The diffu~ion and permeation of aviation fuel (Avtur) and water in commercial and 'model' polysulphide sealants have been studied using simple gravimetric techniques. For Avtur, the mass uptake behaviour is explicable in terms of normal, Fickian diffusion, and the diffusion coefficient determined has been found to be independent of the experimental method and concentration of the liquid. Water, however, exhibits anomalous diffusion behaviour. Mass uptake by the polysulphides is high and equilibrium is not reached after several months. There is no correlation between the results of permeation, absorption and desorption experiments except at low water concentration ... ,,~ . These anomalies have been explained in terms of the formation of water droplets within the rubber. This study shows that the amount of water absorbed is dependent upon the amount and nature of the curing agent residues. The results have been analysed in terms of the osmotic and water vapour pressure and two equations have been derived which satisfactorily predict the amount of water absorbed at equilibrium. It has been shown that the effect of the water droplets on permeation is negligible, and hence the diffusion coefficient found is a measure of the true rate of diffusion. In contrast, the effect of the droplets on mass uptake experiments is large and the apparent overall diffusion rate is greatly reduced. The apparent diffusion coefficient found is dependent upon the water concentration and the concentration of the water-soluble impurities. An equation has been derived showing the relationship between these variables. The results of this work show that the elastic strength of the rubber has negligible effect in determining the water uptake at equilibrium and the apparent diffusion coefficient. However, deterioration in adhesive and cohesive strength occurs with water uptake. At high uptake some of this loss is irreversible. The deterioration in properties is mainly due to breakage of weak physical bonds and plasticisation effects. -

No description available.

The purpose of this work was to investigate the effects of structure, humidity and aging on the mechanical behavior of Nafion® and Dais® ionomers. It was determined that the majority of the properties of these membranes were controlled by the formation and growth of the ionic clusters that were the direct result of the ionic nature of these materials. In the process of this study, the properties of Nafion® and sulfonated Dais® polymers were investigated by dynamic mechanical analysis and thermal gravimetric analysis and their water uptake and sorption and desorption isotherms were measured. A mastercurve and a shift factor plot were constructed for 60% sulfonated Dais® membrane. It was determined that an increase in the degree of sulfonation raised the glass transition temperature of these materials by facilitating the formation of the ionic clusters which acted as physical crosslinks, thereby reducing the mobility of polymeric chains. Water was found to effectively plasticize the membranes, especially in the case of Dais® materials, by reducing the storage modulus and decreasing the structural integrity of the ionomers. The effect of pre-treatment of Nafion® was investigated and the glass transition temperature was found to increase as a function of the severity of the treatment procedure. The maximum water uptakes were determined for virgin and aged Nafion® and Dais® membranes and their vapor phase water sorption diffusion coefficients were calculated. The sorption process was found to follow pseudo-Fickian behavior, while the movement of water out of the membranes during the desorption process was determined to be controlled by mechanisms other than diffusion. Lastly, the effect of exposure of Nafion® and 30% sulfonated Dais® membranes to the saturated environment at elevated temperatures was investigated and found to result in the increase in the glass transition temperature of the materials. Results of the exposure effects on the diffusion properties of Nafion® and Dais® were inconclusive. Preliminary findings attributed the changes in the properties of the materials to the counteractive actions of physical aging and the growth of the ionic clusters. / Master of Science

Au cours des 30 dernières années, d'importants progrès ont été faits dans le domaine de l'oncologie. Les cancers pédiatriques ont été les grands bénéficiaires des progrès des thérapies anticancéreuses et aujourd'hui, le cancer de l'enfant peut être soigné, dans les pays développés, dans 75 à 80% des cas. Cependant, ces thérapies sont connues pour leurs effets gamétotoxiques, et seulement 33 % des garçons qui ont survécu à leur cancer durant l'enfance produisent du sperme de bonne qualité une fois arrivé à l'âge adulte. Actuellement, la seule mesure de préservation envisageable pour ces enfants est de procéder à un prélèvement et à une cryoconservation de tissu testiculaire. Aujourd'hui, il est donc important de mettre au point un procédé capable de produire des spermatozoïdes à partir de tissus testiculaire dans le but de restaurer leur fertilité. Pendant plusieurs décennies, les biologistes de la reproduction ont essayé de développer une technologie pour accomplir in vitro la spermatogenèse chez les mammifères. Malgré des investissements importants dans la recherche, aucune méthode n'a permis de reproduire in vitro l'ensemble de ce processus chez l'homme. Dans cette étude, la société de biotechnologie Kallistem a développée, en collaboration avec des partenaires académiques incluant le laboratoire Ingénierie des Matériaux Polymères (projet ARTIS financé par la Canceropôle Lyon Auvergne Rhône-Alpes) un système de culture tridimensionnel constitué d'un hydrogel de chitosane capable de réaliser in vitro l'ensemble de la spermatogenèse chez différents mammifères incluant l'homme. Le système de culture 3D est un hydrogel physique de chitosane sous forme de tube obtenu après neutralisation d'une solution aqueuse de chitosane, sans aucun agent réticulant. Avantageusement, le tissu testiculaire est confiné dans la lumière du tube ce qui permet de conserver l'architecture 3D in vivo des tissus. L'influence de plusieurs paramètres structuraux du chitosane et de paramètres liés au procédé d'élaboration sur la microstructure, les propriétés mécaniques et de diffusion des hydrogels a été évaluée, dans le but d'optimiser la capacité du système de culture à assurer la survie et la différentiation cellulaire / During the past 30 years, huge progress has been performed in the field of oncology. In particular, pediatric cancers have been the beneficiaries and can now achieve cure rates of 75-80% in developed countries. However, cancer therapies are known for their gametotoxic effects and only 33% of male children who have survived cancer during childhood produce sperm of normality quality when they are adults. Currently, the only feasible conservation protocol for these boys is to make a collection and cryopreservation of their testicular tissue. There is thus a need to provide a process enabling to produce spermatozoa starting from testicular tissue in order to restore fertility. For several decades, reproductive biologists have been trying to develop a technology to achieve spermatogenesis in vitro in mammals. Despite sustained investment in research, no method has now reproduced in vitro this entire process in humans. In this work, Kallistem (Biotech Company) has developed, in collaboration with academic laboratories including “Polymer Materials Engineering” laboratory (project ARTIS financed by the Cancéropôle Lyon Auvergne Rhône-Alpes) a 3D culture system made of chitosan hydrogel enabling to make a complete spermatogenesis in vitro in several mammals including human. The 3D culture system is a tube of chitosan physical hydrogel obtained from neutralization of aqueous chitosan solution, without any external cross-linking agent. Advantageously, the testicular tissue is confined in the lumen of tube which enables to reproduce in vivo 3-dimensional architecture. The impact of several material and processing parameters on microstructure, mechanical and diffusion properties of resulting hydrogels was evaluated, in order to optimize the culturing and maturation ability of 3D culture system

Ce travail de thèse parti de l'observation que la maintenance des fonctions cellulaires est basée sur l'orchestration précise d'interactions fonctionnelles entre biomolécules telles que l'ADN, l'ARN et les protéines. Bien que ces processus basiques ne montrent pas généralement une organisation spatiale stricte, ils semblent néanmoins contraints par des schémas dynamiques ou spatiaux précis. Cela pose ainsi la question des forces pouvant, dans un microenvironnement cellulaire, diriger les différents acteurs de processus biochimiques complexes au bon endroit, au bon moment et dans le bon ordre afin d'assurer les fonctions cellulaires essentielles. L'existence de forces sélectives à longue portée de nature électromagnétique, pouvant être responsables de l'extraordinaire efficacité des machineries biomoléculaires, est prédite par la mécanique quantique et l'électrodynamique; par longue portée, nous entendons entre 0.1 à 1 micron, ce qui est bien au delà de celle des forces traditionnelles reconnues comme les forces électrostatiques, de van der Waals-London ou les liaisons hydrogènes. Aucune procédure expérimentale ne fut proposée à ce jour pour confirmer ou infirmer cette hypothèse d'une utilisation efficace de telles forces électromagnétiques dans la matière vivante. Si ces forces sélectives de recrutement à longue portée sont effectivement actives au niveau biomoléculaire, cela constituerait un pas important vers une compréhension des processus et mécanismes cellulaires fondamentaux (expression génique, division cellulaire, signalisation, etc.). / The main subject of the present thesis work stems from the observation that the maintenance of cell functions is based on a precise orchestration of functional interactions between biomolecules such as DNA, RNA and proteins. Although these basic processes generally do not exhibit strict spatial organization, they seem constrained into a very accurate temporal - or dynamic - pattern. This raises the question of what types of physical forces can, in the cellular microenvironments, bring the various actors of complex biochemical processes both in the right place, at the right time and in the right order so as to ensure the essential cellular functions. The existence of selective, long-range forces of electromagnetic nature that may be responsible for the extraordinary efficiency of the biomolecular machineries is predicted by quantum mechanics and electrodynamics ; long-range meaning here of the order of 0.1-1 micron, well beyond the traditionally recognized forces, electrostatic ones, hydrogen bonds, van der Waals-London, etc.). Yet, to date, no experimental test has been proposed to disprove or confirm the hypothesis of an effective exploitation of such electromagnetic forces in living matter. If these selective, long-range recruitment forces were found to be active at the biomolecular level, this would represent an important step forward to the understanding of fundamental cellular processes and mechanisms (gene expression, cell division, signalling, etc.).