The research carried out in this thesis describes the processing of liquids and ceramic suspensions, having a viscosity >100mPa s, using electrostatic atomization, mainly in the stable cone-jet mode. Electrostatic atomization, also called electrospraying, refers to a process where a liquid or a suspension is made to flow through a needle. The liquid or suspension is subjected to a high voltage maintained between the needle and a ground electrode. Two major physical properties, namely electrical conductivity and viscosity, affect electrostatic atornization in the stable cone-jet mode and the investigations described in this thesis focussed on the latter. Firstly, a set of liquid mixtures were prepared using distilled water and glycerol. The dc electrical conductivity of these mixtures were kept constant and the viscosity was varied. The mixtures were subjected to electrostatic atornization and in each case the mode of atornization, the cone/jet characteristics and relic sizes were studied as a function of viscosity. The effect of applied voltage on the conejet mode electrostatic atornization of glycerol having a viscosity of 1338mPa s was also investigated. Secondly, the possibilities of electrostatically atomizing ceramic suspensions were studied in detail. Several alumina suspensions were used including one containing a high volume fraction of solids (20 vol. % - the highest filler loading attempted to date using any jet-based processing route). Applied voltage - flow rate - atornization mode maps were constructed for this suspension incorporating even pico-flow rate regimes. This is a new input into the aerosol science and engineering literature. This section also highlights the importance of controlling the applied voltage and flow rate as these parameters affect the jet diameter and relic/droplet size generated. The effect of the geometry of the ground electrode used for electrostatic atornization was also investigated. In particular, the use of a point-like ground electrode was studied for the very first time. The third and most innovative facet of this research was the discovery of ceramic electrostatic atornization printing (CEAP) and the use of electrostatic atornization to produce ceramic foams. In CEAP a point-like ground electrode is used to focus the spray which was printed as characters, collection of characters and single tracks. This investigation was extended to explore the printing of multiple tracks produced with the aid of several needles and ground electrodes which worked simultaneously. A ring shaped ground electrode was used to electrospray ceramic droplets onto a polyurethane template and this paved the way for the development of a new method to prepare open-cell ceramic foams with a very high porosity. This method was extended to prepare ceramic structures and complex components.

The better understanding of the behavior of emulsions and suspensions is important in many applications. In general, emulsions allow the delivery of insoluble agents to be uniformly distributed in a more efficient way. At the same time suspensions of rigid particles are used as “smart materialsâ€� as their properties can be changed by the interaction with a magnetic or electric field. In the first part of the talk we consider a periodic emulsion formed by two Newtonian fluids in which one fluid is dispersed under the form of droplets of arbitrary shape, in the presence of surface tension. We assume the droplets have fixed centers of mass and are only allowed to rotate. We are interested in the time-dependent, dilute case when the characteristic size of the droplets aε, of arbitrary shape, is much smaller than the period length ε. We obtain a Brinkman type of fluid flow for the critical size aε = O(ε3) as a replacement of the Stokes flow of the emulsion. Additionally, using Mosco convergence and semigroup theory we extend the convergence to the parabolic case. For the case when the droplets convect with the flow, it can be shown again using Mosco-convergence that, as the size of the droplets converges to zero faster than the distance between the droplets, the emulsion behaves in the limit like the continuous phase and no “strangeâ€� term appears. Moreover, we determine the rate of convergence of the velocity field for the emulsion to that of the velocity for the one fluid problem in both the H1 and L2 norms. Additionally, a second order approximation is determined in terms of the bulk and surface polarization tensors for the cases of uniform and non-uniform surface tension. The second part of the talk is devoted to the study of MR fluids. We consider a suspension of rigid magnetizable particles in a non-conducting, viscous fluid with an applied external magnetic field. Thus, we use the quasi-static Maxwell equations coupled with the Stokes equations to capture the magnetorheological effect. We upscale using two scale asymptotic expansions to obtain the effective equations consisting of a coupled nonlinear system in a connected phase domain as well as the new constitutive laws. The proposed model generalizes the model of Rosenweig by coupling the velocity of the fluid and the magnetic field intensity. Using the finite element method we compute the effective coefficients for the MR fluid. We analyze the resulting MR model for Poiseuille and Couette flows and compare with experimental data for validation.

Steady state crossflow microfiltration (CMF) is an important and often necessary means for varying sized particle separation. It has been widely used in both industrial and biomedical processes, including a wearable water removal device intended to maintain end stage renal disease (ESRD) patients euvolemic. For kidney replacement therapies, there are few options available. Kidney transplantation still represents the optimal treatment for ESRD patients, even though it often requires daily post-transplant medication including immunosuppressant drugs to avoid rejection of the transplanted organ. The transplanted kidney itself has an average lifespan of only 10 years. The biggest engineering contribution to the cited problem was made about 60 years ago with the invention of dialysis machines (or some variation thereof). Dialysis still represents the optimal and most widely used therapeutic approach to renal replacement during long waits on a transplant list. The present-day dialysis system is bulky, totally mechanical, and extracorporeal, leading to a widely used therapy that is only effective in extracting water and toxins out of the blood-stream, but still with major drawbacks (i.e. intermittent treatments, 5-hours thrice-weekly, and forcing clinic-centered therapy) that are permanently costly. These drawbacks pose a major impediment to rehabilitation or any other lifestyle activity such as working or studying. Of all the vital organs, the kidney is both the most subtle in its homeostatic action and the most complex in terms of the structures it uses to accomplish its action. This thesis proposes a single facet of the multiple complexity of this vital organ: filtration. To that effect, CMF of blood suspensions through a microsieve were studied. Experiments, reported here, have correlated macroscopic measurements - filtration rates, transmembrane pressures (TMP), shear rates - during filtration through a photolithographically pored semiconductor membrane with direct observation of erythrocyte behavior at the filtering surface. Erythrocytes, the preponderant particles in blood, are believed to dominate filtration resistance. At low filtration rates (low TMP), erythrocytes roll along the filter, but at higher rates (higher TMP), there is an increasing probability of their sticking to the sieve. The design of membrane separation processes requires quantitative expressions relating the separation performance to material properties. The factors controlling the performance of CMF have been and continue to be extensively reviewed. There have been a number of influential approaches in CMF. Most have been based on the rate limiting effects of the concentration polarization of rejectate at the sieving surface. Various empirical and intuitive models exist which have been critically assessed in terms of their predictive capability and applicability to CMF from a microfluidic channel. Chapter 1 summarizes this assessment. Chapter 2 takes a closer look at how erythrocytes behave in a microfiltration environment. Maximum steady-state filtration flux has been observed to be a function of wall shear rate, as predicted by any conventional cross-flow filtration theory, but to show weak dependence on erythrocyte concentration, contrary to theory based on convective diffusion. Flux is known to be directly proportional to the TMP; however, since the pressure drop across a channel decreases along the direction of flow, TMP must modulate along the channel (highest at the leading edge of the membrane and lowest at the trailing edge). As a consequence, an area of stuck particles growing from the inlet (regimen of high TMP) has been observed, leading to a “fouling cascade.” Post-filtration scanning electron micrographs revealed significant capture and deformation of erythrocytes in all filter pores in the range 0.25 to 2 m diameter. This was then found to form a self-assembled partially complete monolayer. Filtration rates through these filters were reported and a largely unrecognized mechanism was proposed, which allows for stable filtration in the presence of substantial cell layering. Chapter 3 proposes a microfiltration model that pertains to non-deformable particles that are large enough to intrude significantly into the shear layer of a microchannel. A stable, stationary multilayer of particles was studied, whose thickness is shear-limited. The structure and parameters in that limit of steady filtration in this environment was then identified. A steady cake-layer thickness was observed and because of the simple geometry afforded by uniform spheres, the force balance, cake resistance, and filtration rate were derived from first principles. The good fit of the data to the proposed mechanism, provides a firm basis for the semi-quantitative analysis of the behavior of more complex suspensions. Finally, in Chapter 4, a design methodology was imposed to maintain the TMP constant throughout the whole sieving surface by introducing a flow chamber beneath and parallel to the sieve’s main flow. Co-current filtration was found to allow the TMP to remain stable along the membrane surface, enabling the entire sieve to perform optimally, and thus allowing greater stable filtration rates to be achieved. Co-current flow conditions allowed for twice as much filtration flux compared to a conventional CMF modality.

O estudo da dispersão e estabilização de barbotinas de porcelana de cinza de ossos é uma etapa muito importante no processo de conformação de peças cerâmicas, assim como também a etapa de obtenção da sua principal matéria-prima que é a cinza de ossos, devido a que constitui 50% em peso da porcelana e por ser uma matéria-prima renovável, reciclável e com alto valor agregado na fabricação de porcelana. Neste trabalho se investigou a influência das temperaturas de calcinação dos ossos (700, 800, 900 e 1000 °C) moídos e lavados, no seu tamanho, forma das partículas, composição química, comportamento elétrico superficial das partículas com o meio líquido, grupos funcionais e possíveis contaminantes nas superfícies das partículas dos ossos calcinados, que poderiam prejudicar a preparação de barbotinas de porcelana de ossos. Mostra-se também a dispersão, preparação e a estabilização da mistura de porcelana de ossos (50% cinza de ossos, 25% de caulim, 25% de feldspato) por meio dos ensaios de viscosidade e mobilidade eletroforética, conseguindo dispersar, homogeneizar e estabilizar as suspensões de porcelana de ossos aplicando tempos de envelhecimentos apropriados. / The study of the dispersion and stabilization of slip casting of bone porcelain is a very important stage in the process of preparation of suspensions ceramic, as well as the obtaining of its main material, that it is the bone ash, so that it constitutes 50% in weight of dry mass, and also that is one raw material renewable, recyclable and with high value added in the porcelain production. In the present research, the influence from the calcination of bovine bones to different temperatures (700, 800, 900 and 1000 °C) was investigated besides the size and form of the particles, variation in its chemical compositions, variations in its electric superficial behavior of the particles in contact with the liquid medium and also the groups present functional in the particles of ash of bones, kaolin and feldspar. Reveals the behavior of the particles during the dispersion and stabilization of the bone porcelain (50% ash of bones, 25% kaolin, 25 % feldspar) by means of the tests of viscosity and electrophoretic mobility, being able to disperse, to homogenize and to stabilize the suspensions of bone china with appropriate ageing time.

Este trabalho teve por finalidade desenvolver um método para a caracterização do perfil de dissolução de suspensões de mebendazol (MBZ), discriminatório para as formas polimórficas do fármaco. Pertencendo a classe II do Sistema de Classificação Biofarmacêutica (SCB), além da baixa solubilidade, o MBZ é bastante crítico por apresentar-se comercialmente disponível em duas formas polimórficas (A e C) e misturas destas. Além disso, pouca informação é encontrada acerca de métodos de dissolução de suspensões. O material apresentado está dividido em três capítulos, sendo o primeiro deles uma revisão da literatura sobre a dissolução de suspensões de fármacos que apresentam polimorfismo. Neste capítulo é feita uma abordagem sobre questões relacionadas ao desenvolvimento de métodos, como inserção das amostras na cuba de dissolução, agitação, uso de tensoativos no meio e a quantificação do fármaco. No segundo capítulo é apresentado o desenvolvimento do método de dissolução, com ênfase no estudo da solubilidade das formas polimórficas A e C de MBZ e sua interação com tensoativos. Foram realizados ensaios de solubilidade pelo método do equilíbrio, cálculo de concentração micelar crítica para os tensoativos lauril sulfato de sódio e polissorbato 80, sendo ao final realizado delineamento experimental (DOE) para o desenvolvimento do método. Pela avaliação do DOE, o local de inserção da amostra não influencia a dissolução de MBZ, por outro lado, a presença de tensoativo, assim como a forma polimórfica empregada, exercem efeito nos resultados apresentados. A partir destas informações, o método indicado para avaliação das suspensões de MBZ com potencial discriminatório de suas formas polimórficas foi definido pela utilização do aparato 2 (pá) a 75 rpm, com 2 litros de HCl 0,1 M sem tensoativo, como meio de dissolução. No último capítulo, o método desenvolvido foi utilizado na avaliação de especialidades farmacêuticas adquiridas no Brasil e em alguns países da América Latina, sendo os respectivos perfis de dissolução, comparados por meio de uma análise multivariada de componentes principais, com formulações contendo o MBZ em diferentes proporções de polimorfos. A partir dos resultados, foi possível observar que grande parte das formulações comercializadas não apresentaram perfil de dissolução satisfatório, isso pode estar relacionado com a presença considerável de polimorfo A nas matérias-primas utilizadas, comprometendo assim a sua solubilidade. / The aim of this work was to develop a method for characterization of the dissolution profile of mebendazole (MBZ) suspensions, being discriminatory for the polymorphic forms of the drug. MBZ belongs to class II of the Biopharmaceutics Classification System (BCS), besides its low solubility, it is very critic, being commercially available in two polymorphic forms (A and C) and their mixtures. Moreover, there is low information about dissolution methods for suspensions. The text presented herein is divided into three chapters, the first chapter is a literature review about dissolution of suspensions containing drugs that present polymorphism. In this chapter is made a discussion about the variables of the method, as sample insertion in the dissolution vessel, rotation speed, use of surfactants in the dissolution medium and drug quantification. The development of the dissolution method, focused on the solubility study of MBZ polymorphic forms A and C and their interaction with surfactants is presented in the chapter 2. Some tests were performed: solubility using shake flask method, calculation of micellar critical concentration for the surfactants sodium lauryl sulphate and polysorbate 80, and an experimental design (DOE) was done for developing the method. By DOE evaluation, the sample insertion site does not influence on MBZ dissolution, but the presence of surfactant and the polymorphic form used, show effect on the results. Based on these information, the method indicated for evaluation of MBZ suspensions, with discriminatory power for its polymorphic forms was defined by using apparatus 2 (paddle) at 75 rpm and 2 L of 0.1M HCl without surfactant as dissolution medium. In chapter 3, the method developed was used to evaluate pharmaceutical suspensions from Brazil and from some countries of Latin America. The respective dissolution profiles were compared by means of multivariate analysis of principal components with formulations containing MBZ in different polymorphs ratios. From the results, it was possible to observe that a great part of the commercially available formulations do not presented a satisfactory dissolution profile, and this fact can be related to a considerable amount of the crystalline form A in the raw material, which compromises its solubility.

Utilization of a large, diverse sample provided a rare opportunity to advance our understanding of gender, race, and socioeconomic differences in school-based problem behavior. Yearly assessment of discipline referrals and suspensions received within the school context from 5th- through 11th-grade, as well as assessment of school dropout, provided an opportunity to examine these issues through an extended prospective longitudinal design. Results highlight the middle school transition as a time when discipline referrals and suspensions increase markedly, while student reports of connections to others, motivation, and optimism decline sharply. Results indicate that boys, African-American students, and students from low socioeconomic status backgrounds report lower levels of connections to others, motivation, and optimism in 5th-grade. Boys, African-American students, and students from low socioeconomic status backgrounds also receive more discipline referrals and suspensions from 5th-grade onward and are more likely to experience dropout. However, regardless of demographic group membership, students who report stronger connections to others, motivation, and optimism in 5th-grade receive fewer referrals and suspensions from 5th- through 11th grade, and are much less likely to dropout of school than are students who report lower levels of connections, motivation, and optimism in 5th-grade. These results highlight the need to address students' sharp declines in functioning across the middle school transition through both ecological and person-centered prevention and school restructuring efforts. Results also highlight the utility of movement away from a static, demographic based understanding of problem behavior toward a clearer understanding of person and environment factors that may underlie both between and within demographic group differences in outcomes. Placing emphasis upon factors that are potentially amenable through school based prevention efforts considerably increases the likelihood that all of our nation's children are provided with equal opportunity to achieve their fullest potential.

Transport properties of concentrated suspensions are of interest to many industries. Mineral slurries at higher solids concentrations have shown some rheologically interesting characteristics such as shear thickening, the increase of viscosity of a multi-phase mixture with increasing shear rate. The general literature on the rheology of suspensions records the presence of yield stresses, shear thinning and normal stress differences. Little is said specifically about shear thickening behaviour except for colloidal suspensions. The aim of this study is to examine the behaviour of coarse shear thickening suspensions and determine the causes of this phenomenon. The study intended to achieve the following objectives to; develop the appropriate techniques for rheometric studies of shear thickening suspensions; investigate the nature of particle-fluid interaction; develop a model of shear thickening behaviour as it occurs in non-colloidal suspensions and to develop a method of applying the rheology results to flows and flow geometries of practical relevance. The effects of wall slip dominate much of the literature of shear thickening materials. To investigate this aspect a significant portion of the experimental work examined the effect of shear thickening on torsional flow. The rheogram produced from parallel plate rheometry was reassessed as a non-controlled flow and a rheology model dependant analysis demonstrated that the effects of slip are considerably more problematic for shear thickening suspensions, particularly as wall slip is an increasing function of shear stress. As a consequence of the rheometric method described above it was observed that the rate of change of the first normal stress difference, N1, with shear rate changes as shear thickening commences for non-colloidal suspensions. N1 is initially negative and is increasingly negative at low shear rates. Additional rheometric analysis examined the transient effects in the behaviour of a non-colloidal shear thickening suspension. By employing large angle oscillating strain tests the strain required to initiate a shear thickening response was determined. Coherent back scattering of laser light experiments were able to show the change in orientation of the particles with respect to its rotation around the vorticity axis. After a viscosity minimum was reached the orientation became more random as particle rotation and lamina disruption occurred. This was considered to be the cause of the measured shear thickening. A model of shear thickening in concentrated, non-colloidal suspensions of non-spherical particles was developed. Based on hydrodynamic interaction in the Stokes flow regime, the flow of interstitial fluid subjected the adjacent particles to lubricating and Couette type forces, acting as a couple. When a series of force balances on a particle contained between two moving laminae are conducted as a time sequence, the particle orientation and motion can be observed. The model has qualitative agreement with several aspects of the experimentally observed behaviour of shear thickening suspensions, such as viscosity change with shear rate and concentration, and the first normal stress difference increasing with shear rate. Pipe line flow experiments were conducted on the model suspension. Particle settling produces unusual patterns in shear thickening suspensions, with an annulus of delayed settling near the wall.

This research presents an experimental study of the formation of drops of suspensions consisting of a viscous liquid and spherical, neutrally buoyant, noncolloidal particles. Pendant drop formation and low Reynolds number jetting of suspensions are investigated, as is the transition between the two. Throughout, the particles utilized are on the order of 100 μm and the orifice from which the drops are formed is on the order of 1 mm. The presence of the particulate phase causes the structure at pinch-off in the pendant drop regime to change noticeably from that of pure liquids. Thick cone-like structures, termed "spindles" here, form at either end of the slender thread and are the result of particle motions during necking. These spindles become more pronounced with increasing particle concentration. Depending on particle concentration, the particles can have either a destabilizing effect (low concentration) on drop formation or a stabilizing one (high concentration). At low concentrations, the particles lead to earlier rupture of the thread and much shorter jet lengths, while at elevated concentrations the particles stabilize the thread after rupture and lead to fewer satellite drops as well as induce jetting at lower flower rates. A two-stage model has been proposed to describe the necking process for particle-laden suspensions in the pendant drop regime. The first stage occurs when the thread is thick relative to the particles and the effect of the particles can be attributed solely to a change in the effective viscosity of the mixture. The second stage occurs nearer pinch-off when the thread has thinned to only a few particle diameters. In this stage the individual particle motions within the thread determine the behavior and the thread ultimately ruptures over a region of the thread devoid of particles.

No description available.

Nanoparticles (such as, carbon nanotubes, carbon black, clay etc.) have one or more dimensions of the order of 100 nm or less. Owing to very high van der Waals force of attraction, these nanoparticles exist in a highly aggregated state. It is often required to break these aggregates to truly experience the “nanosize” effect for any required end use. There are several strategies proposed for dispersing/exfoliating nanoparticles but limited progress has been made towards controlling their dispersion state. The ability to tailor nanoparticle dispersion state in liquid and solid media can ultimately provide a powerful method for tailoring the properties of solution processed nanoparticle-filled polymer composites. This dissertation reports the use of a variety of stimuli-responsive polymers to control the dispersion state of single-walled carbon nanotubes. Stimuli-responsive polymers exhibit conformational transitions as a function of applied stimulus (like pH, temp, chemical etc.). These variations in conformations of the polymer can be used tailor nanotube dispersion state in water and solid composites.The use of pH and temperature responsive polymers to stabilize/disperse single walled carbon nanotubes (SWNTs) in water is presented. Non-covalent functionalization of SWNTs using pH and temperature responsive polymer show tailored dispersion state as a function of pH and temperature, respectively. Carbon nanotube microstructure in these aqueous suspensions was characterized using several techniques (cryo-TEM, viscosity measurements, uv-vis spectroscopy, zeta potential measurements and settling behavior). Furthermore, nanotube dispersion state in aqueous suspensions is preserved to a large extent in the composites formed by drying these suspensions as evidenced by SEM images and electrical conductivity measurements. Based on the results obtained a mechanism is proposed to explain the tailored dispersion of SWNTs as a functions of applied external stimulus (i.e., pH, temperature). Such stimuli-controlled dispersion of carbon nanotubes could have a variety of applications in nanoelectronics, sensing, and drug and gene delivery systems. Furthermore, this dissertation also contains a published study focused on controlling the dispersion state of carbon black (CB) in epoxy composites using clay.