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<p>A colloid of magnesium hydroxide is used to stabilize droplets of monomers before suspension polymerisation. The characteristics of precipitated magnesium hydroxide changes significantly during the first hours. The viscosity is high and flucctuating at first but decreases and becomes low and stable after a few hours. When the colloid ages the primary particles agglomerate into larger particles which increases in size by time due to, among other things, Oswald ripening and aggregation. This can cause problems with poor reproducibility in the production. Therefore, the purpose of this study was finding a way to age the colloid without an increase in particle size and without changing any other features. Several experiments were made to optimize the precipitation procedure and to find out what parameters that are most important. The results showed that the stirring rate and colloidal concentration have big influence.</p><p>Small amounts of chemicals that modifies the surface of the colloid was added. This made the particle size near constant over time and the colloid was aged for two months without increasing in size or changing other properties. This was confirmed by making microspheres that had the same characteristics as microspheres made with a fresh colloid.</p>

A colloid of magnesium hydroxide is used to stabilize droplets of monomers before suspension polymerisation. The characteristics of precipitated magnesium hydroxide changes significantly during the first hours. The viscosity is high and flucctuating at first but decreases and becomes low and stable after a few hours. When the colloid ages the primary particles agglomerate into larger particles which increases in size by time due to, among other things, Oswald ripening and aggregation. This can cause problems with poor reproducibility in the production. Therefore, the purpose of this study was finding a way to age the colloid without an increase in particle size and without changing any other features. Several experiments were made to optimize the precipitation procedure and to find out what parameters that are most important. The results showed that the stirring rate and colloidal concentration have big influence. Small amounts of chemicals that modifies the surface of the colloid was added. This made the particle size near constant over time and the colloid was aged for two months without increasing in size or changing other properties. This was confirmed by making microspheres that had the same characteristics as microspheres made with a fresh colloid.

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-16Bitstream added on 2014-06-13T19:29:33Z : No. of bitstreams: 1 ravaro_lp_me_bauru.pdf: 967737 bytes, checksum: 4467c85af230546c2464c3465069b809 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dióxido de estanho (Sn'O IND. 2') é um semicondutor do tipo n, que é transparente na região do ultravioleta/visível. Possui muitas aplicações como, por exemplo, eletrodos transparentes, sensores de gás, coletores solares e dispositivos eletro-ópticos. Quando dopado com íons terras-raras, Sn'O IND. 2' pode ser utilizado na confecção de dispositivos para comunicação óptica, principalmente na forma de filmes finos. Os íons terras-raras têm grande relevância devido às transições eletrônicas, que vão do ultravioleta ao infravermelho próximo. Outro aspecto importante está ligado às características físico-químicas da suspensão coloidal de onde são depositados os filmes. Filmes obtidos com pH elevado da suspensão apresentam alta resistividade elétrica e baixa cristalinidade em relação aos filmes obtidos com pHs das suspensões ácidas. O nível mais profundo de energia dos defeitos em Sn'O IND. 2' foi alterado da energia de 140eV até 67eV para variação do pHs 11, até 6, de acordo com a avaliação da energia de ativação. Os difratogramas destes filmes indicam aumento de cristalinidade com a diminuição do pH. Xerogéis de Sn'O IND. 2':Er2% com alteração do pH em relação a suspensão neutra apresentaram espectro de emissão mais intenso na região infravermelha para a amostra com pH7 e um pequeno alargamento dos picos de emissão para a amostra com pH4 e mais acentuado para a amostra com pH11, em bom acordo com medidas de Raman. Relatamos também a emissão na região visível de filme fino de Sn'O IND. 2' dopado com 'Er POT. 3+', que é um formato adequado da amostra para confecção de dispositivos. / Tin dioxide (Sn'O IND. 2') is an n-type oxide semicondutor, which is transparent in the ultraviolet/visible range. It presents many types of applications, such as transparent electrodes, gas sensors, solar collectors and eletro-optical devices. When doped with rare-earth ions, Sn'O IND. 2' may be used to make optical communication devies, in the thin film configuration. Rare-earth ions have great relevance due to their electronic transitions, covering from ultraviolet to near infrared. Another important characteristic is related to the physical-chemical properties of the starting colloidal suspension to deposit the films. Films obtained with high pH of the suspension presents high electric resistivity and low crystallinity compared to films obtained with acid pH. The deepest energy level of the defects in Sn'O IND. 2' has been changed from the energy of 140 eV to 67 e V when the pH changes from 11 to 6. Diffractograms of these films show increase in the crystallinity with pH decrease. Sn'O IND. 2':Er2% xerogels with modified pH show more intense emission spectra in the infrared for sample with pH 7 and a low broadening of emission peaks for the sample with pH 4 and moer intense for pH 11, suggesting an ideal pH for higher emission samples, in good agreement with Raman shift spectra. We also report emission in the visible range from of an 'Er POT. 3+' -doped thin film, which is a very convenient form for devices fabrication.

Orientador: Luis Vicente de Andrade Scalvi / Banca: Maximo Siu Li / Banca: Aguinaldo Robinson de Souza / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Resumo: Dióxido de estanho (Sn'O IND. 2') é um semicondutor do tipo n, que é transparente na região do ultravioleta/visível. Possui muitas aplicações como, por exemplo, eletrodos transparentes, sensores de gás, coletores solares e dispositivos eletro-ópticos. Quando dopado com íons terras-raras, Sn'O IND. 2' pode ser utilizado na confecção de dispositivos para comunicação óptica, principalmente na forma de filmes finos. Os íons terras-raras têm grande relevância devido às transições eletrônicas, que vão do ultravioleta ao infravermelho próximo. Outro aspecto importante está ligado às características físico-químicas da suspensão coloidal de onde são depositados os filmes. Filmes obtidos com pH elevado da suspensão apresentam alta resistividade elétrica e baixa cristalinidade em relação aos filmes obtidos com pHs das suspensões ácidas. O nível mais profundo de energia dos defeitos em Sn'O IND. 2' foi alterado da energia de 140eV até 67eV para variação do pHs 11, até 6, de acordo com a avaliação da energia de ativação. Os difratogramas destes filmes indicam aumento de cristalinidade com a diminuição do pH. Xerogéis de Sn'O IND. 2':Er2% com alteração do pH em relação a suspensão neutra apresentaram espectro de emissão mais intenso na região infravermelha para a amostra com pH7 e um pequeno alargamento dos picos de emissão para a amostra com pH4 e mais acentuado para a amostra com pH11, em bom acordo com medidas de Raman. Relatamos também a emissão na região visível de filme fino de Sn'O IND. 2' dopado com 'Er POT. 3+', que é um formato adequado da amostra para confecção de dispositivos. / Abstract: Tin dioxide (Sn'O IND. 2') is an n-type oxide semicondutor, which is transparent in the ultraviolet/visible range. It presents many types of applications, such as transparent electrodes, gas sensors, solar collectors and eletro-optical devices. When doped with rare-earth ions, Sn'O IND. 2' may be used to make optical communication devies, in the thin film configuration. Rare-earth ions have great relevance due to their electronic transitions, covering from ultraviolet to near infrared. Another important characteristic is related to the physical-chemical properties of the starting colloidal suspension to deposit the films. Films obtained with high pH of the suspension presents high electric resistivity and low crystallinity compared to films obtained with acid pH. The deepest energy level of the defects in Sn'O IND. 2' has been changed from the energy of 140 eV to 67 e V when the pH changes from 11 to 6. Diffractograms of these films show increase in the crystallinity with pH decrease. Sn'O IND. 2':Er2% xerogels with modified pH show more intense emission spectra in the infrared for sample with pH 7 and a low broadening of emission peaks for the sample with pH 4 and moer intense for pH 11, suggesting an "ideal" pH for higher emission samples, in good agreement with Raman shift spectra. We also report emission in the visible range from of an 'Er POT. 3+' -doped thin film, which is a very convenient form for devices fabrication. / Mestre

In this thesis we used atomic force microscopy (AFM) to investigate systematically the behaviour of both electrostatically stabilised silica and sterically stabilised polystyrene (PS) colloidal systems on freshly cleaved mica substrates. For the silica colloidal nanoparticles we explored the effect of colloidal suspension concentration, particle size, and different application techniques on both the adsorption behaviour and subsequent structuring of the particles. For the PS colloidal nanoparticles we explored concentration effects and experimented with both dip-coating and droplet application techniques. We showed that silica nanoparticles adsorbed onto mica via irreversible adsorption that possessed lateral mobility due to the weak attraction between the nanoparticles and the substrate, facilitating subsequent capillary structuring of the nanoparticles during drying. We associated the effects of volume fraction with Debye screening, and kinetics effects with particle size and volume fraction. We also successfully imaged a partially dried film and showed the role of convective/capillary forces in the structuring of the nanoparticles. Studies with variations in particle size generated a number of different topography structures; with dewetting phenomena observed for 10 nm nanoparticles and the formation of crystalline structures for 100 nm nanoparticles. Spin coating techniques were used to produce even larger crystalline structures of nanoparticles. Size dependent ordering occurred for low concentration samples due to the polydispersity of the colloidal suspension. We showed that acceleration can affect interparticle spacing. We also studied the role of rotational speed on the crystallinity of the particle configurations and showed how fine tuning of rotational speed can generate large scale monolayer crystalline formations of nanoparticles.

Agglomeration of nanoparticles occurs in a number of colloidal systems related, for example, to material processing and drug delivery. The present work is motivated by the need to improve fundamental understanding of the agglomeration and structure formation processes that occur in catalyst inks used for the fabrication of polymer electrolyte fuel cells (PEMFCs). Particle dynamics simulations are performed to investigate agglomeration under various conditions. The interaction between particles is defined using realistic physical potentials, rather than commonly used potential models, and a novel analysis of the agglomeration and structure formation process is performed using network science concepts. The simulated systems correspond to catalyst inks consisting primarily of carbon nanoparticles in solution. The effect of various conditions such as different force magnitude, shape of the force function, concentration etc. are investigated in terms of network science parameters such as average degree and shortest path. An "agglomeration timescale" and a "restructuring timescale" introduced to interpret the evolution of the agglomeration process suggest that the structure, which has a strong impact on the performance of the eventual catalyst layer, can be controlled by tuning the rate at which particles are added based on the restructuring timescale. / Graduate

Nous avons cherché à comprendre le comportement sous écoulement de suspensions colloïdales d'argiles naturelles. Les particules constitutives de ces argiles ont comme particularité d'être extrêmement anisotropes puisqu'elles se présentent (en moyenne) sous la forme de disques de 200 nm de diamètre pour une épaisseur de 1 nm. Ces matériaux présentent des propriétés mécaniques remarquables parmi lesquelles une forte rhéofluidification ainsi que l'apparition de seuils d'écoulement et ce, pour de très faibles fractions volumiques en particules (environ 1%). Afin de comprendre l'origine de ces propriétés mécaniques, nous avons mis en place un dispositif expérimental permettant d'effectuer simultanément des mesures de viscosité (en cellule de Couette cylindrique) et des mesures de diffusion de rayons-X aux petits angles. Le champ orientationnel de particules 2D très anisotropes en écoulement cisaillé a ainsi été mesuré. En l'absence de cisaillement, et dans la phase de liquide isotrope, les particules s'orientent librement et occupent statistiquement un volume équivalent à celui de la sphère de volume exclu englobant la particule. En appliquant un cisaillement croissant on confine les particules discoïdales, faisant passer progressivement le volume de fluide piégé dans le mouvement moyen des particules de la sphère de volume exclu à un ellipsoïde à double anisotropie. Connaissant le champ orientationnel des particules on peut alors, par le biais d'une relation viscosité - fraction volumique de type Quemada, reconstruire la rhéofluidification de ces suspensions en prenant en compte, non pas la fraction volumique en disques mais celle en ellipsoïdes de confinement / We focussed our interest on the flow behaviour of colloidal suspensions of natural swelling clays. Such systems are strongly anisotropic since the disk-shaped particles in suspensions display an average diameter around 200 nm with a thickness close to 1 nm. Under flow, and for very low volume fractions (around 1%), these materials display remarkable mechanical properties going from quasi-Newtonian liquid to yield stress gel. In order to understand the mechanisms leading to such macroscopic behaviour, we have set up an experimental device that enables us to perform simultaneously viscosity (in a cylindrical Couette cell) and small angles x-ray scattering measurements. Thanks to this Rheo-SAXS device, we measured the orientational field of strongly anisotropic bi-dimensional particles in shear flow. When no shear is applied (and in the isotropic liquid phase), the particles are randomly oriented and occupy statistically a volume equivalent to that of the sphere of excluded volume encompassing the particle. The stronger is the applied shear stress, the more confined are the disk-like particles and consequently the small amount of fluid trapped in the statistical motion of the particles decreases from that of the sphere of excluded volume to that of an oblate ellipsoid with double anisotropy. Thus, knowing the orientational field of the particles (measured by SAXS) and applying an effective approach as the one suggested by Quemada for hard spheres, we tried to rebuild the shear-thinning behaviour of these suspensions by taking the volume fraction in statistical ellipsoid instead of that of disk-shaped particles

This thesis reports on a comprehensive experimental study of the collective dynamics of colloidal hard sphere suspensions. The main quantity measured is the coherent Intermediate Scattering Function (ISF) using a range of techniques based on Dynamic Light Scattering (DLS). The collective dynamics are measured as a function of scattering vector for volume fractions spanning from dilute samples, through the fluid phase and the metastable region, up until deep in the glass region. This work describes two major explorations: (i) the effect of volume of fraction on the q-dependency of the collective dynamics; and (ii) a study of the ageing processes in colloidal glasses. The present work is unique in the application of several advanced experimental techniques, and in the level of averaging that has been carried out, enabling a more sophisticated analysis than has previously been possible. This includes the characterization of non-Fickian processes and the determinatio n of the current-current correlation function (CCCF) in the metastable fluid, and the quantitative characterization of the ageing process in the hard sphere glass. In addition, by combining aspects of the coherent and incoherent ISFs, this work also allows the expression of the collective dynamics in terms of the single particle displacement. The results show a dynamical change at the freezing point (f), which exposes the incapacity of the system to dissipate thermal energy via diffusing momentum currents, i.e. viscous flow. The structural impediments responsible for this, associated with dynamical heterogeneities, begin at the structure factor peak, and spread to other spatial modes as the volume fraction increases. Above the glass transition (g), structural relaxation becomes arrested at all spatial modes probed, i.e. flow is arrested. It is found that, following the quench, samples above the glass volume fraction approach some final

Les pièces en aluminium sont largement utilisées dans le domaine aéronautique en raison de leurs bonnes propriétés mécaniques. Mais elles nécessitent un traitement de surface pour améliorer leur tenue en corrosion. Soumises à de nouvelles normes sur l'utilisation de produits chimiques et à la prise de conscience de la protection environnementale et humaine, les industries aéronautiques doivent à présent impérativement remplacer les procédés de traitements de surface actuels, devenus obsolètes car incluant des composés CMR. L'objectif de ces travaux de recherche est de développer un traitement de surface par voie liquide, à la fois innovant et conforme à la législation REACH, pour améliorer les propriétés d'anticorrosion des alliages d'aluminium ; le procédé d'élaboration présentement étudié, est composé d'une anodisation poreuse puis d'un colmatage par imprégnation de particules au sein des pores. Un film anodique poreux " modèle " a tout d'abord été élaboré et caractérisé : son épaisseur est de 10 µm, tandis que les pores sont rectilignes et ont un diamètre moyen de 120 nm. Puis, nous avons étudié la synthèse par voie aqueuse, de nanoparticules de boehmite, l'optimisation des différents paramètres de synthèse ayant permis finalement d'obtenir des particules d'une taille inférieure à celle des pores du film anodique. Deux techniques d'incorporation ont ensuite été expérimentées : le trempage-retrait et l'électrophorèse. La compréhension des mécanismes mis en jeu et de l'influence de différents paramètres opératoires, a permis une maitrise des procédés et l'insertion effective de particules. Des caractérisations microstructurales ont en particulier montré que l'insertion de particules est plus aisée dans le cas d'une électrophorèse avec une tension pulsée. Enfin, la mise en œuvre d'un post-traitement hydrothermal après l'imprégnation, a permis d'obtenir un colmatage complet des pores du film anodique, et d'augmenter significativement les propriétés anticorrosion. / Aluminum parts are widely used in the aeronautical field because of their good mechanical properties. But they require a surface treatment to improve their resistance to corrosion. Subject to new standards on the use of chemicals and awareness of environmental and human protection, the aeronautical industry must now replace current surface treatment processes, which have become obsolete because they include CMR compounds. The aim of this research is to develop a surface treatment, both innovative and REACH compliant, to improve the anticorrosion properties of aluminum alloys; the process here studied, is composed of a porous anodization and a sealing by impregnation of particles within the pores. A "model" porous anodic film was first prepared and characterized: its thickness is 10 µm, while the pores are straight and have a mean diameter of 120 nm. Then, we studied the aqueous synthesis of boehmite nanoparticles; the optimization of the synthesis parameters finally allowed to obtain a particle size smaller than the pore diameter. Two incorporation techniques were then tested: dip-coating and electrophoresis. The understanding of the involved mechanisms and of the influence of different operating parameters, allowed a control of the processes and the effective insertion of particles. In particular, microstructural characterizations showed that the particle insertion is easier using pulsed voltage electrophoresis. Finally, a hydrothermal post-treatment after the impregnation, allowed to obtain a complete sealing of the anodic film pores, and to significantly increase the anticorrosion properties.