Ho Chi-hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 50-51). / Abstracts in English and Chinese. / Chapter CHAPTER ONE: --- INTRODUCTION --- p.1 / Introduction --- p.1 / Motivation of the Problem --- p.1 / Organization of this Thesis --- p.2 / Chapter CHAPTER TWO: --- LITERATURE SURVEY --- p.3 / Introduction --- p.3 / Electrorheological Fluid --- p.3 / Magnetorheological Fluid --- p.4 / Ferrofluid --- p.4 / "Comparison Amount ER, MR and Ferrofluid" --- p.5 / Chapter CHAPTER THREE: --- THEORETICAL ANALYSIS OF MR FLUIDS FOR MICRO DEVICES --- p.8 / Introduction --- p.8 / Minimal Volume --- p.8 / Magnetic Field Requirement --- p.10 / Particle Size --- p.14 / Chapter CHAPTER FOUR: --- PROCESSING TECHNOLOGY --- p.15 / Introduction --- p.15 / Processing Technology --- p.15 / Chapter CHAPTER FIVE: --- MR FLUID PILLARS --- p.18 / Introduction --- p.18 / Description of Experimental Setup --- p.18 / Finite element Analysis of the Experiment --- p.23 / Alignment Theory of MR Fluid Pillar --- p.29 / Discussion of Fluid Surface Tension --- p.36 / Chapter CHAPTER SIX: --- APPLICATIONS --- p.39 / Introduction --- p.39 / MR Fluid Actuator --- p.39 / Micro Brake --- p.45 / Micro Brake --- p.46 / Micro Clutches --- p.46 / Damper for Micro-Robot System --- p.46 / Chapter CHAPTER SEVEN: --- CONCLUSION --- p.48 / APPENDIX --- p.49 / BIBLIOGRAPHY --- p.50

"Excessive discharge of heavy metals has been one of the major causes of water pollution worldwide. Various traditional methods of heavy metal removal have been devised but certain drawbacks like high cost, high energy requirement, and the production of toxic sludge have limited their use. Hence, biosorption is one of the alternative methodologies. This study combined biosorption and diafiltration in an attempt to optimize Polymer Enhanced Diafiltration to study copper removal from aqueous solutions by the use of a biopolymer, lambda-carrageenan. Lambda-carrageenan was studied as a biosorbent owing to properties such as low cost, good water solubility, non-gelling nature and the presence of sulfate groups which can sequester cations. Conditions for binding such as pH, temperature and concentration of copper and lambda-carrageenan were studied. Equilibrium dialysis experiments were performed to study the metal ion membrane transport kinetics and to determine the metal ion binding capacity and strength of the copper-biopolymer association. Rheological measurements were performed to determine how the viscosity of lambda-carrageenan changes with increase in shear stress and with increase in metal concentration. The solution was found to be shear thinning. However, with increase in metal concentration, viscosity was found to increase when high concentrations of polymer (8 g/L and 12 g/L) were used. Solution viscosity was found to decrease with increase in metal concentration when 4 g/L of polymer was used. Polymer Enhanced Diafiltration studies showed no leakage of the polymer through the membrane and no significant binding elsewhere in the PEDF system. It also showed an impressive retention of copper inspite of a rather high metal ion-polymer dissociation constant suggesting a yet not understood series of events occurring on the membrane of the PEDF system. Lambda-carrageenan is a linear polysaccharide, which might be stacking up on the membrane after forming layers, and not allowing any free metal ion to escape. Other reasons could be the sieving effect, degradation of the polymer due to shear and compaction of molecule on metal binding such that the polymer is not itself escaping through the membrane, but also not allowing the free metal ion to escape. Hence, this study suggests the need for more information on the metal-polymer interactions on the surface of the membrane by designing a direct observation experiment with a mini-tangential flow filtration system."

Les mousses de ciment présentent d'intéressantes propriétés : une faible densité, une faible consommation de matière première et une bonne résistance thermique. Certaines propriétés finales de la mousse dépendent de sa morphologie. Pour mieux comprendre cette dépendance, on veut créer des échantillons de mousse de ciment avec une structure bien contrôlée. On crée des échantillons de mousses de ciment composés de bulles de même taille, en choisissant la quantité d'air, de ciment, d'eau et de tensioactif. Pour ce faire, on mélange d'une part une mousse aqueuse de morphologie contrôlée, stabilisée par des tensioactifs, et d'autre part une pâte de ciment. Le but de cette thèse est d'étudier comment conserver cette structure jusqu'à la prise du ciment. Tout d'abord, nous étudions d'interaction entre tensioactifs et pâte de ciment. Certains tensioactifs ne sont pas compatibles avec la solution alcaline présente dans la pâte de ciment et ne permettent pas de produire une mousse dans ces conditions. Parmi les tensioactifs compatibles avec la solution interstitielle de ciment, certains s'adsorbent sur les grains de ciment. Cette adsorption change les interactions entre grains de ciment et par conséquent, la contrainte seuil de la pâte. A faible concentration en tensioactif, la monocouche de molécules adsorbée rend les grains de ciment hydrophobes, ce qui produit une attraction hydrophobe entre grains et une augmentation de la contrainte seuil de la pâte. A forte concentration en tensioactif, les micelles adsorbées engendrent une répulsion stérique entre les grains de ciment et une chute de la contrainte seuil. Dans un deuxième temps, nous étudions l'effet des bulles d'air sur la contrainte seuil d'une pâte de ciment aérée, lorsque celle-ci contient moins de 40% d'air. Les mesures sont normalisées par la contrainte seuil de la pâte interstitielle afin d'être comparées à la littérature. Lorsque le tensioactif utilisé s'adorbe peu sur les grains de ciment, les résultats sont semblables à ceux de la littérature obtenus sur des fluides à seuil modèles. En revanche, lorsque le tensioactif utilisé a une grande affinité avec les grains de ciment, la contrainte seuil normalisée est bien au-dessus des prédictions. Notre hypothèse pour expliquer ce résultat est une modification des propriétés de surface des bulles à cause de l'adsorption des grains de ciment rendus partiellement hydrophobes par le tensioactif. Ensuite, nous nous focalisons sur la stabilité des mousses de ciment avant la prise, pour une fraction d'air de 83%. On s'intéresse tout d'abord à trois séries de mesures, en gardant pour chacune le rapport eau-sur-ciment et la taille des bulles constante. Pour chacune des trois séries, seule la contrainte seuil de la pâte de ciment est changée par l'addition de superplastifiant ou d'une grande quantité de tensioactif anionique. On obtient alors un résultat inattendu : la meilleure stabilité est observée pour des tailles de bulles relativement faibles. La comparaison avec les mesures des propriétés rhéologiques de la mousse fait penser que la bonne stabilité aux faibles contraintes seuil est due à la réorganisation des grains de ciment en un réseau granulaire plus dense. Pour aller plus loin sur l'étude de la stabilité des mousses, nous avons ensuite fait varier la taille des bulles, la rapport eau-sur-ciment et la quantité de tensioactif. Nous avons pu définir un critère de stabilité pour l'ensemble de ces mousses qui dépend de la contrainte seuil interstitielle de la pâte de ciment confinée par les bulles et de la taille des bulles. Pour finir, nous mesurons la résistance en compression de mousses de ciment et leur vitesse d'imbibition afin de corréler ces propriétés à leur structure / Cement foams advantages compared to normal concrete is their low density, low material need and thermal insulation properties. To better understand how the morphology of the cement foam affects its properties, we create solid cement foam with well controlled structure. This involves two steps: the creation of the fresh cement foam with chosen structure, and the stability of this structure up to cement hardening. Our cement foam fabrication protocol allows us to obtain fresh cement foams samples with very well controlled parameters. For each sample, all the bubbles have the same size, and we can select the content of air, water, cement and surfactant. This technique consists in mixing a well-controlled precursor aqueous foam stabilized by surfactant, with a cement paste prepared separately. First, we study the interaction of surfactants and cement paste. Some surfactants cannot stabilize foam in cement paste highly alkaline solution. Some others, mainly anionic surfactants, adsorb on cement grains surface, which modifies interactions between cement grains and consequently the yield stress of the cement paste. At low surfactant concentration, cement grain surface becomes hydrophobic and yield stress increases due to hydrophobic attraction between cement grains. At high surfactant concentration, adsorbed micelles create a steric repulsion between cement grains and make yield stress of cement paste drop. In a second chapter, we study the effect of bubbles on the yield stress of aerated cement paste. To compare the results with the literature, the measured yield stress is normalized by the yield stress of the suspending cement paste, i.e. taking into account the effect of surfactant. For a surfactant with low affinity to cement grains surface, results are consistent with literature, whereas reduced yield stress is much higher than expected when surfactant strongly adsorb on cement grain surface. This effect is attributed to the change of the bubble surface properties due to the adsorption of hydrophobic cement grains at the air-liquid interface. Then, we focus on cement foam stability, at air content 83%. We first study three series of experiments at given water-to-cement ratio and bubble size. For each series, the yield stress of the cement paste is changed by addition of superplasticizer or high amount of anionic surfactant. Unexpectedly, the best foam stability is obtained for relatively low yield stress. Rheological measurements on the fresh cement foams allowed us to understand this improved stability as a consequence of the reorganization of cement grains into denser packing. In a second part on stability, we study the influence of bubble size, water-to-cement ratio and surfactant content. A stability criterion is defined from the bubble size and the interstitial cement paste yield stress. Eventually, we observe that cement foam structure affects water imbibition velocity and mechanical resistance to compression of hardened cement foams

Orientador: Vânia Regina Nicoletti / Banca: Izabel Cristina Freitas Moraes / Banca: Poliana Moser / Resumo: Emulsões óleo em água (O/W) são sistemas formados por dois líquidos imiscíveis, envolvendo a presença de uma fase contínua (água), uma fase dispersa (óleo), um emulsificante e energia introduzida por meio de agitação ou cavitação. A energia transmitida é capaz de aumentar a área interfacial entre as fases dispersa e contínua, enquanto o emulsificante adsorve na interface, estabilizando o sistema. A emulsificação é uma etapa anterior e fundamental à microencapsulação de compostos lipofílicos por spray drying, em que gotas de emulsão são rapidamente desidratadas em uma câmara de secagem, possibilitando a microencapsulação da fase dispersa. Neste trabalho, objetivou-se produzir emulsões O/W utilizando microgéis de isolado proteico de soja (SPI) como estabilizantes, avaliar a estabilidade e o comportamento reológico das emulsões em diferentes concentrações de cloreto de sódio (NaCl) e, posteriormente, produzir microcápsulas por spray drying, avaliando o potencial dos microgéis de SPI como material de parede. Suspensões com 10% m/m de SPI foram preparadas em água deionizada e submetidas à desnaturação por aquecimento a 80 ºC por 30 minutos, seguido de resfriamento a 4 ºC por 12 h. Após a formação do gel, as suspensões foram diluídas para 6% m/m de SPI com água ou soluções de NaCl e homogeneizadas sob alta pressão ou sonicadas para produção dos microgéis, usados para estabilizar emulsões O/W com diferentes teores de óleo produzidas por homogeneização a alta pressão ou sonicação... / Abstract: Oil-in-water (O/W) emulsions are systems formed by two immiscible liquids, involving a continuous phase (water), a dispersed phase (oil), an emulsifier and energy input by homogenization or cavitation. The transmitted energy is able to increase the interfacial area between the dispersed and continuous phases, while the emulsifier adsorbs at the interface, stabilizing the system. The emulsification is an earlier and fundamental step to microencapsulation of lipophilic compounds by spray drying, wherein emulsion droplets are rapidly dehydrated in a drying chamber, enabling the microencapsulation of the dispersed phase. The objective of this work was to produce emulsions using soybean protein isolate (SPI) microgels as O/W emulsion stabilizers, to evaluate the stability and rheological behavior of the emulsions at different concentrations of sodium chloride (NaCl), and to produce microcapsules by spray drying of the emulsions, evaluating the potential of SPI microgels as wall material. Suspensions with 10 wt% SPI were prepared in deionized water and subjected to gelation by heating at 80 °C for 30 minutes, followed by cooling at 4 °C for 12 h. After gel formation, the suspensions were diluted to 6 wt% SPI with water or NaCl solutions and homogenized under high pressure or sonication to produce the microgels, which were used to stabilize O/W emulsions with different oil contents produced by high-pressure or ultrasound homogenization. The emulsions were then submitted to drying ... / Mestre

Este trabalho propõe contribuir no desenvolvimento do processo de extrusão para a produção de compósitos cimentícios, mediante metodologia que possibilite a obtenção de formulações extrudáveis utilizando cimento Portland de alta resistência inicial, sílica ativa, calcário, polpa de celulose de eucalipto, fibras de polipropileno e aditivos. Para isso, foram caracterizadas as matérias-primas como subsidio para as discussões. O efeito dos diferentes componentes da formulação no comportamento reológico da mistura foi avaliado utilizando reômetro extrusor. As propriedades físicas e mecânicas dos compósitos elaborados com combinações de calcário, sílica ativa e cimento foram modeladas estatisticamente com o propósito de estimar o comportamento das matrizes. A demanda de água dos sistemas cimentícios foi determinada experimentalmente e utilizada na extrusão das matrizes. Selecionada uma matriz, suas propriedades mecânicas e físicas foram modeladas, estatisticamente, com diferentes teores de polpa celulósica de eucalipto e fibras de polipropileno. As formulações com características desejadas foram avaliadas ao envelhecimento acelerado por 200 ciclos de imersão-secagem. Finalmente foi analisada a reprodutibilidade utilizando o módulo de Weibull para as formulações selecionadas. O estudo reológico constatou que as fibras de polipropileno apresentam os maiores aumentos nos valores dos parâmetros reológicos se comparados com os efeitos do calcário, sílica ou celulose de eucalipto, repercutindo em maiores pressões de extrusão. O incremento do modificador reológico hidroxipropilmetilcelulose reduz no compósito cimentício o módulo de ruptura mesmo que durante o processamento, promova o incremento da pressão de extrusão. Os modelos estatísticos empregados para modelar a matriz reforçada foram de maior complexidade e com menor coeficiente de determinação se comparados com os utilizados na modelagem das matrizes. O preço de mercado do fibrocimento é aproximadamente 64% menor do que os determinados utilizando unicamente os valores das matérias-primas e aditivos do fibrocimento extrudado no presente estudo. / This work intends to contribute in the development of the extrusion process for the production of cementitious composites, through methodology that makes it possible to obtain formulas using high resistance Portland cement, silica fume, limestone, eucalyptus pulp, polypropylene fibers and admixtures. With this intention, the raw materials were characterized as a support for the discussions. The effects of the different components of the formula on the rheological behavior of the mixture were evaluated using an extrusion rheometer. The physical and mechanical properties of the composites elaborated with the combinations of limestone, silica fume and cement were modeled statistically with the purpose of estimating the behavior of the matrix. The water demand of the cementitious systems was determined experimentally and used in the matrixes extrusion. After the Matrix Selection, their mechanical and physical properties were modeled statistically, with different pulp eucalyptus and polypropylene fibers quantities. The formulas with the expected characteristics were evaluated to the accelerated aging for 200 wet-drying cycles. Finally the reproducibility was analyzed using the Weibull module for the selected formulas. The rheological studies verified that the polypropylene fibers demonstrate the largest increase in the values of the rheological parameters when compared with the effects of the limestone, silica fume or eucalyptus pulp, inducing larger extrusion pressures. The increment of the rheological modifier hydroxypropyl methylcellulose decreases the module of rupture in the cementitious composite, and simultaneously during the process it promotes the increment of the extrusion pressure. The statistical models used to reinforce the matrix modeling were of large complexity and with smaller coefficient determination when compared to matrixes used for modeling. The fiber cement market price is approximately 64% smaller than the raw materials and admixtures used in extruded fiber cement in this study.

The aim of this thesis was to understand how a non-Newtonian fluid like chocolate fluidises under vibration. The problem was approached both experimentally and computationally, employing the finite element method as implemented in oomph-lib. In order to model a non-Newtonian fluid its constitutive behaviour has to be known. For this purpose, rheological measurements on tempered chocolate were performed. The chocolate was modelled using generalised Newtonian models for the viscosity and it was found that the Sisko model provided the best fit to the data. The generalised Newtonian Navier-Stokes equations were implemented within oomph-lib and their validation against analytical solutions yielded excellent agreement. Both the experiments and the computations for a sessile drop of chocolate, which is vibrated vertically, spreading on a layer of the same fluid yielded qualitatively similar results. The parameter which controls the spreading is the acceleration arising from the vibration. The drop rests on the layer and does not spread under gravity and small accelerations. However, as the acceleration increases and exceeds a threshold the drop starts to spread out. For a constant amplitude vibration, the spreading rate increases with increasing frequency and for large frequencies approaches a theoretical spreading law which corresponds to viscous dominated spreading of a Newtonian drop.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 288-296. / by Steven Minh Dinh. / Sc.D.

Foamed concrete has considerable potential as a material for use in the construction industry. However, although some researches have been conducted on the characteristics of foamed concrete, thus far, knowledge on the behaviour of foamed concrete has been limited. Hence, predictions of the stability of foamed concrete under different conditions and mix constituents have been uncertain. The aim of the presented study is to investigate causes of instability of foamed concrete by examining its rheological properties and microstructure. This study explores the complex causes of instability in foamed concrete by examining the rheological parameters, the yield stress and the plastic viscosity, since the rheological properties affect the hardened state. Using flowability as a guide, the relationships are examined between yield stress and viscosity, specifically with reference to their effect on density and w/c ratio. Other factors affecting the rheological properties related to the proportions and fineness of the mix constituents are also considered. Thereafter, the microstructure of foamed concrete is examined to establish links with the rheological values and the relationship with stability. The microstructure, best described by the bubble sizes, has been found to be a function of yield stress, plastic viscosity, material fineness and surfactant types. The bubble diameters have been shown to range between 0.1 to 0.5 mm. Bubbles less than 0.35 mm in diameter correspond to stable mix with a drop in level of less than 5% in height in densities of 1000 kg/m3 and higher. The big bubbles link to unstable mixes and have been found to be a source of instability. Other chemical additions were shown to result in disintegration of bubbles. As this study unfolds, a relationship is established between bubbles and the yield stress values. Bubble sizes reduced when the yield stress increased. For flowability out of Marsh cone test taken between 1 to 2 minutes, the corresponding yield stress was between 6.0 N/m2 to 8.5 N/m2. For this range, the empirical bubble sizes were found to be between 0.33 to 0.35 mm in diameter. In examining the possible causes of instability, it was found that stability improved markedly with increase in density and lesser effect by other factors such as w/c ratio, constituent materials and specimen height. However, the rate of hardening was a dominant factor in stability as evidenced by the use of Calcium Sulfoaluminate cement, CSA and CEM I 52.5R cement which increased the setting times. Stability was drastically achieved even at lower density 300 kg/m3. Blends of CSA with CEM I 52.5R and fine fly ash, FAf, demonstrated similar results. This research has implications for the development of foamed concrete as a material that could be more widely used in certain construction contexts where stability in lightweight density foamed concrete is crucial. It has contributed to better understanding of the rheological properties and the effect on the microstructure, even though the results are based on empirical values. Hence, it is anticipated that the prediction of stability can be made through a selection of materials and proportions to suit different contexts and their requirements.

One of the most costly diseases in the dairy industry is mastitis, which is an inflammation of the mammary gland. Mastitis influences the quality of milk and therefore reduces financial returns to both the farmer and the processor. Early detection of mastitis typically reduces treatment cost and a significant amount of research has been done in this field. Currently, the three major methods for mastitis detection are: • The Foss Analysis, which physically counts each cell and is performed off-site. • The Whiteside Test, which is based on a direct relationship between the number of the blood cells and the intensity of a gel formed between NaOH and cells. It was developed for on-site mastitis detection, but is no longer used routinely. • The California Mastitis Test (CMT), which can be done on-site, but is only a quantitative indication of the severity of the infection. The California Mastitis Test has previously been adapted to determine the somatic cell count (SCC) in infected milk by correlating viscosity to cell count. Although highly successful, some uncertainty exists regarding the rheology of the gel formed during the test as well as factors that may influence the accuracy of the test. In this thesis, studies were undertaken on the rheology of the gel formed during the California Mastitis Test in order to develop an understanding of the mechanism of gel formation and how various factors influence the rheology of the gel. Basic biochemistry and physico-chemistry of the gel has been reviewed and it was found that the CMT gel is a DNA/histone/surfactant complex, which forms when SDS is introduced into infected milk with elevated somatic cell counts. Based on literature and some initial experimentation it was found that the gel is a time- and sheardependent, non-Newtonian fluid. Since the reliability of the CMT hinges on the correlation between viscosity and SCC, this study investigated specific factors that may influence gelation, these were: iii • rheology • testing conditions, such as time delay prior to viscosity testing, shear rate and temperature • surfactant type and concentration • milk composition, including fat content, somatic cell count and protein content. It was found that when using capillary viscometry a linear relationship exists between the relative viscosity of the gel and the SCC. The surfactant concentration determines the slope of this linear relationship and it was found that at least 3% SDS is necessary for accurate results. Using more than 3% SDS resulted in more scatter in the data. It was also found that a linear relationship exists between the maximum apparent viscosity and SCC. Either capillary or Brookfield viscometry can be used, however, Brookfield viscometry was found to be more sensitive at the lower SCC range. It was found that the combination of surfactant concentration and SCC influenced the rheology of the gel. The lower the SCC the more SDS was required for gel formation. It was found that when using 1% SDS the critical SCC was 79 k cell/ml, while using 3% SDS this was lowered to 59 k cell/ml. It was found that above the critical SCC the gel is a non-Newtonian rheopectic fluid. Dependent on shear rate, the gel shows rheodestructive behaviour. With a delay time, the peak viscosity of the gel formed faster with longer delay times. However, more than 30 seconds delay had no additional influence on gel formation. It was found that the shear rate or spindle speed influences both the time to reach the peak viscosity as well as the magnitude of this maximum. Higher shear rates shortened the time to reach the maximum apparent viscosity as well as the maximum viscosity. This is likely due to physical breakdown of the gel which is accelerated due to increased shear. Different surfactants have different effects on raw milk. Both acetic acid and Triton- 114 were found to be ineffective as CMT reagents. Acetic acid only denatures proteins and the increased viscosity is due to the precipitation of casein. Triton-114 cannot lyse nuclei walls and therefore gel formation was prohibited due to no DNA/histone complexes being released. Mixing SDS with Triton-114 was found to be less effective than SDS alone either due to the nucleus not being lysed, or because iv of interaction effects between SDS and Triton-114, reducing the available SDS for gelation. Lastly it was concluded that protein and fat content only contributes to the viscosity of milk by changing the solids content of milk and neither of these affects gelation during the CMT. Also, temperature only has a small influence on the relative viscosity and this influence could be neglected if the CMT is done around room temperature.

With China’s continuing economic boom, the demand for nickel has seen unprecedented growth over the past 10 years. Most of the world’s nickel is present in nickel laterite deposits. These high volume, low grade deposits are now being exploited and processed. An understanding of nickel laterite rheology and the ability to obtain meaningful rheological data is essential to process intensification and stability. / The properties and physical characteristics of 8 industrial nickel laterite slurries as well as two alumina slurries were examined using various rheological techniques. The samples chosen covered a wide range of physical conditions such as differing pH, particle size distributions, solids densities and mineralogy as well as country and deposit of origin. The rheological parameters investigated were the yield stress and shear stress vs. shear rate of the particulate slurries. Considerable attention was focused on the techniques used in shear stress vs. shear rate characterisation, including capillary rheometry, smooth and roughened cup and bob rheometry and the vane in infinite medium technique. / This work confirmed the finding of previous works, showing nickel laterite slurry rheological behaviour ranging from time independent to thixotropic to rheopectic. It found the vane in infinite medium technique highly suitable for testing nickel laterites at process relevant yield stresses. This technique gave data that correlated well with vane yield stresses and capillary rheometry data. Cup and bob tests showed significant slip at lower shear rates. In a number of cases, the cup and bob techniques also showed erroneously high stresses at higher shear rates. / The vane yield stress was found to be a fast and accurate method for monitoring nickel laterite sample aging and the samples tested exhibited 100 Pa yield stresses at solids fractions ranging from 0.389 to 0.524. Blending of nickel laterites was found to be nonlinear, and confirmed that characterisation at various blend ratios is necessary if blending is to be utilised during production.