To see the other types of publications on this topic, follow the link: Nanostructures and nanocomposites.
Dissertations / Theses on the topic 'Nanostructures and nanocomposites'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Nanostructures and nanocomposites.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Kulkarni, Dhaval Deepak. "Interface properties of carbon nanostructures and nanocomposite materials." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49092.
Full textAbstract:
Two different interfaces were the focus of study: 1) the interface between disordered amorphous carbon and inorganic materials (metal nanostructures and silicon), and 2) the interface between partially ordered graphene (graphene oxide) and synthetic polymer matrix. Specifically, the uniqueness of this study can be summarized through the following novel findings, fabrication processes, and characterization techniques:
• A simple and efficient process for faster, greener, less-expensive, and highly localized transformation of amorphous carbon nanostructures into graphitic nanostructures using low temperature heat and light treatments was developed for the fabrication of low-resistance interfaces between carbon nanomaterials and inorganic metal surfaces.
• A new protocol for high resolution mapping the charge distribution and electronic properties of nanoscale chemically heterogeneous domains on non-homogeneous surfaces such as graphene oxide was established.
• High strength laminated mechanical nanocomposites based on high interfacial stress transfer between polymer matrices and large area, flat, and non-wrinkled graphene oxide sheets were suggested and demonstrated.
• Scanning Thermal Twist Microscopy – a thermal microscopy based technique was developed and demonstrated for characterizing the thermal properties of homogeneous and heterogeneous interfaces with nanoscale spatial resolution and high thermal sensitivity unachievable using traditional techniques.
2
Mahanta, Nayandeep Kumar. "Thermal Transport in Isolated Carbon Nanostructures and Associated Nanocomposites." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1334602932.
Full text
3
Venkatachalapathy, Viswanathan. "PLASMA PROCESSING FOR RETENTION OF NANOSTRUCTURES." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4197.
Full textAbstract:
Plasma spray processing is a technique that is used extensively in thermal barrier coatings on gas and steam turbine components, biomedical implants and automotive components. Many processing parameters are involved to achieve a coating with certain functionality. The coating could be required to function as thermal barrier, wear resistant, corrosion resistant or a high temperature oxidation resistant coating. Various parameters, such as, nozzle and electrode design, powder feeding system, spray distances, substrate temperature and roughness, plasma gas flow rates and others can greatly alter the coating quality and resulting performance. Feedstock (powder or solution precursor) composition and morphology are some of the important variables, which can affect the high end coating applications. The amount of heat a plasma plume has to offer to the particles being processed as a coating depends primarily on the dissociation of the atoms of gaseous mixtures being used to create the plasma and the residence time required for the particle to stay in the flame. The parameters that are conducive for nanostructured retention could be found out if the residence time of the particles in the flame and the available heat in the plume for various gas combinations could be predicted. If the feedstock is a liquid precursor instead of a powder feedstock, the heat that has to be offered by the plasma could be increased by suitable gas combination to achieve a good quality coating. Very little information is available with regard to the selection of process parameters and processing of nano materials feedstock to develop nanostructured coatings using plasma spray. In this study, it has been demonstrated that nano ceramics or ceramic composites either in the form of coatings or bulk free form near net components could be processed using DC plasma spray. For powder feedstock, analytical heat transfer calculations could predict the particle states for a given set of parameters by way of heat input from the plasma to the particles. The parameter selection is rendered easier by means of such calculations. Alumina nano ceramic particles are processed as a coating. During Spray drying, a process of consolidation of nano alumina particles to spherical agglomerates, parameter optimization for complete removal of moisture has been achieved. The parameters are tested for alumina nanoparticles with a plasma torch for the veracity of calculations. The amount of heat transfer from the surface of the agglomerates to the core has been quantified as a function of velocity of particles. Since preparation of nanostructured feedstock for plasma spray is expensive and cumbersome, alternative solution precursor route for direct pyrolysis of precursor to coating has been studied in case of nanocrystalline rare earth oxides. Thus, it has also been shown by this research that nanostructured coatings could be either from a powder feedstock or a solution precursor feedstock. MoSi2-Si3N4, Ni-Al2O3, W-HfC nano ceramic composite systems have been processed as a bulk free form nanocomposite with 60-70% retained nanostructures. The importance of selection of substrates, roughness and the substrate temperature for development of free form bulk components has been highlighted. The improvement in mechanical and high temperature properties associated with having such nanostructured coatings or bulk nanocomposites are revealed. These nanostructured coatings are known for their low thermal conductivity, high wear resistance and can be potentially used as steam and gas turbines coatings for improved thermal efficiency. In summary, bulk nanocomposite through plasma spray processing is a viable alternative to conventional processes such as sintering, HIP for high fracture toughness and hardness applications.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering;<br>Engineering and Computer Science<br>Materials Science & Engr PhD
4
Behler, Kristopher Gogotsi IU G. "Chemically modified carbon nanostructures for electrospun thin film polymer-nanocomposites /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2920.
Full text
5
Kim, Kwang-Hyon. "Ultrafast nonlinear optical processes in metal-dielectric nanocomposites and nanostructures." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16495.
Full textAbstract:
Diese Arbeit ist der theoretische Untersuchung nichtlinearer optischer Prozesse in metall-dielektrischen Medien gewidmet, wobei Möglichkeiten zur Ausnutzung der erhöhten nichtlinearen Koeffizienten und der Feldüberhöhung durch metallische Nanoteilchen untersucht wurden. Die wichtigsten Ergebnisse beziehen sich auf eine Untersuchung der zeitabhängigen sättigbaren Absorption in Gläsern, die mit metallischen Nanoteilchen dotiert sind, ihrer physikalischen Ursache sowie verschiedener Anwendungen in der nichtlinearen Optik. Zur Untersuchung der Zeitabhängigkeit der nichtlinearen Rückwirkung wird unter Verwendung des semi-klassischen Zwei-Temperatur-Modells eine zeitabhängige Gleichung für die nichtlineare dielektrische Funktion der Metalle hergeleitet. Die Ergebnisse zeigen, dass solche Gläser, sich als sehr effiziente sättigbare Absorber im Spektralbereich vom sichtbaren bis nahen IR eignen. Für kurzwellige Laser im blau/violetten Spektralbereich wird die Dynamik der Modenkopplung in Festkörper- und Halbleiter-Scheibenlaser untersucht. Weiterhin wird ein neuer Mechanismus für die Realisierung von langsamem Licht vorgeschlagen und im Detail untersucht, der in solchen dotierten Gläsern in einem Pump-Probe Regime infolge der sättigbaren Absorption in der Nähe der Plasmonresonanz realisierbar ist. Weiterhin untersuchten wir die Möglichkeit einer Femtosekunden Plasmon Impulserzeugung durch Modenkopplung eines Oberflächen Plasmonlasers mit einem Bragg Resonator, der aus einer dünnen Schicht aus Silber sowie einem sättigbaren Absorbers und einem Verstärker besteht. Im letzten Teil der Arbeit werden Ergebnisse zur Erzeugung hoher Harmonischer in Edelgasen in der Nähe einer metallischen fraktalen rauen Oberfläche untersucht. Die Berechnungen zeigen eine Reduzierung der geforderten Intensität um drei Größenordnungen und eine um zwei Größenordnungen erhöhte Effizienz gegenüber der bisher experimentell realisierten HHG in der Nähe von metallischen "bow-tie"Nanostrukturen.<br>This work reports results of a theoretical study of nonlinear optical processes in metal-dielectric nanocomposites used for the increase of the nonlinear coefficients and for plasmonic field enhancement. The main results include the study of the transient saturable nonlinearity in dielectric composites doped with metal nanoparticles, its physical mechanism as well its applications in nonlinear optics. For the study of the transient response, a time-depending equation for the dielectric function of the nanocomposite using the semi-classical two-temperature model is derived. By using this approach, we study the transient nonlinear characteristics of these materials in comparison with preceding experimental measurements. The results show that these materials behave as efficient saturable absorbers for passive mode-locking of lasers in the spectral range from the visible to near IR. We present results for the modelocked dynamics in short-wavelength solid-state and semiconductor disk lasers; in this spectral range other efficient saturable absorbers do not exist. We suggest a new mechanism for the realization of slow light phenomenon by using glasses doped with metal nanoparticles in a pump-probe regime near the plasmonic resonance. Furthermore, we study femtosecond plasmon generation by mode-locked surface plasmon polariton lasers with Bragg reflectors and metal-gain-absorber layered structures. In the final part of the thesis, we present results for high-order harmonic generation near a metallic fractal rough surface. The results show a possible reduction of the pump intensities by three orders of magnitudes and two orders of magnitudes higher efficiency compared with preceding experimental results by using bow-tie nanostructures.
6
Khanadeev, V. A., B. N. Khlebtsov, G. S. Terentyuk, et al. "Mesoporous Silica and Composite Nanostructures for Theranostics." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35481.
Full textAbstract:
We discus methods for fabrication of silica and composite nanoparticles, which can be used in various biomedical applications. The most promising types of such nanostructures are hollow silica nanosheres, sil-ica coated plasmon-resonant nanoparticles (gold nanorods and gold-silver nanocages) and nanorattles. Mesoporous silica shell can be doped by desirable targeting molecules. Here we present the results of for-mation of nanocomposites composed of gold nanorods and double-layer silica shell. The secondary mesopo-rous silica shell is doped with a photosensitizer (hematoporphyrine in our case). We demonstate some of promising theranostics applications of these nanocomposites for bioimaging and in vivo therapy of tumors.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35481
7
Abdelaaziz, Muftah Ali. "Synthesis of nanocomposites with nano-TiO2 particles and their applications as dental materials." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/1534.
Full textAbstract:
Thesis submitted in fulfilment of the requirements for the degree
Magister of Technology: Dental Technology
In the Faculty of Health and Wellness Sciences
At the Cape Peninsula University of Technology, 2012<br>A study of the modification of dental nanocomposites with nanosized fillers is presented. The incorporation of TiO2 (titania) nanoparticles, via a silane chemical bond, to a standard dental acrylic resin matrix was explored to determine whether there was an increase in the wear resistance, flexural strength and surface hardness properties of the dental nanocomposites. The principal aim of this study was to synthesize dental nanocomposites with different sizes, treated, nano-TiO2 fillers in urethane dimethacrylate (UDMA) for potential application in posterior restoration and to evaluate their mechanical properties.
Treatment of the nano-TiO2 particles was carried out with a silane coupling agent, 3-(methacryloyloxy)propyltrimethoxysilane (MPTMS), to improve bonding between the nano-TiO2 particles and acrylic matrix (UDMA), and reduce agglomeration of the nano-TiO2. Characterisation of products was carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR). TEM results were used to compare the particle size distributions of untreated TiO2 and treated TiO2 under various experimental conditions in an ethanol solvent, while SEM images showed the adhesion between the matrix (UDMA) and the nano-TiO2. FTIR was used to show the qualitative composition of untreated TiO2 and treated TiO2.
Eighteen groups of experimental dental nanocomposites were evaluated. Each group contained different average particle sizes of nano-TiO2 (filler): 5 nm, 21 nm and 80 nm. Each particle size category was treated with three different concentrations of the silane, (MPTMS): 2.5, 10 and 30 wt %. Samples were prepared by mixing the monomer resin matrix of UDMA and nano-TiO2 particles. For comparison, a commercially available dental resin was reinforced with untreated and treated nano-TiO2 particle sizes 5, 21 and 80 nm.
Wear resistance, flexural strength and surface hardness of TiO2 nanocomposites treated with 2.5 wt % MPTMS were significantly higher compared to those treated with 10 and 30 wt% MPTMS. The nanocomposites with 5 nm TiO2 had higher wear loss, lower flexural strength and lower surface hardness values compared to those with 21 nm and 80 nm TiO2. Statistical analysis showed that the effect of the concentrations of MPTMS on wear resistance and surface hardness of specimens was significant (p<0.001), which is less than 0.05, while the effect of the concentration of MPTMS on flexural strength was statistically not significant, (p=0.02). Control composites reinforced with treated 80 nm TiO2 particles had much better mechanical properties than any of the other specimens. It was concluded that the most available commercial product for dental restorations could be improved by the addition of nano-TiO2 with relatively large particle size.
8
Kana, Jean Bosco Kana. "Towards stimuli-responsive functional nanocomposites : smart tunable plasmonic nanostructures Au-VO2." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8032_1299494958.
Full textAbstract:
<p>The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in VO2 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-VO2 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of VO2 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of VO2 thin films. A reversible thermal tunability of the optical/dielectric constants of VO2 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in VO2 host matrix.</p>
9
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 Al<sub>2</sub>O<sub>3</sub>-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.
10
Koh, Pei Yoong. "Deposition and assembly of magnesium hydroxide nanostructures on zeolite 4A surfaces." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37159.
Full textAbstract:
A deposition - precipitation method was developed to produce magnesium hydroxide / zeolite 4A (Mg(OH)₂ - Z4A) nanocomposites at mild conditions and the effect of processing variables such as precursor concentration, type of base added, and synthesis time on the composition, size, and morphology of the nanocomposite were studied. It was determined that the precursor concentration, basicity, and synthesis time had a significant effect on the composition, size, and morphology of the deposited magnesium hydroxide (Mg(OH)₂) nanostructures. The properties of the Mg(OH)₂ - Z4A such as surface area, pore volume and composition were characterized. Mg(OH)₂ - Z4A samples and bare zeolite 4A were dispersed in Ultem® polymer to form a mixed matrix membrane. The thermal and mechanical properties of the resulting films were investigated. It was found that the addition of rigid bare zeolites into the polymer decreased the mechanical properties of the polymer composite. However, some of these adverse effects were mitigated in the polymer composite loaded with Mg(OH)₂ - Z4A samples. Isotherms for the adsorption of Mg(OH)₂ petals on zeolite 4A were measured in order to determine the optimum conditions for the formation of magnesium hydroxide / zeolite 4A nanocomposites at ambient conditions. The loading of the Mg(OH)₂ can be determined from the adsorption isotherms and it was also found that the adsorption of Mg(OH)₂ on zeolite A occurs via 3 mechanisms: ion exchange, surface adsorption of Mg²⁺ ions, and surface precipitation of Mg(OH)₂. Without the addition of ammonium hydroxide, the predominant processes are ion exchange and surface adsorption of Mg²⁺ ions. In the presence of ammonium hydroxide, Mg(OH)₂ crystals are precipitated on the surface of zeolite 4A at moderate Mg²⁺ ions concentration and the loading of Mg(OH)₂ was found to increase with increasing Mg²⁺ ions concentration. A detailed examination of the interactions between Mg(OH)₂ and functional groups on the zeolite surface was conducted. Solid-state 29Si, 27Al, and 1H NMR spectra were coupled with FTIR measurements, pH and adsorption studies, and thermogravimetric analyses to determine the interactions of Mg(OH)₂ with surface functional groups and to characterize structural changes in the resulting zeolite after Mg(OH)₂ deposition. It was discovered that acid - base interactions between the weakly basic Mg(OH)₂ and the acidic bridging hydroxyl protons on zeolite surface represent the dominant mechanism for the growth of Mg(OH)₂ nanostructures on the zeolite surface.
11
Belchi, Raphaëlle. "Architectures à base de nanostructures de carbone et TiO₂pour le photovoltaïque." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS329/document.
Full textAbstract:
Le photovoltaïque est une énergie renouvelable pouvant aider à lutter contre le réchauffement climatique et l’épuisement des ressources fossiles utilisées pour la production d’énergie. La filière émergente à base de matériaux pérovskites (photovoltaïque de 3ème génération) est très prometteuse car elle utilise des matériaux abondants et faciles à mettre en œuvre (technologie bas-coût) et a montré de plus des rendements record compétitifs en peu de temps. Il reste cependant des verrous technologiques à lever afin de pouvoir développer cette technologie à grande échelle. L’un deux consiste à améliorer la couche de TiO₂ qui transporte les électrons et dont les défauts limitent les performances et la durée de vie des cellules photovoltaïques pérovskites. Ce travail propose l’utilisation de matériaux à base de nanostructures de carbone et de TiO₂ pour améliorer le transport et la collecte des électrons au sein de ces cellules photovoltaïques et ainsi améliorer leur rendement. Pour cela, la pyrolyse laser, technique singulière de production continue de nanoparticules, a été adaptée pour l’élaboration de nanocomposites TiO₂/graphène aux propriétés contrôlées. Ces matériaux ont été caractérisés puis intégrés aux cellules photovoltaïques pérovskites qui ont démontré une meilleure efficacité en présence de graphène. Par ailleurs, ce travail présente une architecture innovante à base de nanotubes de carbone alignés verticalement, en vue d’une application pour la collecte des électrons photo-générés des cellules photovoltaïques pérovskites. Les matériaux carbonés présentent donc de fortes potentialités pour l’optoélectronique, et plus particulièrement pour le photovoltaïque de 3ème génération<br>Photovoltaic is a promising renewable energy to tackle global warming and the depletion of fossil resources. The emerging field of perovskite solar cells (3rd generation photovoltaic) is very attractive because it uses abundant and easy-processing materials (low-cost technology) and provides competitive efficiencies.Still, efforts remain to be performed to develop this technology, especially concerning the improvement of efficient and reliable charge transporting electrodes. Titanium dioxide layer, commonly used for electron extraction, presents defects that limit the performance and lifetime of the perovskite solar cells.This work proposes the use of materials based on TiO₂ and carbon nanostructures to improve the electron transport and collection within the solar cells, in order to enhance the power conversion efficiency. The singular technique of laser pyrolysis, which is a continuous process of nanoparticles synthesis, was adapted to produce TiO₂/graphene nanocomposites with well-controlled properties. These materials have been characterized and integrated into perovskite solar cells that demonstrate an improved efficiency in presence of graphene.Besides, this work presents an innovating architecture based on vertically aligned carbon nanotubes for the electron collection of a perovskite solar cell. We show then the strong potential of carbon materials for optoelectronic, especially 3rd generation photovoltaic
12
Chunder, Anindarupa. "FABRICATION OF FUNCTIONAL NANOSTRUCTURES USING POLYELECTROLYTE NANOCOMPOSITES AND REDUCED GRAPHENE OXIDE ASSEMBLIES." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3082.
Full textAbstract:
A wide variety of nanomaterials ranging from polymer assemblies to organic and inorganic nanostructures (particles, wires, rods etc) have been actively pursued in recent years for various applications. The synthesis route of these nanomaterials had been driven through two fundamental approaches -  Top down and  Bottom up . The key aspect of their application remained in the ability to make the nanomaterials suitable for targeted location by manipulating their structure and functionalizing with active target groups. Functional nanomaterials like polyelectrolyte based multilayered thin films, nanofibres and graphene based composite materials are highlighted in the current research. Multilayer thin films were fabricated by conventional dip coating and newly developed spray coating techniques. Spray coating technique has an advantage of being applied for large scale production as compared to the dip coating technique. Conformal hydrophobic/hydrophilic and superhydrophobic/hydrophilic thermal switchable surfaces were fabricated with multilayer films of poly(allylaminehydrochloride) (PAH) and silica nanoparticles by the dip coating technique, followed by the functionalization with thermosensitive polymer-poly(N-isopropylacrylamide)(PNIPAAM) and perfluorosilane. The thermally switchable superhydrophobic/ hydrophilic polymer patch was integrated in a microfluidic channel to act as a stop valve. At 70 degree centigrade, the valve was superhydrophobic and stopped the water flow (close status) while at room temperature, the patch became hydrophilic, and allowed the flow (open status). Spray-coated multilayered film of poly(allylaminehydrochloride) (PAH) and silica nanoparticles was fabricated on polycarbonate substrate as an anti-reflection (AR) coating. The adhesion between the substrate and the coating was enhanced by treating the polycarbonate surface with aminopropyltrimethoxylsilane (APTS) and sol-gel. The coating was finally made abrasion-resistant with a further sol-gel treatment on top of AR coating, which formed a hard thin scratch-resistant film on the coating. The resultant AR coating could reduce the reflection from 5 to 0.3% on plastic. Besides multilayered films, the fabrication of polyelectrolyte based electrospun nanofibers was also explored. Ultrathin nanofibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylaminehydrochloride) (PAH) were fabricated using the electrospinning technique and methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. The fiber was also loaded with a real life anti-depressant drug (2,3-tertbutyl-4-methoxyphenol) and fiber surface was made superhydrophobic. The drug loaded superhydrophobic nanofiber mat was immersed under water, phosphate buffer saline and surfactant solutions in three separated experiments. The rate of release of durg was monitored from the fiber surface as a result of wetting with different solutions. Time dependent wetting of the superhydrophobic surface and consequently the release of drug was studied with different concentrations of surfactant solutions. The results provided important information about the underwater superhydrophobicity and retention time of drug in the nanofibers. The nanostructured polymers like nanowires, nanoribbons and nanorods had several other applications too, based on their structure. Different self-assembled structures of semiconducting polymers showed improved properties based on their architectures. Poly(3-hexylthiophene) (P3HT) supramolecular structures were fabricated on P3HT-dispersed reduced graphene oxide (RGO) nanosheets. P3HT was used to disperse RGO in hot anisole/N, N-dimethylformamide solvents, and the polymer formed nanowires on RGO surfaces through a RGO induced crystallization process. The Raman spectroscopy confirmed the interaction between P3HT and RGO, which allowed the manipulation of the composite's electrical properties. Such a bottom-up approach provided interesting information about graphene-based composites and inspired to study the interaction between RGO and the molecular semiconductor-tetrasulphonate salt of copper phthalocyanine (TSCuPc) for nanometer-scale electronics. The reduction of graphene oxide in presence of TSCuPc produced a highly stabilized aqueous composite ink with monodispersed graphene sheets. To demonstrate the potential application of the donor (TSCuPc) acceptor (graphene) composite, the RGO/TSCuPc suspension was successfully incorporated in a thin film device and the optoelectronic property was measured. The conductivity (dark current) of the composite film decreased compared to that of pure graphene due to the donor molecule incorporation, but the photoconductivity and photoresponsivity increased to an appreciable extent. The property of the composite film overall improved with thermal annealing and optimum loading of TSCuPc molecules.<br>Ph.D.<br>Department of Chemistry<br>Sciences<br>Chemistry PhD
13
Bersani, Marco. "Chemical methods for the preparation of gold particles based nanostructures and nanocomposites." Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3425973.
Full textAbstract:
In this thesis, the potential functional interactions of gold nanoparticles with organic, hybrid, inorganic and biological systems have been investigated. Nanoparticles with varying sizes have been synthesized following different preparation methods.
Molecular-like (D < 2 nm), highly fluorescent few-atoms clusters were prepared by a slow reduction of gold salts in organic solvent, yielding a colloidal solution that can be easily redispersed in a variety of solvents and matrices, including sol-gel silica and a hybrid copolymer. The emission wavelength has a lifetime in the ns and can be tuned from the near UV to the whole visible range by adjusting the reaction parameters, and the luminescence is stable for months both in intensity and wavelength. Use of alternative precursors and solvents, influence of reaction temperature and purification methods are all currently being investigated, together with potential application as biolabels and sensitizers for rare-earth-based optical amplifiers.
Uncapped nanoparticles with 3 nm < D < 10 nm were obtained in situ in fluorinated polyimides via thermal reduction-precipitation with the concurrent matrix imidization. The doping profile, monitored with RBS analyses, can be easily varied both for thick (30 mm) and thin (< 1 mm) film samples. The selective permeability properties that are typical of polyimides suggest potential employment as both optical and electic gas sensors, and the first measurements are now underway.
Eventually, 10 nm nanoparticles were synthesized with the traditional Turkevich citrate method, capped with streptavidin and used to functionalize DNA origami structures. Liquid cell AFM technique allows to image the effectiveness of the proposed method for positioning nanoscopic objects with nm resolution thanks to the peculiar design features of these DNA-based structures. The specific interest is here related to the possibility of using them as lego-like building blocks for nanoelectronics, and the focus is at present centered on the self-induced or externally directed organization of the functionalized origami on substrates. At present, self-assembly on patterned surfaces is being studied together with AFM electrophoresis, but new interesting strategies are being proposed on a daily basis as further interesting origami peculiarities emerge.
14
Vieitas, de Amaral Dias Ana Inês. "Plasma based assembly and engineering of advanced carbon nanostructures." Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2019/document.
Full textAbstract:
L’environnement réactif du plasma constitue un outil puissant dans la science des matériaux, permettant la création de matériaux innovatifs et l'amélioration de matériaux existants qui ne serait autrement pas possible.Le plasma fournit simultanément des fluxes de particules chargées, des molécules chimiquement actives, des radicaux, de la chaleur, des photons, qui peuvent fortement influencer les voies d'assemblage à différentes échelles temporelles et spatiales, y compris à l’échelle atomique.Dans cette thèse de doctorat, des méthodes tenant pour base des plasmas micro-ondes ont été utilisées pour la synthèse de nanomatériaux de carbone, y compris graphène, graphène dopé à l'azote (N-graphène) et structures de type diamant.À cette fin, ce travail est lié à optimisation de la synthèse de nanostructures 2D du carbone, comme graphène et N-graphène par la poursuite de l'élaboration et du raffinement de la méthode développée en Plasma Engineering Laboratory (PEL). La synthèse de graphène de haute qualité et en grandes quantités a été accomplie avec succès en utilisant des plasmas d'Ar-éthanol à ondes de surface dans des conditions de pression ambiante. De plus, le N-graphène a été synthétisé par un procédé en une seule étape, de l'azote a été ajouté au mélange d’Ar-éthanol, et par un procédé en deux étapes, en soumettant des feuilles de graphène préalablement synthétisées ont été exposées à un traitement plasma argon-azote à basse pression. Les atomes d'azote ont été incorporés avec succès dans le réseau de graphène hexagonal, formant principalement liaisons pyrroliques, pyridiniques et quaternaires. Un niveau de dopage de 25 at.% a été atteint.Différents types de nanostructures de carbone, y compris du graphène et des structures de type diamant, ont été synthétisées au moyen d'un plasma d’argon en utilisant du méthane et du dioxyde de carbone comme précurseurs du carbone.De plus, des plasmas à couplage capacitif ont également été utilisés pour la fonctionnalisation du graphène et pour la synthèse de nanocomposites, tels que les composites de Polyaniline (PANI)-graphène. Les utilisations potentielles de ces matériaux ont été étudiées et les deux structures ont démontré avoir des attributs remarquables pour leur application aux biocapteurs<br>Plasma environments constitute powerful tools in materials science by allowing the creation of innovative materials and the enhancement of long existing materials that would not otherwise be achievable. The remarkable plasma potential derives from its ability to simultaneously provide dense fluxes of charged particles, chemically active molecules, radicals, heat and photons which may strongly influence the assembly pathways across different temporal and space scales, including the atomic one.In this thesis, microwave plasma-based methods have been applied to the synthesis of advanced carbon nanomaterials including graphene, nitrogen-doped graphene (N-graphene) and diamond-like structures. To this end, the focus was placed on the optimization of the production processes of two-dimensional (2D) carbon nanostructures, such as graphene and N-graphene, by further elaboration and refinement of the microwave plasma-based method developed at the Plasma Engineering Laboratory (PEL). The scaling up of the synthesis process for high-quality graphene using surface-wave plasmas operating at atmospheric pressure and argon-ethanol mixtures was successfully achieved. Moreover, N-graphene was synthetized via a single-step process, by adding nitrogen to the argon-ethanol mixture, and via two-step process, by submitting previously synthetized graphene to the remote region of a low-pressure argon-nitrogen plasma. Nitrogen atoms were usefully incorporated into the hexagonal graphene lattice, mainly as pyrrolic, pyridinic and quaternary bonds. A doping level of 25% was attained.Different types of carbon nanostructures, including graphene and diamond-like nanostructures, were also produced by using methane and carbon dioxide as carbon precursors in an argon plasma.Additionally, capacitively-coupled radio-frequency plasmas have been employed in the functionalization of graphene and in the synthesis of Polyaniline (PANI)-graphene composites. The potential uses of these materials were studied, with both showing favourable characteristics for their applicability in biosensing applications
15
Volodin, A. A., B. P. Tarasov, A. A. Belmesov, E. V. Gerasimova, A. D. Zolotarenko, and D. V. Shchur. "Electro-Conductive Composites Based on Metal Oxides and Carbon Nanostructures." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35124.
Full textAbstract:
Optimal conditions were found for the formation of carbon-oxide composites by the treatment of mixtures
of oxides of aluminum or titanium with carbon nanotubes and nanofibers in a planetary ball mill.
The dependences of the electrical conductivity of composites on the content of carbon nanomaterials (1-5%
by mass) were determined. It is shown that the addition of 3%(wt) of CNT to the oxides leads to a sharp increase
in the electrical conductivity: from 5.0×10-8 to 2.8×10-4 S/cm for Al2O3 and from 5.0×10-6 to 2.2×10-2
S/cm for TiO2. It was shown that the carbon-oxide composites are promising carriers of the catalysts of
electrode processes in electrochemical devices. It was revealed that Pt/TiO2 - CNT catalyst containing 5%
(mass) of carbon nanotubes has the best catalytic activity in oxygen reduction, in an electrode-modeling
cathode of a fuel cell.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35124
16
Choi, Han Ho. "Synthesis and chacterization [sic] of tailored zinc oxide nanostructures and their engineered nanocomposites." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008248.
Full text
17
Shi, Yupeng. "Functionalized Silica Nanostructures : Degradation Pathways and Biomedical Application from 2D to 3D." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS122/document.
Full textAbstract:
Les nanoparticules de silice sont très largement étudiées pour les applications biomédicales. Elles permettent une facilité et une flexibilité de la synthèse des particules et une bio-toxicité limitée. Cette thèse a mené une grande diversité de résultats impliquant des nanomatériaux de silice. Premièrement, les propriétés physicochimiques et les propriétés de biodégradation de trois types de nanoparticules de silice structurées ont été étudiées dans un tampon, un milieu de culture et au contact de fibroblastes cutanés humains suggérant que les nanoparticules de silice doivent être principalement considérées comme dégradées par hydrolyse, et non biodégradé. Ensuite, des nanoparticules de silice multifonctionnelles constituées de nanoparticules de silice creuses et de nanoparticules de MnO2 ont été synthétisées. Ainsi le contrôle de la libération du médicament et la performance de l’imagerie de ces nanoplates ont été étudiées à partir de modèles 2D à 3D. Cette approche pourrait être utilisée pour une évaluation rapide de la bio-fonctionnalité des nanoparticules avant de mettre en place des expériences in vivo. En outre, un nouveau nanocomposite 3D à base de collagène utilisant des tiges de silice a été étudié et les relations entre la composition composite, la structure et les propriétés mécaniques, mettant en évidence le rôle clé des interactions collagène-silice. L'influence de ces paramètres sur l'adhésion et la prolifération des cellules fibroblastiques a également été étudiée. De plus, nous avons préparé et utilisé des nanobatonnêts de silice magnétiques pour contrôler l’orientation des particules dans le réseau de collagène grâce à un champ magnétique externe. Tous les résultats apportent de nouvelles connaissances sur la préparation et les propriétés des bionanocomposites et ouvrent la voie à des hydrogels multifonctionnels<br>Silica nanoparticles, thanks to the great easy and adaptability of particle synthesis and limited biotoxicity, is very widely studied for biomedical applications. This thesis conducted a large diversity of investigations involving silica nanomaterials. Firstly, the physicochemical properties and biodegradation properties of three types of structured silica nanoparticles were studied in a buffer, a culture medium and in contact with human dermal fibroblasts that suggest that, under these conditions, the silica nanoparticles must be mainly considered as degraded by hydrolysis and not biodegraded. Then, multifunctional silica nanoparticles which are consist of hollow silica nanoparticles and MnO2 nanosheets were synthesized. And the control drug release and imaging performance of this nanoplatforms were studied from 2D to 3D models. This approach could be used for a rapid assessment of the biofunctionality of nanoparticles before setting up in vivo experiments. Furthermore, a new 3D collagen-based nanocomposites using silica rods were studied and the relationships between the composite composition, structure and mechanical properties, emphasizing the key role of collagen-silica interactions. The influence of these parameters on the adhesion and proliferation of fibroblast cells was also investigated. In addition, we prepared and used magnetic silica nanorods to control particle orientation within the collagen network thanks to an external magnetic field. All the results bring new insights on the preparation and properties of bionanocomposites and open the route to multifunctional hydrogels
18
Georgieva, Petya. "DEVELOPMENT OF THERMALLY PROCESSED NANOCOMPOSITES WITH CONTROLLED SURFACES." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2883.
Full textAbstract:
The ever increasing need for technology development requires the integration of inexpensive, light weight and high strength materials which are able to meet the high standards and specifications for various engineering applications. The intention of this work is to show that the suitable material selection and the utilization of plasma spray processing can be of potential interest to a large number of industrial, biomedical and everyday life applications. This research demonstrates also that plasma processing is a promising engineering tool for multifunctional coatings and near-net-shape manufacturing. Further, the theoretical and experimental results are combined in order to explain the mechanisms behind nanostructure retention and enhanced properties. Proper design of experiments, an appropriate material selection and experimental methodology are discussed herein. The experimental conditions were optimized in order to achieve the best materials properties according to their explicit properties and functions. Specific materials were consolidated according to their prospective performance and applications: 1) Plasma spraying of nano-Ceria-stabilized Zirconia free form part for stem cells scaffolds, 2) Plasma spraying of FeCrAlY on Ti-alloy plate, additionally coated with nano-size Hydroxyapatite for bone tissue engineering, 3) Wire-arc spraying of nano-based steel wires for aerospace and automotive applications. The performance and characteristics of all of the developed coatings and free-form-parts are evaluated using state-of-the art characterization techniques.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering;<br>Engineering and Computer Science<br>Materials Science and Engineering
19
Guimaraes, de Sa Rafael. "In-situ and ex-situ incorporation of carbon nanostructures into ceramic-carbon-metal nanocomposites." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526358.
Full text
20
Do, Isabelle. "Nanocomposites nanotubes de carbone/élastomère : Propriétés rhéologiques et électriques." Pau, 2007. http://www.theses.fr/2007PAUU3005.
Full textAbstract:
L'incorporation de nanotubes de carbone (NTC) dans une matrice polymère est difficile du fait de leur forte tendance à s'agglomérer, ce qui réduit leur intérêt en tant que renforts. Afin de pallier ce problème, beaucoup de solutions reposent sur la modification de l'interface NTC/polymère. Le but de notre étude est d'établir la relation existant entre la nature de l'interface NTC/polymère et l'organisation spatiale des NTC d'une part, les propriétés rhéologiques et électriques du nanocomposite NTC/polyacrylate de méthyle (PMA) obtenu, d'autre part. L'interface NTC/matrice est contrôlée via l'utilisation de polyacide acrylique (PAA), soit en le greffant à la surface des nanotubes, soit en l'utilisant comme agent de surface. L'étude de la morphologie des composites par microscopie électronique a montré la nécessité de distinguer la distribution des NTC au sein de la matrice (c'est-à-dire la répartition des amas de nanotubes dans tout l'échantillon), de leur dispersion (c'est-à-dire leur individualisation au sein de ces amas). Cette distinction est centrale, car elle permet d'expliquer les propriétés physiques des nanocomposites. L'étude des propriétés viscoélastiques linéaires et électriques des composites obtenus a permis de mettre en évidence un phénomène de percolation. Nous avons également montré que les propriétés électriques des composites sont sensibles à la dispersion des NTC, alors que les propriétés rhéologiques le sont à la qualité de distribution. L'utilisation de PAA, greffé ou adsorbé sur les nanotubes, permet d'augmenter la conductivité électrique et de mieux disperser les NTC, abaissant ainsi les seuils de percolation électrique<br>Since carbon nanotubes (CNT) tend to remain as entangled agglomerates, homogeneous dispersed states within a polymer is not easily obtained, which reduces the interest of nanotubes as reinforcements. Many of the solutions proposed to address this issue rely on the modification of the interface between carbon nanotubes and the polymer matrix. The aim of the study is to establish the relationship between the nature of the CNT/polymethylacrylate (PMA) interface and the spatial organization of the CNTs in the matrix, on the one hand, and rheological and electrical properties of the nanocomposites, on the other hand. The interface is controlled by using polyacrylic acid (PAA), either by grafting it on the nanotubes surface, or by using it as a surfactant. The study of the morphology of the composites by electronic microscopy showed the importance of distinguishing the distribution of CNTs in the matrix (i. E. The repartition of the nanotubes clusters in the whole sample), from their dispersion (i. E. Their individualization within the clusters). This distinction is central as it allows explaining the physical properties of the nanocomposites. The studies of the linear viscoelastic and electrical properties of the composites highlighted the existence of percolation phenomena. We also showed that the electrical properties of the composites are sensitive to the CNTs dispersion, whereas the rheological ones are sensitive to the quality of distribution. The use of PAA, either grafted or adsorbed on nanotubes, allows an increase in electrical conductivity as well as a better dispersion of the nanotubes, thus lowering the electrical percolation thresholds
21
Habis, Christelle. "Development of ZnO-FTO nanocomposites for the use in transparent conductive thin films." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0192.
Full textAbstract:
Cette thèse s'inscrit dans le cadre de développement de couches d'oxyde transparentes avec des techniques à faible cout, basées sur des matériaux non polluants permettant de fonctionnaliser des dispositifs opérationnels efficace, donc à haut rendement pour la production d'énergies renouvelables. Notre choix s'est porté plus particulièrement sur l'étude des couches TCO à base d'étain et dopés au fluor, F :SnO2, dénommées FTO pour « Fluor Tin Oxydes ». Les FTO sont des oxydes à large bande interdite, à l'instar du ZnO, TiO2, Al2O3, purs ou dopés. Ces couches possèdent en principe un facteur de diffusion, défini précédemment, élevé afin d'améliorer le chemin optique et l'absorption. De plus, la texture optique des TCO peut être facilement contrôlée par dépôt de suspensions de nanostructures avant le dépôt de la couche. Généralement, ces nanostructures sont des nanoparticules voire nano-fils de carbone ou nano-fils métalliques (argent, cuivre, …) et plus récemment des nano-fils de TiO2 (présentant l'inconvénient de l'élément titane) ou de ZnO non-dopés qui diminuent, malheureusement la conductivité du fait de l'augmentation de la résistance d'interface avec la concentration des nanoparticules. C'est pourquoi, nous proposons l'étude de couches de FTO, pures et également en présence de nanofibres de ZnO et ZnO:Al par électrofilage à partir d'une solution à base de PVA afin d'avoir une couche nanostructuré ayant des propriétés de transparence et de conductivité électrique améliorées pour être intégrer comme électrodes transparentes dans les cellules photovoltaïques, répondant aux critères performatifs définis ci-dessus. Les croissances des couches seront suivies par des études morphologiques et structurales, en utilisant des techniques de caractérisations disponibles au sein du laboratoire LMOPS et de l'Université de Lorraine ( tel que: MEB, Raman, EDX, DRX, spectroscopie UV-vis, ATG, AFM, profilomètre). Enfin, les propriétés électriques et optiques, en particulier l'absorption et le facteur de Haze, seront aussi largement investies sur les couches sélectionnées présentant les meilleures propriétés structurales et morphologique<br>My thesis work entitled “Development of ZnO-FTO nanocomposites for the use in transparent conductive thin films” is supervised by Professor Michel Aillerie at University of Lorraine. This work was mainly made at the “Laboratoire des Matériaux Optiques, Photoniques et Systèmes” LMOPS in Centrale Supélec, Metz. Although this work forms a whole in the elaboration of transparent conductive oxides, it is divided into two parts. The first part consists on identifying the properties of bulk materials (ZnO and FTO) deposited in the form of thin film. Whereas, the second part is about the elaboration and characterization of Zinc Oxide (ZnO) and Aluminum doped Zinc Oxide (AZO) nanofibers, then associated to FTO thin films to form nanocomposite. The main objective of this work is to make flexible electrodes using low cost and abundant material, but also improving the optical properties and more specifically the haze factor of the nanocomposite layers.Transparent conductive oxides (TCOs) are technologically significant class of materials extensively used in thin film solar cells due to their ability to transmit light and collect charge carriers. In addition to the fundamental qualities of transparency and conductivity, the TCOs are frequently desired to have a certain degree of surface roughness (i.e., texture) in order to effectively scatter transmitted light into the active materials, therefore lengthen the optical path and, as a result, enhance the performance of the cell and light absorption. This thesis focuses on the development of low-cost fabrication techniques for transparent oxide layers using non-polluting materials to enable the functionalization of operational devices with high efficiency for renewable energy production. The choice was made to study tin-based TCO layers doped with fluorine, F:SnO2, known as FTOs for "Fluor Tin Oxides". FTOs are wide band gap oxides, like ZnO, TiO2, Al2O3, pure or doped. In principle, these layers have a high scattering factor, as defined above, in order to improve the optical path and absorption. In addition, the optical texture of TCOs can be easily controlled by depositing suspensions of nanostructures before the film deposition. Generally, these nanostructures are nanoparticles or even carbon nanowires or metallic nanowires (silver, copper, ...) and more recently nanowires of TiO2 (presenting the disadvantage of the titanium element) or of undoped ZnO which unfortunately decrease the conductivity due to the increase of the interface resistance with the concentration of the nanoparticles.Therefore, we propose the study of FTO thin films, pure and also in the presence of ZnO and AZO nanofibers by electrospinning from a PVA-based solution in order to have a nanostructured layer with improved transparency and electrical conductivity properties to be integrated as transparent electrodes in photovoltaic cells, meeting the performance criteria defined above. With the characterization techniques available in the LMOPS laboratory and the University of Lorraine (SEM, Raman, EDX, DRX, UV-vis Spectro, ATG, AFM, profilometer) the growth will be followed by morphological and structural studies of the layers. Finally, electrical and optical properties, in particular absorption and scattering factor, will also be extensively investigated on selected layers with the best structural and morphological properties and the minimum of interface defects when deposited on a PV structure
22
Abeywickrama, Thulitha Madawa. "Metal-Organic Hybrid Nanocomposites For Energy Harvesting Applications." TopSCHOLAR®, 2016. http://digitalcommons.wku.edu/theses/1748.
Full textAbstract:
Various synthetic methods have been developed to produce metal nanostructures including copper and iron nanostructures. Modification of nanoparticle surface to enhance their characteristic properties through surface functionalization with organic ligands ranging from small molecules to polymeric materials including organic semiconducting polymers is a key interest in nanoscience. However, most of the synthetic methods developed in the past depend widely on non-aqueous solvents, toxic reducing agents, and high temperature and high-pressure conditions. Therefore, to produce metal nanostructures and their nanocomposites with a simpler and greener method is indeed necessary and desirable for their nano-scale applications. Hence the objective of this thesis work is to develop an environmentally friendly synthesis method to make welldefined copper and iron nanostructures on a large-scale. The size and shape-dependent optical properties, solid-state crystal packing, and morphologies of nanostructures have been evaluated with respect to various experimental parameters.
Nanostructures of copper and iron were prepared by developing an aqueous phase chemical reduction method from copper(II) chloride and Fe(III) chloride hexahydrate upon reduction using a mild reducing agent, sodium borohydride, under an inert atmosphere at room temperature. Well-defined copper nanocubes with an average edge length of 100±35 nm and iron nanochains with an average chain length up to 1.70 μm were prepared. The effect of the molar ratios of each precursor to the reducing agent, reaction time, and addition rate of the reducing agent were also evaluated in order to develop an optimized synthesis method for synthesis of these nanostructures. UV-visible spectral traces and X-ray powder diffraction traces were obtained to confirm the successful preparation of both nanostructrues. The synthesis method developed here was further modified to make poly(3-hexylthiophene) coated iron nanocomposites by surface functionalization with poly(3-hexylthiophene) carboxylate anion. Since these nanostructrues and nanocomposites have the ability to disperse in both aqueous-based solvents and organic solvents, the synthesis method provides opportunities to apply these metal nanostructures on a variety of surfaces using solution based fabrication techniques such as spin coating and spray coating methods.
23
Thiagarajan, Suraj Joottu. "Thermoelectric properties of rare-earth lead selenide alloys and lead chalcogenide nanocomposites." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196263620.
Full text
24
Repa, Kristen Lee Stojak. "Confinement Effects and Magnetic Interactions in Magnetic Nanostructures." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6573.
Full textAbstract:
Multifunctional nanocomposites are promising for a variety of applications ranging from microwave devices to biomedicine. High demand exists for magnetically tunable nanocomposite materials. My thesis focuses on synthesis and characterization of novel nanomaterials such as polymer nanocomposites (PNCs) and multi-walled carbon nanotubes (MWCNTs) with magnetic nanoparticle (NP) fillers.
Magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) NPs with controlled shape, size, and crystallinity were successfully synthesized and used as PNC fillers in a commercial polymer provided by the Rogers Corporation and poly(vinylidene fluoride). Magnetic and microwave experiments were conducted under frequencies of 1-6 GHz in the presence of transverse external magnetic fields of up to 4.5 kOe. Experiments confirm strong magnetic field dependence across all samples. When incorporated in to a cavity resonator device, tangent losses were reduced, quality factor increased by 5.6 times, and tunability of the resonance frequency was demonstrated, regardless of NP-loading.
Work on PNC materials revealed the importance of NP interactions in confined spaces and motivated the study of confinement effects of magnetic NPs in more controlled environments, such as MWCNTs with varying diameters. MWCNTs were synthesized with diameters of 60 nm, 100 nm, 250 nm, and 450 nm to contain magnetic NP fillers (~10 nm) consisting of ferrites of the form MFe2O4, where M = Co2+, Ni2+, or Fe2+. All confined samples exhibit superparamagnetic-like behavior with stronger magnetic response with respect to increasing MWCNT diameter up to 250 nm due to the enhancement of interparticle interactions.
This thesis provides the first systematic study of this class of nanocomposites, which paves the way to inclusion of novel nanostructured materials in real-world applications.
25
Mayne-L'Hermite, Martine. "Elaboration, microstructure et comportement au fluage de nanocomposites Si3N4/SiC." Limoges, 1997. http://www.theses.fr/1997LIMO0021.
Full textAbstract:
L'objectif de ce travail a ete d'elaborer des nanocomposites si#3n#4/sic presentant une aptitude au formage a chaud. Pour cela, une seconde phase nanometrique sicn(o) ou sic(o) a ete introduite au sein de la matrice si#3n#4 de maniere a developper des microstructures a grains fins et equiaxes favorables a la deformation plastique a haute temperature. Les poudres nanometriques sicn(o) synthetisees par pyrolyse laser possedent des caracteristiques communes, a savoir la presence d'agregats durs au sein desquels les particules sont liees par des liaisons fortes. Ces poudres se decomposent sous atmosphere d'helium ou se niturent sous atmosphere d'azote. Un protocole de melange des poudres dans un liquide organique (acetophenone) et de mise en forme de precompacts a ete adapte a la realisation des nanocomposites. La densite elevee des precompacts obtenus par coulage (57%) temoigne de la bonne desagglomeration et de l'homogeneite des barbotines. L'etude cinetique de la densification des nanocomposites par frittage sous charge en presence d'ajouts (y#2o#3, al#2o#3) montre que la vitesse de densification depend de la nature et de la composition de la seconde phase nanometrique. Les nanocomposites sont constitues de plusieurs phases a savoir si#3n#4 , si#3n#4 , sic et une phase intergranulaire vitreuse (ysialonc). On a pu montrer que le carbure de silicium entraine une augmentation du taux de transformation si#3n#4 (equiaxe) (aciculaire), d'autant plus importante que la teneur en sic est elevee. De plus, la presence de nanoparticules de carbure de silicium aux joints de grains limite la croissance aciculaire des grains si#3n#4. La resistance au fluage en compression des nanocomposites est accrue lorsque la teneur en nanoparticules sic augmente. A partir d'une certaine duree, la deformation est regie par un mecanisme de diffusion aux joints de grains, contrairement au monolithe pour lequel il existe un long stade pseudo-stationnaire. Ce phenomene suggere une stabilite microstructurale induite par les nanoparticules de carbure de silicium. Les nanocomposites contenant 10% de carbure de silicium presentent une aptitude a la deformation en traction a haute temperature (1600 c - 1650c). Des allongements de l'ordre de 40%, obtenus en traction, devraient permettre la fabrication de pieces par formage a chaud.
26
Rebuttini, Valentina. "Functional iron oxide-based hybrid nanostructures." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2014. http://dx.doi.org/10.18452/17049.
Full textAbstract:
In der vorliegenden Arbeit wird das Prinzip der chemischen Oberflächenmodifikation als allgemeine Synthesestrategie beschrieben. Davon ausgehend werden verschiedene Ansätze der chemischen Funktionalisierung dargestellt, mit denen die Eigenschaften der erhaltenen Materialien eingestellt werden können. Im Fokus der Arbeit stehen Eisenoxid-Nanopartikel, die über die „Benzylalkohol-Route“ dargestellt werden. Es wird auf Basis dieser einfachen und vielseitig anwendbaren Funktionalisierung die Herstellung von neuartigen Hybridmaterialien gezeigt. Zur Funktionalisierung zweier magnetischer molekularer Rezeptoren wurde eine Synthesestrategie entwickelt, bei der organische Gruppen kovalent angebunden wurden. Der erste Rezeptor kann zur Erkennung von Biomarkern und den Metaboliten von Pharmazeutika eingesetzt werden. Die Beschichtung der Oberflächen der Eisenoxid-Nanopartikel gelang dabei durch die Verwendung von Organosilan-basierten Kopplungsreagenzien. Der zweite Rezeptor konnte zur Auftrennung eines racemischen Gemisches eines chiralen cavitand eingesetzt werden. Die Darstellung von Graphenoxid-Eisenoxid-Kompositen gelang erfolgreich durch ein ex-situ Verfahren. Es wurde der Einfluss der Oberflächenfunktionalitäten auf die Beladung und Verteilung der Eisenoxid-Nanopartikel untersucht. Dazu wurden via Diazoniumchemie verschiedene Funktionalitäten auf der Graphenoxid-Oberfläche eingeführt. Die Entwicklung einer wasserfreien one-pot Synthese von Gold-Eisenoxid-hetero-Nanostrukturen beschrieben wurde. Insbesondere wurden die Auswirkungen kleiner organischer Moleküle auf die Bildung der Heterostrukturen untersucht.<br>This thesis describes diverse approaches of chemical functionalization as a general strategy to tailor material properties depending on the target application. Particular attention was dedicated to the surface chemistry of iron oxide nanoparticles. Crystalline 10 nm-sized magnetite nanoparticles synthesized through the “benzyl alcohol route” exhibit superparamagnetic behaviour. For this reason they are regarded as suitable solid supports for the fabrication of recoverable devices, which is a fundamental requirement for several of the reported studies. Here it is demonstrated, via the fabrication of novel hybrid materials, that the ease of functionalization of iron oxide nanoparticles renders this material a versatile platform for the development of diverse surface chemistries. A covalent organic functionalization strategy was developed for the synthesis of two recoverable magnetic molecular receptors. The first targeted the recognition of drugs metabolites and biomarkers. It is based on the use of organosilanes coupling agents. A second approach aimed to the heterogeneous resolution of a racemic mixture of an inherently chiral cavitand. Graphene oxide-iron oxide composites were successfully fabricated through an ex-situ approach based on non-covalent interactions between the component phases. The effects of surface functionalities on the loading and distribution of iron oxide nanoparticles were studied by introducing selected functionalities at the graphene oxide surface through diazonium chemistry. Finally, the development of a non-aqueous one-pot synthesis route to gold-iron oxide hetero-nanostructures was described. Particular emphasis was dedicated to study the influence of small organic molecules in promoting the formation of the heterostructures.
27
Isa, Michaël. "Etude du mécanisme de nanostructuration oxydante de ZrAu : application à la synthèse de nanocomposites or-zircone pour microcapteurs de gaz." Toulon, 2003. http://www.theses.fr/2003TOUL0011.
Full textAbstract:
L'étude de l'alliage ZrAu a permis de déterminer ses structures cristallines, d'étudier sa cinétique d'oxydation unique sous air et à 25°C et d'envisager des perspectives d'applications de type microcapteurs catalytiques. ZrAu est triphasé en température : Pour T°C>569°C sa structure est une structure de CsCI. Pour 400<br>The study of ZrAu alloy allowed to determine its cristallographic structures, to study its ultrafast oxidation kinetic under air and at 25°C, and to consider catalytic application as microsensors. For T>569°C, ZrAu is a CsCI superstructure. For 400
28
Zaitsev, Andrii. "Exploration de la voie plasma pour la synthèse de nanostructures et de nanocomposites à base de polyaniline." Thesis, Le Mans, 2015. http://www.theses.fr/2015LEMA1014/document.
Full textAbstract:
Les nanostructures de polymères suscitent un grand intérêt grâce à leurs propriétés uniques comme le facteur de forme important. Cette propriété est essentielle pour l’utilisation dans des domaines où les interactions de surface sont mises en jeu. Un exemple d’une telle application est la détection de gaz. La polyaniline (PANi) s’est montrée prometteuse pour l’utilisation dans les capteurs d’ammoniac. La synthèse conventionnelle (chimique ou électrochimique) de nanofibres de PANi a été largement décrite dans la littérature mais cette voie possède de nombreux inconvénients. Parmi eux, figurent plusieurs étapes de synthèse (la synthèse, la purification, le dépôt sur le substrat) et l’utilisation de produits chimiques (oxydants, acides) peu respectueux de l’environnement. La polymérisation assistée par plasma froid (PECVD) permet de s’en affranchir car seul le monomère est utilisé qui se polymérise directement sur le substrat. Ainsi, ce travail de thèse a pour objectif d’élaborer des nanostructures de polyaniline plasma tout en conservant au mieux l’unité monomère dans le polymère. Le paramètre essentiel qui détermine le processus de nanostructuration est la puissance de décharge. A forte puissance, des films fortement structurés sont obtenus mais les molécules de monomère sont totalement fragmentées. En revanche, une faible puissance conduit à des films avec conservation de l’entité monomère mais sans structure morphologique particulière. Nous avons développé une méthode permettant de combiner les avantages de chaque régime : ce procédé dit « bottom-up » est réalisé en variant la puissance au cours du dépôt selon deux ou trois étapes. Les paramètres qui influencent les structures chimique et morphologique sont déterminés et les procédés à deux et trois étapes sont comparés. Par ailleurs, la synthèse « top-down » de nanostructures par gravure de la couche mince de PANi est également étudiée en fonction des paramètres du plasma (puissance et temps de décharge, débit du gaz de gravure et polarisation du substrat). Finalement, nous avons synthétisé, en phase plasma, des nanocomposites associant les nanostructures de PANi et des particules métalliques de Pd déposées par pulvérisation. La structure chimique des films de PANi est caractérisée par les spectroscopies UV-Vis, IR-TF et XPS. Pour mettre en évidence la nanostructuration des couches minces, les microscopies MEB et AFM sont utilisées. Cette dernière permet également de calculer la valeur de rugosité ainsi que la surface spécifique de la PANi. La spectroscopie EDX est utilisée pour mettre en évidence et pour quantifier le palladium dans les films synthétisés. Les couches obtenues sont finalement caractérisées sous gaz par mesures de variation d’absorbance afin de déterminer leur sensibilité et leur temps de réponse à l’ammoniac<br>Polymer nanostructures are of great interest due to their unique properties such as high shape factor. This property is essential for applications where surface interactions are involved. One example of such an application is the gas detection. Polyaniline (PANi) has been shown as a promising material for ammonia detection. Conventional synthesis (chemical orelectrochemical) of PANi nanofibers has been widely described in the literature but this way has many drawbacks. They include several steps (synthesis, purification, deposition on the substrate) and the use of chemicals (oxidants, acids) which are not environmentally friendly. The polymerization assisted by cold plasma (PECVD) allows overcoming it, as only themonomer is used and is directly polymerized on the substrate. This thesis work aims to develop plasma polyanilinenanostructures while retaining the monomer unit in the polymer. The key parameter that determines thenanostructuring process is the discharge power. At high power, highly structured films are obtained but the monomer molecules are totally fragmented. On the contrary, low power allows conservation of the monomer unit but no surface structuring is observed. We developed a method which combines the advantages of each regime. This "bottom-up" process consists to vary the input power during deposition in two or three stages. Parameters influencing the chemical and morphological structures are determined and the two and three steps methods are compared. Furthermore, the "top-down" synthesis of nanostructures by etching the PANi layer is also studied according to the plasma parameters (power and discharge time, etching gas flow rate and substrate bias). Finally, in plasma phase, we synthesized nanocomposite by combining PANi nanostructures and sputtered Pd particles. The chemical structure of the PANi films is characterized by UV-Vis spectroscopy, FT-IR and XPS. In order to highlight the nanostructuring of thin films, SEM and AFM microscopy areused. The latter one allows also the calculation of the roughness and specific surface of the PANi. EDX spectroscopyis used to bring out the presence of palladium and to quantify it. Finally, the obtained layers are characterized under gas byabsorbance variation measurements in order to determine their sensitivity and response time to ammonia
29
Dubois, Jean-Baptiste. "Conducteurs nanocomposites métalliques élaborés par déformation plastique sévère : formation et stabilité thermo-mécanique des nanostructures, propriétés induites." Poitiers, 2010. http://theses.univ-poitiers.fr/26782/2010-Dubois-Jean-Baptiste-These.pdf.
Full textAbstract:
Ces travaux de thèse concernent l'étude de matériaux nanocomposites métalliques à base de cuivre/niobium (Cu/Nb), combinant conductivité électrique et limite d'élasticité élevées et développés pour la fabrication de bobines résistives de champs magnétiques pulsés intenses. Les conducteurs nanocomposites Cu/Nb continus sont élaborés par une méthode de déformation plastique sévère (DPS), basée sur des cycles d'extrusions, d'étirages et d'empilements successifs, conduisant à la formation d'un matériau nanostructuré multi-échelle. Afin d'optimiser le procédé de fabrication, l'effet des traitements thermiques sur les textures ainsi que leur formation au cours de l'élaboration ont été étudiés par diffraction des rayons X en laboratoire. Des expériences complémentaires de traitements thermiques in-situ sous rayonnement synchrotron ont permis une meilleure compréhension des mécanismes élémentaires de restauration de la microstructure et la définition d'un traitement thermique optimisé. La stabilité thermique des conducteurs apparaît aussi fortement dépendante des dimensions microstructurales : une frustration des phénomènes de restauration, de recristallisation et de croissance des grains est observée pour les conducteurs nanostructurés. Ces résultats ont permis de fabriquer des conducteurs « co-axiaux » optimisés, renforcés par des nanofilaments et des nanotubes de niobium. Leurs propriétés microstructurales et physiques ont été caractérisées et comparées aux anciennes générations de conducteurs nanocomposites Cu/Nb. Les propriétés obtenues et la possibilité d'élaborer de grandes longueurs de fils rendent ces matériaux compétitifs pour les futures applications en champs pulsés<br>This thesis concerns the study of metallic nanocomposite copper/niobium (Cu/Nb) wires, combining high electrical conductivity and high strength, as required for the design of high magnetic field resistive coils. The reinforced continuous nanocomposite Cu/Nb conductors are fabricated via a severe plastic deformation process (SPD), which consists in repeated extrusion, drawing and bundling cycles (Accumulative Drawing and Bundling : ADB) and leads to the nanostructuration of the Nb reinforcements and a multi-scale Cu matrix. In order to optimize the process, the effect of heat treatments on texture and its development during the process were analysed by means of laboratory X-ray diffraction. Complementary in-situ heat treatments under synchrotron radiation gave a better insight into the elementary annealing mechanisms and enabled defining optimized heat treatments. These experiments also revealed that the thermal stability of Cu/Nb conductors is extremely dependent of the microstructure size: recovery, recrystallization, grain growth and all relaxation processes are frustrated in the case of nanocomposites. From these results, optimized “co-axial” conductors reinforced by Nb nanofilaments and nanotubes were processed. Their microstructure and physical properties have been characterized and compared to those of previous Cu/Nb nanocomposite conductors. With the possibility to produce long wires with improved properties, these new Cu/Nb nanocomposites offer a great alternative to existing conductors for future high magnetic field applications
30
Aldroe, Hanaya. "Analyse des propriétés physiques et mécaniques des nanocomposites polyamide 12 / cloisite® 30B en lien avec leurs nanostructures." Thesis, Tours, 2014. http://www.theses.fr/2014TOUR4034/document.
Full textAbstract:
Les nanocomposites suscitent un intérêt croissant depuis leur développement dans les années 90 par Toyota. Par conséquent, l'amélioration des propriétés de ce type de matériaux est un enjeu fort tant d'un point de vue fondamental qu'industriel. Cette amélioration peut passer par un choix pertinent des charges renforçantes ajoutées à la matrice notamment en ce qui concerne le type, la géométrie, la proportion et le traitement de ces charges. L’optimisation des paramètres d’élaboration du mélange y joue aussi un rôle important. L’objectif de ce travail est de contribuer à l’identification et à la compréhension des mécanismes à l'origine du renforcement des matrices thermoplastiques par des nanocharges. Cet aspect est abordé à travers l’étude des propriétés thermiques et mécaniques des nanocomposites formés d’une matrice Polyamide 12 (PA12) chargées par des nanoparticules d’argile organiquement modifiée. Plus précisément, nous avons analysé les effets de la fraction massique des charges et du vieillissement naturel sur les propriétés structurales, thermiques et mécaniques de ces nanocomposites. L’influence des conditions de mélangeage sur ces propriétés ont aussi été examinées. Nous avons particulièrement mis l’accent sur l’identification des liens qui existent entre les propriétés macroscopiques et la structure des nanocomposites. Nous avons aussi fait une étude comparative des propriétés viscoélastiques de ces matériaux à l'état fondu et à l'état solide, ce qui représente une des originalités forte de ce travail<br>Nanocomposites are interestingly growing since their development in the 1990s by Toyota Company. Therefore, improving the properties of such materials is a major issue from fundamental and industrial point of view. This improvement can pass through a relevant choice of reinforcing loads added to the matrix particularly regarding the type, geometry, the proportion, and the treatment of these fillers. The processing parameters of the mixture play also a key role. The objective of this work is to contribute to the identification and understanding of the mechanisms at the origin of the reinforcing thermoplastic matrices by nanofillers. This aspect presented through the study of the thermal and mechanical properties of nanocomposites formed by a polyamide 12 matrix (PA12) filled with organically modified clay nanoparticles. More specifically, we analysed the effects of the filler mass fraction and environmental aging on structural, thermal and mechanical properties of these nanocomposites. The mixing conditions on these properties were also examined. A particular attention has been paid to the study of relationships between the macroscopic properties and the structure of nanocomposites. Viscoelastic properties of these materials in both melt and solid states were compared, which represents one of the originalities of this work
31
Gupta, Maneesh Kumar. "Stimuli-responsive hybrid nanomaterials: spatial and temporal control of multifunctional properties." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45920.
Full textAbstract:
Recently, technological advancement and the promise of next-generation devices have created an overwhelming push for the continued miniaturization of active systems to the micro- and nanometer scale. In this regime, traditional mechanical systems are largely inaccessible and as a result new active or stimuli-responsive materials are required. The work presented in this dissertation provides an understanding of the responsive nature of polymer and biopolymer interfaces especially in contact with metal nanoparticles. This understanding was utilized in conjunction with top-down template-based and self-assembly fabrication strategies to create hybrid protein based films and active polymer-metal hybrids that exhibit large and well-defined modulation of mechanical and optical properties. These materials processing developments represent advancement in the current state of the art specifically in three major areas: 1. template-based top-down control of protein chain conformation, 2. high-throughput synthesis and assembly of strongly coupled plasmonic nanoparticles with modulated optical properties (both near- and far-field), 3. field-assisted assembly of highly mobile and non-close packed magnetic nanorods with capabilities for rapid actuation.
32
Gonzato, Carlo. "Chemical nanosensors based on molecularly imprinted polymer nanocomposites synthesized by controlled radical polymerization." Compiègne, 2012. http://www.theses.fr/2012COMP2035.
Full textAbstract:
Les polymères à empreintes moléculaires (MIP, pour molecularly imprinted polymers en anglais) sont des récepteurs synthétiques, parfois appelés "anticorps en plastique", capables de reconnaitre et fixer spécifiquement une molécule cible. L’impression moléculaire s’est imposée, durant les trente dernières années, comme une technique pour la synthèse des structures réticulées possédant une remarquable affinité et sélectivité vis-à-vis d’une espèce chimique utilisée comme molécule empreinte dans un procédé de moulage au niveau moléculaire. La grande variété de matériaux et de formats accessibles à cette technique lui ont permis de trouver un grand nombre d’applications, telles que la séparation, les capteurs, la catalyse, le ré-largage contrôlé de médicaments. Depuis leur apparition, la plupart des MIPs a été synthétisée par polymérisation radicalaire libre (FRP) des monomères vinyliques. Cette méthode de polymérisation représente un excellent choix en termes de simplicité de mise en place, tolérance par rapport aux solvants et aux différents groupements fonctionnels des ingrédients. Cependant, plusieurs désavantages liés à cette technique limitent la possibilité d’obtenir un contrôle adéquate vis-à-vis de certaines caractéristiques fondamentales pour des applications en nano-technologies. L’introduction des techniques de polymérisation radicalaire contrôlée/vivante (CRP) a donc représentée une avancée importante et a permis de dépasser certains limites associés aux MIPs synthétisés par FRP. Dans ce contexte, ce travail de thèse a étudié les avantages provenant de l’utilisation d'une méthode CRP, le RAFT, pour la synthèse des MIP. Ce travail a été mené en se focalisant sur les caractéristiques principales des CRPs : le caractère vivant et, en même temps, contrôlé. Dans un premier temps, nous avons utilisé l’aspect vivant de la polymérisation pour la synthèse des nanocomposites MIP, possédant des propriétés superparamagnétiques. Celle-ci a été effectuée par polymérisation de couches p(EGDMA-co-MAA) par RAFT amorcée à la surface des particules de Fe3O4 préfonctionnalisées avec des groupements amine. Le greffage de ces couches a été obtenu en employant des ultrasons comme source d'agitation, et en testant différents solvants pour en apprécier l’influence sur la structure et la morphologie des composites résultants. Nous avons démontré que le greffage se produit d’une façon homogène, et que grâce au caractère vivant de la polymérisation RAFT, les composites peuvent être fonctionnalisés davantage, par exemple par des chaines p(EGMP), pour ajuster leur propriétés de surface. Dans un deuxième temps, nous nous sommes consacrés à une étude comparative visant la mise en évidence des avantages de la RAFT par rapport à la FRP en termes de performances des MIP acryliques et méthacryliques. Pour mieux apprécier les différences induites par la méthode de polymérisation, le dégrée de réticulation et donc la flexibilité des réseaux ont été variés de façon systématique. Cette stratégie a permis de bien apprécier les différences induites par chaque technique de polymérisation. Les résultats ont démontré que la RAFT permet de synthétiser des MIPs ayant une meilleure affinité pour leur molécule cible, et que cette amélioration est due à une distribution plus homogène des points de réticulation au sein du réseau. Finalement, nous avons appliqué la RAFT pour la synthèse de nanocapteurs individuels basés sur des composite MIP intégrant des nanoparticules d'or, et utilisant la spectroscopie Raman exaltée (SERS) pour la détection<br>Molecularly imprinted polymers (MIPs) are synthetic receptors, also known as antibody mimics, that can specifically bind target molecules. Molecular imprinting has emerged, over the last 30 years; it is an extremely versatile strategy for synthesizing networks possessing high affinity and selectivity for a chemical species, used as a molecular template during their synthesis. The wide variety of materials and formats that are accessible through this strategy has resulted in a broad spectrum of applications for such MIPs, ranging from separation to sensing, catalysis, drug delivery, etc. Since the beginning, the great majority of the imprinted networks has been synthesized by assembling vinyl monomers via free-radical polymerization (FRP). This polymerization method represents a convenient choice for synthesizing MIPs, due to its easy setup, versatility, tolerance with respect to many solvents and functional groups. However, some drawbacks greatly affect the possibility of achieving of suitable degree of control over some “polymeric” parameters which become important for specific applications. The introduction of controlled/”living” radical polymerization (CRP) techniques has then represented an opportunity for MIPs to reduce, and in some cases even to overcome, some of their limits arising from FRP. In this respect, this Ph. D. Thesis has studied how the use of RAFT polymerization, one of the most applied CRPs, can be advantageously used to syntheze MIPs. This has been done by focusing on the main characteristics of CRPs: their living and controlled nature. The living nature has been exploited during the first part of this work, which involved the synthesis of superparamagnetic molecularly imprinted nanocomposites via surface-initiated RAFT polymerization of p(EGDMA-co-MAA) on amino-modified Fe3O4 nanoparticles. The polymer grafting has been performed using an unusual stirring technique (i. E. Ultrasonication) during the polymerization step, and by testing different polymerization solvents for evaluating their effect on the composite structure. It has been observed that the grafting resulted in homogeneous polymer layers, the thickness of which could be controlled by adjusting the RAFT/radical source ratio. Moreover, the living nature of RAFT fragments has been exploited for post-functionalizing the surface of a composite particle with p(EGMP) brushes, thus demonstrating the potential of fine-tuning the particle surface properties through the living chain ends. In the second part of the thesis, an in-depth study has been performed on the effects induced by the use of controlled (RAFT) polymerization conditions on the binding behaviour and structural parameters of bulk acrylic and methacrylic MIPs and the corresponding non-imprinted polymers, synthesized by RAFT and FRP with varying cross-linking degree. This strategy actually provided scaffolds with progressively increased degree of flexibility (especially in the case of acrylics) which allowed visualize the enhancement of binding and structural differences arising from the polymerization technique. As a result, it has been observed that the use of controlled (RAFT) conditions induced, on the imprinted networks, an increased template affinity over equivalent FRPs, and it has been demonstrated that this improved affinity can be related to more homogeneous distributions of the cross-linking points achieved during RAFT polymerization. The third part presents preliminary results toward the synthesis by RAFT of individual multi-composite MIP nanosensors using enhanced Raman spectroscopy (SERS) for detection
33
Hoang, Minh Tuan. "Modélisation et simulation multi échelle des effets de taille et des couplages électromécaniques dans les nanostructures." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1074/document.
Full textAbstract:
Les nanostructures, et en particulier les nanofils semi-conducteurs, ont suscité ces dernières années un très grand intérêt pour de nombreuses applications comme les systèmes de récupération d'énergie ou les capteurs de très haute précision. Dans de telles structures des expérimentations et des calculs théoriques ab-initio ont mis en évidence des effets de taille, pouvant modifier significativement les propriétés électromécaniques pour des diamètres de fils en dessous de 10 nm. L'objectif de ce travail de thèse est de proposer des modélisations multi échelle des nanostructures électromécaniques, telles que les nanofils ioniques et des nanocomposites stratifiés, permettant de reproduire les effets de taille associés à l'échelle nanométrique dans un cadre continu, en se basant sur des calculs ab-initio pour identifier et valider les modèles. Dans une première partie, les effets de surface dans des nanofils piézoélectriques isolés homogènes sont modélisés. Une approche multi échelle est développée, incluant une modélisation continue des nanofils en prenant en compte une énergie de surface supplémentaire dans un cadre piézoélectrique, dont les paramètres associés sont identifiés par calculs ab-initio. Pour cela, une procédure basée sur un modèle de films minces est développée, permettant au travers de calculs ab-initio sur des films d'épaisseurs successives d'isoler l'énergie volumique et de surface, et d'en déduire les coefficients élastiques et piézoélectriques de surface. Les équations du modèle continu sont ensuite résolues par une méthode d'éléments finis incluant des éléments de surface adaptés. Le modèle multi échelle continu est comparé à des calculs ab-initio impliquant des modèles atomistiques complets de nanofils de différents diamètres (de 0,6 à 3,9 nm) pour valider les effets de taille des propriétés électromécaniques. Dans une deuxième partie, des modèles multi échelles sont construits en vue de modéliser les effets de taille pour des nanostructures hétérogènes. Ces structures incluent des nanofils revêtus, ou des nanocomposites stratifiés. Pour les nanofils avec hétérogénéités radiales, l'approche précédemment développée est étendue au cas des surfaces revêtues, et le modèle continu fait intervenir une énergie de surface incluant les effets du revêtement. Pour les nanocomposites stratifiés AlN/GaN, les effets de taille observés par calculs ab-initio sont dus à des effets d'interface et induisent des propriétés élastiques dépendantes des épaisseurs des couches. Un modèle de matériau homogénéisé continu est proposé, incluant un modèle d'interface imparfaite, permettant d'inclure les effets de taille, identifié par calculs ab-initio. Dans une dernière partie, des applications à des systèmes de nanogénérateurs à base de nanofils sont proposées, faisant intervenir des ensembles de nanofils alignés dans une matrice polymère et surmontés par une feuille de graphène. Les approches précédemment développées sont utilisées pour modéliser ces structures par éléments finis<br>Nanostructures, and more specifically semiconductor nanowires, have drawn special attention in recent years for many applications such as energy harvesting systems or sensors of very high precision. Many recent experiments and theoretical ab-initio calculations have evidenced size effects, which can significantly modify the electromechanical properties of nanowires for diameters below 10 nm. The objective of this thesis is to provide multi-scale modeling of electromechanical properties of nanostructures, such as ionic nanowires and laminated nanocomposites, to reproduce the size effects associated with nanoscale in a continuum model, based on ab-initio calculations to identify and validate the models. In a first part, the surface effects in isolated homogeneous piezoelectric nanowires are modeled. A multi-scale approach is developed, including continuous nanowires modeling taking into account an additional surface energy in the piezoelectric laminates where the associated parameters are identified by ab-initio calculations. For this, a procedure based on slabs is developed, allowing through first-principles calculations on successive slabs thicknesses to isolate the surface energy and to deduce the surface elastic and piezoelectric coefficients. The equations of the continuous model are then solved by a finite element method including appropriate surface elements. The continuous multi-scale model is compared with ab-initio calculations involving full atomistic models of nanowires with different diameters (from 0.6 to 3.9 nm) to validate model regarding size effects of electromechanical properties. In the second part, multi-scale models are constructed to describe the size effects for heterogeneous nanostructures. These structures include coated nanowires or laminated nanocomposites. For nanowires with radial heterogeneity, the previously developed approach is extended to the case of coated surfaces, and involves a continuous surface energy incorporating the effects of the coating. For laminated AlN/GaN nanocomposites, size effects observed by ab-initio calculations are caused by the presence of the interfaces and induce size-dependent elastic properties with respect to the layer thickness. A continuum model based on an imperfect interface is proposed to describe the size dependent effective elastic properties of the overall composite, which are identified by ab-initio calculations. In the last part, nanogenerators system based on nanowires are modeled, involving nanowires arrays aligned in polymer substrates with graphene electrode. The previously developed finite element models are used to simulate the electromechanical properties of such systems
34
Budimir, Milica. "Modification of carbon nanocomposites by electromagnetic irradiation for biomedical application." Thesis, Lille 1, 2020. http://www.theses.fr/2020LIL1I050.
Full textAbstract:
La contamination microbienne est un problème très important dans le monde entier qui affecte de nombreux aspects de notre vie quotidienne: soins de santé, systèmes de purification de l'eau, stockage des aliments, etc. Les thérapies antibactériennes traditionnelles deviennent moins efficaces, car une utilisation et une élimination inadéquates des antibiotiques ont déclenché des mutations chez les bactéries qui ont conduit à de nombreuses souches résistantes aux antibiotiques. Par conséquent, il est très important de développer de nouveaux matériaux antibactériens pour combattre de manière efficace les bactéries planctoniques et leurs biofilms. Dans ce contexte, l'objectif de cette thèse était de développer deux nanocomposites différents carbone / polymère (oxyde de graphène réduit / polyéthylénimine et nanostructures de carbone / polyuréthane) originaux qui présentent d'excellentes propriétés antibactériennes à travers deux effets différents : photothermique et photodynamique. Une irradiation électromagnétique a été utilisée (rayonnement laser proche infrarouge ou rayons gamma) dans le but de déclencher l'effet photothermique et d'améliorer l'effet photodynamique des nanocomposites. Dans la première partie expérimentale de cette thèse, une stratégie simple et efficace pour la capture de bactéries et leur éradication par destruction photothermique est présentée. Le dispositif développé consiste en une interface à base de Kapton modifié avec des nano-trous d'or (Au NH), et recouvert d’une couche mince d'oxyde de graphène/ polyéthylèneimine (K / Au NH / rGO-PEI). Le dispositif K / Au NH / rGO- PEI a été efficace pour capturer et éliminer à la fois les bactéries planctoniques à Gram positif Staphylococcus aureus (S. aureus) et à Gram négatif Escherichia coli (E. coli) après 10 min d'irradiation à 980 nm. De plus, le dispositif développé s’est avéré efficace pour détruire et éradiquer des biofilms de Staphylococcus epidermidis (S. epidermidis) après 30 min d'irradiation. Dans la deuxième partie expérimentale de ce travail de thèse, la préparation d'un nanocomposite à base de nanostructures de carbone hydrophobes / polyuréthane (hCQD-PU) avec des propriétés antibactériennes améliorées induites par un prétraitement par irradiation gamma est présentée. Des nanostructures de carbone hydrophobes (hCQD), capables de générer des espèces réactives de l'oxygène (ROS) suite à une irradiation avec une lumière bleue de faible puissance (470 nm), ont été incorporées dans la matrice polymère en polyuréthane (PU) pour former un nanocomposite photoactif. Le nanocomposite ainsi formé a été exposé à différentes doses d'irradiation gamma (1, 10 et 200 kGy) afin de modifier ses propriétés physiques et chimiques et d'améliorer son efficacité antibactérienne. Le prétraitement par irradiation gamma a considérablement amélioré les propriétés antibactériennes du nanocomposite, et le meilleur résultat a été obtenu pour la dose d'irradiation de 200 kGy. Cet échantillon a permis l'élimination totale des bactéries après 15 min d'irradiation par la lumière bleue, pour les souches à Gram positif et à Gram-négatif<br>Microbial contamination is a very important issue worldwide which affects multiple aspects of our everyday life: health care, water purification systems, food storage, etc. Traditional antibacterial therapies are becoming less efficient, because inadequate use and disposal of antibiotics have triggered mutations in bacteria that have resulted in many antibiotic-resistant strains. Therefore, it is of great importance to develop new antibacterial materials that will effectively combat both planktonic bacteria and their biofilms in an innovative manner. In this context, the goal of this thesis was to develop two different carbon/polymer nanocomposites (reduced graphene oxide/polyethylenimine and carbon quantum dots/polyurethane) which exhibit excellent antibacterial properties through two different effects: photothermal and photodynamic. Electromagnetic irradiation was used (near-infrared laser radiation or gamma rays) in these experiments, for the purpose of triggering the photothermal effect and enhancing the photodynamic effect of the nanocomposites. In the first experimental part of this thesis, a simple and efficient strategy for bacteria capture and their eradication through photothermal killing is presented. The developed device consists of a flexible Kapton interface modified with gold nanoholes (Au NH) substrate, coated with reduced graphene oxide-polyethyleneimine thin films (K/Au NH/rGO-PEI). The K/Au NH/rGO–PEI device was efficient in capturing and eliminating both planktonic Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria after 10 min of NIR (980 nm) irradiation. Additionally, the developed device could effectively destroy and eradicate Staphylococcus epidermidis (S. epidermidis) biofilms after 30 min of irradiation. In the second experimental part, the preparation of a hydrophobic carbon quantum dots/polyurethane (hCQD-PU) nanocomposite with improved antibacterial properties caused by gamma-irradiation pre-treatment is presented. Hydrophobic quantum dots (hCQDs), which are able to generate reactive oxygen species (ROS) upon irradiation with low power blue light (470 nm), were incorporated in the polyurethane (PU) polymer matrix to form a photoactive nanocomposite. Different doses of gamma irradiation (1, 10 and 200 kGy) were applied to the formed nanocomposite in order to modify its physical and chemical properties and improve its antibacterial efficiency. The pre-treatment by gamma-irradiation significantly improved antibacterial properties of the nanocomposite, and the best result was achieved for the irradiation dose of 200 kGy. In this sample, total bacteria elimination was achieved after 15 min of irradiation by blue light, for Gram-positive and Gram-negative strains
35
Shi, Yupeng. "Functionalized Silica Nanostructures : Degradation Pathways and Biomedical Application from 2D to 3D." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS122.pdf.
Full textAbstract:
Les nanoparticules de silice sont très largement étudiées pour les applications biomédicales. Elles permettent une facilité et une flexibilité de la synthèse des particules et une bio-toxicité limitée. Cette thèse a mené une grande diversité de résultats impliquant des nanomatériaux de silice. Premièrement, les propriétés physicochimiques et les propriétés de biodégradation de trois types de nanoparticules de silice structurées ont été étudiées dans un tampon, un milieu de culture et au contact de fibroblastes cutanés humains suggérant que les nanoparticules de silice doivent être principalement considérées comme dégradées par hydrolyse, et non biodégradé. Ensuite, des nanoparticules de silice multifonctionnelles constituées de nanoparticules de silice creuses et de nanoparticules de MnO2 ont été synthétisées. Ainsi le contrôle de la libération du médicament et la performance de l’imagerie de ces nanoplates ont été étudiées à partir de modèles 2D à 3D. Cette approche pourrait être utilisée pour une évaluation rapide de la bio-fonctionnalité des nanoparticules avant de mettre en place des expériences in vivo. En outre, un nouveau nanocomposite 3D à base de collagène utilisant des tiges de silice a été étudié et les relations entre la composition composite, la structure et les propriétés mécaniques, mettant en évidence le rôle clé des interactions collagène-silice. L'influence de ces paramètres sur l'adhésion et la prolifération des cellules fibroblastiques a également été étudiée. De plus, nous avons préparé et utilisé des nanobatonnêts de silice magnétiques pour contrôler l’orientation des particules dans le réseau de collagène grâce à un champ magnétique externe. Tous les résultats apportent de nouvelles connaissances sur la préparation et les propriétés des bionanocomposites et ouvrent la voie à des hydrogels multifonctionnels<br>Silica nanoparticles, thanks to the great easy and adaptability of particle synthesis and limited biotoxicity, is very widely studied for biomedical applications. This thesis conducted a large diversity of investigations involving silica nanomaterials. Firstly, the physicochemical properties and biodegradation properties of three types of structured silica nanoparticles were studied in a buffer, a culture medium and in contact with human dermal fibroblasts that suggest that, under these conditions, the silica nanoparticles must be mainly considered as degraded by hydrolysis and not biodegraded. Then, multifunctional silica nanoparticles which are consist of hollow silica nanoparticles and MnO2 nanosheets were synthesized. And the control drug release and imaging performance of this nanoplatforms were studied from 2D to 3D models. This approach could be used for a rapid assessment of the biofunctionality of nanoparticles before setting up in vivo experiments. Furthermore, a new 3D collagen-based nanocomposites using silica rods were studied and the relationships between the composite composition, structure and mechanical properties, emphasizing the key role of collagen-silica interactions. The influence of these parameters on the adhesion and proliferation of fibroblast cells was also investigated. In addition, we prepared and used magnetic silica nanorods to control particle orientation within the collagen network thanks to an external magnetic field. All the results bring new insights on the preparation and properties of bionanocomposites and open the route to multifunctional hydrogels
36
Sauvage, Xavier. "Transformations de phases induites par déformation plastique intense. Cas des aciers perlitiques tréfilés et des nanocomposites filamentaires Cu/Nb." Rouen, 2001. http://www.theses.fr/2001ROUES032.
Full textAbstract:
Les aciers perlitiques tréfilés et les nanocomposites filamentaires Cu/Nb sont élaborés par tréfilage à froid. La déformation plastique conduit à un allongement des grains le long de l'axe du fil et à une réduction importante de leurs dimensions dans la section transverse. Ainsi, les lamelles de cémentite des aciers perlitiques ne font plus que quelques nanomètres d'épaisseur et les fibres de niobium des composites Cu/Nb ont un diamètre moyen compris entre 10 et 60 nm. Ces nanostructures ont été caractérisées en microscopie ionique, sonde atomique, MET et METHR. Dans les aciers perlitiques, la dissolution partielle de la cémentite a pu être clairement mise à jour. Plus les lamelles sont fines, plus elles sont dissoutes. La dissolution est parfois totale et les zones transformées semblent alors évoluer vers une structure de type martensitique. La dissolution de la cémentite résulterait de l'accroissement considérable de la proportion d'interfaces. En considérant un effet de type Gibbs-Thomson, cette dissolution a pu être simulée. Toutefois, le taux de cémentite dissoute est sous-estimé car la modélisation de la cinétique ne prend pas en compte un terme de transport lié au champ de contraintes internes. Dans les nanocomposites filamentaires Cu/Nb, la déformation plastique n'affecte généralement pas la nature des différentes phases : le niobium et le cuivre restent purs. Toutefois, dans les zones où la taille de grains est inférieure à 15 nm, les analyses en sonde atomique révèlent une interdiffusion du cuivre et du niobium. Ces zones de mélange pourraient être amorphes comme le suggèrent nos observations en METHR. Cette amorphisation résulterait de l'accroissement considérable de l'énergie d'interface et de l'énergie élastique résultant des contraintes internes. La cinétique serait, quant à elle, favorisée par l'accroissement de la densité de lacunes au cours du tréfilage et par le champ de contraintes internes.
37
Adireddy, Shivaprasad Reddy. "High Yield Solvothermal Synthesis of Hexaniobate Based Nanocomposites via the Capture of Preformed Nanoparticles in Scrolled Nanosheets." ScholarWorks@UNO, 2013. http://scholarworks.uno.edu/td/1726.
Full textAbstract:
The ability to encapsulate linear nanoparticle (NP) chains in scrolled nanosheets is an important advance in the formation of nanocomposites.These nanopeapods (NPPs) exhibit interesting properties that may not be achieved by individual entities. Consequently, to fully exploit the potential of NPPs, the fabrication of NPPs must focus on producing composites with unique combinations of morphologically uniform nanomaterials. Various methods can produce NPPs, but expanding these methods to a wide variety of material combinations can be difficult. Recent work in our group has resulted in the in situ formation of peapod-like structures based on chains of cobalt NPs. Building on this initial success, a more versatile approach has been developed that allows for the capture of a series of preformed NPs in NPP composites.
In the following chapters, various synthetic approaches for NPPs of various material combinations will be presented and the key roles of various reaction parameters will be discussed. Also, uniform hexaniobate nanoscrolls were fabricated via a solvothermal method induced by heating up a mixture of TBAOH, hexaniobate crystallites, and oleylamine in toluene. The interlayer spacing of the nanoscrolls was easily tuned by varying the relative amount and chain lengths of the primary alkylamines.
To fabricate NPPs, as-synthesized NPs were treated with hexaniobate crystallite in organic mixtures via solvothermal method. During solvothermal treatment, exfoliated hexaniobate nanosheets scroll around highly ordered chains of NPs to produce the target NPP structures in high yield. Reaction mixtures were held at an aging temperature for a few hours to fabricate various new NPPs (Fe3O4@hexaniobate, Ag@hexaniobate, Au@hexaniobate, Au-Fe3O4@hexaniobate, TiO2@hexaniobate, CdS@hexaniobate, CdSe@hexaniobate, and ZnS@hexaniobate).
This versatile method was first developed for the fabrication of magnetic peapod nanocomposites with preformed nanoparticles (NPs). This approach is effectively demonstrated on a series of ferrite NPs (≤ 14 nm) where Fe3O4@hexaniobate NPPs are rapidly (~ 6 h) generated in high yield. When NP samples with different sizes are reacted, clear evidence for size selectivity is seen. Magnetic dipolar interactions between ferrite NPs within the Fe3O4@hexaniobate samples leads to a significant rise in coercivity, increasing almost four-fold relative to free particles. Other magnetic ferrites NPPs, MFe2O4@hexaniobate (M = Mn, Co, Ni), can also be prepared. This synthetic approach to nanopeapods is quite versatile and should be readily extendable to other, non-ferrite NPs or NP combinations so that cooperative properties can be exploited while the integrity of the NP assemblies is maintained. Further, this approach demonstrated selectivity by encapsulating NPs according to their size.
The use of polydispersed NP systems is also possible and in this case, evidence for size and shape selectivity was observed. This behavior is significant in that it could be exploited in the purification of inhomogeneous NP samples. Other composite materials containing silver and gold NPs are accessible. Partially filled Fe3O4@hexaniobate NPPs were used as templates for the in situ growth of gold to produce the bi-functional Au- Fe3O4@hexaniobate NPPs. Encapsulation of Ag and Au NP chains with a hexaniobate nanoscroll was shifted the surface plasmon resonance to higher wavelengths.
In these composites NPs can be incorporated to form NPP structures, decorated on nanosheets before scrolling, or attached to the surfaces of the nanoscrolls. The importance of this advancement is the promise it holds for the design and assembly of active nanocomposites. One can create important combinations of nanomaterials for potential applications in a variety of areas including catalysis, solar conversion, thermoelectrics, and multiferroics.
38
Matsumura, Masashi. "Synthesis, electrical properties, and optical characterization of hybrid zinc oxide/polymer thin films and nanostructures." Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2009r/matsumura.pdf.
Full textAbstract:
Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.<br>Title from PDF t.p. (viewed Feb. 3, 2010). Additional advisors: Derrick R. Dean, Sergey B. Mirov, Sergey Vyazovkin, Mary Ellen Zvanut. Includes bibliographical references (p. 122-145).
39
Laurent, Christophe. "Contribution à l'étude de nanocomposites à matrice céramique. Alumine-alliages fer-chrome et alumine-zircone-fer et alliages fer-chrome." Toulouse 3, 1994. http://www.theses.fr/1994TOU30017.
Full textAbstract:
Les nanocomposites alumine-metal, dans lesquels les particules metalliques nanometriques sont dispersees dans la matrice ceramique possedent des proprietes mecaniques superieures a celles de l'alumine pure ou renforcee par des particules metalliques micrometriques. L'elaboration de poudres nanocomposites alumine-fer, alumine-chrome et alumine-alliages fer-chrome a ete realisee par calcination puis reduction selective sous hydrogene de solutions solides d'oxydes obtenues par decomposition de precurseurs oxaliques mixtes. Une etude de l'influence des temperatures de calcination et de reduction sur la formation des nanocomposites alumine-fer a ete menee, notamment par spectroscopie mossbauer, mettant en evidence plusieurs modes de formation du fer metallique. Cette etude a ete etendue aux alliages fer-chrome, et il est montre que les particules metalliques les plus petites sont les plus riches en chrome. La localisation des nanoparticules metalliques, intragranulaire ou en surface des grains d'alumine, a ete mise en evidence par thermogravimetrie et correlee a la teneur en metal. Des composites massifs ont ete prepares par frittage sous charge des poudres nanocomposites. Les meilleures proprietes mecaniques (charge a rupture et tenacite) sont obtenues pour des composites hybrides ou la phase metallique est dispersee a la fois sous forme de particules nanometriques a l'interieur des grains d'alumine et sous forme de particules micrometriques situees aux joints de grains de la matrice. Le choix approprie des temperatures de calcination et de reduction des poudres permet d'optimiser les caracteristiques mecaniques. L'oxydation sous air de ces materiaux est negligeable jusqu'a 1000c; au-dela, les nanocomposites contenant du chrome sont plus stables que les nanocomposites alumine-fer. Des composites hybrides alumine-zircone-fer et alumine-zircone-alliages fer-chrome ont ete elabores par quatre methodes. Suivant la microstructure obtenue, il y a amelioration des proprietes mecaniques par rapport a celles des nanocomposites alumine-metal, ou bien annihilation partielle des differents mecanismes de renforcement
40
Kintz, Harold. "Réalisation de couches minces nanocomposites par un procédé original couplant la pyrolyse laser et la pulvérisation magnétron : application aux cellules solaires tout silicium de troisième génération." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00958453.
Full textAbstract:
Ce travail porte sur la synthèse de couches minces de nanoparticules de silicium (np-Si) encapsulées dans une matrice diélectrique en vue d'une application en tant que couche active pour les cellules solaires de 3ème génération. La technique utilisée pour la synthèse des np-Si est la pyrolyse laser. Cette technique nous a permis d'obtenir des np-Si cristallines d'environ 5 nm de diamètre avec une distribution en taille étroite. Par ailleurs, l'utilisation de gaz précurseurs spécifiques (PH₃, B₂H₆) dans le mélange réactionnel a rendu possible le dopage (type n ou p) des np-Si. Le dopage effectif des np-Si a pu être mis en évidence par des mesures de résonance paramagnétique électronique (RPE). Des films de np-Si seules ont pu être déposés in-situ via la création d'un jet supersonique de gaz contenant les particules de silicium. Les caractérisations optoélectroniques de ces couches ont montré un effet de confinement quantique fort au sein de films, garantissant ainsi un élargissement important du gap du silicium de 1.12 eV (pour le silicium massif) à environ 2 eV (pour les np-Si) ; prérequis indispensable pour réaliser une cellule tandem tout silicium. Des mesures de résistivité sur ces films ont permis de confirmer l'activité des dopants au sein des np-Si. Pour les np-Si dopées au phosphore une diminution de la résistivité de plus de 5 ordres de grandeurs par rapport au np-Si intrinsèques a été observée. Le couplage entre la pyrolyse laser et la pulvérisation magnétron via notre dispositif original de synthèse s'est révélé parfaitement adapté à l'élaboration de couches minces nanocomposites np-Si/SiO₂. Un comportement de type diode a pu être mis en évidence sur une jonction constituée par la superposition d'une couche nanocomposites (type n) sur un substrat de silicium massif (type p). Au-delà de la simple application au photovoltaïque, le procédé couplé, largement éprouvé et optimisé au cours de ce travail de thèse, pourrait permettre la réalisation d'une multitude de couches nanocomposites différentes, puisque la nature chimique des particules et de la matrice peuvent être choisies indépendamment.
41
Kim, Kwang-Hyon [Verfasser], Thomas [Akademischer Betreuer] Elsässer, Alejandro [Akademischer Betreuer] Saenz, and Claus [Akademischer Betreuer] Ropers. "Ultrafast nonlinear optical processes in metal-dielectric nanocomposites and nanostructures : passive mode-locking, slow light, high harmonic generation / Kwang-Hyon Kim. Gutachter: Thomas Elsässer ; Alejandro Saenz ; Claus Ropers." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://d-nb.info/1021720437/34.
Full text
42
Thilly, Ludovic. "Exploration theorique et experimentale de fils nanocomposites continus presentant des proprietes extremes de conductivite electrique et de limite elastique : application future : Coilin 100 t." Toulouse, INSA, 2000. http://www.theses.fr/2000ISAT0028.
Full textAbstract:
Des conducteurs renforces nanocomposites cuivre/niobium et cuivre/tantale ont ete elabores par etirage pour le developpement des bobines resistives de champs magnetiques pulses intenses, dont le cahier des charges impose une limite elastique maximale pour supporter les contraintes crees par les forces de lorentz et une conductivite electrique elevee pour une duree d'impulsion prolongee. L'etude de l'effet de la deformation et des basses dimensions a ete menee en parallele : - sur les proprietes mecaniques, en faisant appel aux techniques post-mortem de microscopie electronique (en transmission et haute resolution), atomique (sonde tomographique 3d) ainsi qu'a la technique de deformation in-situ en microscope electronique, revelant les mecanismes de la deformation dans ces nanostructures. La modelisation du comportement des dislocations a permis de simuler les proprietes mecaniques et de determiner les parametres structuraux d'optimisation. - sur la conductivite electrique afin d'en determiner les parametres d'optimisation. Ces parametres ont permis d'elaborer des conducteurs composes d'une matrice de cuivre contenant 52. 2 millions et 4. 4 milliards de nanowhiskers de niobium aux proprietes extremes. Parallelement, l'etude du systeme cuivre/tantale a revele des problemes de compatibilite de deformation dus a la difference de modules de cisaillement et caracterises par le developpement d'une rugosite interfaciale macroscopique menant a la fracture prematuree du tantale. Ce phenomene a ete etudie theoriquement et experimentalement selon le formalisme des instabilites de grinfeld. L'etude de deux modes de deformation (etirage et extrusion) a permis de definir une methode d'elaboration permettant l'elaboration de nanocomposites cuivre/tantale.
43
Barin, Gabriela Borin. "Preparação e caracterização de nanoestruturas de carbono por método hidrotérmico a partir de biomassa." Universidade Federal de Sergipe, 2011. https://ri.ufs.br/handle/riufs/3511.
Full textAbstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Nanostructured carbon materials production can constitute an alternative for a sustainable management of residues originated from petrochemical waste and agriculture activities, toward the development of multifunctional ―green‖ materials. The coconut processing industry generate a significant amount of waste (45% of mass). The shell, fibers and coconut coir dust have been studied extensively to produce conventional carbon materials. The goal of this work was to produce carbon-clay nanocomposites and carbon nanostructures by hydrothermal route. By using coconut fiber residue as carbonaceous precursor along with lamellar (montmorillonite and kaolinite) and fibrous clays (sepiolite and attapulgite).The obtained materials were characterized by X-ray diffraction, Raman and Infrared spectroscopy, thermogravimetry, scanning and transmission electron microscopy and area and porosity measurements by BET. Carbon phase formation was indicated by infrared results with bands at ~ 1444 cm-1 and ~ 1512 cm-1 assigned to C=C of aromatic groups. Raman spectroscopy results showed presence of carbonaceous species by the appearance of D and G bands assigned to disordered and graphitic crystallites, respectively. The estimated particle size based on Raman bands was found between 8-33 nm. SEM results showed that the morphology of coconut coir dust was preserved and all materials showed overlapping sheets and plates formation. In transmission electron microscopy (TEM) images it was possible to observe three types of carbon nanostructures: sheets, fibers and nanoparticles. It was observed the formation of very thin amorphous sheets, as well as the presence of partially ordered graphitic domains and disperse carbon nanoparticles.<br>A produção de materiais de carbono nanoestruturados pode constituir uma alternativa para a reutilização de resíduos provenientes da indústria petroquímica e atividades agrícolas, abrindo um caminho para o desenvolvimento de materiais ―verdes‖ multifuncionais. Da indústria do processamento do coco, origina-se uma quantidade significativa de resíduos (45% do fruto). A casca, fibras e pó de coco são estudados extensivamente para a produção de materiais de carbono convencionais. A proposta deste trabalho foi produzir nanocompósitos de carbono-argila e nanoestruturas de carbono, via rota hidrotérmica. Para tanto foi utilizado o pó de coco in natura como precursor carbonáceo e argilas lamelares (montmorillonita e caulinita) e fibrosas (atapulgita e sepiolita). Os materiais obtidos foram caracterizados por difração de Raios-X, espectroscopia Raman e no Infravermelho, Termogravimetria, Microscopia eletrônica de Varredura (MEV) e Transmissão (MET), e medidas de área superficial e porosidade por BET. A formação de carbono foi indicada pelos resultados de infravermelho com bandas em ~1444 cm-1 e ~1512 cm-1 atribuídas a C=C de grupos aromáticos. Os resultados de espectroscopia Raman evidenciaram a presença de espécies carbonáceas pelo aparecimento das bandas D e G atribuídas, respectivamente, a presença de desordem e cristalitos de grafite. A faixa de tamanho de partícula estimada a partir das bandas Raman está entre 8-33 nm. Os resultados de MEV mostraram que a morfologia do pó de coco foi preservada e todos os materiais obtidos apresentaram a formação de folhas sobrepostas e placas. Nas imagens de microscopia eletrônica de transmissão (MET) foi possível observar a formação de três tipos de nanoestruturas de carbono: folhas, fibras e nanopartículas. Observou-se a formação de folhas muito finas, de caráter predominantemente amorfo, bem como a presença de domínios grafiticos parcialmente ordenados, e nanopartículas de carbono dispersas.
44
Stolk, Jonathan Douglas. "Development of low thermal expansion, high conductivity nanocomposites /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
Full text
45
Işık, Kıvanç Tanoğlu Metin. "Layered silicate/polypropylene nanocomposites/." [s.l.]: [s.n.], 2006. http://library.iyte.edu.tr/tezler/master/makinamuh/T000532.pdf.
Full text
46
Ye, Yueping. "Microstructure and properties of epoxy/halloysite nanocomposite /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?MECH%202006%20YE.
Full text
47
Yang, Yong. "Carbon dioxide assisted polymer micro/nanofabrication." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1117591862.
Full textAbstract:
Thesis (Ph. D.)--Ohio State University, 2005.<br>Title from first page of PDF file. Document formatted into pages; contains xviii, 226 p.; also includes graphics (some col.). Includes bibliographical references (p. 206-226). Available online via OhioLINK's ETD Center
48
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.
Full text
49
Semaan, Chantal. "Polymères nanostructurés à base de nanotubes de carbone." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14187/document.
Full textAbstract:
Ce travail de thèse concerne l’étude de dispersions de nanotubes de carbone (NTC) dans une matrice polymère afin d’obtenir des matériaux nanocomposites avec des propriétés améliorées. Dans la première partie, nous nous sommes intéressés à l’enrobage des NTC par des copolymères à blocs amphiphiles afin de faciliter la dispersion en solution aqueuse. L’influence de la structure chimique, de la composition et de la masse molaire des copolymères sur les propriétés a été étudiée. Dans une deuxième partie, l’incorporation des NTC dans une matrice polymère a été développée. Des procédés par voie aqueuse et par voie fondue ont été choisis afin de contrôler la répartition des NTC dans une matrice modèle de polyoxyde d’éthylène ainsi que dans des de polyéthylène ou de polyméthacrylate de méthyle. L’étude des propriétés physiques, notamment rhéologiques et électriques des nanocomposites à renfort de nanotubes a été réalisée. Ainsi les relations entre l’état des dispersions, la nature de l’enrobage et le mode d’élaboration des composites ont été établies<br>This work is concerned with the study of carbon nanotubes (CNT) dispersions in a polymer matrix in order to obtain nanocomposite with unique properties. In the first part, we investigated the CNT wrapping by amphiphilic block copolymers to facilitate their suspension in aqueous solution. Based on the results, we could assess the effect on CNT dispersion quality of the molar mass of copolymers, the nature of the hydrophobic block and the length of hydrophilic block. In the second part, the incorporation of CNTs in polymer matrix was developed. Water or melt processing were chosen to control the distribution of CNTs in various polymer matrices (Polyethylene oxide, polyethylene and polymethyl methacrylate) through a prior wrapping of CNT. The studies of physical properties, including rheological and electrical properties, of nanocomposites were undertaken. Relationships between the state of dispersion, the nature of the coating and the method of preparation of composites were established
50
Brown, Elvie Escorro. "Bacterial cellulose/thermoplastic polymer nanocomposites." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Spring2007/e_brown_050207.pdf.
Full text