Purpose:Development of a stability-indicating high-performance liquid chromatography (HPLC) method for pyrimethamine analysis, with subsequent application of that method to assess the 90-day stability of a pyrimethamine suspension compounded from bulk USP-grade pyrimethamine powder, is described. Methods:A stability-indicating method of HPLC with ultraviolet detection specific to pyrimethamine was developed according to pharmacopeial recommendations and validated. The method was applied to investigate the stability of a 2-mg/mL pyrimethamine suspension in a vehicle consisting of Ora-Plus and Ora-Sweet (Perrigo) over a period of 90 days. Three replicate test preparations were stored at room temperature or refrigerated at 4.3–5.2 °C, and samples were analyzed in duplicate immediately after preparation and on study days 1, 2, 4, 7, 10, 14, 21, 30, 48, 60, 75, and 90. Results:The 2-mg/mL suspension of pyrimethamine in Ora-Plus and Ora-Sweet retained 90–110% of the labeled potency to 90 days at both temperature ranges. However, color changes in the samples stored at room temperature observed at day 60 indicated that a beyond-use date less than 90 days from the preparation date should be specified when the suspension is to be stored at room temperature. Conclusion:The study demonstrated that USP-grade pyrimethamine powder can be formulated as a 2-mg/mL suspension in a vehicle of Ora-Plus and Ora-Sweet and is stable when stored at room temperature and when refrigerated, in amber plastic bottles, for 48 and 90 days, respectively.

La relation scalaire entre contrainte et déformation obtenue par le cisaillement simple dans les rhéomètres classiques n'est pas assez riche pour décrire les écoulements complexes. Pour obtenir plus d'information, nous superposons deux écoulements orthogonaux en utilisant la géométrie plan-plan. Le fluide, sous forme cylindrique, peut alors être cisaillé par la rotation mais aussi écrasé par le rapprochement (ou étiré par l'éloignement) des disques. Nous détaillons les calculs théoriques permettant de déterminer les liens entre contraintes et taux de cisaillement et les efforts et vitesses macroscopiques associés. Ensuite, nous décrivons précisément le dispositif expérimental mis en place pour imposer toutes sortes d'écoulements combinant des cisaillements stationnaires ou oscillants, en rotation ou en écrasement. Puis nous présentons les résultats de la comparaison entre l'écoulement de rotation et l'écoulement d'écrasement. Nous présentons enfin les expériences de superposition des deux écoulements. Nous créons des écoulements complexes et divers afin, entre autres, de mesurer et comprendre la loi d'écoulement 3D et le critère d'écoulement 3D des fluides à seuil

Augmenter la durée de vie des piles à combustible de type SOFC en abaissant leur température de fonctionnement tout en maintenant un prix de fabrication raisonnable est un des enjeux du secteur énergétique. Ces travaux de recherche entrent dans ce cadre par l'utilisation de la projection plasma de suspensions pour fabriquer des couches céramiques ou cermets finement structurées sur support métallique poreux. Dans cet objectif, la compréhension du procédé s'est avérée être une étape indispensable. A cette fin l'utilisation de la Vélocimétrie par Image de Particules spécialement adaptée aux contraintes de la projection plasma a permis une meilleure caractérisation des jets injectés mais aussi une compréhension plus poussée des phénomènes régissant le traitement des particules. Fort de ces informations, les couches composant le cœur de pile ont été élaborées : l'anode et l'électrolyte, constituée respectivement d'un cermet nickel-zircone yttriée et de zircone yttriée et enfin la cathode composée d'un conducteur mixte La2NiO4.

Actuellement, les industries cimentières utilisent des polymères, appelés superplastifiants, pour faciliter la mise en place des pâtes de ciment. Cependant, ces suspensions, en présence de superplastifiants, deviennent souvent instables et sédimentent. Nous avons montré que l'utilisation de polymères thermoassociatifs permet en changeant la température, de préparer des suspensions qui d'une part ne sédimentent pas et de l'autre ont un faible seuil d'écoulement. Les données rhéologiques ont été corrélées avec des mesures d'adsorption du polymère sur les particules de ciment. . Nous avons ainsi pu prouver que la partie du polymère thermoassociatif active dans l'épaississement était celle qui était adsorbé à la surface des particules. Une autre partie de cette thèse consistait à utiliser des systèmes modèles (particules de silices monodisperses et bidiperses, quartz) afin d'obtenir une meilleure compréhension du comportement rhéologique des pâtes de ciment sans ou en présence de polymère.

L'impact du confinement sur diverses propriétés des polymères demeure le centre de beaucoup de recherches depuis plus d'une décennie. En particulier, la dynamique et la transition vitreuse (Tg) de divers polymères se trouvent modifiées par le nanoconfinement. Dans cette thèse, nous étudions la dynamique des polymères confinés dans les nanoparticules. On s'est penché à déterminer tout d'abord l'effet de la proximité dans un système de mélange de polymères dans lequel on sera capable de contrôler et caractériser la structure et la morphologie de confinement d'inclusions de polystyrène dispersées dans une autre matrice PBMA réticulée. On constate que le comportement de la dynamique des nanoparticules PS est affecté par la dynamique de la matrice PBMA qui les entoure. Dans le cas du polystyrène confiné dans les nanoparticules sur substart, on constate une réduction de Tg très claire quand il s'agit de particules individuelles. Cependant, cette réduction peut être totalement inhibée lorsque un contact de 6 entre particules prend lieu.

Today's product development process should be rapid andcost-efficient, and should result in innovative and reliableproducts. A crucial factor is the dynamic behaviour of theproduct. This thesis focuses on theoretical, numerical andexperimental approaches to achieve a comprehensiveunderstanding of dynamical phenomena occurring in nonlinearproducts, especially in products with parts that includeimpacts. The aim is to show the usefulness of nonlineartheories to better understand and optimise the dynamicbehaviour of products and thereby account for nonlinearphenomena already in the product development process. This is achieved through an investigation of researchefforts in the field of nonlinear dynamics; identification ofimportant research directions; a study on the effect ofcouplings between nonlinear parts; a detailed study on thedynamic behaviour of a product component; investigations oflow-cost strategies for controlling the dynamics of a nonlinearsystem; and the design and implementation of experimentalset-ups of two studied products. The investigation of research efforts shows that nonlinearparts are frequently included in products. Most common areparts that are nonlinear due to impacts and friction. Twoimportant areas are identified; to study coupling effectsbetween nonlinear subsystems and to study how nonlinearanalysis can be used to improve existing designs. Considering the studied products; a pantograph on a trainand a Braille printer, it can be concluded that thecharacteristics of a part can largely affect the dynamicbehaviour of the product. Typical nonlinear behaviour, such ascoexisting solutions and irregular motions, do occur. Theanalysis of the pan- tograph motion shows important aspects toconsider in the modelling process; coupling effects. In thecase of the Braille printer it is shown possible to create alow-cost control, by taking advantage of an existingdiscontinuity, to achieve a desired motion. Altogether, this work contributes to improved understandingof the be- haviour of nonlinear parts in products, especiallythose including impacts, pro- viding greater knowledge aboutaspects to consider in the design process. Keywords:Nonlinear Dynamics, Impacts, Discontinuities,Subsystems, Chaos, Irregular Behaviour, Printer Dynamics,Suspensions, Coupled Systems, Control. / QC 20100621

<p>This thesis will investigate previously unexplored concepts in magnetic manipulation including controlling the assembly of magnetic and nonmagnetic particles either in bulk fluid or near a substrate. Both uniform glass interfaces and substrates with magnetic microstructures are considered. The main goal of this work is to discuss new strategies for implementing magnetic assembly systems that are capable of exquisitely controlling the positions and orientations of single-component as well as multi-component particle suspensions, including both magnetic and non-magnetic particles. This work primarily focuses on controlling spherical particles; however, there are also several demonstrations of controlling anisotropically shaped particles, such as microrods and Janus colloids. </p><p> Throughout this work, both conventional magnetophoresis and inverse magnetophoresis techniques were employed, the latter relying on ferrofluid, i.e. a suspension of magnetic nanoparticles in a nonmagnetic carrier fluid, which provides a strong magnetic permeability in the surrounding fluid in order to manipulate effectively non-magnetic materials. In each system it was found that the dimensionless ratio between magnetic energy and thermal energy could be successfully used to describe the degree of control over the positions and orientations of the particles. One general conclusion drawn from this work is that the ferrofluid can be modeled with a bulk effective permeability for length scales on the order of 100 nm. This greatly reduces modeling requirements since ferrofluid is a complex collection of discrete nanoparticles, and not a homogenous fluid. It was discovered that the effective magnetic permeability was often much larger than expected, and this effect was attributed to particle aggregation which is inherent in these systems. In nearly all cases, these interactions caused the ferrofluid to behave as though the nanoparticles were clustered with an effective diameter about twice the real diameter.</p><p> The principle purpose of this thesis is to present novel systems which offer the ability to manipulate and orient multi-component spherical or anisotropic particle suspensions near surfaces or in the bulk fluid. First, a novel chip-based technique for transport and separation of magnetic microparticles is discussed. Then, the manipulation of magnetic nanoparticles, for which Brownian diffusion is a significant factor, is explored and modeled. Parallel systems of nonmagnetic particles suspended in ferrofluid are also considered in the context of forming steady state concentration gradients. Next, systems of particles interacting with planar glass interfaces are analyzed, modeled, and a novel application is developed to study the interactions between antigen-antibody pairs by using the self-repulsion of non-magnetic beads away from a ferrofluid/glass interface. This thesis also focuses on studying the ability to manipulate particles in the bulk fluid. First, simple dipole-dipole aggregation phenomenon is studied in suspensions of both nonmagnetic polystyrene particles and endothelial cells. For the sizes of particles considered in these studies, currently accepted diffusion limited aggregation models could not explain the observed behavior, and a new theory was proposed. Next, this thesis analyzed the interactions that exist in multi-component magnetic and nonmagnetic particle suspensions, which led to a variety of novel and interesting colloidal assemblies. This thesis finally discusses the manipulation of anisotropic particles, namely, the ability to control the orientation of particles including both aligning nonmagnetic rods in ferrofluid as well as achieving near-holonomic control of Janus particles with optomagnetic traps. General conclusions of the viability of these techniques are outlined and future studies are proposed in the final chapter.</p> / Dissertation

Interparticle interactions determine the microstructure, stability, rheology, and optical properties of concentrated colloidal suspensions involved in paint, paper, cosmetic, and pharmaceutical industries, etc. Frequency domain photon migration (FDPM) involves modeling the photon transport in a multiple scattering medium as a diffusion process in order to simultaneously determine isotropic scattering and absorption coefficients from measured amplitude attenuation and phase shift of the propagating photon density wave. Using FDPM, we investigated the impact of electrostatic interaction upon the optical properties and structure of dense charged suspensions. We demonstrated that electrostatic interactions among charged polystyrene latex may significantly affect the light scattering properties and structure of dense suspensions at low ionic strength (<0.06 mM NaCl equivalent) by actual FDPM measurement. We showed that the structure factor models addressing electrostatic interaction can be used to describe the microstructure of charged suspensions and quenched scattering due to electrostatics, and demonstrated that FDPM has the potential to be a novel structure and surface charge probe for dense suspensions. We also showed that the FDPM measured isotropic scattering coefficients may respond to the change in effective particle surface charge, and displayed the potential of using FDPM for probing particle surface charge in concentrated suspensions. We presented that the interference approximation implies a linear relationship between the absorption coefficient and volume fraction of suspension. We illustrated that FDPM measured absorption coefficient varies linearly with suspension volume fraction and affirmed the interference approximation from a perspective of light absorption. The validation of the interference approximation enables us to develop the methodology for estimating absorption efficiencies and imaginary refractive indices for both particles and suspending fluid simultaneously using FDPM. We further demonstrated a novel application of FDPM measured absorption coefficients in determining pigment absorption spectra, and displayed the potential of using FDPM as a novel analytical tool in pigment and paint industry.

The studies of the dynamics, phase behavior, interparticle interactions, and hydrodynamics of stimuli-responsive pNIPAm-co-AAc microgels were described in this thesis. Due to their responsiveness to external stimuli, these colloidal particles serve as excellent model systems to probe the relationship between colloidal interactions and phase behavior. As a first step, we established our core experimental methodology, by demonstrating that particle tracking video microscopy is an effective technique to quantify various parameters in colloidal systems. Then we used the technique in combination with a microfluidic device that provides in situ control over sample pH to probe the phase behavior of pNIPAm-co-AAc microgel suspensions. In essence, the experimental set-up enables changes in effective particle volume fractions by changing pH, which can be used to construct the phase diagram. In order to explain the unique features of the microgel phase diagram, we measured the underlying pairwise interparticle potential of pNIPAm-co-AAc microgels directly in quasi-2D suspension and proved that the interactions are pH dependent and can range from weakly attractive to soft repulsive. Finally, the hindered Brownian diffusion due of colloidal particles confined by hard walls was investigated systematically and striking differences between hard sphere and soft sphere were found, with soft pNIPAm-co-AAc microgels showing surprising mobility even under strong confinement.

Thermal properties of complex suspension flows are investigated using numerical computations. The objective is to develop an efficient and accurate computational method to investigate heat transport in suspension flows. The method presented here is based on solving the lattice Boltzmann equation for the fluid phase, as it is coupled to the Newtonian dynamics equations to model the movement of particles and the energy equation to find the thermal properties. This is a direct numerical simulation that models the free movement of the solid particles suspended in the flow and its effect on the temperature distribution. Parallel implementations are done using MPI (message passing interface) method. Convective heat transfer in internal suspension flow (low solid volume fraction, φ<10%), heat transfer in hot pressing of fiber suspensions and thermal performance of particle filled thermal interface materials (high solid volume fraction, φ>40%) are investigated. The effects of flow disturbance due to movement of suspended particles, thermo-physical properties of suspensions and the particle micro structures are discussed.