Orientador:Italo Odone Mazali / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-21T15:30:46Z (GMT). No. of bitstreams: 1 Carneiro_NathaliaMedeiros_M.pdf: 9366113 bytes, checksum: 4f9f537dfbffde8a3c9aa6436d02965b (MD5) Previous issue date: 2012 / Resumo: O controle do tamanho e da morfologia dos nanomateriais abre novas perspectivas quanto a novas propriedades e sua aplicação nas mais diversas áreas como eletrônica, física e medicina. Com a redução do tamanho, a superfície dos nanomateriais passa a exercer um papel importante sobre sua reatividade. Nanomateriais de óxidos individuais de ferro, cobre, zinco, hidróxido de cobalto, hidróxido de níquel, óxidos binários, como: ferro-cobalto e ferro-níquel e hidróxido de cobalto-níquel foram sintetizados através do método hidrotérmico. A etapa de síntese inicial consistiu na síntese de óxido de ferro monitorando-se tamanho e morfologia através dos fatores: contra-íon (NO3 ou Cl), pH do meio, tempo de reação e concentração de reagentes. Foram obtidas amostras de hematita (Fe2O3) e amostras com uma mistura de hematita e goethita (FeOOH) com morfologias que variam de esferas a bastões. As curvas de magnetização apresentadas são características de materiais antiferromagnéticos e ferromagnéticos fracos. A mesma síntese com variação apenas do fator contra-íon foi aplicada a níquel e cobalto, levando a formação dos hidróxidos correspondentes na forma de placas hexagonais. A mesma síntese aplicada a cobre resulta na mistura dos óxidos CuO e Cu2O na forma de placas, no entanto para zinco são formados agregados sem uma morfologia definida. Óxidos binários foram obtidos na forma de ferritas de cobalto-ferro e níquel-ferro (MFe2O4) conforme observado através de XRD. A mistura cobalto-níquel resulta em uma solução sólida caracterizada como um hidróxido de níquel-cobalto cristalino com morfologia de placas hexagonais, que é preservada após tratamento térmico e conversão a NiCo2O4. Os materiais foram caracterizados por difratometria de raios X (XRD), espectroscopia no infravermelho (FTIR) e Raman, microscopia eletrônica de varredura (SEM) e transmissão (TEM) e medidas magnéticas (VSM) / Abstract: Size and morphology control of nanomaterials opens new perspectives through their new properties and applications in several areas such as electronics, physics and medicine. With the reduction in size, the surface of nanomaterials plays a major role in their reactivity. Nanomaterials of the individual iron, copper and zinc oxides, cobalt hydroxide, nickel hydroxide, cobalt-nickel hydroxide, mixed iron-cobalt and iron-nickel oxides were synthesized by the hydrothermal method. The initial synthetic step consisted in the synthesis of iron oxide by monitoring morphology and size by the factors: counter-ion, pH, reaction time and concentration of reagents. The samples obtained consisted in hematite (Fe2O3) and a mixture of goethite and haematite (FeOOH) with varying morphology from spheres to rods. The magnetization curves showed antiferromagnetic and weak ferromagnetic materials. The same synthetic procedure varying only the counter-ion has been applied to nickel and cobalt, leading to the formation of the corresponding hydroxides in the form of hexagonal plates. The same synthetic applied to copper resulted in a mixture of CuO and Cu2O as plates, however for zinc clusters without a defined morphology were formed. Iron-cobalt and iron-nickel binary oxides were obtained in the form of ferrites (MFe2O4) as observed by XRD. The cobalt-nickel mixture resulted in a solid solution characterized as a nickel-cobalt hydroxide with crystalline morphology of hexagonal plates which is preserved after heat treatment and conversion to NiCo2O4. The materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) for magnetic property measurement / Mestrado / Quimica Inorganica / Mestra em Química

Through biomass gasification, biomass can be converted at high temperature to a product gas rich in carbon monoxide, hydrogen, and methane. After cleaning and upgrading, the product gas can be converted to biofuels such as hydrogen; methanol; dimethyl ether; and synthetic diesel, gasoline, and natural gas. Particulate matter (PM) is formed as a contaminant in the gasification process, and the aim of this work was to develop and apply a method for sampling and characterization of PM in the hot product gas.   A particle measurement system consisting of a dilution probe combined in series with a bed of granular activated carbon for tar adsorption was developed, with the aim of extracting a sample of the hot product gas without changing the size distribution and composition of the PM. The mass size distribution and concentration, as well as the morphology and elementary composition, of PM in the size range 10 nm to 10 µm in the product gas from a bubbling fluidized bed (BFB) gasifier, a circulating fluidized bed (CFB) gasifier and an indirect BFB gasifier using various types of biomass as fuel were determined.   All gasifiers and fuels displayed a bimodal particle mass size distribution with a fine mode in the <0.5 µm size range and a coarse mode in the >0.5 µm size range. Compared with the mass concentration of the coarse mode the mass concentration of the fine mode was low from all gasifiers. The evaluation of the results for the fine-mode PM was complicated by condensing potassium chloride for the CFB gasifier when using miscanthus as fuel and by condensing tars for the indirect BFB gasifier when using wood C as fuel. The mass concentration of the coarse-mode PM was higher from the CFB gasifier than from the two BFB gasifiers. The coarse-mode PM from the BFB gasifier when using wood A as fuel was dominated by char. In the CFB gasifier the coarse-mode PM was mainly ash and bed material when using all fuels. The coarse-mode PM from the indirect BFB gasifier when using wood C as fuel was mainly ash.

Master of Science / Food Science Institute / Jayendra K. Amamcharla / Milk protein concentrate (MPC) powders are high-protein dairy ingredients obtained from membrane filtration processes and subsequent spray drying. MPC powders have extensive applications due to their nutritional, functional, and sensory properties. However, their flow properties, rehydration behavior, and morphological characteristics are affected by various factors such as processing, storage, particle size, and composition of the powder. Literature has shown that knowledge about the powder flowability characteristics is critical in their handling, processing, and subsequent storage. For this study, FT4 powder rheometer (FT4, Freeman Technologies, UK) was used to characterize the flowability of MPC powders during storage. This study investigated the flowability and morphological characteristics of commercial MPC powders with three different protein contents (70, 80, and 90%, w/w) after storage at 25ºC and 40ºC for 12 weeks. Powder flow properties (basic flowability energy (BFE), flow rate index (FRI), permeability, etc.) and shear properties (cohesion, flow function, etc.) were evaluated. After 12 weeks of storage at 40ºC, the BFE and FRI values significantly increased (P < 0.05) as the protein content increased from 70 to 90% (w/w). Dynamic flow tests indicated that MPC powders with high protein contents displayed higher permeability. Shear tests confirmed that samples stored at 40ºC were relatively less flowable than samples stored at 25ºC. Also, the lower protein content samples showed better shear flow behavior. The results indicated that MPC powders stored at 40ºC had more cohesiveness and poor flow characteristics than MPC powders stored at 25ºC. The circle equivalent diameter, circularity, and elongation of MPC powders increased as protein content and storage temperature increased, while the convexity decreased as protein content and storage temperature increased. Overall, the MPC powders evidently showed different flow properties and morphological characteristics due to their difference in composition and storage temperature. Literature has shown various methods for determining the solubility of dairy powders, but it requires expensive instruments and skilled technicians. The front-face fluorescence spectroscopy (FFFS) coupled with chemometrics could be used as an efficient alternative, which is commonly used as fingerprints of the various food products. To evaluate FFFS as a useful tool for the non-destructive measurement of solubility in the MPC powders, commercially procured MPC powders were stored at two temperatures (25 and 40ºC) for 1, 2, 4, 8, and 12 weeks to produce powders with different rehydration properties, which subsequently influenced their fluorescence spectra. The spectra of tryptophan and Maillard products were recorded and analyzed with principal components analysis. The solubility index and the relative dissolution index (RDI) obtained from focused beam reflectance measurement was used to predict solubility and dissolution changes using fluorescence spectra of tryptophan and Maillard products. The solubility index and RDI showed that the MPC powders had decreased solubility as the storage time and temperature increased. The results suggest that FFFS has the potential to provide rapid, nondestructive, and accurate measurements of rehydration behavior in MPC powders. Overall, the results indicated that solubility and dissolution behavior of MPC powders were related to protein content and storage conditions that could be measured using FFFS.

<p>Shallow foundations are used to support small-to-medium size structures, and their capacity derives from the strength of strong, near-surface soils. The design of shallow foundations is done by proportioning the plan dimensions of the foundation element by considering three factors: (1) the structural stability of the foundation, (2)  the allowable bearing pressure of the soil supporting the foundation to prevent ultimate bearing capacity failure, and (3) the tolerable total and differential settlements to meet serviceability requirements under normal working loads. Different theories have been developed to estimate the bearing capacity of a foundation, mostly relying on the Terzaghi (1943) form of the bearing capacity equation with the superposition of three terms. The partly theoretical and empirical methods of bearing capacity predictions rely on an assumed failure mechanism within the soil. In addition, the soil itself is considered to be a perfectly plastic material and its strength is accounted for through non-dimensional bearing capacity factors. However, the boundary-value problem of footing penetration, in reality, is quite complex and the use of the traditional bearing capacity, with use of the principle of superposition, leads to somewhat conservative results. The challenges involved in a footing penetration problem emanate not only from the difficulties in estimating soil strength parameters but also because the footing penetration problem involves large deformations and strains, which localize to form shear bands that propagate in the soil domain until the "collapse" of the sand-footing system.</p> <p>The overarching aim of this research is the study of the response of shallow foundations on clean silica sands by investigating the measured bearing capacities and getting insights into the failure mechanisms that develop as a result of the soil displacements below the base of the foundation element. This was experimentally achieved using a combination of physical modelling (by performing a series of model footing 1g load tests inside a novel half-circular calibration chamber) and image analysis (using digital image correlation technique). The load-settlement response of the model footings is investigated by performing displacement-controlled load tests on model strip and square footings placed either on the surface or embedded in the sand samples of varying relative densities prepared inside the calibration chamber using the method of air-pluviation. A series of high-resolution images collected during model footing loading were analyzed using the digital image correlation (DIC) technique to obtain the displacement and strain fields in the sand domain. Two fully characterized silica sands, Ohio Gold Frac (OGF) and Ottawa 20-30 (OTC) are used in the research. Different testing variables that were considered in the experimental setup are: (1) sand particle morphology, (2) sand sample's relative density, (3) sand layer thickness, and (4) footing shape, size, and embedment depth. A detailed test matrix was formulated to isolate these variables and study the effects of each on both the bearing capacity and the associated failure mechanism. Accordingly, this article-based dissertation is organized to describe the results of three studies.</p> <p>In the first study, the effects of relative density and particle morphology on the bearing capacity and failure mechanism of a model strip footing were investigated. This was done by using two silica sands: OGF sand and OTC sand, both the sands have comparable mineralogy, gradation, and particle sphericity; however, they have markedly different values of particle roundness. Samples of both sands were prepared at relative densities of 90%, 65%, and 30%. The evolution of the footing's collapse mechanism was considered by selecting relevant points on the load-settlement curves. A novel methodology was adapted to record the thickness of the shear band that developed in the sand domain. In the second study, the effects of the presence of a stiff layer below the strip footing were investigated. This was achieved by load testing the model strip footing on OTC sand layer of limited thickness. To simulate the sand-bedrock system, a half-circular steel plate supported by a stack of hollow concrete blocks was used. Load tests on model strip footing were performed on OTC sand samples without the presence of a stiff base and on the sand samples underlain by a stiff base located at depths equal to 0.5B and 1B below the base of the footing. The effect of the presence of the stiff base on the limit unit bearing capacity of the footing and stiffness of the sand-footing system were investigated. In addition, the contours of the cumulative maximum shear strains, horizontal displacements, and vertical displacements that develop in the sand layer are presented for both cases of with and without the presence of the stiff base. In the third study, the effects of footing geometry and embedment on the bearing capacity and failure mechanism were investigated. Load tests were performed on surface and embedded model strip and square footings on dense, medium dense, and loose OTC sand samples. The effects of choice of flow rule (associative versus non-associative) on the bearing capacity calculation and the increase in bearing capacity due to footing embedment (bearing capacity ratio) were determined. In addition, a framework is proposed to experimentally determine the shape and depth factors using strip and square footings of equal widths considering the flow rule non-associativity, conditions of low confinement, and different loading paths.</p> <p>The results of the experimental program presented in this research on bearing capacity, displacement fields, strain fields, and failure mechanisms for different footing sizes and shapes under different testing conditions show that that the footing's collapse mechanism depends on the relative density of the sand sample, sand particle morphology, and the footing geometry. Significant differences in the bearing capacity of model footings due to sand particle morphology and sand sample density were observed. The shear band thickness is also shown to be dependent on the shape of the sand particles. It was also observed that the scale effects in model footing tests are closely related to sand dilatancy. For a sand layer of finite thickness underlain by a stiff base it is shown that the critical depth of the stiff base is greater for stiffness calculation than that for the bearing capacity calculation. DIC analysis results provided valuable insights to the footing penetration problem and corroborated the theoretical knowledge about the failure modes in sandy soils. It is shown that the failure mechanism extend deeper and wider for sands with angular particles as compared to the sand with rounded particles. DIC analysis also revealed that as the distance between the footing base and stiff layer reduces, the shear bands are more readily formed but their lateral extents are reduced considerably. The high-quality experimental data provided in this dissertation is aimed to be useful to researchers working on the validation of numerical simulations of footing penetration in sands.</p>

This investigation aims to understand and improve the deposition quality and rates of cold spray for additive manufacturing in a way that is economically sound and without the detrimental temperature effects seen in traditional metallic additive manufacturing processes. It focuses on materials that are desired by the additive manufacturing community and built upon the current knowledge in cold spray. This thesis is presented as a collection of published, or soon to be published, manuscripts accompanied by an introduction, literature review, and conclusion. The effect of a non-spherical particle morphology was the first objective investigated. Titanium has been shown repeatedly to require pure helium at very high temperatures and pressures to get dense coatings, however, the unique coral-like morphology resulting from the Armstrong Process was revealed as a key to successful deposition with nitrogen. Using low pressure cold spray, under conditions that would be considered mild, a deposition efficiency of 100% and a porosity of nearly 0% was achieved. This is a promising approach for cold spray as a method for additive manufacturing of titanium parts. The low powder cost and the advantages of additive manufacturing could allow for a substantial cost savings in titanium part production when compared to traditional manufacturing methods. With these cost saving advantages, additive manufacturing of titanium using Armstrong process powder and CS could lead to a paradigm shift of titanium production, allowing titanium to enter markets that under traditional methods would be far too expensive. Unfortunately, this unique powder morphology was not available in other materials. To address the low deposition efficiency of the other metals of interest, such as aluminum and stainless steel, the concept of mixing the propellant gas was introduced in the second objective. Considering the relative costs of gases, powder, electricity, and labour, the second paper focuses on the concept of optimizing the amount of helium to produce the minimum component cost. It was found that for the specific stainless steel and aluminum alloy powders discussed, costs could be reduced by 44% and 59%, respectively, using the gas mixing system. However, no cost saving was found for the most inexpensive of the powders, pure aluminum. For gas mixing to be effective, the cost of helium must be offset by the cost of the powders. Therefore, low-cost powders, such as pure aluminum, results in pure nitrogen as the least expensive option. This however doesn’t address the low deposition efficiency that is preventing its adoption in cold spray additive manufacturing. The third objective addresses just this, an improvement in deposition efficiency without the introduction of expensive helium. In this study, aluminum particles were preheated using a novel particle preheater that does not clog. This resulted in a deposition efficiency increase of 260% with a minimal increase in electrical costs. These three objectives, while studied and published separately, all relate to the purpose of this work to improve the process economics without detrimental temperature effects. These findings have been (or will be) published in international peer reviewed journals to add to the collective knowledge.

U.S. Federal regulations requiring on-board diagnostics of diesel particulate filters have created a demand for compact, inexpensive, fast, and accurate sensors for measuring the particulate matter (PM) content of diesel exhaust. An electronic sensor capable of measuring the carbonaceous fraction (soot) of PM has been developed at The University of Texas at Austin. The behavior and performance of this sensor was characterized in both an older style non-emission controlled diesel engine and a modern heavy-duty diesel certified in 2008 to meet current federal emissions standards. The ability of the sensor to detect particulates at the regulated level of 15 mg/bhp-hr downstream of a leaking particulate filter was demonstrated. Under optimal conditions, the sensor was shown to have a resolution of 0.003 mg/bhp-hr, or 0.005 mg/m3. The sensor operated by measuring the flux of charged particles, ions, and electrons to an electrode immersed in an exhaust gas flow. Two distinct modes of operation were demonstrated. In the first, the sensor detected particles carrying residual charge from the combustion process. In this mode, the sensor was shown to be relatively insensitive to particle morphology and to be sensitive to exhaust gas velocity. In the second, charge carriers (particles, electrons, and ions) were created in the strong electric field produced by a second electrode at high voltage. In this mode, the sensor was found to be relatively insensitive to exhaust gas velocity, but quite sensitive to the orientation of the sensor in the exhaust flow. The size and number density of the particles was found to have a strong influence on the sensor sensitivity: as number density increased with increasing load or decreasing EGR rate, so did sensor sensitivity. Thus, as changes in engine operating condition affect particle morphology, the behavior of the sensor changes. A numerical model of the discharge mechanism in the form of an atmospheric pressure glow discharge was implemented to model the charge creation and transport. The model accurately predicted the nanoamp-level electrode currents produced in a real sensor to within a half order of magnitude with no empirical fits. The model tended to over-predict the sensitivity of sensor output to applied voltage but matched the observed sensitivity within an order of magnitude. Due to the lack of modeling flow field effects it predicted a 250% increase in sensitivity for a gap width reduced by 50% where a comparison of real sensors showed a decrease in sensitivity of 25% with a 50% reduction in gap width. / text

The objectives of this project were to synthesise semi-conducting ceramic nanoparticles including zinc oxide (ZnO) and aluminium doped zinc oxide (AZO) through a wet chemistry route to obtain nanoparticles with a controlled size and morphology. Wet chemistry methods (co-precipitation method and hydrothermal method) were used to synthesise ZnO and AZO particles. In the synthesis, various compounds and morphologies were synthesised. ZnO, Zn(OH)2 and unknown phases were co-precipitated, with only ZnO obtained following hydrothermal treatment. Morphologies ranging from platelets, flower-like, nanorods and microflowers were obtained. Particle sizes as small as 11 nm were characterised. Nanorod and nanosphere AZO particles were also synthesised with the results indicated the average grain size decreasing with increasing Al atomic content. Three orthogonal arrays were carried out to investigate the effects of the reaction parameters on the size and morphology of ZnO particles. The applicability of the orthogonal array was successful, with the optimum parameters of both hydrothermal experiments showing an increase in aspect ratio. The L/D ratio of ZnO nanorods obtained in the confirmation experiment increased to 9.4 which was larger than the ZnO synthesised using other reaction conditions (1.0 8.0). Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were used to characterise the properties of the obtained particles. Morphology, crystallinity and particle size were all characterised.

Les emballages alimentaires et pharmaceutiques doivent de nos jours répondre à de nombreux critères : ils doivent non seulement préserver le produit emballé, mais également être inoffensifs, économes en énergie et jetables. Les polymères barrières ont permis de répondre à ces besoins, en offrant des alternatives à des matériaux plus demandeurs en énergie et plus lourds tels que le verre ou les métaux, tout en conservant une faible perméabilité à l’eau et/ou à l’oxygène. Parmi la grande variété de polymères barrières existants, les copolymères du poly(chlorure de vinylidène) (PVDC) offrent une protection plus complète aux contaminants extérieurs, grâce à leurs faibles perméabilités à l’eau et à l’oxygène. Cependant, les films de PVDC sont sujets à des processus de dégradation ayant lieu lors du thermoformage ou sous exposition aux rayonnements UV. Ces effets sont encore plus prononcés dans le cas de films obtenus à partir de latex, dû à des quantités plus importantes d’additifs qui accentueraient les phénomènes de dégradation du polymère. Par conséquent, la synthèse de latex à base de PVDC pour des applications en tant que films barrières aux stabilités thermique et UV améliorées revêt un grand intérêt. Des latex composites à base de PVDC ont tout d’abord été synthétisés en présence de latex semences à fonctionnalité époxy en vue d’améliorer la stabilité thermique du polymère. En effet, les groupements époxy jouent le rôle de stabilisants thermiques en piégeant le chlorure d’hydrogène, dégagé lors du thermoformage et présentant un effet catalytique indirect sur le processus de dégradation du polymère. Dans une première étape, des latex semences à fonctionnalité époxy ont été synthétisés par copolymérisation en émulsion du methacrylate de glycidyle (GMA) et du methacrylate de butyle (BMA). Lors d’une seconde étape, la copolymérisation en émulsion ensemencée du chlorure de vinylidene et de l’acrylate de méthyle a été effectuée en présence des semences de poly(GMA-co-BMA). Des analyses thermogravimétriques effectuées sur les échantillons composites ont mis en évidence le rôle de stabilisant thermique joué par les fonctions époxy. La seconde partie du projet concerne la synthèse de latex hybrides à base d’oxyde de cérium (CeO2) afin d’améliorer la résistance du PVDC aux rayonnements UV. Les nanoparticules d’oxyde de cérium sont en effet attrayantes en tant que stabilisants UV en raison de leur haute absorption des rayonnements UV et d'une faible activité photocatalytique. Cependant, étant donné l’incompatibilité intrinsèque entre les phases inorganique et organique, la synthèse de latex hybrides requiert souvent une étape préliminaire de modification de surface des particules minérales. Le greffage d’alcoxysilanes a d’abord été entrepris sur des particules d’oxyde de cérium afin d’encourager la réaction de polymérisation à leur surface. Des observations par cryo-Microscopie Electronique à Transmission (cryo-MET) effectuées sur les latex hybrides obtenus par cette stratégie ont montré que le greffage d’alcoxysilanes ne permettait pas d’améliorer efficacement la compatibilité entre les phases inorganique et polymère. Enfin, des macro-agents RAFT amphiphatiques ont été employés comme agents comptabilisant réactifs afin de promouvoir la réaction de polymérisation à la surface de l’oxyde de cérium. Des oligomères RAFT ont été obtenus par des réactions de co- ou terpolymérisation en présence d’un agent de contrôle RAFT. Après caractérisation de l’adsorption des macro-agents RAFT à la surface de l’oxyde de cérium, les particules modifiées ont été utilisées dans des réactions de polymérisation en émulsion. Les observations des latex hybrides par cryo-MET ont confirmé l’efficacité de la méthode pour l’obtention de structures hybrides. Cette stratégie semble ainsi la plus prometteuse pour la synthèse de latex hybrides CeO2/PVDC pour des applications en tant que films barrières présentant une stabilité UV améliorée. / Food and pharmaceutical packages should nowadays fulfill a wide range of requirements : not only should they preserve the packed products from external polluting agents, but they must also be innocuous, more energy-efficient and disposable. Barrier polymers have enabled to meet these criteria, by offering alternatives to more energy-consuming and heavier materials like glass or metals, while maintaining a low permeability to water and/or oxygen. Among the large variety of barrier polymers, poly(vinylidene chloride) (PVDC) copolymers provide a more complete protection to external contaminants, due to their extremely low permeabilities towards water and oxygen. Nonetheless, PVDC films still suffer from limitations as far as their thermal and UV stabilities are concerned. This effect is even more pronounced in the case of films obtained from latexes, due to the presence of higher amounts of additives that could take part in the polymer degradation. Therefore, the synthesis of PVDC-based latexes for use as waterborne barrier films with improved thermal and UV stabilities are of great importance. PVDC-based composite latexes were first synthesized from epoxy-functionalized seed latexes in order to enhance the polymer thermal stability. Given that hydrogen chloride displays an indirect catalytic effect on the polymer degradation, epoxy groups were indeed expected to act as thermal stabilizers by scavenging the HCl released by the polymer under thermal stress. In a first step, epoxy-functionalized seed latexes were synthesized via the emulsion copolymerization of glycidyl methacrylate (GMA) and butyl methacrylate (BMA). In a second step, the seeded emulsion copolymerization of vinylidene chloride and methyl acrylate was carried out in the presence of poly(GMA-co-BMA) seed latexes. Thermogravimetric analyses carried out on the resulting composite samples evidenced the thermal stabilization provided by epoxy groups. The second part of the project focused on the synthesis of cerium oxide-based hybrid latexes so as to improve the stability of PVDC to UV radiation. Cerium oxide (CeO2) nanoparticles are indeed very attractive as UV-stabilizers due to their high absorption of radiation in the UV range and a low photocatalytic activity. However, due to the intrinsic incompatibility between inorganic and polymer phases, the synthesis of inorganic-organic hybrid latexes often requires a preliminary step of modification of the mineral particles surface. The grafting of alkoxysilanes onto nanoceria was first attempted in order to promote the polymerization reaction at the surface of the inorganic particles. Cryo-Transmission Electron Microscopy (cryo-TEM) observations of hybrid latexes obtained via this route showed that this strategy was unsuccessful at improving the compatibility between the inorganic and polymer phases. Amphiphatic macro-RAFT agents were finally considered as reactive compatibilizing agents to direct the polymerization towards the cerium oxide surface. RAFT oligomers were first obtained by co- or terpolymerization reactions in the presence of a RAFT controlling agent. After characterizing the adsorption of amphiphatic macro-RAFT agents at the surface of nanoceria, surface-modified cerium oxide particles were then engaged in reactions of emulsion polymerization reactions. In most cases, cryo-TEM observations carried out on the resulting latexes confirmed the efficiency of the amphiphatic macro-RAFT agent route for the synthesis of hybrid structures. Therefore this route appeared so far to be the most promising for the synthesis of CeO2/PVDC hybrid latexes for use as waterborne barrier films with improved UV-stability.

Spherical agglomerates of benzoic acid crystals have been successfully prepared by drowning-out crystallization in three solvent partial miscible mixtures. Benzoic acid is dissolved in ethanol, bridging liquid is added and this mixture is fed to the agitated crystallizer containing water as the anti-solvent. Small crystals are produced by crystallization of the substance, and the crystals are agglomerated through the action of the bridging liquid. Different solvents: chloroform, toluene, heptane, pentane, cyclohexane, ethyl acetate and diethyl ether are chosen as bridging liquids, all being low soluble in water and showing good wettability for benzoic acid crystals. The influence of process conditions such as concentration of solute, agitation rate, feeding rate, amount of bridging liquid and temperature on the properties of benzoic acid spherical agglomerates, are investigated. Different sets of experiments were accomplished to track how the properties of the particles gradually change during the normal spherical crystallization experiment. Other sets of experiments were performed to examine the influence of agitation and process time for agglomeration. The product properties such as particle size distribution, morphology and mechanical strength have been evaluated. The mechanical strength of single agglomerates has been determined by compression in a materials testing machine, using a 10 N load cell. Compression characteristics for single agglomerates are compared with the data on bed compression. The present study shows that the bridging liquid has significant influence on the product properties, using diethyl ether and ethyl acetate no agglomerates are formed. Using any of the other five solvents (chloroform, toluene, heptane, pentane, and cyclohexane) spherical agglomerates are formed, as long as a sufficient amount of the bridging liquid is used. Using cyclohexane as bridging liquid at 5°C and toluene at 20°C the particles are larger compared to particles formed at other conditions. The highest particle fracture stress is obtained by using toluene as the bridging liquid at 5 and 20°C. Particle morphology depends on the bridging liquid used and the particles are completely spherical when toluene and pentane are used as bridging liquids. Different process parameters are found to have a significant influence on the physico-mechanical properties of the product. The range of operation for spherical agglomeration is relatively narrow and only at certain conditions spherical agglomerates are produced. With increasing amount of bridging liquid the particle size and strength increase and the morphology improves. Particle size decreases and the fracture force increases with increasing feeding rate, but the morphology remains unchanged. For all the solvents, the particle size and the fracture stress increase with decreasing temperature. For four of the solvents the morphology improves with decreasing temperature. For cyclohexane the result is the opposite, in that the particles are spherical at 20°C and irregular at 5°C. Spherical agglomerates of benzoic acid, both as single particles as well as in the form of a bed, have a high compressibility and low elastic recovery, properties that are favorable for direct tabletting. As the feed solution is supplied to the crystallizer the amount of benzoic acid that can crystallize actually does crystallize fairly rapidly. Hydrodynamics are responsible for bringing particles together for the agglomeration. Experiments reveal that during the gradual addition of the feed to the agitated aqueous solution, both particle size and particle number increases. It is clear from the experiments that not only further addition of feed solution leads to larger product particles but also continued agitation. Along the course of the process the properties of the particles change gradually but substantially. By continued agitation, the particle porosity decreases, density, strength gradually increases and also the spherical shape develops gradually. / QC 20110419

Thss thesis presents the results of an experimental programme on the static mono-tonic response of cohesive-frictional granular materials. The purpose of this experimental programme was to gain insight into the mechanical behaviour of uncemented sands, and sands with small percentages of cementation. With this objective in sight, the research involved understanding and delineating the e ects of four variables: the intermediate principal stress, stress inclination, cohesion (or cementation), and particle morphology. The hollow cylinder torsion (HCT) apparatus, which allows control over both the magnitude and direction of principal stresses, was used in this study to carry out a series of elemental tests on the model materials. The test results were analysed in a plasticity theory based framework of critical state soil mechanics. Drained and undrained HCT tests were conducted on a model angular sand to understand the combined influence of intermediate principal stress ratio (b) and principal stress inclination ( ). Sand specimens were reconstituted to a given density and confining pressure, and were sheared to large strains towards a critical state. The stresses at the critical state with varying `b' were mapped on an octahedral plane to obtain a critical state locus. The shape of this locus closely resembles a curved triangle. Also these specimens showed increased non-coaxiality between the stress and strain increment directions at lower strains. This non-coaxiality decreased significantly, and the response at the critical state was by and large coaxial. The effect of `b' and ` ' on the flow potential, phase transformation, and critical state was also investigated. At phase transformation, ` ' plays a more dominant role in determining the flow potential than `b'. The shape and size of the critical state locus remained the same immaterial of the drainage conditions. Next, small amounts of cohesion (using ordinary Portland cement) was added to this sand ensemble to study the mechanical behaviour of weakly cemented sands. The peak in the stress strain curve was used to signal the breakdown of cohesion further leading to a complete destructuring of the sand at the critical state. The response of the cemented sand changes from brittle to ductile with increase in confining pressure, while reverses with increase in density and `b'. Stress-dilatancy response for the weakly cemented materials shows the non coincidence of peak stress ratio and maximum value of dilation unlike purely frictional materials. This mismatch in peak stress ratio and maximum dilation diminishes with increase in confining pressure. The peak stress (cemented structured sand) locus and the critical state (destructured) locus were constructed on the octahedral plane from these HCT tests. The critical state locus of the cemented sand when it is completely destructured almost coincides with the critical state locus of the clean sand. Using this experimental data set, some important stress-dilatancy relationships (like Zhang and Salgado) and failure criteria (Lade's isotropic single hardening failure criteria and SMP failure criteria) were benchmarked and their prediction capabilities of such models were discussed in detail. The effect of particle morphology was also investigated in this testing programme. Rounded glass ballotini and angular quartzitic sand which occupy two extreme shapes were selected, and a series of HCT tests at different `b' values were con-ducted. A larger sized CS locus was obtained for angular particles and it encompassed the critical state locus of the spherical glass ballotini. Spherical particles exhibit a predominantly dilative behaviour, however present a lower strength at the critical state. The mobilization of strength as a result of rearrangement of angular particles and the consequent interlocking is higher. Even with contractive behaviour which is reflected in the higher values of critical state friction angle and the larger size of the yield locus for sand. Finally, a series of unconfined compression tests were performed to understand if there exists a scale separation in cohesive frictional materials. Specimens were reconstituted to a range of sizes while maintaining a constant aspect ratio and density. As the specimen size increased, the peak strength also increases, counter to an idea of a generalized continuum for all model systems. The observed secondary length scale (in addition to the continuum length scale) is obverse to the one observed in quasi-brittle materials such as concrete, rock. In order to ascertain the reason behind this phenomenon, a series of tomography studies were carried out on these contact-bound ensembles. The presence of cohesion between the grains brings about an \entanglement" between the grains, which contributes to increase in strength, with increase in the size of the sample. This in e ect bringing forth a second length scale that controls the behaviour of these cohesive frictional granular materials. This experimental data set provides quantification of various aspects of the me-chanical response of both cemented and uncemented granular materials under myriad stress conditions. This data set is also extremely useful in developing and bench-marking constitutive models and simulations.