition de verre nanocomposite, le temps de relaxation (le temps d'atteindre l'état bloqué) de la chaine du mélange de granulés a été mesurée en changeant systématiquement la taille et la longueur de la sphère et le mélange de la composition. D'avoir mesurer la dynamique de compactage révèle que les inclusions sphériques influencent profondément le temps de relaxation de la chaîne lors de la séparation des nanoparticules caractéristiques ainsi que la taille des nanoparticules est comparable à la taille de la boucle de chaîne. Cette étude nous éclaire sur l'architecture des polymères en présence de nanoparticules, en particulier lorsque les chaînes sont très longues et par conséquent, au-delà de la capacité des simulations informatiques actuels pour être explorées à fond. Ce modèle macroscopique granulaire peut aussi être utilisé pour optimiser la conception de polymères nanocomposites par un choix judicieux de la taille des nanoparticules, de la longueur de la chaîne et la composition du mélange pour des applications industrielles et biomédicales.
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Sontikaew, Somchoke. "PET/organoclay nanocomposites." Thesis, Brunel University, 2008. http://bura.brunel.ac.uk/handle/2438/3280.
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This thesis looks at the study of nanocomposites of Poly(ethylene terephthalate) and organoclays. Two methods of materials blending are investigated for the production of the nanocomposites: solvent blending and melt blending. The main objectives were the investigation of the influence of organoclays and processing conditions on morphological, rheological, mechanical properties, crystal structure and isothermal crystallization kinetics of the nanocomposite and a comparison with unfilled PET. In solvent blending, the use of long sonication time and epoxy led to the formation of a two-dimensional network structure of long, thin particles in a solvent blended PET nanocomposite at low clay loading. The clay network structure seemed not to affect the tensile properties. The long, thin particles were able to be separated and dispersed further by high shear in a twin screw extruder, resulting in a high level of separation and dispersion. The crystallization of the solvent blended nanocomposite was not only influenced by the nanoclay but also by the residual solvent. The extent of clay dispersion did not affect the crystallization of the solvent blended sample. Both solvent blended and melt blended nanocomposites showed that increasing the amount of surfactant improved the degree of nanoclay dispersion in the PET that led to an enhancement in the tensile properties of the nanocomposite compared to the unfilled polymer. The degradation of the organoclay during melt blending did not limit the nanoclay dispersion in the PET. The low thermal stability of the organoclay reduced the strength of the crystalline nanocomposite but it did not affect the strength of the amorphous nanocomposite. In contrast to the solvent blended sample, the extent of clay dispersion influenced the crystallization of the melt blended sample. The poorly dispersed particles were more efficient in nucleating PET crystallization than the well dispersed particles. The crystallization rate of PET increased as the surfactant concentration decreased.
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Elder, Judith. "PMMA clay nanocomposites." Thesis, Durham University, 2009. http://etheses.dur.ac.uk/52/.
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Polymer clay nanocomposites (PCN) of poly(methyl methacrylate) (PMMA) and clay, were synthesised in-situ using a free radical suspension polymerisation technique. The weight fraction of clay in the PCN was systematically varied in order to understand the effect of clay on the physical properties of the resulting PCNs. However, unexpectedly it was found that the weight fraction of clay had a dramatic impact upon the molecular weight of the polymer matrix and a relationship between clay concentration and polymer molecular weight was established. Furthermore, it was also found that the change in molecular weight was dependent upon the clay type. Three different clay types were investigated; an organically modified montmorillonite (Cloisite 15a), a synthetic clay (Laponite RD) and a PEO modified Laponite RD. To produce the modified Laponite RD, mono amino PEO was synthesised via anionic polymerisation using dimethyl ethanol amine as an initiator. The modification of the Laponite RD clay took place in the reaction flask prior to the suspension polymerisation of the PCN. The PCN were characterised using size exclusion chromatography (SEC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and oscillatory shear rheology. Morphological studies of the PCN showed that the extent of clay dispersion depended on the clay type. Within the PMMA/Laponite RD nanocomposites an unusual network structure was formed, which appeared to be continuous throughout the material. Thermal properties of the PCN were investigated using DSC, TGA and Microcalorimetry. From oscillatory shear rheology, the full master curves for the PCN were obtained by applying the time-temperature superposition (TTS) principle. To quantify the effect of the clay upon the rheology, the experimental data was compared to the time dependent diffusion model of Des Cloizeaux for polydisperse polymer melts, which enables polydispersity to be incorporated through the use of the molecular weight distribution obtained via SEC.
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Chen, Biqiong. "Polymer-clay nanocomposites." Thesis, Queen Mary, University of London, 2004. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1854.
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Polymer-clay nanocomposites are attracting global interest principally because property enhancements are obtained at low clay particle loadings (1-5 wt%). However there is lack of fundamental understanding of such composites. The aim of this work is to provide an insight into the interaction between polymer and clay. This includes the driving force for intercalation, the reinforcement mechanisms and property-volume fraction relationships. Functionalised poly(ethylene glycol)-clay, poly(c-caprolactone)-clay and thermoplastic starch-clay nanocomposites with a range of polymer molecular weights, clay volume fractions and with different clays were prepared using solution methods, melt-processing methods, and in situ polymerisation. A reliable X-ray diffraction technique for low angle basal plane spacing of clay, the essential parameter for structure determination, was established obtaining ±0.005 Mn between three diffractometers. The basal plane spacing was found to be unaffected by polymer molecular weight and preparation method but was affected by the nature of the polymer and clay. Increasing clay loading could lead to a lower spacing. As a cautionary observation, poly(ethylene glycol) with high molecular weight (2: 10,000) was found to undergo degradation readily during preparation of nanocomposites with and without clay. Competitive sorption experiments for molecular weight showed that high molecular weight fractions of polymer intercalate preferentially into clay during solution preparation. Thermodynamic studies on the intercalation process found that significant enthalpic change occurred during intercalation, which is coincident with the observation that heat-treated clays without interlayer water can intercalate polymer. The calculation of true volume fraction against nominal volume fraction provided reasonable explanation of property enhancement and helps understand the relation between nanocomposites and conventional composites. At a given clay loading, nanocomposites with better dispersion gave more property enhancement than those with lower dispersion or conventional composites. The crystallinity of semicrystalline polymer was also affected by varying extents of dispersion of clay. The use of X-ray diffraction with an internal standard was explored for quantitative analysis of intercalation and exfoliation.
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Wilde, James Richard. "Ni+TaC nanocomposites." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621704.
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Al-Shahrani, Abdullah A. "Layered silicate nanocomposites." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492712.
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Over the past decade, nanomaterials have been the subject of enormous interest. Notable for their extremely small feature size, they have the potential for wide-ranging industrial applications. Using such materials combined with epoxy resin to synthesise nanocomposite is proposed to enhance the corrosion protection performance of the resin.
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Green, Christopher Duncan. "Polyethylene-montmorillonite nanocomposites." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/65001/.
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Nanocomposite materials are currently attracting much interest due to their possibility of global property improvement – mechanical strength, toughness, electrical breakdown strength, electrical erosion resistance and flame retardancy. In order to disperse montmorillonite clay (MMT) into polyethylene (PE), the clay sheets need to be rendered organophilic. Masterbatches with a high level (~40 %wt) of organomodified clay can then be dispersed into a host by a simple mechanical process. Two chemically different masterbatches were purchased: Nanoblend 2101 from PolyOne Corp. and C30PE from Nanocor Inc. These were let down using a RandcastleTM single screw extruder with a patented mixing device to provide elongational flow. Wide angle X-ray diffraction was used together with transmission electron microscopy to evaluate the particle dispersion, which consisted of intercalated clay organised in clusters up to one micron in diameter. The performance of these materials was assessed in terms of AC ramp breakdown statistics, dielectric spectroscopy, dynamic and tensile mechanical properties. Nanoblend masterbatch consistently improved the breakdown statistics, more than overcoming the inherent demerit of extrusion, which mildly aged the unfilled material (as confirmed by Raman spectroscopy.) On the other hand, even low loading levels of Nanocor could result in reduced breakdown strength and increased scatter. Furthermore, both sets of materials demonstrated large dielectric losses at power frequencies and poorer performance under mechanical tension. These materials would therefore require considerable development before they could confidently be used commercially. The nature of the PE-MMT interactions was examined by investigating the crystallisation kinetics and resulting morphologies with differential scanning calorimetry and scanning electron microscopy. By varying the masterbatch type, loading level and crystallisation temperature, it was possible to study a wide range of supercrystalline morphologies using a permanganic etching technique. This is a useful contribution to the field of nanocomposites research. It is known that the morphologies of polymers can affect their mechanical properties and electrical treeing behaviour, and so it is possible that controlled crystallisation could provide a route toward designer materials with optimised behaviour.
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Paul, Anita N. "Silver-Polymer Nanocomposites." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etd/3077.
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The objective of this research was the development of an efficient method for the preparation of silver-polymer nanocomposites containing finely dispersed silver nanoparticles. The surface of nanosilver was functionalized by thiolation with 2-aminoethanethiol. Amino-modified nanosilver was covalently bonded to polyacrylic acid, biodegradable polymers like acid terminated polylactic acid, ester terminated poly(DL-lactide-co-glycolide) and acid terminated poly(DL lactide-co-glycolide) in the presence of diisopropylcarbodiimide by carbodiimide method. Esterification of the carboxyl groups of Ag-polyacrylic acid by hydrochloric acid in methanol resulted in the formation of a stable colloidal dispersion of Ag nanoparticles in the polymer matrix. It was observed that not just acid terminated polymers but also ester terminated polymers could react with functionalized nanosilver. This unusual reaction was due to the aminolysis of the ester bond in the polymer chain by the surface amino groups. Silver-polymer nanocomposites obtained with acid terminated polylactic acid and poly(DL-lactide-co-glycolide) contained highly dispersed nanosilver in the polymer matrix in comparison with the ester terminated poly(DL-lactide-co-glycolide). Chemical and structural characteristics of the obtained materials were studied by instrumental methods. Attained biodegradable materials confirmed X-ray contrast and bactericidal properties, which could be eventually used for biomedical applications.
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Liu, Yi. "Mesoporous silica/polymer nanocomposites." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31739.
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Thesis (Ph.D)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2010.Committee Chair: Jacob. Karl; Committee Member: Griffin. Anselm; Committee Member: Tannenbaum. Rina; Committee Member: Thio. Yonathan S; Committee Member: Yao. Donggang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Kulkarni, Amit [Verfasser]. "Magnetic nanocomposites / Amit Kulkarni." Kiel : Universitätsbibliothek Kiel, 2013. http://d-nb.info/1032171227/34.
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Wang, Hongzhi. "Perovskite based ceramic nanocomposites." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443007.
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Bilotti, Emiliano. "Polymer / Sepiolite Clay Nanocomposites." Thesis, Queen Mary, University of London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522330.
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Gill, Michael. "Polyaniline-silica colloidal nanocomposites." Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239632.
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The work presented in this thesis provides a new route to a colloidal form of polyaniline, which uses colloidal silica as a dispersant. We obtained stable colloidal dispersions of polyaniline-silica composite particles with a 'raspberry' morphology. Compressed pellets of these particles exhibit solid-state conductivities of 1O-!_10-2 S crrr l, which is approximately 1-2 orders of magnitude lower than that of polyaniline bulk powder. This novel colloidal form of polyaniline has significantly improved processability compared to conventionally synthesised polyaniline. The synthesis and chemical characterisations are presented for various polyaniline-silica colloidal nanocomposites. The quantity of polyaniline incorporated into the nanocomposite particles can be controlled by varying the diameter of the silica dispersant, approximately 20% and 60 % polyaniline content being obtained using 120 nm and 10 nm diameter silica respectively. The average particle size ranges of nanocomposites was found to be 150 to 700 nm and 330 to 560 nm, as determined by transmission electron microscopy (TEM) and disc centrifuge photosedimentometry (DCP) respectively. The nanomorphology and surface composition of the polyanilinesilica particles were determined by small angle X-ray scattering (SAXS) and X-ray photoelectron spectroscopy (XPS) respectively. The average inter-particle separation distance of the silica particles within the polyaniline-silica raspberries was determined by SAXS to be 4 nm, a dimension equivalent to molecular polyaniline. The XPS data suggests that the surface of the particles is silica rich, this is consistant with their long term colloidal stability in 1.2 mole dm-3 HCl. The kinetics of polymerisation was studied using 1H NMR spectroscopy to monitor the disappearance of aniline monomer. Polymerisation rates during the synthesis of polyaniline-silica nanocomposites were appreciably faster than the corresponding precipitation polymerisations carried out in the absence of silica dispersants, due primarily to an increase in the second auto-catalytic step of the reaction. Rate constants were determined for both these types of synthesis; the values obtained for the precipitation polymerisations were in reasonably good agreement with literature values.
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Lowe, David James. "Natural rubber/organoclay nanocomposites." Thesis, Queen Mary, University of London, 2012. http://qmro.qmul.ac.uk/xmlui/handle/123456789/2971.
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Natural rubber (NR)/organoclay nanocomposites were prepared using organomontmorillonite (OMMT) and organo-sepiolite (OSEP). Both were found to improve modulus significantly more than equivalent amounts of conventional fillers such as carbon black for strains up to 100%. OSEP was found to increase modulus more than OMMT for a given filler content, and NR/OSEP nanocomposites also had potentially anisotropic physical properties. OMMT had more effect on vulcanisation than OSEP, although both produced considerable acceleration. The tensile stress-strain behaviour of NR/OMMT and NR/OSEP nanocomposites were studied using a number of different micromechanical models. Some models were found to give a good empirical fit with experimental data, with the best results given by the Halpin-Tsai model. Furthermore, by analysis of the vulcanisation behaviour using rheometry, and particle morphology using transmission electron microscopy (TEM), it was possible to accurately estimate the Young's modulus of a nanocomposite from knowledge of the cure onset time and the shape factor of the particles. It was discovered that unmodified montmorillonite and sepiolite clays could undergo organic modi cation in situ during mixing into NR following the addition of a suitable modifier. This resulted in vulcanisates with very similar physical properties to those found when using pre-modified OMMT or OSEP. TEM and X-ray diffraction showed that the exfoliation state of the clay modified in situ was also similar to that of pre-modified organoclay. Silane coupling agents were also used with NR/OMMT and NR/OSEP nanocomposites, producing significant increases in modulus. However, the increased modulus was only observed above 40% strain for OMMT and above 25% for OSEP. The coupling agents strengthens the rubber- ller interface preventing interfacial slippage and cavitation in the nanocomposite, and these mechanisms only begin to operate when the interfacial stress reaches a significant level. The most effective coupling agent used was bis[triethoxysilylpropyl] tetrasulfide due to its relatively high reactivity.
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Hao, Qing. "Nanocomposites as thermoelectric materials." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61606.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
Thermoelectric materials have attractive applications in electric power generation and solid-state cooling. The performance of a thermoelectric device depends on the dimensionless figure of merit (ZT) of the material, defined as ZT = S2o-T / k, where S is the Seebeck coefficient, o is the electrical conductivity, k is the thermal conductivity, and T is the absolute temperature. In recent years, the idea of using nanotechnology to further improve the figure of merit of conventional thermoelectric materials has triggered active research and led to many exciting results. Most of the reported ZT enhancements are based on thin films and nanowires in which the thermal conductivity reduction plays a central role. We pursue the nanocomposite approach as an alternative to superlattices in the quest for high ZT materials. These nanocomposites are essentially nano-grained bulk materials that are synthesized by hot pressing nanoparticles into a bulk form. The interfaces inside a nanocomposite strongly scatter phonons but only slightly affect the charge carrier transport. Therefore, we can significantly reduce the lattice thermal conductivity and even somewhat increase the power factor S2 U, resulting in higher ZT than for bulk materials. Compared with expensive thin-film superlattices, nanocomposites will have significant advantages in mass production, device construction and operation. This thesis covers my studies on bismuth antimony telluride nanocomposites and some recent work on Co 4Sb12-based nanocomposites. In bismuth antimony telluride nanocomposites, we have achieved a peak ZT of 1.4 at 100 'C, a 40% increase in ZT over the bulk material. This is the first significant ZT increase in this material system in fifty years. The same approach has also yielded a peak ZT around 1.2 in Yb filled Co4Sbi 2 nanocomposites. During the process, great efforts were dedicated to assuring accurate and dependable property measurements of thermoelectric nanocomposites. In addition to comparing measurement results between the commercial setups and a homebuilt measurement system, the high ZT obtained in bismuth antimony telluride nanocomposites was further confirmed by a device cooling test. To better understand the measured thermoelectric properties of nanocomposites, theoretical analysis based on the Boltzmann transport equation was performed. Furthermore, frequency-dependent Monte Carlo simulations of the phonon transport were conducted on 2D periodic porous silicon and 3D silicon nanocomposites. In the thermoelectrics field, the latter one provided the first accurate prediction for phonon size effects in a given nanocomposite. For charge carriers in thermoelectric nanocomposites, their transport can be significantly affected by the interfacial electronic states. To address this, impedance measurements were conducted on nanocomposites to determine the electronic barrier height at the grain interfaces, which is critical for the detailed theoretical analysis of the interfacial charge transport and energy conversion processes. Although large amount of work has been done using this technique to understand the defect states and the barrier height on the grain boundaries of polycrystalline silicon or oxides, this method has not been applied to thermoelectric materials. Along another line, a simple bandgap measurement technique with nanopowders was developed based on the Fourier Transform Infrared Spectroscopy. This provided a convenient way to quickly check the bandgaps of various thermoelectric nanocomposites, which is also crucial for theoretical studies.
by Qing Hao.
Ph.D.
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Hackman, Ian. "Nanocomposites in civil engineering." Thesis, University of Surrey, 2007. http://epubs.surrey.ac.uk/844542/.
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Chemically treated layered silicates (clays) can be combined with normal polymer matrix materials to form a nanocomposite in which clay layers are distributed throughout the material. Previous researchers have shown that these high aspect ratio clays can alter the properties of a range of thermoplastic and thermosetting polymers by a number of mechanisms; improving mechanical and thermal properties and reducing permeability. This study involves the investigation of these novel materials to assess their potential applicability within the civil engineering industry and to assess in which areas and situations they might be used. Extensive research was conducted into the processing required for these materials to achieve sufficient organoclay exfoliation with a range of matrix materials. The subsequent nanocomposite materials were assessed using a range of characterisation techniques including XRD, TEM, SEM, OM, TGA, DSC and FTIR spectroscopy. Organoclay morphology was found to be highly dependent on the type of surfactant and curing agent used and resulted in a variety of different types of nanocomposite being formed. A variety of new manufacturing techniques were developed to generate void free and dimensionally consistent pure polymer and fibre composite specimens that allowed the frequently subtle property variations due to organoclay to be detected. A range of mechanical, thermal and durability properties were investigated to assess the differences that organoclay can generate when incorporated in the pure polymer and in a glass or carbon fibre composite. Mechanical testing of the pure polymer revealed small increases in tensile, flexural and compressive properties in glassy polymers; whereas in elastomeric polymers the properties can be improved by a factor of 3 due to the high relative properties of organoclay compared to the polymer. When incorporated in a fibre composite the organoclay offered little improvement when in a glass fibre composite but was able to increase the properties of a carbon fibre composite. It is thought that this increase does not occur due to increased mechanical properties of the polymer commensurate with the law of mixtures theory but due to changes in the fibre-matrix interphase. The permeability of nanocomposites when exposed to water was not improved, although the solvent permeability of some matrix materials was significantly reduced. Although a high degree of nanoscale exfoliation had been achieved, with highly separated clay platelets, the macroscale dispersion was not sufficient to result in reductions in Fickian water uptake via a tortuous path mechanism. Whereas, the reduction in solvent permeability was thought to arise from changes in the rate of polymer relaxations due to polymer chain mobility being constrained by organoclay and altering the rate of Case II uptake. The mechanical durability of pure polymer and glass fibre nanocomposites and the thermal durability of pure polymer nanocomposites were investigated. Little improvement was observed in the long-term durability properties of these materials after prolonged environmental conditioning as a result of organoclay. The influence that organoclay has on polymer chain constraint was investigated by DSC and DRS to assess which combinations of materials develop significant changes to the polymer network. It was found that the same nanocomposite formulations that resulted in reduced solvent uptake also resulted in increased thermal and reduced dielectric properties. Due to the requirement for high quality processing and the need to control cure cycle the implementation of nanocomposites would only be feasible within a premanufactured product and could not be used onsite with confidence until new and improved materials or processing methods are developed. Reductions in permeability would have to be improved to a level beyond that observed in this investigation and to a level witnessed in a only a few cases involving epoxy nanocomposites to warrant the additional expense of incorporating and processing organoclay It cannot currently be guaranteed that this level of permeability improvement would be established due to the limited number of cases in which this has been achieved. Therefore, the present state of the art does not allow sufficient improvements to be attained and the development of superior organoclays capable of becoming exfoliated with relative ease, or methods of processing that are proven to be highly effective, cost efficient, reproducible and rapid would be required before this technology could be applied to civil engineering materials. However, the future potential of nanocomposite materials remain significant and their application in civil engineering composites will offer significant advantages as the technology develops to allow economical processing and increased property advantages.
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Pillai, Karthik. "Bio-inspired Cellulose Nanocomposites." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/28575.
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Natural composites like wood are scale-integrated structures that range from molecular to the macroscopic scale. Inspired by this design, layer-by-layer (LbL) deposition technique was used to create lignocellulosic composites from isolated wood polymers namely cellulose and lignin, with a lamellar architecture. In the first phase of the study, adsorption of alkali lignin onto cationic surfaces was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Complete coverage of the cationic surface with alkali lignin occured at low solution concentration; large affinity coefficients were calculated for this system at differing pH levels. Adsorption studies with organosolv lignin in an organic solvent, and spectroscopic analysis of mixtures of cationic polymer with alkali lignin revealed a non-covalent interaction. The work demonstrated how noncovalent interactions could be exploited to molecular organize thin polyphenolic biopolymers on cationic surfaces. The second phase of the study examined the adsorption steps during the LbL assembly process to create novel lignocellulosic composites. LbL assembly was carried out using oxidized nanocellulose (NC) and lignin, along with a cationic polymer poly(diallyldimethylammonium chloride) (PDDA). QCM-D was used to follow the sequential adsorption process of the three different polymers. Two viscoelastic models, namely Johannsmann and Voigt, were respectively used to calculate the areal mass and thickness of the adsorbed layers. Atomic force microscopy studies showed a complete coverage of the surface with lignin in all the disposition cycles, however, surface coverage with NC was seen to increase with the number of layers. Free-standing composite films were obtained when the LbL process was carried out for 250 deposition cycles (500 bilayers) on a cellulose acetate substrate, following the dissolution of the substrate in acetone. Scanning electron microscopy of the cryo-fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle was estimated to be 17 nm. The third phase of the study investigated the effect of LbL ordering of the polymers versus a cast film composed of a blended mixture of the polymers, using dynamic mechanical analysis. A tan ï ¤ peak was observed in the 30 â 40 ºC region for both films, which was observed in the neat NC film. Heating of the samples under a compressive force produced opposite effects in the films, as the LbL films exhibited swelling, whereas the cast films showed densification. The apparent activation energy of this transition (65 â 80 kJ mol-1) in cast films, calculated based on the Arrhenius equation was found to be coincident to those reported for the ï ¢ transition of amorphous cellulose. The peak was seen to disappear in case of LbL films in the second heat, whereas it was recurring in case of cast films of the blended mixture, and neat NC films. Altogether, the together the work details a novel path to integrate an organized lignin and cellulose molecular structure, albeit modified from their native form, into a three-dimensional composite material.Ph. D.
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Cao, Feina. "Shape Memory Polyurethane Nanocomposites." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1201922381.
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Rocco, Frédéric. "Matériaux nanocomposites pour l'optique." Bordeaux 1, 2007. http://www.theses.fr/2007BOR13494.
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Les effets intrinsèques de confinement et les fortes interactions aux interfaces, caractéristiques des nano-objets sont à la base de nouvelles propriétés optiques telles que l’émission de lumière, l’absorption ou l’exaltation de la réponse optique non linéaire qui dépendent fortement de l’environnement des nano-objerts et de leur couplage avec celui-ci. Notre but est d’élaborer ces nano-systèmes basés sur la mise en interaction de deux matériaux différents à l’échelle nanométrique afin d’étudier et d’analyser l’origine physique de leurs propriétés optiques linéaires et non linéaires. Nous nous sommes intéressés aux propriétés des systèmes mixtes ou composites suivants : métal / luminophore Agn / Agmx+, semi-conducteur / métal (CdS / Agn)Nanotools show confinement effects and high interactions from their surface. They are th support of new optical properties like photoemission, absorption or non linear optical emission The modification of intrinsic effects depends of the environment and the coupling wit nonmaterials. The aim of this work is to synthesize nanocomposite materials (mixing two differen types of materials) for optics in order to analyse linear and non linear optical properties : Metal Phosphorus Ag / Ag x+ , semi-conductor / métal (CdS / Ag )
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Lossada, Toro Francisco Javier [Verfasser], Andreas [Akademischer Betreuer] Walther, and Rolf [Akademischer Betreuer] Mülhaupt. "Vitrimer-based bioinspired nanocomposites." Freiburg : Universität, 2021. http://d-nb.info/1236550900/34.
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Rafiq, Rehman. "Nylon 12/graphene nanocomposites." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10069.
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A unique combination of excellent mechanical, thermal and barrier properties has made graphene a multifunctional reinforcement for polymers. The goals of this research were to prepare exfoliated functionalized graphene sheets (FG) from expanded graphite, the uniform dispersion of these graphene sheets in the nylon 12 matrix, and understanding the effect of graphene on mechanical, thermal and barrier properties of nylon 12. FG were successfully prepared from various methods and was confirmed by XPS and TEM analysis. FG were melt blended with nylon 12 and their dispersion in the matrix was characterized by SEM. Crystallization behaviour of Nylon 12/ FG was investigated by means of differential scanning calorimetery (DSC). Non isothermal crystallization analysis revealed that the addition of only 1wt% FG in nylon 12 improved its crystallinity to about 67%. Application of Avrami analysis; to study isothermal crystallization kinetics; disclosed an unchanged nucleation mechanism and growth geometry. Polarized optical microscopy (POM) results indicated that FG did act as nucleating agent but hindered the formation of larger size crystals. Study of mechanical performance revealed that the incorporation of very small amount (about 0.6wt %) of the FG caused a significant improvement in ultimate tensile strength, elongation, impact strength and toughness of the nylon 12. With 0.6wt% FG ultimate tensile strength and elongation at break of the nylon 12 is improved by ~ 35% and ~ 200%, respectively. FTIR confirmed the hydrogen bonding between nylon 12 and FG, which contributed towards strengthening of the interface. The KIc of the nylon 12 is ~ 1.28 MPa.m0.5 and the incorporation of 0.6wt% FG causes a significant increase of 72 % (~ 2.2 MPa.m0.5). 0.6wt% FG causes also a significant improvement of 175 % in impact failure energy of the nylon 12. The incorporation of FG caused the increase in amount of γ phase of nylon12 and decreased its crystal size which could be the direct reason for the enhancement of the toughness. Nano-graphite, MWCNTs and carbon black were surface functionalized and their effect on the toughness was investigated. The results proved graphene to be the best nanofiller among three for the toughening of nylon 12. Oxygen and water permeability of nylon 12 was decreased to ~40%, implying the high aspect ratio of graphene which forced the permeant to pass through longer path.
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Işık, Kıvanç Tanoğlu Metin. "Layered silicate/polypropylene nanocomposites/." [s.l.]: [s.n.], 2006. http://library.iyte.edu.tr/tezler/master/makinamuh/T000532.pdf.
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Dai, Prè Marta/M. "Nanocomposites for optical applications." Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3422168.
Full textAbstract:
Nanotechnology is one of the most important fields in the last decades because novel material development involve chemistry, physics, the medicine and also engineering science.
Nanomaterials exhibit size-dependent properties and large surface to volume ratio which can be exploited in a number of applications especially in the optical field.
The main work presented here regards the synthesis of the nanocomposites using different methods, according to the desidered quality of the final material, the easiness and the industrial processability, the size control distribution and the homogeneous dispersibility.
The whole activity of my thesis project can be divided in two parts:
a) nanoparticles and nanocomposites for photovoltaic applications;
b)NIR emitting nanoparticles and nanocomposites.
The first part was partially founded by an European project, ORION, entitled "Optimization of Si solar cells, plastic materials and technologies for the development of more efficient concentRatION photovoltaic systems". The main objective of this project is base on the optimization of materials and technologies involved in Concentration PhotoVoltaic System production in order to reduce the system cost/watt and increase the system efficiency. The goal of my work is to study and develop plastic nanocomposites doped with down-converting nanoparticles for modification of the solar spectrum in order to enhance the absorption efficiency of solar cells. The functional properties of the obtained materials have to be fine-tuned to fulfil the customers' needs in terms of process ability and performance. The material must have good optical properties such as, transmittance of 85-90% for 1-2 mm and light-conversion from 300-500 nm to 600-900 nm. The most important polymers for optical applications is Polymethyl Methacrylate (PMMA).
Different kinds of NPs, ZnS:Mn, CdS:Mn and ZnO, that absorb in the UV range and emit in the visible range, have been synthesized with different colloidal techniques. Precipita\-tion-redispersion protocols have been set up in order to purify and concentrate the particles and transfer them into a suitable organic solvent to direct mixing with the polymer.
Furthermore the major part of the energy losses (~52%) is related to the spectral mismatch, known as thermal or quantum losses. A large part of high-energy photons is lost as heat through phonon scattering, resulting in the limitation of power conversion efficiency of Si solar cells. The ultraviolet (UV) part of the solar spectrum (about 7% of the entire solar
spectrum) cannot efficiently be used by Si solar cells.
So coating of the same nanoparticles were deposited on the front surface of solar cells and comparative electro-optical characterizations have been performed before and after the deposition of the nanostructures to determine the effect of antireflection and down-shifting on the efficiency.
The second part of the work was focused on the synthesis of PbSe nanoparticles (Quantum Dots) and core-shell nanoparticles with a PbSe core and a CdSe shell in order to increase the stability of emission properties of such materials. Then these nanoparticles were introduced in several matrix like Ormocer and PMMA keeping the photoluminescence properties. The future applications are optical microcavity incorporating quantum dots and lithography.Negli ultimi anni le nanotecnologie sono diventate uno dei maggiori campi di interesse e di rilevanza scientifica e la ricerca di nuovi materiali riguarda la chimica, la fisica, la medicina e anche l'ingegneria. I nanomateriali vengono classificati in base alla loro dimensione ed al rapporto superficie/volume, caratteristiche che permettono il loro impiego in numerose applicazioni, soprattutto nel campo ottico. In questi lavoro di tesi sono stati valutati differenti nanocompositi sintetizzati con tecniche messe a punto in modo tale da ottenere peculiari caratteristiche di dimensione, distribuzione, omogeneità e di facile produzione, anche a livello industriale. Il progetto di dottorato può essere suddiviso in due parti: a) nanoparticelle e nanocompositi per applicazioni nel fotovoltaico; b) nanoparticelle e nanocompositi che emettono nel NIR. La prima parte del lavoro si inserisce nel progetto Europeo ORION, ovvero "ottimizzazione di celle solari al silicio, materiali plastici e tecnologie per lo sviluppo di più efficienti sistemi fotovoltaici a concentrazione". Ha riguardato principalmente la messa a punto di materiali e di tecnologie dei sistemi a concentrazione tali da riuscire a ridurre il rapporto costo/watt ed aumentare l'efficienza. Sono stati quindi studiati e sviluppati nanocompositi plastici contenenti nanoparticelle che sono in grado di modificare lo spettro solare e di aumentare di conseguenza l'efficienza di assorbimento delle celle solari. Inoltre le proprietà funzionali dei materiali sviluppati sono state messe a punto in termini di processabilità e di prestazioni. Infatti il materiale deve avere buone proprietà ottiche tra cui una trasmittanza dell'85-92% per 1-2 mm di spessore ed una conversione della luce nel range tra 300-500 nm e 600-900 nm. Il polimetilmetacrilato (PMMA) è risultato essere il polimero di selezione per applicazioni ottiche. Diversi tipi di nanoparticelle che assorbono nell'UV, tra cui ZnS:Mn, CdS:Mn e ZnO, sono state sintetizzate utilizzando tecniche colloidali. Sono stati messi a punto protocolli di precipitazione-ridispersione in modo da purificare, concentrare le nanoparticelle e ridisperdere in seguito in appositi solventi organici, dove è solubile anche il PMMA. Dal momento che la maggior parte dell'energia dissipata (~ 52%) dipende dal mismatch spettrale, definito come perdita termica o quantica, mentre la grande parte ad alta energia viene persa sotto forma di calore legato allo scattering di fotoni e quindi riduce maggiormente l'efficienza di conversione dell'energia delle celle solari a base di silicio. La parte dell'ultravioletto (UV) dello spettro solare (circa 7% dell'intero spettro) non può essere sfruttato completamente dalle celle solari al Si. Sono state così valutate le caratteristiche elettro-ottiche prima e dopo deposizione sulla superficie delle celle solari delle stesse nanoparticelle inserite nel polimero determinando l'effetto antiriflesso e della down-shifting sull'efficienza. La seconda parte del lavoro si è focalizzata sulla sintesi di nanoparticelle di Seleniuro di Piombo (PbSe) and di core-shell, dove l'interno di PbSe è rivestito da uno strato di CdSe, così da stabilizzare le proprietà di emissione di questi materiali. Infine queste nanoparticelle sono state incorporate in diverse matrici, tra cui Ormocer e PMMA mantenendo le loro proprietà di luminescenza. Questi nuovi materiali trovano future applicazioni in microcavità ottiche che incorporano quantum dots e litografia.
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MUREDDU, MAURO. "Mesostructured metal oxide-based nanocomposites as sorbents for H2S removal from syngas coal gasification." Doctoral thesis, Università degli Studi di Cagliari, 2015. http://hdl.handle.net/11584/266555.
Full textAbstract:
Desulphurization of gas phase sulphur compounds has been receiving dramatic attention since
hazardous, corrosive, and toxic gases that cause environmental damages (especially acid rain) and
industrial challenges (i.e., corrosion of equipment and deactivation of catalysts).
This dissertation presents results of R&D efforts to develop efficient MeOx/SBA-15-based sorbents
for H2S removal in view of possible applications in hydrogen purification, air pollution control, and deep
desulphurization of fossil fuels. It is precisely in the latter topic that the research project was born. The
production of power, fuels and chemicals in most countries is predominantly based on oil and, to a minor
extent, on natural gas. It is well-known that the reserves of both of these fuels are limited to a range of
40, 60 years. On the contrary, coal is a widely available fossil fuel, and it is expected to last for about
230 years. The imminent oil production limitations and the longer availability of coal, the wish to improve
the security of the energy supply, and the possibility to reduce greenhouse gas emissions by means of
carbon capture and sequestration (CCS) are sufficient motivations to increase the use of this resource.
Integrated Gasification Combined Cycle (IGCC) process is a high efficiency power generation technology
which gasifies coal to generate the fuel (syngas) for a high efficiency gas turbine. A key challenge for
producing clean power or hydrogen via gasification is cost effective purification of the sour syngas.
There are many commercial treatment techniques that are used to remove H2S, but their disadvantage is
that hot coal gas must be cooled down near to ambient temperature for desulphurization. The cooling
equipment required, and the need to reheat the clean syngas before its use in a gas turbine result in
economic and thermodynamic penalties that decrease the efficiency of a gasification plant. It is for this
reason that hot gas desulphurization technique has attracted more and more attention due to the fact
that it can reduce H2S down to 100 ppm level and avoid heat loss. Mid-temperature desulphurization is
achieved by the use of solid sorbents such as oxides of those metals that form stable sulphides, based on
the non-catalytic reaction between a metal oxide and hydrogen sulphide. The optimum desulphurization
temperature has been recommended in the range of 300 to 450 °C, also in according to the more
favourable thermodynamic equilibrium of sulphur compounds removal. To accomplish this task, Zinc
oxide- and Iron oxide-based materials have been successfully employed for decades in different domains
of the chemical industry. The pure metal oxides used as sorbents, however, suffer from evaporation, loss
in the surface area and porosity due to sintering and mechanical disintegration that affect their
performance and life time adversely. With the purpose of overcoming this problem and to improve their
performance, metal oxides can be confined into a support, where under such conditions the materials
are stable. The main properties required for support materials are inertness, high surface area, large
pores and good mechanical strength.
The thesis reports some simple and versatile routes which can be proposed to prepare a great
variety of MeOx/SBA-15 composites where the mesostructured SBA-15 silica, a high-surface area (up to
1000 m2/g) material, with 6–7 nm-wide regular channels and thick (3–4 nm) pore walls has been used as
efficient and stable support. MeOx active phase, formed inside the mesochannels, can reach the maximum
size of 6-7 nm physically imposed by the pore diameter. Such a structure provides an ideal reactor
where the mesopores act as channels for the transport of reactant. As a consequence, enhancement of
the active phase reactivity might be expected. The proposed “Two-solvents” incipient impregnation
method is easily reproducible and easy to scale up. Furthermore, this method should provide, at least in
principle, ideal systems to be compared, and therefore to understand how the active phase nature
influence their performance.
For the first time, a careful comparative study on the effect of the different nature of the
nanostructured MeOx (Me = Zn, Fe) dispersed into a mesostructured silica matrix (SBA-15) on the H2S
removal performance is carried out.
The behaviour of the MeOx/SBA-15 composites in the removal of H2S is investigated in a fixed-bed
reactor and compared with that of an unsupported ZnO commercial sorbent. The morphological,
structural, and textural features of fresh, sulphided, and regenerated sorbents have been assessed by a
multi-technique approach, including the study of the possible interactions between the guest oxide and
the host silica support. Furthermore, the sorption-desorption behaviour, which is commonly justified only
on the basis of the different nature of the active phase and of the textural features (surface area and
pore volume), is discussed also considering the morphology and the crystallinity of the active phase.
In the literature, to our best knowledge, no one have reported similar correlations. For this reason
this work can give an important contribution to improve the basic knowledge in the field of sorbents for
gas-removal.
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Njoroge, Daniel [Verfasser]. "Thesis: Preparation and characterization of modified-graphene oxide/polypropylene nanocomposites : polypropylene nanocomposites / Daniel Njoroge." Berlin : epubli, 2016. http://www.epubli.de/.
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Lonkar, S. P. "New nanocomposites with improved properties: Elaboration, characterization, properties and durability of PP/LDH nanocomposites." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2010. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3720.
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Kvien, Ingvild. "Characterization of Biopolymer Based Nanocomposites." Doctoral thesis, Norwegian University of Science and Technology, Department of Engineering Design and Materials, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1479.
Full textAbstract:
The field of nanocomposites is gaining considerable attention due to its potential for providing new materials with extraordinary physical properties compared to traditional composite materials. In this thesis cellulose nanowhiskers (CNW) were separated from microcrystalline cellulose (MCC) and dispersed in different biopolymer matrices to obtain polymer nanocomposites based on renewable resources. Moving from microstructure to nanostructure creates new challenges for structure characterization of materials. The overall aim of this work was to characterize the structure of CNW and their nanocomposites with different matrices. The sample preparation and microscopic examination of the bionanocomposites showed to be challenging because they are non-conductive, soft and water sensitive materials and consist of low atomic number elements. In the studies field emission scanning electron microscope was found to be a convenient and important first step in the analysis of the nanocomposite structure. More detailed information about the distribution of CNW was however obtained using transmission electron microscope (TEM) and atomic force microscope. X-ray diffraction analysis showed that the MCC consisted of both amorphous and crystalline regions. The sulfuric acid isolation treatment removed the amorphous regions and separated the cellulose nanowhiskers. From TEM analysis the size of the whiskers was measured to be 210 ± 75 nm in length and 5 ± 2 nm in width. It was also possible to separate the CNW from MCC using dimethyl acetamide containing a small amount of LiCl. It was however difficult to remove the organic solvent after treatment. CNW were well distributed in a hydrophobic matrix by the aid of a surfactant. Untreated CNW or untreated layered silicates in a thermoplastic starch matrix resulted in well dispersed nanocomposites. It was further found that it was possible to obtain oriented CNW in a matrix after exposure to a magnetic field. The dynamic mechanical thermal analysis of the different nanocomposites in this thesis showed that well dispersed cellulose whiskers have a large potential for improving the thermal mechanical properties of biopolymers.
Paper VII: The original publication is available at www.springerlink.com
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Isik, Isil. "Impact Modified Polyamide-organoclay Nanocomposites." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608353/index.pdf.
Full textAbstract:
The effects of melt state compounding and addition order of ethylene-butyl acrylate-maleic anhydride (E-BA-MAH), ethylene-glycidyl methacrylate (E-GMA), ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) terpolymer and/or three types of organoclays (Cloisite®15A, 25A and 30B) on morphology, thermal, mechanical and dynamic mechanical properties of polyamide-6 are investigated. XRD patterns show that the interlayer spacing for Cloisite®
15A remained unchanged
however it increased for the organoclays Cloisite®
25A and Cloisite®
30B in both polyamide-6/organoclay binary nanocomposites and in polyamide-6/organoclay/impact modifier ternary systems. TEM analyses indicate that exfoliated-intercalated nanocomposites are formed. Sizes of elastomeric domains in nanocomposites are larger than the domains in their corresponding blends. The MFI results show that incorporation of elastomer reduces the MFI, due to the formation of graft copolymer. Both storage and loss moduli and complex viscosity of polyamide-6 increase with organoclay addition. In DMA measurements, in rubbery region, all nanocomposites show higher storage modulus than the unfilled counterparts. In general, the organoclays increase tensile and flexural strength, Young&
#8217
s and flexural modulus and elongation at break, but decrease the impact strength, on the contrary, the addition of elastomer has the opposite effect. Generally, Cloisite®
15A containing ternary nanocomposites have higher tensile, flexural and impact strength and Young&
#8217
s and flexural modulus than the ternary nanocomposites prepared with Cloisite®
25A and Cloisite®
30B. In general, nanocomposites processed by adding all the ingredients simultaneously give higher tensile and flexural strength and modulus than the nanocomposites produced by other mixing sequences.
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Yeniova, Canan Esma. "Impact Modified Polystyrene Based Nanocomposites." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610306/index.pdf.
Full textAbstract:
Polystyrene, PS, is a preferable polymer in industry, but, its brittle characteristic restricts its utilization. The aim of this study is to improve the impact strength of PS by the help of elastomeric materials SEBS-g-MA and E-BA-GMA. In order to prevent the reduction in the tensile strength of the materials, three different types of organic montmorillonites, MMT, (Cloisite®30B, 25A and 15A) were used as fillers. Nanocomposite preparation was performed in a co-rotating twin screw extruder. Initially elastomer and organoclay contents were kept at 5wt% and 1-2wt% respectively. Well dispersed silicate layers were obtained for the nanocomposite containing SEBS-g-MA and Cloisite®
25A owing to the high viscosity of SEBS-g-MA and the solubility of polystyrene end block of SEBS with PS matrix. Owing to higher hydrophobicity of Cloisite®
15A a better dispersion was expected compared to Cloisite®
25A, but, it was concluded that two long aliphatic tails of Cloisite®
15A limited the access of polymer chains to the clay surface. The desired impact strength values could not be achieved by using 5wt% elastomeric materials
therefore, it was decided to increase the SEBS-g-MA content up to 15, 20, 30 and 40wt%. With increasing elastomer content, increasing average elastomer domain size was obtained. Also, it was observed that with the addition of organoclay, the elastomeric domain size increases since the clay particles reside in the elastomer phase and at the interphase between elastomer and PS. The mechanical test results showed that the nanocomposites containing 15 and 20wt% SEBS-g-MA have the optimum average domain size that results in better impact strength values without deteriorating tensile properties.
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Isitman, Nihat Ali. "Flame Retardancy Of Polymer Nanocomposites." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614258/index.pdf.
Full textAbstract:
This thesis is aimed to understand the role of nanofiller type, nanofiller dispersion, nanofiller geometry, and, presence of reinforcing fibers in flame retardancy of polymer nanocomposites. For this purpose, montmorillonite nanoclays, multi-walled carbon nanotubes, halloysite clay nanotubes and silica nanoparticles were used as nanofillers in polymeric matrices of poly (methyl methacrylate) (PMMA), high-impact polystyrene (HIPS), polylactide (PLA) and polyamide-6 (PA6) containing certain conventional flame retardant additives. Furthermore, the influence of nanofiller and flame retardant additives on fiber/matrix interfacial interactions was studied.
Materials were prepared by twin-screw extrusion melt-mixing and ultrasound-assisted solution-mixing techniques. Characterization of nanocomposite morphology was done by X-ray diffraction and transmission electron microscopy. Flame retardancy was investigated by mass loss cone calorimetry, limiting oxygen index measurements and UL94 standard tests. Flame retardancy mechanisms were revealed by characterization of solid fire residues by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy and X-ray diffraction. Thermal degradation and stability was studied using thermogravimetric analysis. Mechanical properties were determined by tension tests and fracture surfaces were observed under scanning electron microscope.
Influence of nanofiller type was investigated comparing the behavior of montmorillonite nanoclay and multi-walled carbon nanotube reinforced PMMA nanocomposites containing phosphorous/nitrogenous intumescent flame retardant. Carbon nanotubes hindered the formation of intumescent inorganic phosphate barrier which caused the samples to be exposed to larger effective heat fluxes during combustion. Contrarily, nanoclays physically reinforced the protective barrier without disrupting the intumescent character, thereby allowing for lower heat release and mass loss rates, and increased amounts of residue upon combustion.
Influence of nanofiller dispersion was studied comparing nanocomposite and microcomposite morphologies in montmorillonite nanoclay reinforced HIPS containing aluminum hydroxide flame retardant. Relative to microcomposite morphology, reductions in peak heat release rates were doubled along with higher limiting oxygen index and lower burning rates with nanocomposite formation. Improved flame retardancy was attributed to increased amounts of char residue and lower mass loss rates. Nanocomposite formation allowed for the recovery of tensile strength reductions caused by high loading level of the conventional flame retardant additive in polymer matrix.
Influence of nanofiller geometry was investigated for phosphorus based intumescent flame-retarded PLA nanocomposites. Fire performance was increased in the order of rod-like (1-D) <spherical (0-D) <
<
plate-like (2-D) geometries which matched qualitatively with the effective surface area of nanoparticles in the nanocomposite. Well-dispersed plate-like nanoparticles rapidly migrated and accumulated on exposed sample surface resulting in the formation of strong aluminum phosphate/montmorillonite nanocomposite residue. Mechanical properties were increased in the order of 0-D <
1-D <
2-D nanofillers corresponding to the order of their effective aspect ratios in the nanocomposite. Influence of fiber reinforcement was studied for montmorillonite nanoclay containing short-glass fiber-reinforced, phosphorus/nitrogen based flame-retarded PA6 composites. Substitution of a certain fraction of conventional additive with nanofiller significantly reduced peak heat release rate, delayed ignition and improved limiting oxygen index along with maintained UL94 ratings. Improved flame retardancy was ascribed to the formation of a nanostructured carbonaceous boron/aluminum phosphate barrier reinforced by well-dispersed montmorillonite nanolayers. Fiber/matrix interfacial interactions in flame-retarded PA6 and HIPS containing nanoclays were investigated using a micromechanical approach, and it was found that the influence of nanoclay on the interface depends on crystallinity of polymer matrix. While the fiber/matrix interfacial strength is reduced with nanoclay incorporation into amorphous matrix composites, significant interfacial strengthening was imparted by large surface area, well-dispersed clay nanolayers acting as heterogeneous nucleation sites for the semi-crystalline matrix.
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Prokhorenko, Sergei. "Multiscale modeling of multiferroic nanocomposites." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2014. http://www.theses.fr/2014ECAP0045/document.
Full textAbstract:
Au cours des dernières décennies, la recherche de nouveaux matériaux multiferroïques nanostructurés avec des propriétés optimisées a conduit à l'élaboration d'une grande variété de modèles théoriques et des approches de simulation. Allant des modèles ab initio capables de décrire les propriétés à la température nulle des composés artificiels monocristallins à des approximations phénoménologiques pour la description des composites à la mésoscopique, ces recherches ont soulevé la question fondamentale de la relation entre la géométrie de la structure des systèmes hétérogènes et les propriétés des leurs transitions de phase. Cependant, malgré des progrès significatifs en la matière,cette question n'a pas encore été élucidée et les relations entre les modèles à différentes échelles ne sont pas entièrement distingués. La présente étude est consacrée à lier l’ensemble des modèles décrivant les matériaux nanocomposites multiferroïques à différentes échelles. Tout d'abord, nous présentons un développement méthodologique de l'approche Hamiltonien effectif couramment utilisé pour étudier les transitions de phase structurales. Les modifications introduites permettent d'étendre cette méthode pour prédire les propriétés à la température finie des systèmes hétérogènes. Le modèle construit est ensuite utilisé pour étudier les propriétés des nanostructures et solutions solides (BiFeO3)(BaTiO3). Recourant à des simulations Monte-Carlo, nous montrons que notre modèle fournit des résultats qui sont en ligne avec les observations expérimentales récentes et qu’il permet de prédire théoriquement les propriétés d'une large gamme de systèmes avec différentes géométries composites. La deuxième partie de l'étude consiste en l'application de la théorie de Ginzburg-Landau des transitions de phase à l’étude des propriétés des multicouches ferroélectriques et ferromagnétiques avec des interfaces épitaxiales. Plus précisément, nous décrivons théoriquement l’effet magnétoélectrique exhibé par les hétérostructures autonomes Pb(Zr0.5 Ti0.5) O3-FeGaB et BaTiO3-FeGaB. Enfin, nous montrons que la géométrie multicouche d'un nanocomposite ferroélectrique et ferromagnétique ouvre la voie à une amélioration radicale du signal de charge de sortieDuring past decades, the search for new nanostructured multiferroic materials with optimized properties has lead to the development of a vast variety of theoretical models and simulation approaches. Spreading from first principles based models able to describe zero-temperature properties of artificial single crystal compounds to phenomenological approximations for composites with mesoscale morphology, these investigations have raised the fundamental question of how the geometry of the structure affects the properties of phase transitions exhibited by heterogeneous systems. However, despite significant progress, the answer to this question still lacks clarity and the bridge connecting models at different scales is not fully constructed. The current study is devoted to linking together models of multiferroic nanocomposite materials applicable at different scales. First, we present a methodological development of effective Hamiltonian approach commonly used to study structural phase transitions. The introduced modifications allow to extend this widely used method to predict finite-temperature properties of compositionally heterogeneous systems. The constructed model is then used to study properties of (BiFeO3)(BaTiO3) nanostructures and solid-solutions. Resorting to Monte-Carlo simulations, we show that our model provides results that are in-line with recent experimental observations and allows to theoretically predict properties of a wide range of systems with different composite geometries. The second part of the study consists inapplication of Landau theory of phase transitions to investigate the properties of ferroelectric-ferromagnetic multilayerswith epitaxial interfaces. Specifically, we theoretically describe the strain-mediated direct ME effect exhibited byfree-standing Pb(Zr0.5 Ti0.5 )O3 -FeGaB and BaTiO3 -FeGaB heterostructures. Finally, we show that the multilayer geometry of a ferroelectric-ferromagnetic nanocomposite opens the way for a drastic enhancement of the output charge signal
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Aubrit, Florian. "Films nanocomposites plasmoniques auto-assemblés." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0727/document.
Full textAbstract:
Les métamatériaux sont des matériaux artificiels, formés par l’assemblage de nano-résonateurs, qui ont la capacité d’interagir avec les ondes qui les traversent et de conférer des propriétés inaccessibles aux matériaux homogènes. Afin de fabriquer de tels métamatériaux agissant dans le domaine du visible, un contrôle précis de l’organisation des résonateurs à l’échelle nanométrique est requis. Dans ce projet nous avons donc élaboré des voies de fabrication de type bottom-up, en organisant de façon anisotrope des nanoparticules d’or (AuNPs), qui sont des résonateurs du fait de leurs propriétés plasmoniques, dans un film de copolymères à blocs poly(styrène)-b-poly(vinylpyridine) (PS-b-PVP) nano-structuré en rangées de cylindres de PVP perpendiculaires au substrat.Au cours de ce projet, nous avons élaboré des routes de formulation permettant de produire des films de phase cylindrique hexagonale de copolymères alignés contenant des nanoparticules d’or. L’orientation des cylindres perpendiculaires au substrat a été obtenue en déposant le copolymère grâce à un solvant neutre dont la composition dépend de la fraction volumique en PVP du copolymère. La structure des films avec et sans nanoparticules a été caractérisée par microscopie et diffusion des rayons X en incidence rasante (GISAXS). Plusieurs méthodes d’incorporation des nanoparticules d’or ont été étudiées, soit en synthétisant les nanoparticules au sein du copolymère, en solution avant dépôt ou directement dans le film organisé ; soit en incorporant des nanoparticules pré-formées, en solution de copolymère ou dans le film déposé. Dans le cas de la synthèse in situ, nous avons formé les AuNPs par réduction chimique ou physique (sonication, radiolyse) d’un sel d’or dans le copolymère. L’incorporation des AuNPs pré-formées, elle, a été réalisée grâce à la fonctionnalisation des AuNPs ou par un traitement du film de copolymère afin de faciliter l’insertion des AuNPsMetamaterials are artificial materials, made from the assembly of nano-resonators, which can interact with incoming waves and get properties unknown for homogeneous materials. In order to fabricate metamaterials with an effect over visible light, a precise control over the organization at the nanoscale is required. The goal of this project was then the use of bottom-up approaches to achieve the anisotropic organization of gold nanoparticles (AuNPs), which are resonators due to their plasmonic properties, into a poly(styrene)-b-poly(vinylpyridine) block copolymer film, with a nanostructuration in arrays of PVP cylindrical domains perpendicular to the substrate.During this work, we investigated routes for the fabrication of copolymer films containing ordered gold nanoparticles in a hexagonal cylindrical phase. The orientation of the cylinders normal to the substrate was obtained by casting the copolymer with a neutral solvent whose composition was found dependent on the volumic fraction of PVP in the copolymer. The film structure with and without AuNPs was characterized by microscopy and Grazing-Incidence Small-Angle X-rays Scattering (GISAXS). Several incorporation methods for the insertion of AuNPs were studied, either by the in situ synthesis of the nanoparticles in solution before casting or directly into the ordered film; or by incorporating pre-formed AuNPs in the copolymer solution or in the film as-cast. In the case of the in situ synthesis, the AuNPs were formed by chemical or physical (sonication, radiolysis) reduction of a gold salt in the copolymer. The incorporation of pre-formed AuNPs was, achieved thanks to the functionalization of the AuNPs or by a treatment of the copolymer film in order to facilitate the insertion of the AuNPs
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Brown, Elvie Escorro. "Bacterial cellulose/thermoplastic polymer nanocomposites." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Spring2007/e_brown_050207.pdf.
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Maniar, Ketan K. "A literature survey on nanocomposites." Full text available online (restricted access) Full text available online (restricted access), 2002. http://images.lib.monash.edu.au/ts/theses/maniar.pdf.
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Saxena, Amit. "Nanocomposites based on nanocellulose whiskers." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47524.
Full textAbstract:
Environmental concerns arising from the use of non-degradable plastics have resulted in search for suitable substitutes. The thesis deals with new nanostructured composites based on reinforcement of nanocellulose whiskers in "green" polymers such as xylan. Since the reinforcement filler and the matrix are both biobased and are thereby environmental friendly. Xylan incorporated with cellulose whiskers films provided with improved water and oxygen barrier properties. It appears that the high degree of crystallinity of cellulose whiskers, dense composite structure formed by the whiskers and rigidly hydrogen-bonded cellulose whiskers can cause cellulose whiskers to form integrated matrix which contribute to substantial benefit in the overall reduction of transmission rate. The spectral data obtained for the NCW/xylan nanocomposite films showed that the amount of xylan adsorbed to cellulose increases with the addition of NCW in the matrix. In addition, NMR T2 relaxation experiments studies were conducted to investigate the change in the nature of carbohydrate-water interactions as a result of NCW incorporation. These results facilitated an improved understanding of the mechanisms involved in the superior barrier and mechanical properties of xylan-whisker nanocomposite films. XRD studies show that when a xylan-whisker nanocomposite films is formed the mixing occurs on the atomic scale and NCW loading increases the matrix crystallinity.
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Nassar, Nashaat. "Melt exfoliation in montmorillonitepolystyrene nanocomposites." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19613.
Full textAbstract:
Polymer clay nanocomposites (PCN) exhibit many advantages over conventional composites, while using substantially smaller quantities of filler. For various reasons, it is desirable, in nanocomposite manufacturing, to employ processes based on melt exfoliation of modified clay particles. While various researchers have studied the effects of processing variables and material properties on the effectiveness of melt exfoliation, many issues remain unresolved. This study attempts to deal with some of these. In this study an amorphous polymer, atactic polystyrene (PS), has been chosen to avoid complications related to crystallization. Three grades of (PS), having different molecular weight, were pre-blended with Cloisite® 1OA (a modified montmorillonite) in a twin-screw extruder (TSE). The TSE blends were subsequently fed to a single screw extruder, fitted with one of three specially designed attachments at the front of the screw. The attachments were designed to provide combinations of shear and elongational deformations. The resins, TSE blends, and final nanocomposites were characterized for the degree of exfoliation, mechanical properties, and rheological behavior using capillary and rotational rheometers, FTIR, XRD and TEM. The effects of molecular weight, mixing time, and levels of shear and elongational stresses, on the degree of intercalation and the properties of the nanocomposites were studied. Surprisingly, the complex and shear viscosities of the nanocomposites were found to be lower than the corresponding viscosities of the virgin polystyrene. Intercalation was achieved with in a short residence time. However, the degradation of the clay intercalant increased with residence time which causes degradation of PS.
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Borse, Nitin. "Melt processing of thermoplasticclay nanocomposites." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102777.
Full textAbstract:
Polymer/clay nanocomposites are materials composed of a polymer matrix and nanometer size clay particles. They exhibit significant improvements in tensile modulus and strength, reduced permeability to gases and liquids, compared to the pure polymer. These property improvements can be realized while retaining clarity of the polymer without a significant increase in density (typical clay loading is 2--5%). The aim of this research was to achieve maximum exfoliation of the clay and property enhancement in the nanocomposite by melt processing.The components of the Hansen solubility parameters and the Hamaker constants of the constituents were used to establish the compatibility between the polymer matrix and nanoclay. A mathematical model was formulated to study the mechanism of exfoliation of clay platelets in the polymer matrix. The mechanism of size reduction of clay particles was shown to be by erosion or surface peeling. A novel continuous process (System A) was developed and implemented to produce nanocomposites. The process incorporates chaotic mixing, efficient shearing and stretching of the melt, frequent changes in flow direction and higher residence time, in order to enhance exfoliation.
The efficiency of the process was demonstrated, using transmission electron microscopy, wide angle X-ray diffraction, viscosity measurements, tensile and highspeed impact testing, and oxygen permeability measurements. Polyamide nanocomposites prepared with System A show a higher degree of exfoliation and better enhancements in mechanical and barrier properties than those prepared using conventional twin-screw extrusion (System C). Polystyrene nanocomposites show higher increase in the d-spacing of organoclay and improvement in barrier properties for System A than for System C, indicating higher specific surface area for the filler particles. The Pukanszky parameter was negative for PS nanocomposites, indicating poor polymer/clay adhesion.
The crystallization kinetics of PA-6 nanocomposites were studied using high pressure dilatometry. The nanoclay seems to act as nucleating agent, increasing the rate of crystallization of PA-6 in the nanocomposite. The effect of the clay on the kinetics of formation of different PA-6 crystalline phases was evaluated and explained.
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Hasell, Tom. "Synthesis of metal-polymer nanocomposites." Thesis, University of Nottingham, 2008. http://eprints.nottingham.ac.uk/10495/.
Full textAbstract:
This thesis details the synthesis and characterisation of novel nanocomposite materials. The unifying theme of all the projects investigated, is the aim to combine metal or metal oxide nanoparticles with polymer systems. In order to investigate the structure of the materials produced, the extensive use of advanced electron microscopy techniques is essential throughout. Chapter 1: This introductory chapter outlines key themes that are relevant to all the areas of research in this thesis. Theory, background and applications are provided for the fields of nanoparticles, polymers, and supercritical fluids. Chapters 2, 3 and 4 each report a separate area of research. In each chapter additional theory and background is provided where appropriate, and previous literature is discussed. The aims, results and discussion of each research area are contained within the relevant chapter, as well as conclusions and future work. Chapter 2: Supercritical CO2 is used to impregnate optical polymer substrates with silver complexes, which are then decomposed to form nanoparticles. Chapter 3: Metal oxide nanoparticles are used to stabilise dispersion and suspension polymerisations, providing a method of recovering nanoparticles from aqueous solutions and embedding them on the surface of polymer powders. Chapter 4: Two alternative routes, for creating polymer microspheres surface decorated with silver nanoparticles, are compared. Chapter 5: A detailed description of the synthetic methods, equipment, and analysis techniques used in this research is provided. Chapter 6: A brief but overall conclusion to the research is given.
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Elbasuney, Sherif. "Enhanced flame retardant polymer nanocomposites." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/14587/.
Full textAbstract:
Fire is a continuous threat to life and property. The total annual UK fire loss is estimated to be 0.25% of its gross domestic product (GDP) (Goddard, 1995). According to fire statistics, more than 12 million fires break out every year in the United States, Europe, Russia, and China killing about 166,000 people and injuring several hundreds of thousands (Morgan and Wilkie, 2007). Polymers which take up 80% of the organic chemical industry, are known for their high flammability with the production of heat, corrosive toxic gases, and smoke (Bent, 2010). Improving the fire retardancy of polymeric materials is a major concern and also a major challenge. Nanotechnology could have a significant impact on polymeric materials through the achievement of polymer nanocomposites (PNs) with enhanced functional properties (Giannelis, 1996, Schartel and Batholmai, 2006). If this can be achieved, there will be an enormous increase in the use of improved flame retardant (FR) PNs in mass transportation, aerospace, and military applications where fire safety will be of utmost importance (Horrocks and Price, 2008). In this research project nanoparticles that could have a synergistic effect with traditional FR systems, or that could have a FR action (nano-fire extinguishers), were formulated and surface modified during continuous hydrothermal synthesis (CHS). The bespoke nanoparticles were developed in a structure that could be easily integrated and effectively dispersed into a polymeric matrix. A solvent blending approach for integrating and dispersing colloidal organic modified nanoparticles into polymeric matrices was developed. The impact of nanoparticles of different morphologies including nanospheres, nanoplates, and nanorods on epoxy mechanical, thermal, and flammability properties was evaluated. A laboratory based technique using a Bunsen, video footage, and image analysis was developed to quantify the nanocomposite's direct flame resistance in a repeatable fashion. A new self extinguishing epoxy nanocomposite was developed which showed an enhanced performance in extreme conditions and with good mechanical properties.
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Yao, Kejian. "Higher performance polyurethane-organoclay nanocomposites." Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/7795.
Full textAbstract:
A series of polyurethane (PU)-organoclay nanocompositcs were synthcsised by swelling organically-modified layered silicate (organoclay) in a polyol with subsequent polymerisation. The techniques of wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), Fourier transform infer-red spectroscopy (FTIR), modulated differential scanning calorimetry (MDSQ, contact angle measurement and tensile test were used to investigate the effect of addition of organoclay on curing dynamics, phase structure, tensile properties, dynamical mechanical thermal analysis (DMTA), fatigue durability and surface properties of PUs. FTIR and MDSC revealed that the addition of organoclay has an important influence on curing process of PUs. With increasing organoclay, the reaction between -OH group in polyol and- NCO in isocyanate became fast. WAXD and TEM results showed that PU-organoclay nanocomposites prepared in this research were intercalated materials ones. The addition of organoclay has significant influences on the phase structure of PUs. SAXS results revealed that the long period (average thickness of soft and hard segment) decreased with increasing organoclay. Contact angle measurements showed that the organoclay can affect the surface properties of PU nanocomposites. The addition of organoclay resulted in the decrease in surface energy. AFM results revealed that the adhesion force of the surface of PU nanocomposites decreased with increasing organoclay. Tensile strength and elongation of PUs at break were improved significantly by incorporating organoclay. The tensile strength increased up to 100%, and elongation increased up to 120%. At high soft segment content, with increasing organoclay, the modulus decreased slightly, and at low soft segment content, the modulus increased with increasing organoclay. The addition of organoclay improved significantly thermal stability of PUs. Fatigue measurements uggestedt hat the fatigue durability can significantly be improved by incorporating organoclay. A nanospring concept for understanding the enhancemenht as been proposed.
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Xu, Chen. "Alumina based nanocomposites by precipitation." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:2bc4b631-6b5e-4536-b842-63c591df2832.
Full textAbstract:
This project addressed two main problems pertaining to Al2O3-FeAl2O4 nanocomposites developed via solid state precipitation: the mechanisms for precipitation in ceramic solid solution via reduction reaction, and the mechanisms for the improved mechanical properties and wear resistance of the developed Al2O3-FeAl2O4 nanocomposites. A model was proposed for precipitation in ceramic solid solutions via reduction reactions (the PRCS model). The thermodynamics of reduction reactions during aging treatments under various atmospheres were calculated and discussed relative to the second phase precipitate formation. Attempts were made to measure the corresponding diffusion kinetics using a new theory developed here based on volume fraction profiles of second phase particles in the aged samples. It was found that the measured apparent oxygen vacancy diffusivities conform well to the oxygen vacancy grain boundary diffusion coefficients reported in the literature, and the measured apparent matrix diffusivity conforms well to the Fe3+ ion matrix diffusion coefficients reported in literature. Based on the thermodynamics calculations, diffusion kinetics and some essential mechanisms that were discussed, the PRCS model was proposed. This has two aspects: macroscopic and microscopic. The macroscopic aspect of PRCS model was mainly used to explain the general aspects of microstructure and the distribution of intergranualar second phase particles. The microscopic aspect of the PRCS model was mainly used to explain the precipitation of intragranualar nanoparticles. The mechanical properties, thermal residual stress and wear resistance of selected Al2O3-FeAl2O4 nanocomposites were measured. The results revealed that the Al2O3-FeAl2O4 possessed improved fracture toughness (by around 46%), flexural strength (by around 30%) and abrasive wear resistance (by a factor of around 5) with respect to monolithic alumina. Several mechanisms were proposed to explain the improvements in both mechanical properties and wear resistance. Compressive residual stress was found in the surface layer of Al2O3-FeAl2O4 nanocomposites due to the thermal expansion coefficient mismatch between surface layer and bulk parts. Such residual stress was also interpreted as the main reason for the improvements in both mechanical properties and wear resistance.
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Ranade, Ajit. "Polyamide-imide and Montmorillonite Nanocomposites." Thesis, University of North Texas, 2001. https://digital.library.unt.edu/ark:/67531/metadc2873/.
Full textAbstract:
Solvent suspensions of a high performance polymer, Polyamide-imide (PAI) are widely used in magnetic wire coatings. Here we investigate the effect that the introduction of montmorillonite (MMT) has on PAI. MMT was introduced into an uncured PAI suspension; the sample was then cured by step-wise heat treatment. Polarized optical microscopy was used to choose the best suitable MMT for PAI matrix and to study the distribution of MMT in PAI matrix. Concentration dependent dispersion effect was studied by x-ray diffraction (XRD) and was confirmed by Transmission electron microscopy (TEM). Differential scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA) was used to study impact of MMT on glass transition temperature (Tg) and degradation properties of PAI respectively. Micro-hardness testing of PAI nanocomposites was also performed. A concentration dependent state of dispersion was obtained. The glass transition (Tg), degradation and mechanical properties were found to correlate to the state of dispersion.
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Yang, Yaodong. "Barium Titanate-Based Magnetoelectric Nanocomposites." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/38666.
Full textAbstract:
Barium Titanate (BaTiO3 or BTO) has attracted an ever increasing research interest because of its wide range of potential applications. Nano-sized or nanostructured BTO has found applications in new, useful smart devices, such as sensors and piezoelectric devices. Not only limited to one material, multi-layers or multi-phases can lead to multifunctional applications; for example, nanocomposites can be fabricated with ferrite or metal phase with BTO. In this study, I synthesized various BTO-ferrites, ranging from nanoparticles, nanowires to thin films. BTO-ferrite coaxial nanotubes, BTO-ferrite self-assemble thin films, and BTO single phase films were prepared by pulsed laser deposition (PLD) and sol-gel process. BTO-ferrite nanocomposites were grown by solid state reaction. Furthermore, BTO-metal nanostructures were also synthesized by solid state reaction under hydrogen gas which gave us a great inspiration to fabricate metal-ceramic composites.
To understand the relationship between metal and BTO ceramic phase, I also deposited BTO film on Au buffered substrates. A metal layer can affect the grain size and orientation in BTO film which can further help us to control the distribution of dielectric properties of BTO films.
After obtaining different nanomaterials, I am interested in the applications of these materials. Recently, many interesting electric devices are developed based on nanotechnology, e.g.: memristor. Memristor is a resistor with memory, which is very important in the computer memory. I believe these newly-synthesized BTO based nanostructures are useful for development of memristor, sensors and other devices to fit increasing needs.Ph. D.