Rozprawy doktorskie: „Nanoparticle dispersions”

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Alele, Nkem [Verfasser], i Mathias [Akademischer Betreuer] Ulbricht. "Membrane-based purification of nanoparticle dispersions / Nkem Alele. Betreuer: Mathias Ulbricht". Duisburg, 2016. http://d-nb.info/1106854527/34.

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Milette, Jonathan. "Study of nanoparticle - liquid crystal dispersions using optical microscopy and solid-state NMR". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106294.

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This Thesis presents the synthesis of a new family of liquid crystal (LC)-capped gold nanoparticles (AuNPs) for a rationalized miscibility and assembly in liquid crystal matrices.A new protocol based on the thiol-for-dimethylaminopyridine (DMAP) ligand exchange reaction was developed to prepare 4-5 nm AuNPs with mono and binary capping layers made of alkanethiol (CH3(CH2)mSH; m = 5, 11) and liquid crystal ligand 4'-(n-mercaptoalkoxy)biphenyl-4-carbonitriles (CBO(CH2)nSH; n = 8, 12, 16). AuNPs with a 1 : 1 CH3(CH2)5SH/CBO(CH2)12SH ratio were found to have an unprecedented miscibility in isotropic 4-n-pentyl-4'-cyanobiphenyl (5CB) and 4-n-octyl-4'-cyanobiphenyl (8CB) liquid crystals exceeding 25 wt% Au. While low NP concentrations are normally used to avoid aggregation, concentrated dispersions of these AuNPs form new structures at the LC phase transitions through coupling of the interparticle attractive forces with the LC elastic interactions. Upon cooling to TN-I, the AuNPs form a reversible, micron-scale network by concentrating at the nematic-isotropic liquid interfaces. The network topology and LC director field orientation are controlled by the cooling rate, surface alignment, film thickness, AuNP concentration and ligand shell composition. Completely different structures are formed at the nematic to smectic phase transition. AuNPs dispersed in homotropically aligned LC films reversibly form macroscopic domains of curved or linear arrays with micron scale periodicities. Based on the variation of the arrays with boundary conditions, AuNPs are proposed to concentrate at the edge dislocation defects in the smectic phase. The molecular interactions that determine the miscibility and assembly of the AuNPs in LCs were studied using multinuclear solid-state NMR and isotopically labeled AuNPs and LCs. The interaction of the host LC with the AuNP surfaces is striking manifested by partial alignment of the ligands. The detection of an isotropic-nematic biphasic region of the host LC matrix below TN-I is an important finding that will be used to refine theoretical models of the network formation. Finally another type of nanoparticle network, formed by aerosil in a Schiff-base-type of LC with a small dipole moment was studied by wideline 2H NMR to investigate the effect of different surface anchoring strengths on the memory effects displayed by these dispersions.
Cette Thèse présente la synthèse d'une nouvelle famille de nanoparticules (NPs) d'or enrobées de cristaux liquides (CLs) afin de rationaliser leur miscibilité et assemblage dans des matrices faites de cristaux liquides. Un nouveau protocole basé sur la réaction d'échange de ligand thiol-pour-diméthylaminopyridine (DMAP) a été développé afin de préparer des NPs d'or de 4 à 5 nm de diamètre avec une monocouche simple et binaire faite d'alcanethiol (CH3(CH2)mSH; m = 5, 11) et du ligand CL 4'-(n-mercaptoalkoxy)biphényle-4-carbonitriles (CBO(CH2)nSH; n = 8, 12, 16). Nous avons découvert que les NPs d'or avec un ratio de 1:1 des ligands CH3(CH2)5SH/CBO(CH2)12SH possèdent une miscibilité sans précédent jusqu'à 25% en poids d'or dans la phase isotrope des CLs 4-n-pentyl-4'-cyanobiphényle (5CB) and 4-n-octyl-4'-cyanobiphényle (8CB). Bien qu'une faible concentration en NPs soit normallement utilisée afin d'éviter la formation d'agrégats, les dispersions concentrées de ces NPs d'or forment de nouvelles structures à la tansition de phase du CL par l'entremise du couplage des forces d'attraction interparticulaires avec les intéractions élastiques du CL. En refroidissant à TN-I, les NPs d'or forment de manière réversible un réseau à l'échelle microscopique en se concentrant à l'interphase nématique-isotrope. La topologie et l'orientation du domaine des directeurs CL sont controllées par la vitesse de refroidissement, l'alignement de surface, l'épaisseur du film, et la concentration et composition de la monocouche des NPs d'or. Des structures tout à fait différentes sont formées à la transition de phase nématique à smectique. Les NPs d'or dispersées dans des films de CLs alignés homotropiquement forment de manière réversible des domaines macroscopique de rayures parallèles courbées ou droites ayant une périodicité microscopique. Selon la variation des rayures en function des limites de surface, nous proposons que les NPs d'or se concentrent aux défauts des dislocations coin dans la phase smectique.Les intéractions moléculaires qui déterminent la miscibilité et l'assemblage des NPs d'or dans des CLs ont été étudiées avec l'aide la RMN multinucléaire à l'état solide, et de NPs d'or et CLs marqués isotopiquement. L'intéraction de la matrice CL avec la surface des NPs d'or se manisfeste de manière surprenante par l'alignement partielle des ligands. La détection d'une région biphasique isotrope-nématique de la matrice CL en-dessous de TN-I est une découverte importante qui va être utilisée afin de perfectionner les modèles thèoriques de la formation de réseaux. Finallement, un autre modèle de réseau fait de NPs, formé à partir de la dispersion d'aérosil dans un CL base de Shiff et ayant un moment dipolaire faible, a été étudié par la RMN du 2H. Nous avons examiné l'impact qu'a différentes forces d'ancrage de surface sur l'effet mémoire qu'affiche ces dispersions.

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O'Brien, Kristen Wilson. "Synthesis of Functionalized Poly(dimethylsiloxane)s and the Preparation of Magnetite Nanoparticle Complexes and Dispersions". Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28869.

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Poly(dimethylsiloxane) (PDMS) fluids containing magnetite nanoparticles stabilized with carboxylic acid-functionalized PDMS were prepared. PDMS-magnetite complexes were characterized using transmission electron microscopy, elemental analysis, and vibrating sample magnetometry. PDMS-magnetite complexes containing up to 67 wt% magnetite with magnetizations of ~52 emu gram-1 were prepared. The magnetite particles were 7.4 Â± 1.7 nm in diameter. Calculations suggested that the complexes prepared using mercaptosuccinic acid-functionalized PDMS (PDMS-6COOH) complexes contained unbound acid groups whereas the mercaptoacetic acid-functionalized PDMS (PDMS-3COOH) complexes did not. Calculations showed that the PDMS-3COOH and PDMS-6COOH covered the same surface area on magnetite. Calculations were supported by molecular models and FTIR analyses. The complexes were dispersed into PDMS carrier fluids by ultrasonication, resulting in magnetic PDMS fluids with potential biomedical applications. Magnetite particles (100 nm to 1 mm in diameter) were prepared by crystallization from goethite/glycol/water solutions under pressure. Two methods for particle growth were investigated in which the crystallization medium was varied by adjusting the amount of water or by adding itaconic acid. Particle surfaces were analyzed by x-ray photoelectron spectroscopy (XPS). Particles with clean surfaces were coated with carboxylic acid-functionalized poly(e-caprolactone) stabilizers. Adding itaconic acid to the reactions afforded particles ~100 nm in diameter. The magnetite particles displayed magnetic hysteresis. The particles were dispersed into vinyl ester resins by ultrasonication and it was demonstrated that the ~100 nm particles remained dispersed for three days without agitation. These dispersions have applications in magnetic induction heating for composite repair. Living polymerizations of hexamethylcyclotrisiloxane were terminated with dimethylchlorosilane, phenylmethylchlorosilane, or diisopropylchlorosilane (DIPCS). Platinum-catalyzed hydrosilation of the hydrosilane-terminated PDMS with allyloxyethanol afforded a systematic series of hydroxyalkyl-terminated PDMS. The reactions were successful except for the hydrosilation of the sterically-hindered DIPCS-functionalized PDMS where no reaction was observed. Hydroxyalkyl-terminated PDMS oligomers were successful in initiating the stannous octoate-catalyzed copolymerization of e-caprolactone, which afforded PDMS-b-PCL diblock copolymers of controlled composition.
Ph. D.

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Back, Markus. "Out-of-plane Ferromagnetic Resonance (FMR) measurements on magnetic nanoparticle dispersions for biomedical sensor applications". Thesis, Uppsala universitet, Fasta tillståndets fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-410179.

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In this master work, we investigated the feasibility of a magnetic resonance measurement technique using magnetic nanoparticle dispersions in both liquid and solid form. The implementation is realised as a coplanar waveguide operating in the frequency range of 0.5 - 20 GHz and an electromagnet producing a static magnetic field of strength up to 1.2 T. The Gilbert magnetic damping factor is determined for polymer composites of magnetic nanoparticles and the gyromagnetic ratio is determined for both nanoparticle dispersions in liquid form and polymer composites.

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Kosmala, A. "Development of high loading Ag nanoparticle inks for inkjet printing and Ag nanowire dispersions for conducting and transparent coatings". Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7754.

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The work presented in this thesis focuses on the synthesis of nanomaterials, formulation and printing of Ag nanoparticle and nanowire inks for two distinct applications: a) inkjet printing of Ag nanoparticle films on ceramic substrates with the aim of providing a smaller size of printed feature at lower cost than that can be obtained with the conventionally used screen printing, and b) Ag nanowires films prompted by the wide quest of electronics industry for materials with increased flexibility, lower cost and higher transmittance to replace indium tin oxide. Ag nanoparticles with a size of 50 nm were successfully synthesized and dispersed in aqueous medium. Two preparation routes were compared in order to distinguish the effects of solvents treatment of particles and their influence on the suspension characteristics including Ag loading, rheology, surface tension and later the electrical film properties. The co-polymer Pluronic F127 was found to be an effective as a stabiliser leading to the formulation of high silver loading in inks. The processing and characterization of silver films was performed. The aim was to reduce the number of layers in the silver nanoparticles film by increasing the thickness of a single layer with the goal of obtaining a dense and conductive film. An increase in the Ag loading, from 5 wt % to 45 wt % favoured the achievement of denser and thicker film with one layer printing. Addition of SiO2 to the ink formula resulted in denser structure and better adhesion of the printed track then the one without SiO2. A new method for improving the morphology of inkjet printed tracks has been proposed by printing the ink into the structured channels with predefined topography. Silver nanowires were synthesised and dispersed in methanol with help of copolymer F127. They were subsequently deposited on plastic and glass substrates forming conductive and transparent films.

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Edwards, Bronwyn K. "Effect of combined nanoparticle and polymeric dispersions on critical heat flux, nucleate boiling heat transfer coefficient, and coating adhesion". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53288.

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Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 123-126).
An experimental study was performed to determine thermal performance and adhesion effects of a combined nanoparticle and polymeric dispersion coating. The critical heat flux (CHF) values and nucleate boiling heat transfer coefficients (HTC) of nickel wires pre-coated using 1.0% alumina, 0.1% alumina, 500ppm polyallylamine hydrochloride (PAH), and 0.1% alumina combined with 500ppm PAH dispersions were determined using the pool-boiling method. The adhesion of 0.1% alumina and combined 0.1% alumina and 500ppm PAH coatings was evaluated using the tape and modified bend test methods. Results of the pool boiling experiments showed that the wire heaters pre-coated with combined 0.1% alumina and 500ppm PAH dispersion increase the CHF in water by -40% compared to bare wire heaters, compared to an enhancement of -37% with a 0.1% alumina coating. The combined 0.1% alumina and 500ppm PAH dispersion degrades the wire HTC by less than 1%, compared to a degradation of over 26% with a 0.1% alumina coating. Results from the tape test indicate qualitatively that the combined 0.1% alumina and 500ppm PAH dispersion coating adheres better than the 0.1% alumina nanoparticle coating. Results from the modified bend test showed that the combined 0.1% alumina and 500ppm PAH dispersion coating did not fail at the failure strain of the 0.1% alumina nanoparticle coating (8.108x 10-4). The addition of PAH to alumina nanofluid for creating a nanoparticle coating through boiling deposition was found to improve both coating thermal performance and adhesion over the pure alumina nanofluid.
by Bronwyn K. Edwards.
S.M.and S.B.

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Gollamandala, Deepika Rao. "Brownian dynamic simulations of nanoparticle dispersions in polymer solutions a thesis presented to the faculty of the Graduate School, Tennessee Technological University /". Click to access online, 2009. http://proquest.umi.com/pqdweb?index=13&did=1913184241&SrchMode=1&sid=1&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1265056184&clientId=28564.

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Rhodes, Rhys William. "Controlling the morphology of nanoparticle-polymer composite films for potential use in solar cells". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/controlling-the-morphology-of-nanoparticlepolymer-composite-films-for-potential-use-in-solar-cells(6bc2a3cc-7c11-4615-a202-bead6360af99).html.

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This thesis presents an investigation into the factors affecting the morphology of hybrid inorganic/organic photoactive layers used in photovoltaic cells. Although optimisation of the organic (polymer) phase has received substantial attention, research into the morphology of the inorganic phase (semiconducting nanocrystals) remains limited. It is believed that there is a strong link between the morphology of the final photoactive film and the quality of the initial nanocrystal dispersion. To this end, two nanocrystal systems were investigated; zinc oxide (ZnO) and lead sulphide (PbS). ZnO nanocrystals were synthesised and found to possess reproducible characteristics. It was determined that colloid stability was initially dependent upon the presence of acetate groups bound to the surface, which in turn required a small quantity of methanol to be present in the organic dispersant. It was also discovered that while methanol evaporated readily from the surface of the nanocrystals, another molecule, 1-propylamine (1-PA), did not. Further investigations showed that while methanol only weakly physisorbed to the surface of ZnO nanocrystals, 1-PA formed strong, dative covalent bonds with Zn2+, preventing evaporation despite a low boiling point. Subsequent investigations into the effects of different ligands upon colloid stability found that amine-based groups typically possessed superior stabilising capabilities compared to alcohol-based analogues. The characteristics of nanocrystal / polymer blends were also investigated. It was determined that the nanocrystal dispersion became unstable at higher concentrations of polymer due to depletion aggregation. Films of nanocrystal / polymer blends were cast from dispersions containing either alcohol or amine-based ligands, and it was observed that dispersions stabilised with 1-PA possessed smooth morphologies on the micrometer scale. Investigations at the nanometer scale, however, revealed aggregates large enough to favour recombination.The latter half of this thesis regards the characterisation of PbS nanocrystals and investigations into triggered aggregation. It was determined that while PbS nanocrystals possessed reproducible characteristics, the stabilising molecule, oleic acid (OA) was insulating. The effects of exchanging the OA groups for a shorter ligand, butylamine (BA) were investigated.Finally, PbS nanocrystals were treated with a bidentate ligand, 1,2-ethanedithiol (EDT) to induce triggered aggregation. It was observed that the system was highly sensitive to the concentration of EDT in dispersion, forming small, relatively dispersed aggregates at low [EDT], and micrometer-sized crystalline structures at high [EDT]. The characterisation and entrapment of these nanocrystal structures within semi-conducting polymer films is also discussed.

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Quant, Carlos Arturo. "Colloidal chemical potential in attractive nanoparticle-polymer mixtures: simulation and membrane osmometry". Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7616.

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The potential applications of dispersed and self-assembled nanoparticles depend critically on accurate control and prediction of their phase behavior. The chemical potential is essential in describing the equilibrium distribution of all components present in every phase of a system and is useful as a building block for constructing phase diagrams. Furthermore, the chemical potential is a sensitive indicator of the local environment of a molecule or particle and is defined in a mathematically rigorous manner in both classical and statistical thermodynamics. The goal of this research is to use simulations and experiments to understand how particle size and composition affect the particle chemical potential of attractive nanoparticle-polymer mixtures. The expanded ensemble Monte Carlo (EEMC) simulation method for the calculation of the particle chemical potential for a nanocolloid in a freely adsorbing polymer solution is extended to concentrated polymer mixtures. The dependence of the particle chemical potential and polymer adsorption on the polymer concentration and particle diameter are presented. The perturbed Lennard-Jones chain (PLJC) equation of state (EOS) for polymer chains1 is adapted to calculate the particle chemical potential of nanocolloid-polymer mixtures. The adapted PLJC equation is able to predict the EEMC simulation results of the particle chemical potential by introducing an additional parameter that reduces the effects of polymer adsorption and the effective size of the colloidal particle. Osmotic pressure measurements are used to calculate the chemical potential of nanocolloidal silica in an aqueous poly(ethylene oxide) (PEO) solution at different silica and PEO concentrations. The experimental data was compared with results calculated from Expanded Ensemble Monte Carlo (EEMC) simulations. The results agree qualitatively with the experimentally observed chemical potential trends and illustrate the experimentally-observed dependence of the chemical potential on the composition. Furthermore, as is the case with the EEMC simulations, polymer adsorption was found to play the most significant role in determining the chemical potential trends. The simulation and experimental results illustrate the relative importance of the particles size and composition as well as the polymer concentration on the particle chemical potential. Furthermore, a method for using osmometry to measure chemical potential of nanoparticles in a nanocolloid-mixture is presented that could be combined with simulation and theoretical efforts to develop accurate equations of state and phase behavior predictions. Finally, an equation of state originally developed for polymer liquid-liquid equilibria (LLE) was demonstrated to be effective in predicting nanoparticle chemical potential behavior observed in the EEMC simulations of particle-polymer mixtures.

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Le, Hong Duc. "Modelling of nanoparticles laden jet from a conveying pipe leakage". Phd thesis, Toulouse, INPT, 2018. http://oatao.univ-toulouse.fr/21454/1/LE_Hong_Duc.pdf.

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Since a few years, nanomaterials are more and more used in industrial process. In order to protect the population and the environment from the consequences of an accidental release into the atmosphere, the risk assessment allowed to identify the accidental scenario in transport, manipulation and storage of those products. The accidental leakage of the conveying pipe may lead to a massive release of nanoparticles. In order to evaluate the consequences of this type of accident, our study focuses on the prediction of particles properties dispersed into the air, for example the particle number concentration and the particle diameter distribution. The first step of the study consists in the analyse of physical phenomena related to nanoparticles in order to choose the most predominant physical phenomena to model. The relevant physical phenomena in the present configuration are the agglomerate complex shape, the drag force on agglomerates, the agglomerate breakage by gas, the agglomerate collision and the agglomeration. After that, the modelling of physical phenomena chosen is developed in CFD tool Code\_Saturne. For each physical phenomenon, a simulation test case is realized in order to verify the development in CFD tool. A good agreement between CFD tool Code\_Saturne and 0D tool from Scilab and model in the literature is obtained. Also in the present study, new model for the collision probability of agglomerates is proposed. This new model is validated with the numerical experiment. After that, the numerical tool developed is applied in a simulation of an accidental pipe leakage. The field near the leakage is simulated by Code\_Saturne. The results from Code\_Saturne is used as the input data for ADMS tool, a simulation tool for the particle dispersion in large scale. The results show that the particles are dispersed more than 1 km from the release source, which is in agreement with the distance observed. In perspective, the influences of different parameters as the wind field and the particle properties, on the agglomerate size and number distribution can be tested. An experiment of the microparticle jet is realized at INERIS in order to be able to assess the nanoparticle jet experiment in the laboratory scale.

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

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

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Samuel, Jorice. "Synthèse et dispersion de nanoparticules luminescentes dédiées à la lutte anti-contrefaçon". Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10203.

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Cette thèse aborde la thématique de la synthèse et de la dispersion de nanomatériaux luminescents (silice ou oxydes de terres rares) dédiés à la lutte anti-contrefaçon. La silice est synthétisée par un procédé sol-gel en microémulsion inverse. Des molécules fluorescentes organiques et organo-lanthanides sont incorporées dans les nanoparticules et il est montre que la nature du colorant influence son encapsulation. La fluorescence est obtenue sans lien covalent entre le colorant et la nanoparticule. Les nanoparticules sont ensuite fonctionnalisées dans le milieu de synthèse. Une nouvelle méthode de caractérisation de la fonctionnalisation est proposée et fait notamment apparaitre que la fonctionnalisation ainsi réalisée est homogène mais qu’a l’échelle de la nanoparticule, il y a apparition de nanodomaines. Les oxydes de terres rares sont obtenus par une collaboration. Deux traitements de surface sont particulièrement étudiés : une approche hybride consistant en l’encapsulation des nanoparticules dans une couche de polysiloxane suivie d’une fonctionnalisation adaptée ; et une approche basée sur l’adsorption d’agents tensioactifs. En particulier plusieurs agents tensioactifs représentatifs sont compares. Les nanoparticules ainsi traitées sont dispersées et stables en milieu liquide. Elles peuvent alors être incorporées dans différents polymères témoins (PMMA, PVA et PVC) et il est montre qu’une bonne dispersion en milieu liquide permet une incorporation homogène dans le polymère. Un essai industriel a été réalisé et a prouvé que certains de ces procédés développés pouvaient être transférés à l’échelle industrielle
This work deals with the synthesis and the dispersion of luminescent nanomaterials dedicated to the fight against counterfeiting. The nanomaterials (silica and rare earth oxides) own an optical code which is dispersed into the material to be tagged. The silica is synthesized by a reverse microemulsion sol-gel process. Organic fluorescent dyes and organo-lanthanides metal complexes are incorporated into the nanoparticles and it is shown that the nature of the dye influences its incorporation. The fluorescence is obtained without any covalent link between the dye and the silica matrix. After the synthesis, the nanoparticles are functionalized into the microemulsion. An original method is proposed to characterize the functionalization and it is shown that the functionalization is on the whole homogeneous but that at the nanoscale some nanodomains appear. The rare-earth oxides are obtained by collaboration. Two surface treatments are particularly studied : an hybrid approach based on the encapsulation of the nanoparticles into a polysiloxane shell followed by an adapted functionalization; and a second approach based on the use of surfactants. In particular, several well-known surfactants are compared. These modified nanoparticles are dispersed and stabilized into liquid media such as water or 2-Butanone. They are then incorporated into three polymers (PMMA, PVA and PVC) and it is shown that a good dispersion into a liquid allows obtaining an homogeneous incorporation into the polymers. An industrial test has been realized and has given the proof that some of these processes can be transferred directly at industrial scale

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Dolce, Caterina. "Diffusion of polyelectrolytes in dispersions of nanoparticles". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066569/document.

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Les polyélectrolytes sont des polymères avec des unités de répétition ionisables qui dans un solvant polaire, comme l’eau, se dissocient en libérant des contre-ions. Les polyélectrolytes, du fait leur présence dans de nombreuses formulations, de leur rôle dans les processus industriels, les milieux biologiques et environnementaux ont fait l’objet d’un grand nombre d’études. Pour mieux comprendre et exploiter les polyélectrolytes, leurs propriétés en présence d’autres composés doivent cependant être étudiées plus en détail. Dans cette optique, ce travail se concentre sur la modification des propriétés dynamiques de polyélectrolytes courts en présence de nanoparticules de silice. Dans ce but, nous avons conçu un système expérimental de diffuseurs dispersés au sein de suspensions d’obstacles chargés. Les diffuseurs sont des molécules de carboxylate de différentes tailles : des carboxylates simples jusqu’aux polyélectrolytes (polyacrylate de sodium, PAANa) courts. Les obstacles sont des nanoparticules de silice de différentes tailles et charges de surface. L’étude des carboxylates simples a été suggérée par la nécessité de réduire la complexité des diffuseurs. L’autodiffusion des molécules est étudiée principalement par diffusométrie RMN, technique qui permet d’étudier les mouvements browniens de molécules sur une échelle de temps de 10-1000 ms (10-100 μm en échelle spatiale). Ce travail examine également comment la présence de polyélectrolytes modifie les interactions entre particules de silice en utilisant la diffusion de neutrons aux petits angles
Polyelectrolytes are a particular class of polymers with ionizable repetition units that dissociate in polar solvents (such as water) leading to macro-ions and counterions. Solutions and materials made of polyelectrolytes are extensively used in several formulations and in industrial, biological and environmental processes. For a better insight into these systems, the properties of polyelectrolytes in presence of other particles have to be studied in more detail. This work deals with the modification of the dynamics properties of short polyelectrolytes in presence of charged silica nanoparticles.To study this problem, we design an experimental system made of carboxylate molecules of various sizes, from simple carboxylate (propionate) up to short polyelectrolytes (sodium polyacrylate, PAANa), diffusing in aqueous dispersions of silica nanoparticles of different size and surface charge. Both polyelectrolytes and nanoparticles are negatively charged at high pH. Thanks to the use of simple carboxylates, it is possible to reduce the complexity of the diffusers. The self-diffusion of the molecules is investigated using NMR diffusion experiments, which monitors the Brownian motions of individual molecules on 10-1000 ms timescale (10-100 μm spatial scale). This work also investigates how the presence of polyelectrolytes modifies the phase behaviour of silica particles by using small angle neutron scattering

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Gerlach, Carina, Karsten Berndt, Olfa Kanoun i Maik Berger. "CAD-unterstützte Bestimmung des effektiven Dispergiervolumens beim Ultraschalldispergieren". Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-206889.

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Für nanoskalige Füllpartikel, die stark zum Agglomerieren tendieren, ist das Ultraschalldispergieren mittels Sonotrode eine geeignete Methode, um Agglomerate hinreichend gut zu entbündeln. Um dabei die optimalen Ultraschallparameter ermitteln zu können, ist es nötig, das effektive Dispergiervolumen, in welchem die Agglomerate durch Kavitation aufgebrochen werden, zu kennen. Die hier vorgestellte CAD-basierte Methode zur Berechnung des effektiven Dispergiervolumens ist dabei deutlich weniger zeitintensiv als die bisher üblicherweise verwendete analytische Methode.

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Starkweather, Nathan S. "Controlling Nanoparticle Dispersion For Nanoscopic Self-Assembly". DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/973.

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Nanotechnology is the manipulation of matter and devices on the nanometer scale. Below the critical dimension length of 100nm, materials begin to display vastly different properties than their macro- or micro- scale counterparts. The exotic properties of nanomaterials may trigger the start of a new technological revolution, similar to the electronics revolution of the late 20th century. Current applications of nanotechnology primarily make use of nanoparticles in bulk, often being made into composites or mixtures. While these materials have fantastic properties, organization of nano and microstructures of nanoparticles may allow the development of novel devices with many unique properties. By analogy, bulk copper may be used to form the alloys brass or bronze, which are useful materials, and have been used for thousands of years. Yet, organized arrays of copper allowed the development of printed circuit boards, a technology far more advanced than the mere use of copper as a bulk material. In the same way, organized assemblies of nanoparticles may offer technological possibilities far beyond our current understanding. In the first project, 1D assemblies of nanoparticles were explored. 1D anisotropic assemblies of nanoparticles are the simplest organized nanostructures which may be fabricated. One of the greatest difficulties in developing commercial products is in the transfer of a process from the laboratory to manufacturing scale. While many techniques may be used to develop 1D assemblies in lab, simple techniques are needed to allow the fabrication of these assemblies on a large, cost effective scale. Use of shear, shown previously to induce colloidal ordering in solutions, is a technique that may be readily adapted from the coatings industry as a process for forming 1D assemblies, if the optimal conditions can be found. Atomic force microscopy was used to study the role of shearing forces produced by drawdown and spraying application in the formation of 1D assemblies of nanoparticles. Formation of 1D strings was observed to increase with greater application of simple shear, but greater spraying forces were found to decrease formation of strings. This is explained in terms of greater simple shear providing a greater driving force for string formation, while greater spraying shear acted to irreversibly disperse the particles. The second project focused on the development of a learning module for education of students at various academic levels on the significance of the surface area of nanomaterials. This project was commissioned by the Global Waste Research Institute, a multidisciplinary organization based at Cal Poly, concerned with performing research and education in areas related to waste management, particularly of emerging waste streams. As nanotechnology and nanoparticles become more prevalent in consumer products and industrial processes, the volume of nanowaste is increasing rapidly. To address challenges associated with processing this unique form of waste, understanding of the fundamental processes controlling the unique properties of nanoparticles is necessary. A learning module was developed using a laboratory demonstration and video presentation to illustrate concepts related to differences in the properties between microparticles and nanoparticles. The laboratory demonstration was designed to be simple to understand, and quick, simple, and inexpensive to perform. The video presentation was designed to be a 15 minute presentation relating the concepts of nanotechnology, nanoparticles, surface area, and fundamental differences as compared to conventional materials. Dispersions of particles within aqueous media were used as a framework for the discussion, in a manner comprehensible by students ranging from 12th grade high school students to graduate students in relevant programs. The third and final project focused on self-assembly of particles in nematic liquid crystalline colloids. Dispersions of colloidal particles in liquid crystals (LCs) are a relatively new set of composite materials, host to a variety of interactions not seen in colloids in isotropic media. Presence of colloidal particles disrupts the local nematic director, resulting in a loss of long-range elastic energy. Interactions between particles and LC molecules results in dipolar or quadrupolar defects, depending on the nature of the interactions between particle and LC. The loss of long-range elastic energy can be minimized through aggregation of particles. The defects formed by interactions between particles and LC stabilize these aggregations as linear chains, either along the nematic director in the case of dipolar defects, or at an offset angle in the case of quadrupolar defects. Dispersions of silica microspheres in the nematic phase of a thermotropic liquid crystal were studied using polarizing light microscopy. Strong homeotropic anchoring was observed, indicated by the abundant formation of hedgehog defects. These defects were found to play a role in self-assembly of particles along the nematic director, resulting aggregates containing up to a dozen aligned particles. In addition, particles were observed to aggregate in chains along grain boundaries in the liquid crystal, acting to stabilize the high energy interface between different grain directions, an effect not previously reported in the scientific literature for nematic colloids.

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Schmitt, Céline. "Surface modification of oxide nanoparticles using phosphonic acids : characterization, surface dynamics, and dispersion in sols and nanocomposites". Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS083/document.

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Les dispersions colloïdales de nanoparticules (NPs) sont très répandues dans l'industrie, et permettent d'éviter l'utilisation de NPs sèches, controversée pour des raisons de toxicité. Le contrôle des interactions entre les NPs et le milieu dispersant reste le point clé de ces systèmes. La modulation de ces interactions permet de contrôler l'état de dispersion des NPs dans les sols. De plus, les nanocomposites NPs-polymère se sont avérés prometteurs pour une large gamme d'applications, ainsi l'utilisation de sols pourrait présenter une voie avantageuse d'incorporation des NPs dans le polymère, tout en offrant la possibilité de contrôler leur état de dispersion, et in fine les propriétés du matériau, celles-ci étant liées à l'état de dispersion des NPs. L'objectif de ce travail de thèse est le développement de méthodes de modification de surface de NPs d'oxyde en dispersion colloïdale, tout en contrôlant la dispersion des NPs dans les sols et dans les nanocomposites issus de ces sols. Puis, l'évaluation de cet état de dispersion par SAXS. Deux méthodes de modification de surface ont ainsi été développées : la première implique le greffage d'acides phosphoniques sur des NPs de silice recouvertes d'alumine en dispersion dans l'eau, et la seconde met en jeu le greffage d'acides phosphoniques sur des NPs de TiO2 et leur transfert d'une phase aqueuse à une phase CHCl3. Les NPs modifiées ont été caractérisées par diverses méthodes. Leur état de dispersion a été étudié par DLS et SAS. De plus, pour les NPs de silice-amine, l'impact de la densité de greffage du C8PA sur la structure des NPs (à l'état sec) a été mis en évidence par SAXS et différents processus de relaxation ont été étudiés par BDS pour les NPs nues et modifiées. Enfin, ces NPs ont été incorporées dans un polymère de PEA par voie aqueuse via des latex et leur état de dispersion dans les composites a été mesuré par SANS
Colloidal nanoparticles (NPs) dispersions are largely used in the industry, and avoid the use of dried NPs, which is controversial due to safety concerns. The key point in such systems remains the control of the interactions with the dispersed medium and between the NPs. Mastering these interactions allows controlling the NPs' state of dispersion. Moreover, as polymer-NPs nanocomposites have been found promising for a wide variety of applications, the use of colloidal sols could thus be an advantageous way of NPs' incorporation in the polymer, with a possible control of the NPs state of dispersion, and finally on the properties of the material, as they are linked to the NPs' dispersion. The purpose of this PhD work is to develop surface-functionalization methods of oxide NPs in colloidal sols in order to control the dispersion of NPs in the sols and in polymer nanocomposites derived from these sols, and to evaluate this dispersion using SAXS. Two surface modification methods have been developed to obtain aqueous or organic sols of functionalized NPs. The first one concerns the reaction in water of alumina-coated silica NPs with phosphonic acids (PAs), and the second one involves the simultaneous grafting and phase transfer of TiO2 NPs from an aqueous to a CHCl3 phase using PAs. The resulting NPs were characterized and their state of dispersion was monitored by DLS and SAS measurements. The impact of the C8PA grafting density on the structure of modified alumina-coated silica NPs in the dried state was evidenced by SAXS. The different relaxation processes of bare and grafted NPs were studied by BDS. These NPs were then incorporated in a PEA polymer by an aqueous latex route, and their structure in the nanocomposites was investigated by SANS

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BELENO, LUIS MIGUEL GUTIERREZ. "HYBRID SILICA NANOPARTICLES FOR STABILIZATION OF BIPHASIC DISPERSIONS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=37041@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
As dispersões bifásicas (ex. espumas e emulsões), de grande relevância prática na química e na engenharia, são termodinamicamente instáveis devido à diminuição de energia livre no processo de coalescência. Esta limitação é comumente minimizada através de mecanismos de estabilização eletrostática e estérica. Recentemente, há um interesse crescente na estabilização de emulsões e espumas usando partículas sólidas (tipo Pickering), devido à forte adsorção das mesmas nas interfaces para formar uma película sólida. Dependendo do tamanho e do ângulo de contato, a adsorção das partículas pode tornar-se irreversível, melhorando a estabilidade em comparação com sistemas estabilizados por surfactante. Como nanopartículas de molhabilidade intermédia são relativamente raras, o ajuste deste parâmetro é o principal desafio para obter dispersões estáveis. No presente estudo, nanopartículas de sílica (SiNPs) foram modificadas superficialmente com 3-aminopropil trimetoxisilano e hexadeciltrimetoxisilano como agentes sililantes, para se obter três tipos diferentes de nanopartículas híbridas de maior hidrofobicidade, visando a formulação de dispersões bifásicas altamente estáveis usando um método de baixa energia (agitação manual). As SiNPs modificadas foram caracterizadas através de testes qualitativos, infravermelho, analise termogravimétrica, analise elementar e ressonância magnética nuclear de carbono treze e de silício vinte nove no estado sólido para confirmar o enxerto dos grupos funcionais. As propriedades das NPs em relação à sua dispersabilidade e comportamento em interfaces foram avaliadas por espalhamento de luz dinâmica e a tensão superficial crítica de molhabilidade. Finalmente, foram preparadas espumas líquidas e emulsões água-em-óleo (A/O) utilizando as partículas híbridas obtidas e pequenas quantidades de surfactantes, para facilitar o processo de dispersão. Os resultados mostraram que as NPs mais hidrofílicas estabilizam melhor a interface ar/água (espumas), enquanto a estabilização máxima em emulsões é obtida com as NPs mais hidrofóbicas, uma vez que a interação com a fase contínua é otimizada. Além disso, a presença de grupos funcionais na superfície das SiNPs oferece a possibilidade de obter efeitos de sinergia com os surfactantes, controlando a adsorção mista na interface. As aplicações potenciais destes resultados podem abranger diversas áreas, tais como biomedicina, ciência dos materiais, recuperação de petróleo, cosméticos e alimentos.
Biphasic dispersions (e.g. foams and emulsions) are of practical relevance to many chemical and engineering fields. These dispersions are thermodynamically unstable, since their decay results in a decrease of the free energy. Different mechanisms can prevent the coalescence of the dispersion, such as electrostatic and steric stabilization. Recently, there has been an increased interest in the study of stabilization of emulsions and foams using solid particles (Pickering type), since particles can strongly adsorb at interfaces to form a solid film, replacing the incompatible water-oil(ar) interface by the more favorable oil(ar)-particle and particlewater interfaces. Depending on their size and contact angle of selective wetting, particle adsorption can become irreversible, with increased stability of particle-stabilized dispersions compared to surfactant-stabilized systems. Since particles of intermediate wettability by nature are relatively rare, tailoring particle wettability is the major challenge to obtain stable dispersions. In the present study, hybrid silica nanoparticles (SiNPs) were prepared by modification of their surface using 3 aminopropyltrimethoxysilane and hexadecyltrimethoxysilane as silanizing agents, to obtain three different nanoparticles with increased hydrophobicity, aiming to achieve highly stable biphasic dispersions using a low-energy method. The modified SiNPs were characterized using qualitative tests, FTIR, TGA, CHN and NMR (Si) to confirm grafting of functional groups. In addition, nanoparticle properties regarding aqueous dispersions and behavior at interfaces were evaluated by DLS and critical wetting surface tension. Liquid foams and water-in-oil (W/O) emulsions were prepared using the obtained hybrid particles and small amounts of different surfactants, to facilitate the dispersion process. The results showed that while more hydrophilic NPs stabilize better the air/water interface (foams), maximum stabilization in W/O emulsions is achieved with the most hydrophobic NPs, since interaction with continuous phase is optimized. In addition, the presence of different functional groups at the surface of the SiNPs offers the possibility for increased synergy with surfactants, controlling the mixed adsorption at the interface. The potential applications of these results can cover diverse fields such as biomedicine, materials science, oil recovery, cosmetics and food.

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Kastrisianki-Guyton, Emma. "Dispersion, adsorption properties and separation of nanoparticles". Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683906.

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Recent years have seen a surge in interest into the properties of new materials, and their application in electronic devices. This project has used techniques common for colloidal systems in order to gain insight into these systems. The work has mainly focussed on single-walled carbon nanotubes (SWCNTs), however silicon nanowires have also briefly been studied. Pluronic block copolymers are commonly used to stabilise SWCNTs in water, most commonly F127. Such dispersions were studied using small-angle neutron scattering (SANS) experiments performed at a range of solvent contrast systems. The data were successfully fitted to a relatively simple core-shell cylinder model. Data fitting was consistent with SWCNTs present in small bundles in dispersion, with an average radius of 10 A, surrounded by a water-swollen F127 layer of 61 A thickness, with a water content of 94% in the adsorbed layer. Increasing the temperature of F127 /SWCNT /D20 systems so that they were above the critical micellisation temperature (CMT) of the polymer was seen to have only a small impact on the polymer adsorption, with the adsorbed layer thickness increasing from ~55 to 65 A, and the adsorbed amount increasing by between 50 and 100% (from ~ 1 to 1.5 mg m- 2). Dispersions of SWCNTs in surfactant mixtures of SDS and sodium cholate (SC) are often used to separate SWCNTs by electronic type. SWCNTs were dispersed with SDS and studied using small-angle scattering techniques at various contrasts. Data were fitted to a core-shell cylinder model, and the fits were consistent with small SWCNT bundles of an average radius of 10 A, surrounded by an adsorbed layer of thickness 18 A. The adsorbed amount of SDS at the SWCNT surface was calculated to be 2.5 mg m-2 , however the adsorbed amount at the SDS headgroup/water interface was calculated to be 0.85 mg m- 2 , a value closer to previously reported values for the adsorption of SDS on carbon surfaces. Subsequently, SWCNTs dispersed with SC and mixtures of SDS and SC (1:4 and 3:2 volume ratios of SDS:SC) were studied with SANS, and the dimensions of the decorated SWCNTs were not seen to vary greatly between the different surfactants studied. Finally, the separation of nanoparticles has been investigated. The separation of SWCNTs based on their electronic properties using aqueous PEG/dextran twophase polymer systems was studied. Although absorbance spectra suggested that an electronic separation of SWCNTs had occurred, the process was found to be highly irreproducible. Additionally, variations in temperature were found to have little effect on partitioning and no separation by electronic type was seen when F127-dispersed SWCNTs rather than SC-stabilised SWCNTs were used, suggesting that, unlike F127, SC adsorbs differently to SWCNTs depending on their electronic type. Silicon nanowires (SiNWs) have also been briefly studied, and separating the nanowires by length was attempted using glass bead columns, however no significant separation by length was achieved.

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Meeuw, Hauke, Valea Kim Wisniewski, U. Köpke, Ali Shaygan Nia, Vázquez Adrián Romaní, Martin Rudolf Lohe, Xinliang Feng i Bodo Fiedler. "In‑line monitoring of carbon nanoparticle epoxy dispersion processes". Springer, 2019. https://tud.qucosa.de/id/qucosa%3A70656.

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The new generation of three roll mills is able to monitor occurring process loads while dispersion. This paper focuses on the interpretation of the gathered data to find criteria quantifying the dispersion state online. The aim is process time reduction. We used impedance spectroscopy to identify the dispersion state and correlated it with the occurring process loads. The dispersion process of a wide spectrum of carbon based nano particles, namely carbon black, single walled carbon nanotubes, multi walled carbon nanotubes, a few-layer graphene powder, electrochemically exfoliated graphite and a functionalized electrochemically exfoliated graphite was investigated. The filler content was varied along the material’s electrical percolation threshold. The criteria found led to a reduction of processing time and revealed the prevalent mechanisms during dispersion.

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Kylafis, Georgios Fokion. "The explosion and dispersion potential of engineered nanoparticles". Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15618/.

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This work investigates the explosion and dispersion potential of engineered nanoparticles (ENP). The European Union (EU) sponsored this investigation, firstly to predict or estimate risks posed by the use of engineered nanomaterials (ENM), and secondly to implement procedures for the purpose of risk mitigation. These include establishing exposure control limits and controlling and monitoring exposure, including the accidental explosive or massive release of ENP into the environment. To this end, the release of ENP originating from specific nanopowders was simulated in a 31 m3 airtight chamber of controllable environment. Their loss and dispersion characteristics were studied under ventilated and unventilated conditions. The explosion characteristics of specific ENP in lean hybrid blends of nanoparticles with methane and air, were studied in a 23 L cylindrical combustion vessel providing the adjustment of isotropic turbulence induced by specially designed fans. The influence of ENP on the explosion severity was evaluated by comparing the results obtained for pure methane explosions. Via a 6-jet Collison nebuliser (CN) combined with a considerably modified preparatory process of the tested nanopowders suspensions in water, ENP of Titanium and Silica Dioxide (TiO2 and SiO2) were injected continuously into the dispersion chamber. A specially designed dust injector was used for the introduction of two types of carbon black (CB) nanopowders (Corax N550 and Printex XE2) into the combustion vessel. An arrangement of particulate instrumentation was applied for tracking the evolution of particle number concentration (PNC) and particle size distribution (PSD) at points near to the source within the dispersion chamber. In addition, PSD measurements were conducted in the dust clouds generated for the explosion tests. Using a Log10-normal modal fitting program, the characteristics of groups present within the PSDs, were mathematically described. An indoor aerosol model for the study of the differential effect of coagulation and deposition on the changes of PNC with time in the dispersion chamber, was applied. Finally, the explosion severity was characterised by measurements of the explosion pressure history and of flame speed derived from high speed Schlieren cine photographs. Results indicated that by reducing the ventilation rate the leftover PNC of ultrafine particles (diameter ≤ 100 nm) was gradually increased at the end of the evacuation process. In parallel, at the high ventilation rates the spatial ventilation efficiency was shown to be optimal close to the inlet diffuser. However, by decreasing the ventilation rate, ventilation efficiency was shown to be independent of the location in the chamber. The study of particle interactions under unventilated conditions indicated that different growth rates due to agglomeration were induced on the two types of dispersed ENP. For fine particles (diameter > 100 nm) of both materials, the model indicated that their losses were dominated by deposition at high PNC, whereas for ultrafine particles, heterogeneous coagulation was the main removal mechanism. However, the model indicated stronger deposition at low PNC, and weaker homogeneous coagulation at high PNC, for ultrafine and fine SiO2 particles respectively, compared to their TiO2 counterparts. The explosion tests indicated that the addition of variable concentrations of ENP in methane resulted in higher burning rates and flame acceleration than those demonstrated by the respective particle-free methane air mixtures. In addition, the mixture of the highest fraction in ultrafine ENP yielded the most severe explosion, while this mixture was of the lowest dust concentration. Finally, hybrid mixtures with methane below its lower flammability limit (LFL) were shown to be ignitable. Furthermore, the level of this extension below LFL was shown to be dependent to the material as different extensions were performed by Corax N550 and Printex XE2 hybrid mixtures. The investigation recommends that in order to design efficient ventilation systems for nanotechnology workplace, only specific ventilation rates and arrangements of inlet/outlet diffusers, should be considered. Exposure to accidentally released ENP is expected to be different for different materials and strongly related to their emission profile. Finally, the generation of a dust cloud from a minor amount of a nanopowder combined with a low amount of a flammable gas and an electrostatic spark may result in a severe explosion of higher impacts for human health and installations than those induced by the explosion of a higher dust concentration hybrid mixture. Also this work demonstrated that as the mean particle size in the dust cloud decreases, a hybrid mixture of an extremely low content of gas could become ignitable. The latter could be applicable not only in the field relating to the risk assessment of ENP but also in generic technological applications involving airborne nanoparticles (e.g. soot particles) suspended in flammable gases (e.g. automotive applications that use natural gas).

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Zhang, Li. "FDTD Algorithm for Plasmonic Nanoparticles with Spatial Dispersion". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1452174003.

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Pourcin, Florent. "Synthèse de nanoparticules de forme, taille et dispersion contrôlées pour l'élaboration de couches composites aux propriétés optiques modulables". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0365/document.

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Les nanoparticules de métaux nobles possèdent des propriétés optiques étonnantes. Sous l’effet de la lumière, elles sont capables de résonner pour générer des plasmons de surface localisés. Ces plasmons absorbent ou diffusent la lumière aux longueurs d’ondes de ces résonnances et sont fortement dépendants de la forme, de la taille et de l’environnement des nanoparticules. Dans ce manuscrit, elles sont impliquées dans la conception de matériaux furtifs à des fins militaires.Des nanoparticules d’argent de formes contrôlées ont été associées à un polymère pour élaborer de nouveaux matériaux hybrides déposables par voie liquide sous la forme de couches minces.Un absorbeur quasi-parfait (98,8%) sur une gamme étroite de longueur d’onde a été obtenu en maintenant une très bonne dispersion des nanoparticules dans la couche, alors qu’un absorbeur large bande efficace (~90%) sur toute la gamme spectrale du visible a été réalisé en provoquant l’agrégation des nanoparticules. Une étude qualitative par microscopie et spectroscopie sur la densité et l’organisation des nanoparticules au sein de la couche mince a mis en évidence la présence de couplages plasmoniques de natures et d’intensités différentes en fonction de l’espacement entre les cubes. Il a été montré que les propriétés optiques mesurées étaient indépendantes de la nature du substrat utilisé, mais aussi indépendantes de l’angle de la lumière incidente sur une large gamme angulaire. Enfin, des systèmes multicouches déposés par voie liquide ont été explorés afin d’étendre l’absorption des couches jusqu’au proche infrarouge par l’ajout de matériaux tel que le l’oxyde de tungstène
Nanoparticles of noble metals have unexpected optical properties. Under the effect of light, they are able to resonate, generating localized surface plasmon resonances that are used in many applications. These plasmons absorb and scatter the light at the wavelengths of these resonances and are highly dependent on the shape, the size and the environment of the nanoparticles. In this thesis, they are applied for the design of stealth materials for military purposes. For this, controlled shapes of silver nanoparticles were blended within a polymer to develop new hybrid materials that are solution-processed as thin layers. A quasi-perfect absorber (98,8%) in a precise range of wavelengths has been obtained by maintaining well-dispersed nanoparticles in the layer, while an effective broadband absorber (~90%) over the entire visible range has been achieved by triggering the aggregation of the nanoparticles. Microscopy and spectroscopy qualitative studies performed on the density and organization of the nanoparticles within the thin layers revealed the presence of plasmonic couplings of different natures and intensities as a function of the spacing between the cubes. It has been shown that the optical properties measured are independent of the nature of the substrates used and independent of the angle of the incident light on a wide angular range. Finally, solution-processing of multilayers systems was explored to extend the absorption of the layers to the near infrared by the addition of other materials such as tungsten oxide

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Yourdkhani, Mostafa. "Aspects of nanoparticles dispersion and interaction in polymer nanocomposites". Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123090.

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Polymer nanocomposites have attracted a great deal of attention during the past few decades. Benefiting from the nanoscale geometry, immense surface-to-volume ratio, and exceptional chemical and physical properties, nanoparticles are theoretically expected to enhance the performance of polymer systems. In practice, the preparation of polymer nanocomposites brings its own challenges. To achieve the best reinforcing effect, nanoparticles should be uniformly dispersed within the polymer matrix, and effectively interact with the polymer chains. The strong attractive forces that exist at molecular levels between the nanoparticles through their extensive interfacial area make it very challenging to overcome these issues. Furthermore, the presence of nanoparticles in the polymer matrix significantly alters the processing condition of the polymer system. Therefore, the main objective of this thesis is to investigate the dispersion and interfacial interactions in polymer nanocomposites. To avoid the uncertainties associated with the visual and qualitative analysis of dispersion, which is commonly used by the researchers, a robust algorithm was developed to automatically quantify the state of dispersion in optical and electron micrographs. Several experiments were carried out to perceive the influence of surface modification of nanoparticles on the performance of polymer nanocomposites. Two different material systems were examined: organoclay-modified polylactide (PLA), and carbon nanotube (CNT)-modified epoxy. It was shown that the proper surface modification of nanoparticles could facilitate the dispersion, and consequently, enhance the mechanical and physical performance of the host polymer. To understand the effect of processing conditions on the dispersion quality of nanocomposites, a systematic study on the dispersion stability of CNT-modified epoxy resin was performed. It was found out that at elevated temperatures, CNTs show little affinity for the resin; thereby, any factors that promote the possibility of contacts between the nanotubes may result in their reagglomeration. Consequently, during processing, the dispersion stability is highly influenced with the flow-induced mobility of nanotubes resulting from external shear forces or a change in the viscosity. The insights gained throughout this investigation can be used to optimize the processing conditions and manufacturing methods for maintaining a stable dispersion during processing, and consequently obtaining nanocomposites with enhanced performance.
Les polymères nano-renforcés ont attiré beaucoup d'attention au cours des dernières décennies. Profitant de la géométrie à l'échelle nanométrique, immense rapport surface/volume, et les propriétés chimiques et physiques exceptionnelles, les nanoparticules améliorent en théorie la performance des systèmes de polymères. Dans la pratique, la préparation de polymères nano-renforcés comporte ses propres défis. Pour obtenir le meilleur renforcement possible, les nanoparticules doivent être uniformément dispersées dans la matrice, afin d'interagir efficacement avec les chaînes du polymère. Les forces d'attraction moléculaires qui existent à l'interface entre différentes nanoparticules rendent ces problèmes difficiles à surmonter. En outre, la présence de nanoparticules dans la matrice modifie de manière significative les procédés de fabrication de ce système polymère. Par conséquent, l'objectif principal de cette thèse est d'étudier la dispersion et les interactions interfaciales dans les polymères nano-renforcés. Pour éviter les incertitudes liées à l'analyse visuelle et qualitative de la dispersion, utilisée couramment par les chercheurs, un algorithme robuste a été développé pour quantifier automatiquement l'état de dispersion dans les micrographies optiques et électroniques. Plusieurs expériences ont été réalisées pour comprendre l'influence de la modification de surface des nanoparticules sur la performance des polymères nano-renforcés. Deux matériaux différents ont été examinés: un polylactide (PLA) renforcé avec des organo-argiles, et un époxy renforcé par des nanotubes de carbone (CNT). Il a été démontré qu'une modification appropriée de la surface des nanoparticules pourrait faciliter la dispersion, et par conséquent pourrait améliorer les performances mécaniques et physiques du matériau. Pour comprendre l'effet des procédés de fabrication sur la dispersion des polymères nano-renforcés, une étude systématique sur la stabilité de la dispersion de résine époxyde renforcée par des CNT a été effectuée. Il a été constaté que, à des températures élevées, les nanotubes de carbone présentent peu d'affinité avec la résine, et de ce fait, tous les facteurs qui favorisent la possibilité de contacts entre nanotubes peuvent conduire à leur ré-agglomération. Par conséquent, pendant le procédé de fabrication, la stabilité de la dispersion est fortement influencée par la mobilité induite par l'écoulement de nanotubes résultant de forces de cisaillement externes ou un changement de la viscosité. Les connaissances acquises tout au long de cette enquête peuvent être utilisés pour optimiser les procédés et les méthodes de fabrication afin de maintenir une dispersion stable tout au long de la fabrication, et obtenir ainsi un polymère nano-renforcé avec des performances accrues.

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Kern, Barreto Cynara Caroline. "Dispersão de nanopartículas magnéticas em meios complexos biodegradáveis". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066419/document.

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Les nanocolloïdes magnétiques sont des dispersions de nanostructures magnétiques dans un liquide porteur. Par la combinaison des propriétés du liquide et des particules magnétiques, ces dispersions peuvent être confinées, déplacées, déformées et contrôlées par l'application d'un champ magnétique externe et ont ainsi de nombreuses applications en nanosciences et les nanotechnologies. Nous avons étudié la dispersion de nanoparticules magnétiques (NPM) dans les solvants eutectiques profonds (DES). Ces solvants, constitués d'un mélange entre un sel d'ammonium (ici le chlorure de choline (Ch) et un donneur de liaison H (ici, l'ethyleneglycol (EG) ou l'urée (U)) ont des propriétés proches des liquides ioniques tout en étant biodégradables. L'un des verrous concernant ces dispersions est la nature des forces impliquées dans la stabilité colloïdale. En effet, on ne peut plus expliquer la stabilité des dispersions dans ces milieux par le modèle DLVO, classiquement utilisé dans l'eau, du fait de leur force ionique élevée. Nous avons dans en premier temps caractérisé soigneusement deux DES (ChEH (1:3) et ChU (1:2) en mol) du point de vue de la densité et viscosité pour des températures entre 20 et 45°C. Ceci nous a permis de montrer la forte association de ces liquides. Un protocole de dispersion de nanoparticules de maghémite (Fe2O3) ou de ferrite mixte (CoxZn1-xFe2O4) est ensuite proposé, et les dispersions sont étudiées par diffusion de rayonnement (lumière et SAXS). Il s'est avéré que les particules les plus petites étaient les mieux dispersées. Enfin, un test de synthèse de NPM dans des solutions d'argile a permis d'obtenir une polydispersité plus faible en sortie de synthèse
Magnetic nanocolloids are dispersions of magnetic nanostructures in a carrier fluid. Thanks to the original properties of both the liquid and the magnetic particles, these dispersions can be confined, moved, deformed and controlled by applying an external magnetic field. Such dispersions thus have many applications in nanoscience and nanotechnologies.We studied the dispersion of magnetic nanoparticles in deep eutectic solvents (DES). These solvents (DES), obtained by mixing a quaternary ammonium salt (e.g., choline chloride Ch) and a hydrogen bond donor (e.g., ethyleneglycol EG or Urea U) have properties similar to ionic liquids, and are also biodegradable. One of the questions about these dispersions is the nature of the forces implied in colloidal stability, since the DLVO model classically used in water cannot be invoked here due to the very high ionic strength of the solvent.In a first step, we have carefully characterized two DES ((ChEG (1:3) and ChU (1:2) in mol), measuring the density and viscosity for temperatures between 20 and 45°C. We could thus show the high association in these liquids.A protocol to disperse nanoparticles of maghemite (Fe2O3) or mixed ferrite (CoxZn1-xFe2O4) is then proposed, and the obtained dispersions are studied by dynamic light scattering and SAXS. The size polydispersity was reduced by size sorting, and it reveals that the smallest particles are the most easy to disperse in the DES.Last, a synthesis of NMP in clay dispersion was tested and showed promising results with a reduced size polydispersity

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Crane, Nathan B. 1974. "Strengthening porous metal skeletons by metal deposition from a nanoparticle dispersion". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32385.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.
Includes bibliographical references.
The accuracy of solid freeform fabrication processes such as three-dimensional printing (3DP) and selective laser sintering (SLS) must be improved for them to achieve wide application in direct production of metal parts. This work seeks to reduce sintering and deformation of porous metal skeletons during liquid-metal infiltration by reinforcing the skeletons with metal deposits. This can be accomplished by depositing a metal from a suspension of nanometer-scale iron particles. The nanoparticle deposits from the suspension concentrate in regions of high stress when the solvent is removed by drying. The particles are sintered to create a dense structure that reinforces the porous skeleton-reducing deformation and creep. Generically, this work studies a process for metal deposition from a liquid carrier with unique transport characteristics compared to traditional metal deposition processes such as plating, chemical vapor deposition, evaporation, and sputtering. This process of depositing metal from nanoparticle suspensions is studied using a commercial product of iron nanoparticles. The processed iron particle suspension contains significant carbon from the organic dispersants used to stabilize the suspension. Gas adsorption, X- ray diffraction, and SEM imaging were used to show that the carbon aids reduction of any iron oxide on heating and strongly influences the densification characteristics. The iron nanoparticles are applied to porous steel skeletons produced by sintering stainless steel powder. These are then heated to typical steel infiltration temperatures of 1284 C. The nanoparticle deposits are shown to reduce creep deflections at infiltration temperatures by up to 95% and reduce shrinkage by up to 60%.
(cont.) The best results are obtained by repeating the process of applying the nanoparticles, drying the solvent, and sintering them to 700 C up to four times. The performance in magnetic materials can also enhanced by applying a magnetic field along the magnetic particles. This magnetic field concentrates the nanoparticle deposits into the contact points between the skeleton particles where they provide optimal benefit.
by Nathan Brad Crane.
Ph.D.

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Spence, D'Anne Emmett. "Intercalated MoS2 nanoparticles for enhanced dispersion in smokes and obscurants". College Park, Md. : University of Maryland, 2003. http://hdl.handle.net/1903/56.

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Thesis (M.S.)--University of Maryland, College Park, 2003.
Thesis research directed by: Dept. of Chemistry and Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Cao, Xue-Zheng, Holger Merlitz, Chen-Xu Wu, Goran Ungar i Jens-Uwe Sommer. "A theoretical study of dispersion-to-aggregation of nanoparticles in adsorbing polymers using molecular dynamics simulations". Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A36333.

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The properties of polymer–nanoparticle (NP) mixtures significantly depend on the dispersion of the NPs. Using molecular dynamics simulations, we demonstrate that, in the presence of polymer–NP attraction, the dispersion of NPs in semidilute and concentrated polymers can be stabilized by increasing the polymer concentration. A lower polymer concentration facilitates the aggregation of NPs bridged by polymer chains, as well as a further increase of the polymer–NP attraction. Evaluating the binding of NPs through shared polymer segments in an adsorption blob, we derive a linear relationship between the polymer concentration and the polymer–NP attraction at the phase boundary between dispersed and aggregated NPs. Our theoretical findings are directly relevant for understanding and controlling many self-assembly processes that use either dispersion or aggregation of NPs to yield the desired materials.

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Costa, Elisabete Fernandez Reia Da. "Liquid moulding of carbon nanoparticle filled composites". Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7276.

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This thesis focuses on the incorporation of carbon nanoparticles within continuous fibre reinforcements by liquid composite moulding processes, in order to provide enhanced electrical and delamination properties to the multiscale composites. The mechanisms controlling the flow and filtration of these nanoparticles during liquid composite moulding are studied, in order to develop a predictive 1-D model which allows design of the processing of these composite materials. Five different carbon nanoparticles at 0.25 wt% loading, three unmodified and one surface modified carbon nanotube systems and one carbon nanofibre system, were utilised to modify a commercial two-component epoxy resin utilised to impregnate carbon and glass reinforcements at high fibre volume fraction by resin transfer moulding. The dispersion of the nanofillers in the prepolymer was carried out by ultrasonication, high shear mixing or triple roll milling or a combination of the three. Electrical conductivity measurements of the carbon nanoparticle liquid suspensions during dispersion, alongside optical microscopy imaging and rheological analysis of these allowed the selection of the concentration of nanofiller and the appropriate dispersion technique for each nanoparticle system. The resin transfer moulding process required adaptation to incorporate the dispersion and modify degassing steps, especially when utilising unmodified carbon nanoparticles suspensions, due to their higher viscosity and tendency to be filtered. Nanoparticle filtration was identified by electrical conductivity measurements and microscopy of specimens cut at increasing distances from the inlet. Cake filtration was observed for some of the unmodified systems, whereas deep bed filtration occurred for the surface modified CNT material. Property graded composites were obtained due to filtration, where the average electrical conductivity of the carbon and glass composites produced increased by a factor of two or one order of magnitude respectively. The effect of filler on the delamination properties of the carbon fibre composites was tested under mode I. The results do not show a statistically significant improvement of delamination resistance with the presence of nanoparticles, although localised toughening mechanisms such as nanoparticle pull-out and crack bridging as well as inelastic deformation have been observed on fracture surfaces. Particle filtration and gradients in concentration resulted in non-linear flow behaviour. An 1-D analytical and a finite difference model, based on Darcy’s law accompanied by particle mass conservation and filtration kinetics were developed to describe the flow and filtration of carbon nanoparticle filled thermosets. The numerical model describes the non-linear problem by incorporating material property update laws, i.e. permeability, porosity and viscosity variations on concentration of retained and suspended particles with location and time. The finite difference model is consistent and converges to the analytical solution. The range of applicability of the analytical model is limited to lower filtration coefficients and shorter filling lengths, providing an approximate solution for through thickness infusion; whereas the numerical model presents a solution outside this range, i.e. in-plane filling processes. These models allow process design, with specified carbon nanoparticle concentration distributions achieved via modifying the nanofiller loading at the inlet as a function of time.

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Cruceanu, Florentin I. "AC-calorimetry and dielectric spectroscopy on anisotropic liquid crystal and aerosil dispersions". Worcester, Mass. : Worcester Polytechnic Institute, 2008. http://www.wpi.edu/Pubs/ETD/Available/etd-040908-143149/.

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Dissertation (Ph.D.)--Worcester Polytechnic Institute.
Keywords: phase transitions; quenched random disorder; liquid crystals; dielectric spectroscopy; calorimetry. Includes bibliographical references (leaves 78-83).

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Truong, Bao H. (Bao Hoai). "Critical heat flux enhancement via surface modification using colloidal dispersions of nanoparticles (Nanofluids)". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44775.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.
Includes bibliographical references (leaves 97-103).
Nanofluids are engineered colloidal dispersions of nanoparticles (1-100nm) in common fluids (water, refrigerants, or ethanol...). Materials used for nanoparticles include chemically stable metals (e.g., gold, silver, copper), metal oxides (e.g., alumina, zirconia, silica, titania) and carbon in various forms (e.g., diamond, graphite, carbon nanotubes). The attractive properties of nanofluids include higher thermal conductivity, heat transfer coefficients (HTC) and boiling critical heat flux (CHF) than that of the respective base fluid. Nanofluids have been found to exhibit a very significant enhancement up to 200% of the boiling CHF at low nanoparticle concentrations. In this study, nanofluids were investigated as an agent to modify a heater surface to enhance Critical Heat Flux (CHF). First, the CHF of diamond, Zinc Oxide and Alumina water-based nanofluids at low volume concentration (<1 vol%) were measured to determine if nanofluid enhances CHF as seen in literature. Subsequently, the heaters are coated with nanoparticles via nucleate boiling of nanofluids. The CHF of water was measured using these nanoparticle precoated heaters to determine the magnitude of the CHF enhancement. Characterization of the heaters after CHF experiments using SEM, confocal, and contact angle were conducted to explain possible mechanisms for the observed enhancement. The coating thickness of the nanoparticle deposition on a wire heater as a function of boiling time was also investigated. Finally, theoretical analyses of the maximum CHF and HTC enhancement in term of wettability were performed and compared with the experimental data. The CHF of nanofluids was as much as 85% higher than that of water, while the nanoparticle pre-coated surfaces yielded up to 35% CHF enhancement compared to bare heaters.
(cont.) Surface characterization of the heaters after CHF experiments showed a change in morphology due to the nanoparticles deposition. The coating thickness of nanoparticle was found to deposit rather quickly on the wire surface. Within five minutes of boiling, the coating thickness of more than 1 pm was achieved. Existing CHF correlations overestimated the experimental data.
by Bao H. Truong.
S.M.

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Picard-Lafond, Audrey. "Synthèse de nanoparticules riches en carbone par polymérisation en dispersion". Master's thesis, Université Laval, 2017. http://hdl.handle.net/20.500.11794/27902.

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L’intérêt porté aux nanomatériaux de carbone est en croissance en raison de leur potentiel pour une variété d’applications. Le réseau d’atomes de carbone hybridés sp², commun à tous les matériaux de cette famille, engendre d’excellentes propriétés électroniques et optiques modulées par la forme, la taille et la dimensionnalité du réseau carboné. Parmi ces nanomatériaux, les nanoparticules de carbone (CNP) disposent d’un potentiel singulier en raison de leurs propriétés de photoluminescence, leur photostabilité et leur faible toxicité. En conséquence, l’application des CNP en biomédecine, en optoélectronique et en photocatalyse est grandement étudiée. Néanmoins, les méthodes de synthèse et les techniques de séparation actuelles représentent des limitations à leur mise en œuvre. L’usage de température élevée (>100 °C) nuit au contrôle précis de la forme et de la taille des CNP, les rendements réactionnels sont faibles et la surface du matériau est chimiquement inerte. Dans ce projet, l’objectif est d’établir une méthode de synthèse de CNP palliant aux limitations des procédés actuels. Autrement dit, nous tentons de développer une méthode permettant un contrôle précis de la forme et de la taille des particules en évitant l’utilisation de températures élevées. La stratégie est basée sur la polymérisation en dispersion d’unités organiques riches en alcynes, utilisées comme source métastable de carbone. D’une part, la polymérisation de monomères riches en alcynes permet de synthétiser en une étape simple des polyynes qui, en raison de leur instabilité, réagissent spontanément pour produire un matériau composé majoritairement d’atomes de carbone hybridés sp². D’autre part, la polymérisation en dispersion assure un contrôle morphologique des particules durant la synthèse. En plus de l’objectif principal, la fonctionnalisation en surface des particules est envisagée en exploitant la réactivité d’alcynes résiduels de la structure carbonée. Aussi, nous tentons d’échanger le monomère alcynique afin de bonifier les propriétés de photoluminescence des particules issues du procédé.
The interest in carbon nanomaterials is expanding due to their potential for various applications. The network of sp²-hybridized carbon atoms, common to all materials of this family, generates excellent electronic and optical properties which are modulated by the shape, the size and the dimensionality of the carbon network. Among these nanomaterials, carbon nanoparticles (CNP) have a singular potential due to their photoluminescence properties, their photostability and their low toxicity. Accordingly, the application of CNP in biomedicine, optoelectronics and photocatalysis is greatly studied. However, the current synthetic methods and separation techniques represent limitations to their implementation. The use of high temperatures (>100 °C) hinders the precise control over shape and size of the CNP, the synthetic yields are low and the materials’ surface is chemically inert. In this project, the objective is to establish a route for CNP synthesis which surpasses the limitations of the current preparation methods. In other words, we are trying to develop a method allowing a precise control of the particles’ shape and size, while avoiding the use of high temperatures. The strategy is based on the dispersion polymerization of alkyne-rich organic units, used as a metastable carbon source. On one hand, the polymerization of alkyne-rich monomers allows the one-step synthesis of polyynes which, due to their instability, react spontaneously to produce a material composed mainly of sp²-hybridized carbon atoms. On the other hand, dispersion polymerization ensures a morphological control of the particles during their synthesis. Adding to the main objective, surface functionalization of the particles is intended by exploiting the reactivity of residual alkynes in the carbon structure. Also, we try to exchange the alkyne-rich monomer in order to improve the photoluminescence properties of the particles obtained from the developed process.

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Cabreira, Gomes Rafael. "Dispersions de nanoparticules magnétiques de structure coeur/coquille : propriétés magnétiques et thermodiffusion". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066568/document.

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Nos objectifs sont ici de comprendre comment les propriétés magnétiques de nanoparticules (NPs) sont affectées par la diminution de leur taille et par leur composition chimique, et comprendre ce qui régit leur mouvement thermophorétique et l'effet magnéto-calorique. Des ferrofluides composés de NPs de structure cœur-couronne sont synthétisés ici avec un cœur de ferrite de Mn, de Co ou de ferrite mixte Zn-Mn, recouvert d'une couronne de maghémite. Les mesures magnétiques révèlent une composition magnétique mixte conduisant à l'observation d'un exchange bias qui se manifeste par des cycles d'hystérésis décalés à basses températures. Nous comparons ce phénomène dans le cas de NPs à cœur magnétiquement dur (CoFe2O4) et à cœur magnétiquement mou (MnFe2O4). Indépendamment de la nature du cœur, ce champ d'échange augmente jusqu'à un maximum, obtenu quand le champ de refroidissement est de l'ordre de la moitié du champ d'anisotropie. Les propriétés thermophorétiques des dispersions, sondées par diffusion Rayleigh forcée, sont gouvernées par la physico-chimie du colloïde (ligand de surface, contre-ions, interactions entre NPs) indépendamment de la composition chimique et des propriétés magnétiques en champ nul. Le coefficient Soret est ici négatif (NPs thermophiles) et est relié à la compressibilité osmotique donnée par un formalisme de Carnahan-Starling effectif. On modélise la friction en régime dilué par la loi d'Einstein et en régime concentré, à l'approche de la transition vitreuse, par un modèle de Vogel-Fulcher. Les mesures de l’effet magnéto-calorique démontrent une similarité avec les matériaux commerciaux, avec une forte influence de la composition chimique du cœur
Our objective is to understand how the magnetic properties of nanoparticles (NPs) can be affected by their size reduction and their chemical composition, and also to determine their role on their thermophoretic motion and on the magneto-caloric effect. For this purpose, aqueous ferrofluids are synthesized with core-shell NPs based on a core of Mn-ferrite, Co-ferrite and mixed Zn-Mn ferrites, coated with a maghemite shell. The magnetic measurements evidence a ferrimagnetic core, covered with disordered frozen spins (SGL), driving an exchange bias phenomenon shifting the hysteresis loops, when the system is cooled under a field Hfc. This exchange bias is measured as a function of Hfc, in samples with NPs having either a hard (CoFe2O4) or a soft (MnFe2O4) magnetic core. Whatever the nature of the magnetic core, the exchange bias field grows up to reach a maximum, always found at Hfc of the order of half of the anisotropy field. The thermophoretic properties of the dispersions, probed by Forced Rayleigh Scattering, are ruled by colloidal physico-chemical features (surface ligand, counter ions, interparticle interactions) whatever the chemical composition and the magnetic properties in zero magnetic field. The Soret coefficient is found here negative (thermophilic NPs) and is related to the osmotic compressibility, modeled by an effective Carnahan-Staring formalism. In the dilute regime, the friction follows an Einstein law, while a Vogel-Fulcher formalism describes the concentrated regime, at the approach of the glass transition. The magneto-caloric measurements demonstrate a similarity with commercial materials. They are strongly influenced by the core composition

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Farrugia, Brooke Louise Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "Analysis of nanoparticle dispersion, biological interactions and drug incorporation of polyurethane nanocomposite materials". Awarded By:University of New South Wales. Graduate School of Biomedical Engineering, 2010. http://handle.unsw.edu.au/1959.4/44826.

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The use of polymer nanocomposites (NCs) in industrial applications has received growing attention over the past decade due to their improved mechanical properties. However, little work has been reported which analyses the efficacy of NCs in biological applications, including drug delivery systems and implantable materials. This thesis examines the effect of the chemistry of the organic modifier (OM) on the structure and biological performance of poly(ether)urethane NCs (PUNCs) and the influence of the method of drug incorporation on interactions between drug and NC. Organically modified silicates (OMS) were prepared using OMs varying in terminal functionality and alkyl chain length. PUNCs were solvent cast containing 1 and 3wt% OMS and particle dispersion analysed using X-ray diffraction and transmission electron microscopy. Findings revealed that use of an OM with methyl terminal, dodecylamine (12CH3), resulted in superior dispersion of OMS compared with a carboxyl terminated OM, aminododecanoic acid (12COOH), of equivalent alkyl chain length. This is believed to result from increased self interaction of 12COOH compared with 12CH3. Additionally, increased alkyl chain length was shown to improve NC dispersion with a chain length of sixteen units resulting in the optimum dispersion with a partially exfoliated NC structure. Analysis of cellular interactions with the PUNCs revealed a significant difference in both fibroblast and platelet adhesion to NCs incorporating 12CH3 compared with 12COOH. Surface analysis using ToF-SIMS demonstrated the presence of 12CH3 fragments on the NC surface supporting the hypothesis that surface expressed OMs alter cellular interactions with the NC. Altering the alkyl chain length also affected cellular interaction with an alkyl chain length of twelve units or greater, substantially reducing fibroblast adhesion without affecting cell growth inhibition or viability. Incorporation of a model drug, crystal violet, into the PUNCs demonstrated a lower degree of disruption to OMS dispersion when loaded post NC fabrication compared with pre fabrication. This is believed to result from interactions between the drug and NC constituents which also impacted on drug release from the NC system. Results show PUNC properties and biological interactions can be modulated through OM variation and fabrication method, thus showing potential for use in biomedical applications.

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Voormann, Hauke [Verfasser]. "Smart dispersion of carbon nanoparticle epoxy composites: from nano to application / Hauke Voormann". Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2021. http://d-nb.info/123281296X/34.

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Ragheb, Ragy. "Synthesis and Characterization of Polylactide-siloxane Block Copolymers as Magnetite Nanoparticle Dispersion Stabilizers". Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/31687.

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Polylactide-siloxane triblock copolymers with pendent carboxylic acid functional groups have been designed and synthesized for study as magnetite nanoparticle dispersion stabilizers. Magnetic nanoparticles are of interest in a variety of biomedical applications, including magnetic field-directed drug delivery and magnetic cell separations. Small magnetite nanoparticles are desirable due to their established biocompatibility and superparamagnetic (lack of magnetic hysteresis) behavior. For in-vivo applications it is important that the magnetic material be coated with biocompatible organic materials to afford dispersion characteristics or to further modify the surfaces of the complexes with biospecific moieties.

The synthesis of the triblock copolymers is comprised of three reactions. Difunctional, controlled molecular weight polymethylvinylsiloxane oligomers with either aminopropyl or hydroxybutyl endgroups were prepared in ring-opening redistribution reactions. These oligomers were utilized as macroinitiators for ring-opening L-lactide to provide triblock materials with polymethylvinylsiloxane central blocks and poly(L-lactide) endblocks. The molecular weights of the poly(L-lactide) endblocks were controlled by the mass of L-lactide relative to the moles of macroinitiator. The vinyl groups on the polysiloxane center block were further functionalized with carboxylic acid groups by adding mercaptoacetic acid across the pendent double bonds in an ene-thiol free radical reaction. The carboxylic acid functional siloxane central block was designed to bind to the surfaces of magnetite nanoparticles, while the poly(L-lactide)s served as tailblocks to provide dispersion stabilization in solvents for the poly(L-lactide). The copolymers were complexed with magnetite nanoparticles by electrostatic adsorption of the carboxylates onto the iron oxide surfaces and these complexes were dispersible in dichloromethane. The poly(L-lactide) tailblocks extended into the dichloromethane and provided steric repulsion between the magnetite-polymer complexes.
Master of Science

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Lin, Yaochen. "Dispersion de nanoparticules ferroélectriques dans un cristal liquide : élaboration, transitions de phases et propriétés diélectriques". Thesis, Littoral, 2017. http://www.theses.fr/2017DUNK0443/document.

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Les cristaux liquides sont des matériaux organiques utilisés pour réaliser des dispositifs électroniques ; avant de les intégrer dans des applications, il est nécessaire d'étudier leurs propriétés physico-chimiques et diélectriques pour optimiser leurs performances. Ce travail de thèse est consacré aux nanocolloïdes obtenus par dispersion de nanoparticules ferroélectriques dans un cristal nématique ; il s'agit d'étudier l'influence des inclusions sur les transitions de phases et sur les propriétés diélectriques de la matrice. L'étude des transitions de phases à l'aide de l'Analyse Enthalpique Différentielle (AED) a mis en évidence l'influence des nanoparticules ferroélectriques ; ceci résulte de deux principaux effets ; la polarisation spontanée des nanoparticules et l'ancrage entre les molécules du cristal liquide et les inclusions. La caractérisation diélectrique a révélé le couplage entre la polarisation macroscopique des inclusions et le champ électrique ; ce couplage se manifeste par une augmentation des températures de transitions de phases par rapport à celles déterminées par l'AED. La compétition entre les effets de la polarisation sous champ électrique et de l'ancrage induit une modification des permittivités (parallèle et perpendiculaire) et de l'anisotropie diélectriques. L'utilisation des nanoparticules fortement polaires sélectionnées a confirmé l'importance de la polarisation macroscopique des nanoparticules pour améliorer les propriétés des nanocolloïdes étudiés ; en effet, de très faibles quantités de ces nanoparticules donnent lieu à des améliorations plus significatives que celles obtenues par les nanoparticules brutes
Liquid crystals are organic materials used to make electronic devices ; before using this material in applications, it is necessary to study their physical-chemical and dielectric properties in order to optimize their performance. This study is devoted to the nanocolloids obtained by dispersing ferroelectric nanoparticles in a nematic liquid crystal ; it means an inclusion influences the phase transitions temperatures and the dielectric properties of the host. The phase transitions measured by using Differential scanning calorimetry (DSC) evidenced the ferroelectric nanoparticles influence ; which is attributed two effects : the nanoparticles spontaneous polarization and the anchoring effect between nanoparticles and liquid crystal. The dielectric characterisation revealed the coupling between the macroscopic polarization of the inclusions and the electric field ; this coupling is manafested by an increase of phase transition temperatures compared to those determined by DSC. The competition between the polarization effect under an electric field and the anchoring effect induces a modification of the permittivities (parallel and perpendicular) and the dielectric anisotropy. Using harvested nanoparticles, the study confirmed the importance of the nanoparticles polarization to increase the properties of the studied nanocolloids. In fact, very small quantity of the harvested nanoparticles presents more significant improvements than those obtained with the non-harvested nanoparticles

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Ganapathy, Subramanian Santhana Gopinath. "A continuous impingement mixing process for effective dispersion of nanoparticles in polymers". Texas A&M University, 2006. http://hdl.handle.net/1969.1/4320.

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Mixing refers to any process that increases the uniformity of composition and is an integral part of polymer processing. The effective mixing of nanoparticles into polymers continues to be one of the leading problems that limit large scale production of polymer nanocomposites. Impingement mixing is a novel, relatively simple, continuous flow mixing process wherein mixing is accomplished by immersing a high velocity jet in a slower co-flowing stream. The resulting recirculating flow produces an energy cascade that provides a wide range of length scales for efficient mixing. An impingement mixing process was developed and studied through experiments and simulations. Numerical simulations were conducted using FLUENT to understand better the mechanism of operation of the mixer. The formation of a recirculation zone was found to affect the dispersion of nanoparticles. Results of the simulations were compared with experimental data obtained under similar conditions. While this process may be used for any polymernanoparticle combination, the primary focus of this study was the dispersion of Single Walled Carbon Nanotubes (SWNTs) in an epoxy matrix. The dispersion of SWNTs was evaluated by analyzing SEM images of the composites. The image analysis technique used the concept of Shannon Entropy to obtain an index of dispersion that was representative of the degree of mixing. This method of obtaining a dispersion index can be applied to any image analysis technique in which the two components that make up the mixture can be clearly distinguished. The mixing process was also used to disperse SWNTs into a limited number of other polymers. The mixing process is an "enabling" process that may be employed for virtually any polymer-nanoparticle combination. This mixing process was shown to be an effective and efficient means of quickly dispersing nanoparticles in polymers.

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Kumar, Prashant. "Measurements and modelling of the dispersion of nanoparticles in the urban environment". Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611184.

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Parrenin, Laurie. "Synthèse et formulation d'encres polymères pour couche active de cellules solaires organiques". Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0183/document.

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La limitation de solvants toxiques halogénés dans les procédés de préparation de matériaux photoactifs est primordiale pour l’industrialisation des cellules solaires organiques. L’objectif de ce travail de thèse a été de préparer des nanoparticules composées de polymère π-conjugué (PCDTBT) et d’accepteur d’électron (PC71BM) dans l’eau ou en milieu alcool. Des particules composites (PCDTBT+ PC71BM) ontété synthétisées avec deux types de stabilisants : un tensio-actif anionique (SDS) et un copolymère à blocs P3HT-b-PEO, ainsi que sans stabilisant. L’intégration de ces nanoparticules dispersées en phase aqueuse dans la couche active de cellules solaires organiques a par exemple permis d’obtenir des rendements de l’ordre de1%
The replacement of halogenated toxic solvents is fundamental in photoactive material processes to make the organic photovoltaic sector viable. Herein the use of nanoparticles made of π-conjugated polymer (PCDTBT) and electron-acceptor(PC71BM) was targeted in order to allow for instance the control of the phase separation between the two materials. Thus composite particles of PCDTBT and PC71BM have been synthesized using two kinds of stabilizers: an anionic surfactant (SDS) and a block copolymer P3HT-b-PEO, as well as without stabilizer. As an example such nanoparticles were integrated as active layer into photovoltaic device enabling a power conversion efficiency of 0.94% from aqueous based inks

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Kossi, Alaedine. "Consolidation de dispersions colloïdales d'oxyde de titane sous compression osmotique". Nice, 2012. http://www.theses.fr/2012NICE4115.

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Segovia, Mera Alejandro. "Effets de la dispersion de nanoparticules dans un cristal liquide ferroélectrique sur les propriétés ferroélectriques et de relaxations diélectriques". Thesis, Littoral, 2017. http://www.theses.fr/2017DUNK0461/document.

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Ces travaux de thèse ont porté sur des matériaux constitués de dispersions de particules colloïdales nanométriques, issues d'un matériau ferroélectrique, dans un cristal liquide chiral à phase smectique ferroélectrique. Ils ont pour but d'étudier les effets occasionnés par ces dispersions sur les propriétés du nanocolloïde, notamment celles liées à leur ferroélectricité. Cette étude a montré que les comportements mésomorphes et ferroélectriques de ces matériaux sont conservés. Une baisse de polarisation spontanée ainsi qu'un recul des températures des transitions ont été mis en évidence pour des faibles concentrations en NPs. Une "transition" de ces comportements a été observée pour une concentration critique au-delà de laquelle les particules s'agrègent pour former des amas au sein du milieu cristal liquide. Nous nous sommes intéressés ensuite à deux modes de relaxation diélectriques. Le premier lié aux mouvements de distorsions de l'hélice dans la phase ferroélectrique, le second aux mouvements de compression des couches smectiques de part et d'autre de la transition ferroélectrique-paraélectrique. Les comportements observés semblent être gouvernés par les modifications des propriétés visco-élastiques des nanocolloïdes, occasionnés par l'intercalation des nanoparticules entre les couches smectiques
The present thesis work concerns materials made of dispersions of nanometric colloidal particles, from a bulk ferroelectric material, dispersed within a chiral smectic phase of a ferroelectric liquid crystal. The goal of this work is to study the effect of the dispersed nanoparticles over the nanocolloïd properties, specially the ones related to ferroelectricity. This study showed no change over mesomorphic and ferroelectric behavior of the materials. A decrease in spontaneous polarization and phase transition temperatures was found for low nanoparticle concentrations. A "transition" of these behaviors was observed for a critical concentration, beyond which, nanoparticles aggregate and form clusters inside the liquid crystal matrix. Afterwards, we have studied two dielectric relaxation modes. The first one related to distorsions of the helix in the ferroelectric phase and the second one to the compression movements of the smectic layers around the ferroelectric-paralectric transition. The observed behaviors seem to be due to modifications of the visco-elastic properties of nanocolloids, produced by intercalation of nanoparticles between the smectic layers

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Daoura, Oscar. "Towards anti-coking and anti-sintering Ni@Silica based catalysts for the dry reforming of methane". Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS679.

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Le reformage à sec du méthane est un processus de conversion de CH4 et CO2 en H2 et CO ou gaz de synthèse avec un rapport molaire de 1, lequel peut servir comme matière première pour la production de carburant liquide par Fischer-Tropsch. Les catalyseurs à base de nickel sont des candidats prometteurs pour cette réaction. Ils présentent une très bonne activité, sont peu coûteux et sont plus disponibles en comparaison avec les matériaux à base de métaux nobles, mais ils se désactivent par frittage et dépôt du coke. La stabilisation de Ni par confinement et/ou par amélioration de la dispersion et de l'interaction des nanoparticules avec la silice font/fait partie des méthodes les plus efficaces et moins coûteuses pour lutter contre la désactivation lors du reformage, ce qui correspond à l’objectif principal de ce travail. Ainsi, de nouveaux catalyseurs à base de Ni, ont été synthétisés, caractérisés et testés en catalyse de reformage à sec de CH4. Trois points principaux ont été examinés: (i) Le test de l’efficacité de nouveaux supports mésoporeux (MCF) en variant la nature des précurseurs de Ni (sels ou colloïdes) incorporés par imprégnation ou synthèse directe après ajustement du pH, (ii) la préparation de monolithes mésoporeux de type SBA-15 avec une très bonne dispersion de Ni incorporé par voie « one-pot », (iii) le contrôle de la dispersion, de la taille des particules de Ni et donc de l’interaction avec de la silice non poreuse via la formation de phyllosilicates de Ni. Au final, les monolithes de type SBA-15 incluant Ni par voie « one-pot » et les particules de Ni0 issues de la réduction des phyllosilicates se sont avérés être les catalyseurs les plus performants
Dry reforming of methane is a process for the conversion of CH4 and CO2 into “syngas”, a gaseous mixture of H2 and CO (with a molar ratio value of 1) that can serve as feedstock for the production of liquid fuel by the mean of Fischer-Tropsch procedure. Nickel-based catalysts are promising candidates for this reaction displaying high activity, lower cost and wider availability than noble metal-based materials but deactivating by sintering and/or coke deposition. Stabilization of Ni0 nanoparticles within siliceous supports either by confinement and/or by improving their dispersion and interaction with the support are among the best and the less expensive methods to overcome the deactivation in dry reforming which represents the main objective for this work. Here, new stable nickel-based catalysts were synthesized, characterized and tested in dry reforming. Three main issues were examined: (i) Testing the efficiency of new mesoporous supports (mesocellular silica foams) using different nickel precursors (salt or colloidal form) incorporated by impregnations or pH adjustment assisted one-pot methods, (ii) designing highly dispersed nickel-based mesoporous monoliths through an original sol-gel method (iii) controlling the nickel size, dispersion and therefore its interaction with the support onto non-porous silica carriers by the mean of phyllosilicates. Monoliths of the SBA-15 type incorporating Ni0 by a one-pot method, and Ni0 obtained through the reduction of nickel phyllosilicates turned out to be the most stable and efficient catalysts

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Bonnefond, Sylvain. "Amplification de la fluorescence par diffusion multiple : une étude exploratoire vers des conditions biocompatibles". Thesis, Université Côte d'Azur (ComUE), 2019. http://www.theses.fr/2019AZUR4080.

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L’objet de cette thèse a consisté à mettre au point une méthode d’amplification de la fluorescence en utilisant la diffusion multiple (introduction de nanoparticules diélectriques, élastiques et passives) qui sera applicable sur des échantillons biologiques. Cela a nécessité de faire le lien entre le concept de laser biologique et de laser aléatoire pour une utilisation dans un régime amplifié, qui précède le régime laser, applicable aux marquages cellulaires et tissulaires. La génération d’une amplification passe par l’utilisation de diffuseurs (nanoparticules de dioxyde de titane dans ce travail) répartis de façon homogène. Il a fallu mettre au point des conditions de stabilisation colloïdale par adsorption de protéine (BSA) pour éviter l’agrégation des nanoparticules en tampons et milieux biologiques. Un montage optique a été mis au point pour exciter les fluorophores de façon reproductible, en évaluant précisément l’énergie de pompe et la réponse impulsionnelle de fluorescence, tout en optimisant la fenêtre d’observation pour limiter le photoblanchiment des fluorophores et la phototoxicité des cellules. Une première amplification stimulée a été montrée et validée avec une dispersion colloïdale dans une solution aqueuse homogène de FITC à une concentration de 200 µM. Cette expérience a prouvé qu’il est possible d’atteindre un gain de fluorescence jusqu’à 40 associé à une diminution de la largeur spectrale jusqu’à 5 nm, et une réduction globale de la durée de vie. La présence du processus d’émission stimulée dans l’amplification est confirmée par la corrélation entre la fluorescence et la concentration des nanoparticules ou l’énergie de pompe. Cette première démarche a été étendue à des concentrations de 2 et 20 µM pour lesquelles une saturation rapide du gain (respectivement ~ 10 et 20) a été constatée. Enfin une amplification a été montrée et validée sur des cellules en suspension marquées par la CFSE ou exprimant la GFP dans leur milieu de culture. Dans ces conditions une diminution du gain par rapport aux conditions précédentes a été constatée (jusqu’à 6 – 10 fois). L’explication de ce gain moindre a été explorée en testant les modifications des milieux sur l’amplification, et la présence d’une couche de BSA entourant les nanoparticules semble en être la cause car elle diminue probablement l’indice de réfraction effectif de la nanoparticule conduisant à une faible diffusion
The purpose of this PhD has been to develop a method of amplification of the fluorescence by using the multiple scattering (introduction of dielectric, elastic and passive nanoparticles) that will be applicable to biological samples. This required doing the link between the biological laser and random laser concept for a use in an amplified regime, which precedes the laser regime, applicable to cell and tissue labelling. The generation of an amplification passes by the use of scatterers (nanoparticles of titanium dioxide in this work) homogeneously distributed. It required developing conditions of the colloidal stabilization to avoid the aggregation of nanoparticles into biological media and buffers by the adsorption of proteins (BSA). An optical setup has been developed to excite the fluorescence, by accurately evaluating the pump energy and the pulse response of fluorescence, while optimizing the observation window to limit photobleaching of fluorophores and cell toxicity. A first stimulated amplification was shown and validated with a colloidal suspension in a homogeneous aqueous solution of FITC at a concentration of 200 µM. This experiment has shown that it is possible to achieve a fluorescence gain up to 40 associated with a decrease in spectral width up to 5 nm, and an overall reduction in lifetime. The presence of the stimulated emission process in amplification is confirmed by the correlation between fluorescence and nanoparticle concentration or pump energy. This first step was extended to concentrations of 2 and 20 µM for which a rapid saturation of the gain (respectively ~ 10 and 20) was observed. Finally, amplification has been shown and validated on CFSE-labeled or GFP-expressing suspension cells in their culture medium. In these conditions, a decreasing of the gain compared with the previous conditions has been observed (up to 6 – 10 times). The explanation of this lower gain has been explored by testing the changes of media on amplification, and the presence of a layer of BSA surrounding the nanoparticles seems to be the cause because the protein decreases probably the refractive index of the nanoparticle leading a weak scattering

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Baranauskas, Victor Vincent. "Cobalt Nanoparticle-Macromolecular Complexes and Their Conversion to Oxidatively Stable Entities". Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/27376.

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The goal of the research presented in this dissertation was to synthesize novel macromolecular materials that would afford oxidative stability to magnetic cobalt nanoparticles under ambient conditions. The cobalt nanoparticles were formed via the thermolysis of Co2(CO)8 in concentrated solutions of toluene containing the macromolecular dispersion stabilizers. The copolymers were designed to encapsulate the nanoparticles with a number of thin protective coatings to prevent their undesirable oxidation under ambient condtions. Cobalt nanoparticles encased with an organic glass were synthesized by stabilizing cobalt nanoparticles with poly(methyl methacrylate-co-2-vinylpyridine-g-dimethylsiloxane) whereas nanoparticles encapsulated with triazine networks were formed via the thermal treatment of cobalt particles complexed with poly(styrene-b-4-vinylphenylcyanate). Cobalt nanoparticles coated with a combination of carbonaceous and silica char were obtained by pyrolyzing cobalt particles stabilized with poly (4-vinylphenoxyphthalonitrile-co-4-vinylphenoxytriethoxysilane-g-dimethylsiloxane) graft copolymers. Moreover, cobalt nanoparticles encapsulated with either phthalonitrile networks or graphitic char were prepared via the thermal treatment of nanoparticles stabilized with poly(styrene-b-4-vinylphenoxyphthalonitrile). Oxidatively-stable, magnetic cobalt nanoparticle complexes may be prepared by heating cobalt nanoparticles encapsulated in poly(styrene-b-4-vinylphenoxyphthalonitrile) block copolymers at elevated temperatures. The block copolymers were synthesized through the sequential anionic polymerization of styrene and tert-butyldimethylsilyloxystyrene. The silyl ether protecting groups on the second block were hydrolyzed under acidic conditions to afford poly(styrene-b-4-vinylphenol), and the pendent phenols of the diblock copolymer were chemically modified with 4-nitrophthalonitrile to afford poly(styrene-b-4-vinylphenoxyphthalonitrile). Stable suspensions of ~8-10 nm diameter cobalt metal nanoparticles were formed by thermolysis of dicobalt octacarbonyl in solutions of toluene containing poly(styrene-b-4-vinylphenoxyphthalonitrile). The cobalt-polymer nanoparticle complexes were pyrolyzed under argon to afford highly magnetic cobalt nanoparticles encased in graphitic coatings. Magnetic susceptibility measurements indicate that the cobalt-graphitic particles are oxidatively-stable and retain their high saturation magnetizations (~ 95-100 emu g-1) for at least a year under ambient conditions.
Ph. D.

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Schneider, Wolfgang Benedikt. "Quantenchemie in elektrochemischen Prozessen". Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-169966.

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Kern der vorliegenden Arbeit ist die Anwendung quantenchemischer Methoden auf Probleme der elektrochemischen Katalyse vor dem Hintergrund der Sauerstoffreduktion, wie sie an kohlenstoffgeträgerten Platinkatalysatoren abläuft. In diesem Zusammenhang werden die Stabilität des Katalysatorsystems und der Mechanismus der Sauerstoffreduktion untersucht, sowie ein Algorithmus zur Berechnung von Molekülen unter einem gegebenen Potential vorgestellt. Zuerst werden die Wechselwirkungen von Platinnanopartikeln mit polyzyklischen Aromaten als Modellverbindungen des Katalysatormaterials untersucht. Weiterhin wird untersucht, wie Modifikationen des Kohlenstoffträgers und variierende Größe des Platinsystems diese Wechselwirkungen beeinflussen. Weiterhin beschäftigt sich diese Arbeit mit dem Reaktionsmechanismus der Sauerstoffreduktion. Zu diesem Zweck wird das Zersetzungsverhalten von H2O2 als mögliches Intermediat der Sauerstoffreduktion an Platinoberflächen untersucht. Weiterhin wird geprüft, inwieweit dem Elektrolyten hinzugefügte Ionen die Zersetzungsreaktionen beeinflussen. Abschließend werden Rückschlüsse auf den Reaktionspfad der Sauerstoffreduktion gezogen. Zuletzt wird ein theoretischer Ansatz zur Berechnung von Systemen im Rahmen der Dichtefunktionaltheorie vorgestellt, bei dem nicht die Anzahl der Elektronen, sondern das elektrochemische Potential vorgegeben ist und die Elektronenzahl potentialabhängig modifiziert wird. Ebenso wird die Relevanz von Rechnungen mit konstantem Potential demonstriert.

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Iranzo, Audrey. "Electrosynthèse assistée par ultrasons de nanoparticules de fer à valence zéro : étude de la croissance de dépôts et de leur dispersion par ondes acoustiques". Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30317/document.

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La synthèse de nanoparticules de fer zéro-valent, par le couplage des procédés d'ultrasonication et d'électrodéposition, est étudiée selon deux approches. La première partie de l'étude s'intéresse à l'influence du substrat, utilisé pour l'électrodéposition, sur la croissance des dépôts de fer et sur leur dispersion par ultrasonication. L'énergie interfaciale ainsi que l'énergie d'adhésion du dépôt sur le substrat (Y_(Fe/substrat) et W_(Fe/substrat) respectivement) étant reliées à l'énergie de surface et à la rugosité du substrat, un intérêt particulier a été porté à ces deux propriétés. Ainsi, deux matériaux présentant des énergies de surface différentes, l'or (Au) et le carbone vitreux (VC), ainsi que des rugosités différentes ont été testés. Un développement théorique basé sur les interactions de Van der Waals a permis de démontrer que Y_(Fe/VC)>Y_(Fe/Au) ce qui suggère une meilleure affinité du dépôt de fer avec l'or qu'avec le VC. Cette différence influence la morphologie (croissance 2D sur or et 3D sur le VC) mais aussi l'adhésion des dépôts. En effet, les expériences réalisées pour étudier l'effet des ultrasons sur le dépôt de fer révèlent une dispersion du dépôt progressive et complète pour le cas du VC alors qu'aucun détachement du dépôt n'est obtenu en utilisant l'or. La seconde partie de l'étude est consacrée à la synthèse de nanoparticules de fer par une nouvelle approche : l'électrodéposition de dépôts de fer ramifiés est étudiée dans une cellule de Hele-Shaw intégrant un élément vibrant (diaphragme piézoélectrique) permettant à la fois la formation de dépôts de fer et leur fragmentation. Les expériences menées révèlent que les bulles d'hydrogène, formées lors de la co-réduction des protons libres durant l'électrodéposition du fer, influencent fortement le processus de fragmentation. En utilisant des hautes fréquences et amplitudes de vibration du PZT, les bulles d'hydrogène oscillent avec des déformations de surface. Celles-ci génèrent des vitesses d'interface suffisamment hautes (˜ 4 m/s) pour permettre aux bulles de fragmenter des dépôts ramifiés en particules de fer, de tailles comprises entre 1 µm et 100 nm, et présentant une grande surface spécifique due à leur morphologie dendritique. Cette deuxième partie de l'étude permet d'ouvrir la voie à une nouvelle technologie de fabrication des nanoparticules
This study concerns the coupling of the ultrasounds with the electrodeposition process for the synthesis of zero-valent iron nanoparticles; it is structured in two sections. The first focuses on the electrode substrate used for the iron electrodeposition and aims to determine its influence on both the deposit growth and its dispersion by ultrasonication. The interfacial and the adhesion energies of the deposit on the substrate (Y_(Fe/substrate) and W_(Fe/substrate) respectively) being related to the surface energy and the roughness of the substrate, a particular focus is put on the influence of these two properties. Thus, two materials of different surface energies, gold (Au) and vitreous carbon (VC), as well as various roughnesses, are tested. Considering only the Van der Waals interactions, a theoretical development has enabled to determine that Y_(Fe/VC)>Y_(Fe/Au) which suggests a better affinity of the iron deposit with the gold than with the VC substrate. This difference impacts the deposit morphology (2D growth on the gold and 3D growth on the VC substrate) but also the deposit adhesion. Indeed, experiments performed to study the effect of ultrasounds on the iron electrodeposit reveal its progressive and complete dispersion for the vitreous carbon case while no dispersion (no removal of the deposit from the electrode) is obtained with the gold substrate. The second section of the present study deals with the synthesis of iron nanoparticles; to this end, the electrodeposition of branched deposits has been investigated in a Hele-Shaw cell integrating a vibrating element (piezoelectric diaphragm), expected to allow both the deposit formation and its fragmentation. Experiments reveal that the hydrogen bubbles, formed by the co-reduction of free protons during the iron electrodeposition, strongly influence the fragmentation process. Using high vibration frequencies and high amplitudes, the bubbles oscillate with surface deformations, inducing interface velocity sufficiently high (˜ 4 m/s) to allow the fragmentation of the deposit into particles of sizes ranging between 1 µm and 100 nm and showing a high specific surface due to their dendritic morphology. Thus this work opens the way for a new particles manufacturing technology

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Gers, Romain. "Analyse locale de l'hydrodynamique d'un broyeur à billes agité pour le traitement de dispersions solide-liquide". Thesis, Toulouse, INPT, 2009. http://www.theses.fr/2009INPT024H/document.

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Le broyage réalisé dans un broyeur à billes agité est un procédé permettant de produire des nanoparticules en suspension dense. L’étude réalisée a pour objet l’analyse de l’influence de l’hydrodynamique sur le processus de réduction de taille. La première partie de l’étude a porté sur la modélisation de l'hydrodynamique globale dans ce broyeur en considérant un fluide équivalent de propriétés rhéologiques variables, représentant le mélange des billes de broyage et de la suspension à broyer. Les champs de vitesse, obtenus par simulation numérique directe (DNS), ont permis de déterminer une cartographie des collisions avec leurs caractéristiques et d'en déduire les mécanismes responsables de la fragmentation. A partir de la connaissance des vitesses d'impact et des nombres de Reynolds caractéristiques des collisions dans le broyeur, un dispositif expérimental a été conçu reproduisant, à plus grande échelle, le rapprochement d'une bille de broyage mobile vers une bille fixe. Les profils de vitesse de drainage ont été mesurés par vélocimétrie par image de particules (PIV) sous différentes conditions expérimentales et différentes configurations d'impact. Ces mesures ont permis de calculer les trajectoires de particules fictives dans l'entrefer entre les sphères et d'estimer une efficacité de capture des particules. On observe qu'une augmentation des effets d'inertie de ces particules, en agissant soit sur leur diamètre, soit sur la vitesse de collision, est favorable à leur capture et par conséquent à leur fragmentation. De manière complémentaire, l'examen des trajectoires de particules réelles déposées à la surface de la sphère immobile a révélé que l'efficacité de capture est réduite lorsque le nombre de Stokes des particules augmente
The stirred media mill is used to produce nanoparticles from dense suspensions. The purpose of our study is to analyse the influence of the hydrodynamics on the fragmentation process. The first part is devoted to the flow modelling in the mill for an equivalent fluid. The constitutive law is accounting for the properties of grinding beads and suspended particles. Velocity fields, obtained by direct numerical simulations, have permitted to analyse the collision characteristics and to determine the major mechanisms leading to fragmentation. By determining the impact velocities and collisional Reynolds we were able to set up an experiment modelling two approaching grinding beads. One bead is mobile while the other is fixed. The flow velocities in the fluid have been measured by PIV for a wide range of conditions. These velocity fields have been used to calculate particle trajectories within the gap between the two beads. This yields to estimate a capture efficiency for particles. We concluded that an increase of the particle diameter or an increase of the impact velocity increases the probability of capture. Additionally, trajectories of deposited particle at the surface of the fixed spheres show that the capture efficiency decreases when the Stokes number of the particle increases

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Thompson, Michael Shane. "Enabling Synthesis Toward the Production of Biocompatible Magnetic Nanoparticles With Tailored Surface Properties". Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/28395.

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Amphiphilic tri- and penta-block copolymers containing a polyurethane central block with pendant carboxylic acid groups flanked by hydroxyl functional polyether tails were synthesized. Our intention was to investigate the activities of these copolymers as dispersants for magnetite nanoparticles in biological media. A benzyl alkoxide initiator was utilized to prepare poly(ethylene oxide) (BzO-PEO-OH), poly(propylene oxide) (BzO-PPO-OH) and poly(ethylene oxide-b-propylene oxide) (poly(BzO-EO-b-PO-OH)) oligomeric tail blocks with varying lengths of PEO and PPO. The oligomers had a hydroxyl group at the terminal chain end and a benzyl-protected hydroxyl group at the initiated end. The polyether oligomers were incorporated into a block copolymer with a short polyurethane segment having approximately three carboxylic acid groups per chain. The block co-polyurethane was then hydrogenated to remove the benzyl group and yield primary hydroxyl functionality at the chain ends. End group analysis by 1H NMR showed the targeted ratio of PEO to PPO demonstrating control over block copolymer composition. Number average molecular weights determined by both 1H NMR and GPC were in agreement and close to targeted values demonstrating control over molecular weight. Titrations of the pentablock copolymers showed that the targeted value of approximately three carboxylic acid groups per chain was achieved. Heterobifunctional poly(ethylene oxide) (PEO) and poly(ethylene oxide-b-propylene oxide) (PEO-b-PPO) copolymers were synthesized utilizing heterobifunctional initiators to yield polymers having a hydroxyl group at one chain end and additional moieties at the other chain end. For PEO homopolymers, these moieties include maleimide, vinylsilane, and carboxylic acid functional groups. Heterobifunctional PEO oligomers with a maliemide end group were synthesized utilizing a double metal cyanide coordination catalyst to avoid side reactions that occur with a basic catalyst. PEO oligomers with vinylsilane end groups were synthesized via alkoxide-initiated living ring-opening polymerization, and this produced polymers with narrow molecular weight distributions. Heterobifunctional PEO-b-PPO block copolymers were synthesized in two steps where the double metal cyanide catalyst was used to polymerize propylene oxide (PO) initiated by 3-hydroxypropyltrivinylsilane. The PPO was then utilized as a macroinitiator to polymerize ethylene oxide (EO) with base catalysis. Heterobifunctional PEO and PEO-b-PPO block copolymers possessing carboxylic acid functional groups on one end were synthesized by reacting the vinyl groups with mercaptoacetic acid via an ene-thiol addition.
Ph. D.

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Bonnevide, Marine. "Nanocomposites élastomère-nanoparticules de silice greffées : de la synthèse aux mécanismes de dispersion". Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0354.

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L’ajout de charges nanométriques dans une matrice polymère permet d’améliorer les propriétés d’usage des matériaux. L’optimisation du renforcement des nanocomposites est liée à l’état de dispersion des charges dans la matrice ainsi qu’aux interactions charge/charge et charge/polymère. Dans l’industrie du pneu, ces paramètres ont fait l’objet de nombreuses recherches dans le but de maîtriser le renforcement de matrices élastomères par des particules de silice. Ainsi à l’échelle industrielle, on utilise des agents de couplage, comme le bis(triéthoxysilyl)propyl tétrasulfide ou des polymères fonctionnels qui permettent d’améliorer la dispersion des particules de silice dans des élastomères. Cependant il est difficile de moduler certains paramètres susceptibles d’influencer l’état de dispersion et les interactions, comme la densité de greffage, la nature et la longueur des chaînes de polymère greffées à la surface des particules. Afin de remédier à ces limites nous proposons, dans ce travail de thèse, de synthétiser des nanoparticules de silices greffées de polyisoprène, polybutadiène et copolymère poly(butadiène-co-styrène) par la méthode de « grafting from » associée à une polymérisation contrôlée par les nitroxydes. Pour cela une alcoxyamine est greffée sur la surface en deux étapes en maintenant la stabilité colloïdale des particules. Après l’optimisation des conditions de greffage et la polymérisation des monomères à partir de l’alcoxyamine greffée, les nanoparticules greffées ainsi obtenues sont caractérisées et leur état de dispersion est étudié en solution et dans des matrices de masses molaires et de compositions différentes après l’élaboration de nanocomposites
The addition of nanometric fillers into a polymer matrix significantly improves its use properties. Optimization of nanocomposite reinforcement is related to the filler dispersion state in the matrix as well as to the filler/filler and filler/matrix interactions. In the tire industry, numerous studies have been devoted to these parameters in order to understand and control the reinforcement of elastomeric matrices such as Styrene Butadiene Rubber by silica nanoparticles. On an industrial scale, functional polymer or coupling agents such as bis(triethoxysilyl)propyl tetrasulfide are used to improve the dispersion of silica particles in elastomers and strengthen the matrix. However, it is difficult to control the grafting density and to modulate some parameters that may influence the dispersion state and interactions e.g. the nature and molar mass of the polymer chains covalently attached to the surface. To address these limitations, in this project we propose to synthesize silica nanoparticles grafted with polyisoprene, polybutadiene and statistical poly(butadiene-co-styrene) chains using the “grafting from” method associated to nitroxide mediated polymerization. In this aim, an alkoxyamine is grafted onto the nanoparticle surface in two steps by keeping the colloidal stability of the particles. After optimizing grafting parameters and polymerize the different monomers, the obtained grafted nanoparticles are characterized in terms of molar mass, microstructure, grafting density and gyration radius of the grafted chains. Their dispersion state is evaluated in solution as well as in matrices of various molecular weight and composition after the elaboration of nanocomposites

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Soemo, Angela Renee. "Microenvironment of Monorhamnolipid Biosurfactant Aggregates and Monorhamnolipid Effects on Aqueous Dispersion Properties of Metal Oxide Nanoparticles". Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/293563.

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The purpose of this dissertation was two-fold: 1) explore the micelle structure and microenvironment of monorhamnolipids (mRL), produced by Pseudomonas aeruginosa ATCC 9027, and their mixtures with synthetic surfactants in order to postulate possible applications of these materials in industrial products and 2) examine the effects of mRL on commercial metal oxide nanoparticle (NP) aqueous dispersion behavior to reveal the potential impact of microbial secondary metabolites on NP fate and transport in the environment. The mixing behavior of mRL with cetylpyridinium chloride (CPC) was measured using surface tensiometry. Electrostatics resulted in cooperative enhancement in mixture properties, but were not significant until α(CPC) ≥ 0.25. Steady-state and time resolved fluorescence quenching measurements in mRL micelles revealed that quenching proceeded via a combined static and dynamic mechanism. Static quenching was preferred in mRL illustrating the reactants form a globular micelle. Changing the structure of the reactants displayed changes in the degree and mechanism of quenching further supporting this aggregate model. Fluorescence measurements on mRL-Tween 20 micelles supported that a geometrically-driven shape transition occurs as mRL decreases. The corresponding decrease in probe lifetime indicated the polarity of the micelle was decreasing. Tween "sealed" the mRL micelles making them less susceptible to water penetration. The effect of mRL on metal oxide NP dispersions was evaluated on adsorption strength, NP aggregate size and stability, and zeta potential under different conditions. Silica NPs showed little adsorption of mRL and was impervious to all variables in altering the solution stable aggregate size. NP aggregate size decreased at very high mRL concentrations due to osmotic and electrosteric repulsions of mRL micelles in solution. Titania, despite expectations, indicated fairly low adsorption of mRL and displayed similar aggregate dispersion stability as that of silica. Spectroscopic investigations exposed that the commercial titania NPs were contaminated with silica altering NP surface properties. Zinc oxide (ZnO) dispersions were substantially affected by the adsorption of mRL. Without mRL, ZnO NPs were unstable independent of pH. The addition of mRL stabilized the ZnO dispersions and lowered the zeta potentials. Furthermore, mRL coating prevented the dissolution of ZnO, the major factor implicated in ZnO toxicity.

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