The motions of particles dispersed in liquid crystals can be influenced by the application of an electric field, the effect depending on the field frequency and field amplitude. Sandwich cells under the application of electric field are widely used as the tool in order to investigate the fundamental research relating to electro-optic display technology. Therefore, the aim of this experimental work is to find and investigate novel motion of the particles dispersed in the liquid crystal phases, held within a sandwich cell. For the liquid crystal–particle systems in the sandwich cells in this thesis, the particle shapes, temperature and cell geometry are all shown to have an influence on the regime of the particle’s motions, with different phenomena observed using three different phases of liquid crystals. The experiments are designed to find and investigate the novel motion of the micron sized silica particles in the liquid crystal phases. In the chiral nematic phase, spherical particles are shown to exhibit linear motion, which is related to the electrophoretic mobility. Such spherical particles are also observed to show circular motion which is found to have a field dependency that can be related to Quincke rotation. A maximum frequency for motion occurs which is found to possibly be related to the effect of the ion diffusion in the liquid crystal-particle composite system. The direction of the circular motion is found to be independent of the handedness of the chiral nematic material. In the isotropic phase of a chiral nematic liquid crystal, the spherical particles do not exhibit any linear motion, which shows the system does not follow the traditional electrophoresis observed in normal isotropic liquids. The circular motion of the spherical particle that is observed in the isotropic phase is analysed in terms of the Quincke rotation and again shows the Maxwell relaxation time. The electric-field induced motion of elongated particles in four different nematic systems is examined. In this case of planar aligned systems, linear motion is observed, in which the velocity shows a minimum for particles of the same length as the cell gap. A novel field-induced defect texture appears in the homeotropic device containing a nematic liquid crystal of negative dielectric anisotropy. Interestingly, the motion of the particle is found to be strongly coupled with the defects formed.

The spectrum of 1,3-dichloro-2-ethenylbenzene partially oriented in nematic liquid crystalline solvents has been analysed using a number of complimentary nuclear magnetic resonance (NMR) techniques. The analysis of this spectrum poses a considerable problem due to its complexity and the uncertain geometry and orientation of the molecule. The technique of multiple quantum NMR (MQNMR) has the capability of tremendously simplifying complex spectra. The multiple quantum spectrum was measured and proved very useful in the analysis but unavoidable resolution difficulties in the MQNMR experiment prevented a complete solution of the problem using this spectrum alone. While the spectrum of 1,3-dichloro-2-ethenylbenzene is dominated by only a few large interactions, the lines are split by relatively small dipolar couplings and the limited resolution available in the multiple quantum spectrum makes the determination of the smaller couplings difficult. To overcome this difficulty a frequency selective excitation of the multiple quantum spectrum was adapted and developed. After testing the experiment on the relatively simple spectrum of 1,1,2-trichloroethane dissolved in a nematic solvent, this selective experiment was applied to the much more complex spectrum of 1,3-dichloro-2-ethenylbenzene where it proved capable of directly measuring the small couplings in the spectrum without interference from any of the larger interactions. This information contributed greatly to the eventual analysis of the spectrum. MQNMR experiments can be very time consuming and as a result the spectroscopist must frequently make do with very limited time domain signals from which the spectrum must be extracted. This creates a number of difficulties when the signals are analysed with the fast Fourier transform (FFT), the standard method of spectral analysis used in NMR. With these problems in mind, the suitability of MQNMR time domain signals for analysis by a method of spectral estimation due to Burg, commonly called the maximum entropy method (MEM), was examined. By testing Burg's MEM with the MQNMR spectra of a number of different solutes partially oriented in nematic phases, it was found to be a useful adjunct to the FFT when dealing with MQNMR interferograms. While some care is required in its application, this method of spectral analysis should find important uses in the estimation of MQNMR spectra. Solution of the spectrum yielded information on the molecular geometry and the orientation of the 1,3-dichloro-2-ethenylbenzene in the nematic solvents used. While an extensive analysis of molecular geometry proved impossible, the information on molecular orientation was examined in terms of two different models. The orientation data shows excellent agreement with a recently developed model for orientation based upon the shape of the solute. / Science, Faculty of / Chemistry, Department of / Graduate

This thesis presents a review of the theories currently being used to describe the structure of the liquid-vapor interface. The fluids considered are those consisting of "argon-like" molecules, which have radially symmetric potentials. "Wall effects" upon the interface are assumed to be negligible. The derivations of several theories have been recast into forms which depend upon a few common principles. The technique of functional differentiation is extensively used in this regard. This allows each theory to be identified with one of three different approaches: mean-field theory, integro-differential equations, or fluctuation theory. Good agreement is found between the results of theories within each class. The three approaches are shown to be different aspects of a single consistent model of the liquid-vapor interface. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The objective of this investigation was to develop quantitative isocratic HPLC methods for the analysis of digoxin and digitoxin. An HPLC system that employs a reverse-phase column, UV detection at 220 nm and solvent systems consisting of various proportions of water, methanol, isopropanol and dichlormethane was developed for the separation of digoxin, digitoxin and their potential degradation products and metabolites. HPLC separations of the above compounds by isocratic, solvent switchover and gradient elution modes were carried out in chromatographic times of 27, 16 and 13 minutes, respectively. For purposes of monitoring the separation of dihydro metabolites of digoxin, a 100% fluid recovery system was developed for use in the HPLC analysis of digoxin and its metabolites after fluorogenic post-column derivatization using the air-segmentation process. As an evidence of selectivity, the isocratic HPLC systems were utilized for the separation of a mixture of ten closely related steroids and the isolation of digitoxin from Digitalis purpurea leaf. The isocratic HPLC systems were found to be applicable for the quantitative analysis of digoxin and digitoxin in their respective dosage forms. The HPLC assay of digoxin and digitoxin dosage forms was carried out in less than forty-five minutes. These methods were found to be precise, accurate, sensitive enough for single tablet assay, and capable of simultaneously monitoring the potential degradation products or metabolites of digoxin and digitoxin. A comparison of the assay of digoxin and digitoxin dosage forms by HPLC and USP methods indicated that: (a) the precision and accuracy of both methods were comparable and within acceptable limits; (2) analysis by HPLC can be completed in less than forty-five minutes whereas the USP methods require over four hours; and (3) the HPLC methods have the advantages of higher sensitivity, selectivity and simplicity over the USP methods. The HPLC methods were used for the stability study of digoxin and digitoxin in their respective dosage forms. Lanoxin and digitoxin tablets were found to be stable under all the conditions of storage used in this study. Natigoxin tablets, Lanoxin injection and elixir were found to be subject to varying degrees and patterns of degradation. On the basis of the stability results it was observed that the assortment of pathways that may be involved at different conditions and times of storage'would make it difficult to estimate digoxin shelf-life from data obtained by accelerated aging. From the results of this investigation, it was concluded that the isocratic HPLC methods were suitable for the assay of digoxin and digitoxin dosage forms as well as for purposes of stability testing and simultaneous monitoring of degradation products or metabolites. This abstract represents the true contents of the thesis submitted. / Pharmaceutical Sciences, Faculty of / Graduate

L’augmentation permanente des densités de flux de chaleur mises en jeu, en contexte aéronautique notamment, et l’évacuation de celles-ci, constitue actuellement une problématique majeure pour les industriels du secteur. Les solutions de refroidissement utilisées jusqu’à aujourd’hui ne suffisent plus à assurer la tenue thermique de ces systèmes, nécessitant l’apport de nouveaux moyens. A ce titre, parmi les solutions existantes, le caloduc oscillant suscite un intérêt croissant de part ses nombreux avantages, comparé aux systèmes diphasiques classiques. C’est pourquoi le projet Optimal, dans lequel s’inscrivent ces travaux de thèse, se propose d’employer cette technologie dans le but d’optimiser le refroidissement de nouvelles turbomachines électriques. Le principe de fonctionnement du caloduc oscillant, simple au demeurant, recèle néanmoins des aspects encore peu maîtrisés. Cette thèse a donc pour objectif, d’une part, d’évaluer les performances d’un tel système dans ce contexte industriel et, d’autre part, d’apporter de nouveaux éléments visant à accroître la compréhension de son fonctionnement, par des moyens expérimentaux mais également numériques.Pour se faire, l’étude expérimentale réalisée au cours de ce projet a consisté au développement d’un prototype, à partir duquel des campagnes d’essais ont été effectuées. Ces essais ont permis de caractériser les performances du système au travers d’investigations paramétriques (fluide de travail, taux de remplissage, inclinaison, puissance injectée, température de source froide, boucle ouverte ou fermée). Il a ainsi pu être observé une amélioration évidente des performances plus spécifiquement sous certaines conditions opératoires, mais également des comportements particuliers liés au fonctionnement de ce système. A cette approche expérimentale s’ajoute une étude théorique basée sur le développement d’un modèle numérique. Face à la complexité des mécanismes thermo-physiques régissant le fonctionnement du caloduc oscillant, ce modèle s’intéresse à un système simplifié, caractérisé par le déplacement d’un système bulle de vapeur, bouchon liquide, dans lequel un film liquide déposé en aval est soumis à une évaporation. Le but ultime étant à terme de décrire précisément la dynamique de ce film liquide, ce modèle a conduit dans le cadre de cette thèse à mettre en évidence l’ensemble des phénomènes physiques associés à l’évaporation en film dans un tube capillaire, et d’établir une cartographie des domaines d’utilisation de ce modèle selon les hypothèses considérées, pour une utilisation ultérieure liée à l’identification expérimentale des paramètres de ce film. / The continuous increase of heat flux densities involved in aeronautic context, and their evacuation, represent a major issue nowadays. The solutions used until now are no longer sufficient to ensure the thermal maintenance of these systems, requiring new technologies. Among them, the pulsating heat pipe induces a growing interest. Thus, the French FUI project Optimal suggests employing this technology in order to optimize the cooling of new electric turbomachines. The work led in this PhD aims to evaluate the performances of such a system in this context, by experimental and numerical means.The experimental study which has been conducted consisted in the development of a prototype, starting from which experiments have been led. These tests allowed characterizing the thermal performances of the system through parametric investigations. Thereby, it has been observed an obvious improvement of these performances under some operating conditions, but also several particular behaviors. In addition to that approach, one adds a theoretical study based on the development of a numerical model. Given the complexity of the mechanisms governing the pulsating heat pipe’s operation, this model focuses on a simplified system, characterized by the motion of vapor bubble-liquid slug structure, in which a liquid film, deposited downstream, is subjected to evaporation. This model has conducted to highlight the physical phenomena associated to the thin film evaporation in a capillary tube, and to establish a cartography of its applicability fields, according to the considered assumptions.

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A "liquid crystal" is a substance whose properties are intermediate between those of a crystalline solid and an isotropic liquid. The molecules within a liquid crystal are partially ordered, but they are able to translate easily in at least one direction.

Several hydroxy-terminated, low molecular weight polymers were reacted to form esters bearing mesogenic endgroups. The effect of the different repeating unit structures with a common mesogenic unit based on an oxybenzoylterephthalate dyad ester on the formation and properties of liquid crystals was studied by microscopic and thermal analysis techniques. The polymeric glycols used were polyethylene glycols (PEG), polytetramethyl ene glycols (PTMG), polybutadiene glycol (PB), and hydrogenated polybutadiene glycol (HPB) with molecular weight of 650 ^ 6000, in addition to 1 ,12-dodecanediol for the model compound. Conversion of the mesogenic dyad ester to a dyad containing a carboxylic acid group was shown to permit mesophase formation over a wide temperature range. The HPB product of this series was found to be a liquid crystalline elastomer with a low viscosity above the melting point, and with film forming ability. On examining the effect of endgroups on physical properties, it was found that both the length v of mesogen and hydrogen bonding interaction by carboxyl groups proved to be the most important factors to form liquid crystals with the PB and HPB polymers. Texture observation of macroglycol products on a polarizing microscope gave neither sharp T.. (clearing temperature) nor typical pattern of mesomorphic state. This result may be explained on the basis of the low stability of liquid crystal phase. These results were consistent with the differential scanning calorimetry (DSC) measurement that showed isotropic transition endotherms on heating but no peak on cooling. Low molecular weight precursors with liquid crystalline end groups associate to form high molecular weight polymers which resulted in films. Until now physical properties have been poor, but there is a possibility that further research in this area might provide a route to useful polymers which could be adaptable to the RIM process.