The Chfr checkpoint is a point at which a cell checks whether it is safe to enter mitosis. Chfr is a protein that functions at this particular checkpoint to ensure safe entry into mitosis, but the molecular mechanism by which this protein functions is not entirely clear. The hypothesis in this thesis is that Ubc13, Chfr, and Uev1/Mms2 function together in mitosis. The results were observed using immunocytochemistry, the mitotic shake off procedure, Western blot analysis, and coimmunoprecipitation. High Ubc13, Mms2, and Chfr-Ub levels at the interphase-early prophase transition, indicate that these proteins function together at the Chfr checkpoint. Localization of Chfr to decondensed chromatin in interphase cells and to decondensing chromatin in telophase cells indicates a decondensing function for Chfr. Interaction between Chfr and Ubc13, Chfr and phosphorylated histone H3, as well as Ubc13 and phosphorylated histone H3, further indicates that these proteins may function together at the Chfr checkpoint, because phosphorylated histone H3 is a mitotic protein at that particular point in mitosis. Localization of Chfr, Ubc13, and Mms2 to the centrosomes, indicates that they function together at these sites to target substrates important in centrosome maturation, separation, and spindle formation. Furthermore, there are two molecular states of Chfr: Chfr and Chfr-Ub. Chfr is predominant at late prophase, whereas, Chfr-Ub is predominant at interphase-early prophase. Chfr increases in level upon nocodazole exposure at late prophase to counteract the mitotic stress; and it also looses its ubiquitin signal upon passage into mitosis. High Ubc13 and Mms2 levels coincide with high Chfr-Ub levels at the interphase-early prophase transition, indicating that they function together at the Chfr checkpoint. The ubiquitin signal could be either K-48-linked or K-63-linked in nature. The Chfr, Ubc13, and Mms2 protein complex could function through a self ubiquitination-decondensation-Chfr destruction-recondensation mechanism. Chfr could bind to pH3 and its auto-ubiquitin signal to serve as a bulky modification that hinders chromosome condensation.

En mécanique des matériaux et des structures, l'interface entre deux composants matériels ou deux éléments structuraux est traditionnellement et le plus souvent supposé parfaite. Au sens mécanique, une interface parfaite est une surface à travers laquelle le vecteur de déplacement et le vecteur de contrainte sont tous les deux continus. L'hypothèse des interfaces parfaites est inappropriée dans de nombreuses situations en mécanique. En effet, l'interface entre deux corps ou deux parties d'un corps est un endroit propice aux réactions physico-chimiques complexes et favorable à l'endommagement mécanique. L'intérêt pour les interfaces imparfaites devient depuis quelques années grandissant avec le développement des matériaux et structures nanométriques dans lesquels les interfaces et surfaces jouent un rôle prépondérant. A partir de la configuration de base où une interphase de faible épaisseur sépare deux phases, ce travail établit trois modèles d'interface imparfaite généraux qui permettent de remplacer l'interphase par une interface imparfaite dans les cas de la conduction thermique, de l'élasticité linéaire et de la piézoélectricité sans perturber les champs en questions à une erreur fixée près. La dérivation de ces modèles est basée sur le développement de Taylor et sur une approche originale de géométrie différentielle indépendante de tout système de coordonnées. Les trois modèles généraux permettent non seulement de mieux appréhender certains modèles phénoménologiques d'interface imparfaite mais aussi de décrire les effets d'interface que les modèles existants ne sont pas en mesure de prendre en compte. Les modèles d'interface imparfaite établis sont appliqués dans la détermination des propriétés effectives thermiques, élastiques et piézoélectriques d'un matériau composite constitué d'une matrice renforcée par des particules ou fibres enrobées d'une interphase. La méthode utilisée pour rendre compte des effets des interfaces imparfaites sur les propriétés effectives repose sur une condition d'équivalence énergétique qui ramène un matériau hétérogène avec interfaces imparfaites à un matériau hétérogène avec interfaces parfaites

Analytic and computational micromechanics techniques based on the composite cylinders method and the finite element method, respectively, have been used to determine the effective coefficient of thermal expansion (CTE) of carbon nanotube-epoxy nanocomposites containing aligned nanotubes. Both techniques have been used in a parametric study of the influence of interphase stiffness and interphase CTE on the effective CTE of the nanocomposites.  For both the axial and transverse CTE of aligned nanotube nanocomposites with and without interphase regions, the computational and analytic micromechanics techniques were shown to give similar results.  The Mori-Tanka method has been used to account for the effect of randomly oriented fibers.   Analytic and computational micromechanics techniques have also been used to assess the effects of clustering and clustering with interphase on the effective CTE components.  Clustering is observed to have a minimal impact on the effective axial CTE of the nanocomposite and a 3-10%.  However, there is a combined effect with clustering and one of the interphase layers. / Master of Science

Research is presented which encompasses a study of epoxies based on diglycidyl ether of bisphenol A (DGEBA) cured with 2-ethyl-4-methylimidazole (EMI-24) in the presence of the nonionic surfactant Triton X-100. Interest in this epoxy system is due partially to the potential application as a waterborne replacement for solvent cast epoxies in E-glass laminated printed circuit boards. This research has revealed that the viscoelastic behavior of the cured epoxy is altered when serving as the matrix in a glass composite. The additional constraining and coupling of the E-glass fibers to the segmental motion of the epoxy matrix results in an increased level of viscoelastic cooperativity. Current research has determined that the cooperativity of an epoxy/E-glass composite is also sensitive to the surface chemistry of the glass fibers. Model single-ply epoxy/E-glass laminates were constructed in which the glass was pretreated with either 3-aminopropyltriethoxysilane (APS) or 3-glycidoxypropyltrimethoxysilane (GPS) coupling agents. Dynamic mechanical analysis (DMA) was then used to create master curves of the storage modulus (E') in the frequency domain. The frequency range of the master curves and resulting cooperativity plots clearly varied depending on the surface treatment of the glass fibers. It was determined that the surfactant has surprisingly little effect in the observed trends in cooperativity of the composites. However, the changes in cooperativity due to the surface pretreatment of the glass were lessened by the aqueous phase of the waterborne resin. Moisture uptake experiments were also performed on epoxy samples that were filled with spherical glass beads as well as multi-ply laminated composites. No increases in the diffusion constant could be attributed to the surfactant. However, the surfactant did enhance the final equilibrium moisture uptake levels. These equilibrium moisture uptake levels were also sensitive to the surface pretreatment of the E-glass. / Ph. D.

The interphase is a localized region adjacent to a manufactured inclusion that is surrounded by granular soil. These regions are ubiquitous in civil infrastructure and often are components of large-scale composite systems. The interphase region influences load-deformation behavior of the entire composite system. However, mechanisms that control the mechanical behavior of the interphase region and, in turn, control the composite structure behavior, are not clearly understood. Few relationships exist for predicting interphase behavior from properties of granular materials and the inclusion surface that can be measured in the laboratory. A two dimensional discrete element model of a general interphase system was developed and validated against laboratory data. Numerical experiments are conducted with varying soil to inclusion relative geometry. A new micromechanics-based approach, which utilizes microscopic quantities to explain the mechanics of granular media from a continuum point view, is adopted to investigate the mechanisms that underlie the interphase behavior. It is shown that the grain to inclusion surface relative geometry controls the degree of granular media strength mobilization by controlling development of fabric and contact force anisotropy inside the interphase region. A unique bilinear relationship exists between the mobilized granular media strength and the principal direction of average contact force anisotropy at the interface between the particles touching the surface and the inclusion. These findings suggest the problem is one of contact and can not be solved using purely geometric correlations, as past research presumed. A fundamental mechanism of behavior, long sought in geomechanics problems, is presented. Publications resulting from this research are significant and original contributions to the geoengineering, material science, geophysics and granular physics literature. / Ph. D.

As fiber reinforced polymer matrix composites find greater use in markets such as civil infrastructure and ground transportation, the expectations placed on these materials are ever increasing. The overall cost and reliability have become the drivers of these high performance materials and have led to the disappearance of resins such as bismaleimides (BMI), cyanate esters and other high performance polyimides and epoxys. In their place polymers, such polyester and vinylester have arisen. The reinforcing fiber scenario has also undergone changes from the high quality and performance assured IM7 and AS4 to cheaper and hybrid systems consisting of both glass and low cost carbon. Manufacturing processes have had their share of changes too with processes such as pultrusion and other mass production techniques replacing hand lay-up and resin transfer molding. All of this has however come with little or no concession on material performance. The motivation of the present research has therefore been to try to improve the properties of these low cost composites by better understanding the constituent materials (fiber and matrix) and the region that lies in-between them namely the interphase. In order to achieve this, working with controls is necessary and the present discourse therefore deals with the AS4 fiber system from Hexcel Corporation and the vinyl ester resin, Derakane 441-400 from The Dow Chemical Company. The following eight chapters sum up the work done thus far on composites made with sized fibers and the above mentioned resin and fiber systems. They are in the form of publications that have either been accepted, submitted or going to be submitted to various peer reviewed journals. The sizings used have been poly(vinylpyrrolidone) PVP and Polyhydroxyether (Phenoxy) thermoplastic polymers and G' an industrial sizing material supplied by Hexcel. A number of issues have been addressed ranging from viscoelastic relaxation to enviro-mechanical durability. Chapter 1 deals with the influence of the sizing material on the fatigue response of cross ply composites made with the help of resin infusion molding. Chapter 2 describes the effects of a controlled set of interphase polymers that have the same chemical structure but differ from each other in polarity. The importance of the atomic force microscope (AFM) to view and perform nano-indentations on the interphase regions has been demonstrated. Finally, it attempts to tie everything together with the help of the fatigue response of the different composites. Chapter 3 deals only with the vinyl ester resin and examines the influence of network structure on the molecular relaxation behavior (cooperativity) of the glassy polymer. It also tries to make connections between structural features of the glass and fracture toughness as measured in its glassy state. Chapter 4 extends the results obtained in chapter 3 to examine the cooperativity of pultruded composites made with the different sizings. A correlation between strength and cooperativity is found to exist, with systems having greater cooperativity being stronger. Chapter 5 moves into the area of hygrothermal aging of Derakane 441-400 resin. It looks specifically at identifying a mechanism for the unusual moisture uptake behavior of the polymer subjected to a thermal-spiking environment. This it does by identifying the presence of hydrogen bonding in the resin. Finally, chapters 6 to 8 present experimental and analytical results obtained on PVP K90, Phenoxy and G' sized, AS4/Derakane 411-350 LI vinyl ester composites that were pultruded at Strongwell Inc., on their lab-scale pultruder in Bristol, Virginia. / Ph. D.

Composite durability can be influenced by varying the properties of the fiber/matrix interphase region. One method to modifY the properties of this interphase is through the application of a sizing to the carbon fiber. Recent work at Virginia Tech has shown that polymer-modified interphases can lead to increases by as much as two orders of magnitude in notched fatigue lifetime. In the present work, an apparatus was constructed to uniformly coat carbon fiber tow with water-soluble and dispersible polymers. Few such devices have been developed for use in academic settings because of the processing complexities presented by the aqueous coating system. Due to the high surface tensions of the aqueous solutions, fiber clumping and heterogeneous sizing deposition were major bottlenecks. Our novel process utilizes high tensions, high spreading, and low line speeds to accomplish the sizing step. Each processing independent variable can be continuously monitored and controlled which allowed for statistical correlation to the sizing level and uniformity. The sizing process was shown to satisfy three criteria for quality. 1. The average sizing level or weight percent on the final fiber can be readily controlled to achieve typical target values. 2. Filament clumping as a result of cohesion between corresponding filaments is kept to a minimum. 3. The sizing process must produce fiber with a consistent level of polymer sizing. In addition, characterization techniques for the sized fiber were developed. Pyrolysis in a high temperature nitrogen furnace was developed as a precise technique to ascertain the quantitative sizing level on the carbon fiber. SEM and ESCA were utilized to determine fiber clumping and sizing homogeneity. The sizing process along with the statistical process model and the characterization techniques allow for the precise development of optimal interphase materials that are tailored to meet the performance requirements of the composite consumer. / Master of Science

Graphene nanoplatelets have been introduced into the interphase between electrically insulating glass fibre and polymer matrix to functionalize the traditional composite. Owing to the distribution of network structure of GNPs, the interphase can transfer the signals about various internal change of material. Consequently, due to the novel bio-inspired overlapping structure, our GNPs-glass fibre shows a unique opportunity as a micro-scale multifunctional sensor. The following conclusions can be drawn from present research: • We prepared GNPs solution via a scalable and highly effective liquid-phase exfoliation method. This method produces high-quality, unoxidized graphene flakes from flake graphite. We control the thickness and size of GNPs by varying the centrifugation rate. • A simple fibre oriented capillary flow which can suppress ‘coffee ring’ effect to deposit GNPs onto the curved glass fibre surface. The GNPs form continuous fish scales like overlapping structure. • The electrical conductivity of our GNPs-glass fibre shows semiconductive property. The electrical resistance value scattering and the advancing contact angle value scattering indicate a uniform deposit structure. The uniform overlapping structure is a key factor for higher electrical conductivity compared with our previous work with CNTs. • The contact angles of our GNPs-glass fibre with water indicate that the GNPs are almost unoxidized, so the inert GNPs coating decreases the interfacial shears strength. • A micro scale GNPs-glass fibre sensor for gas sensing is achieved by deposit GNPs onto glass fibre surface. This sensor can be used to detect solvents vapours, such as water, ethanol and acetone. All these vapours work as electron acceptor when reacting with GNPs. The acetone shows the highest sensitivity (45000%) compared with water and ethanol. • The doping-dedoping of GNPs-glass fibres during adsorption-desorption cycles of acetone result in the efficient “break-junction” (GNPs lost electron carrier concentration) mechanism, which provides the possibility to fabricate the electrochemical “switch” in a simple and unique way. • The resistance of our GNPs-glass fibre shows exponential relationship with RH. This is attributed to two points. Firstly, the water vapours show similar exponential adsorption on carbon surface; secondly, the bandgap of GNPs increases with the increase of adsorbed water vapour concentration. • Due to the weak van der Waals interaction when water molecules are adsorbed on GNPs surface, our GNPs-glass fibre shows extreme fast response and recovery time with RH. It is potential for our GNPs-glass fibre being used to monitor the breath frequency. • Utilizing the negative temperature coefficient of GNPs, our GNPs-glass fibre can be used as temperature sensor with a sensing region of -150 to 30 °C. • Through the observed abnormal resistance change at a temperature of about – 18 °C, we discovered a phase change of the trance confined water in graphene layers. Based on the resistance change, we can study the interaction of water and carbon nanoparticles. • The bio-inspired novel overlapped multilayer structure of GNPs coating shows structural colours. Even more, our GNPs-glass fibre can be used to monitor the loading force in the interphase when it is embedded into epoxy resin. • Our GNPs-glass fibre shows an excellent piezoresistive property, the single GNPs-glass fibre shows a larger gauge factor than the commercial strains sensor. • The semiconductive interphase was formed when the GNPs-glass fibre was embedded in polymer matrix. This semiconductive interphase is very sensitive to the deformation of material, therefore, an in-situ strain sensor was manufactured to real-time monitor the microcracks in a composite instead of external sensors. The area of resistance ‘jump’ increase can be seen as the feature area for damage’s early warning. • Monitoring the resistance variation of the single fibre composite was conducted under cyclic loading with progressively increasing the strain peaks in order to further investigate the response of in-situ sensor to the interphase damage process. The deviation of resistance/strain when the stress is larger than 2 % highlights the accumulation of damage, which gives insight into the mechanism of resistance change.

Les études en laboratoires montrent que les propriétés de l'eau liquide sont perturbées lorsqu'elle est proche d'une surface (≈ 1nm) ou occluse dans des pores de taille inférieure à la dizaine de nanomètres : au-delà de ces seuils, ses propriétés sont supposées volumiques. Paradoxalement, des observations de terrains suggèrent que le comportement de l'eau peut s'écarter de son comportement volumique pour des tailles de pores de l’ordre de quelques microns. Nous présentons une étude expérimentale des effets, et de leur portée, d'une surface solide, paroi interne d’une cavité fermée, sur les propriétés vibrationnelles et thermodynamiques de l'eau occluse. D’abord, nous avons développé et calibré une fonction de partition prenant en compte les modes inter- et intramoléculaires de l'eau, afin de convertir ses propriétés vibrationnelles en propriétés thermodynamiques. Cette fonction nous permet de calculer la variation d’enthalpie libre que représente une déviation du spectre IR par rapport au spectre de référence. Des mesures IR dans des canaux ont été réalisées en fonction de leur hauteur, de 100 à 5 nm, qui ont mis en évidence que les propriétés de l'eau sont modifiées entre 5 et 20 nm. Si ces distances restent dans les valeurs admises pour l’influence interfaciale, l’intensité thermodynamique des variations (jusqu’à 1.5 kJ/mol) est surprenante, de même que leur sens de variation : l’activité de l’eau augmente. Le moteur de cette évolution pourrait être la restriction géométrique, et des effets de pression de disjonction. Au contraire, des mesures de micro-spectroscopie IR haute résolution et Raman ont été menée dans des micro-cavités fermées (inclusions fluides synthétiques), en fonction de la distance aux interfaces solide/liquide et liquide vapeur. Elles ont montré que les propriétés de l'eau sont progressivement perturbées sur une distance de 1 à 3 μm. Proche de la surface, la variation thermodynamique est au-delà du kJ/mol d’eau, et traduit une augmentation de l’activité de l’eau. Le moteur de ce qu’on appelle une « interphase », vu son épaisseur, associe la tension de surface solide-solution aqueuse et des effets osmotiques, liés à une stratification chimique de la solution depuis la surface jusqu’au centre de la cavité. D'un point de vue thermodynamique, l’eau confinée et l’eau impliquée dans l’interphase apparaissent plus réactives que l’eau volumique : ces mesures ouvrent donc des perspectives d’interprétation des interactions solide-solution dans les milieux naturels. Quelques applications à des observations sont évoquées. / Laboratory studies shows that water properties are disturbed when it is located close to a surface (≈1nm) or occluded in a pore with size less than ten nanometers: beyond these thresholds, its properties are supposed to be bulk. Paradoxically, field observations suggest that the water behavior can deviate with respect to its bulk one for pore sizes of few microns. We present an experimental study of the effects and the scope of a solid surface, internal wall of closed cavity, on the occluded water vibrational and thermodynamic properties. First, we have developed and calibrated a partition function, that takes into account the water inter- and intramolecular modes, to convert its vibrational properties into its thermodynamic counterparts. This function allows us to calculate the free enthalpy corresponding to an IR spectrum deviation with respect to a reference spectrum. IR measurements were performed in channel in function of their height, from 100 to 5 nm. They highlighted that water properties are modified between 5 and 20 nm. Although these distances are within the accepted values for the interfacial influence, the intensity of thermodynamic variations are surprising, as its variation direction: the water activity increases. This evolution could be drive by the geometrical restrictions and the disjoining pressure effects. On the contrary, high resolution IR and Raman micro-spectroscopies measurements were carried out in closed micro-cavities (synthetic fluid inclusions), in function of the distance to the solid/liquid and liquid/vapor interfaces. They demonstrated that water properties are progressively disturbed on a distance from 1 to 3 μm. Close to the surface, the thermodynamic variation is beyond kJ/mol of water, and reflects an increasing of water activity. The driver of the so-called interphase, because of its thickness, involves the solid-aqueous solution surface tension and osmotic effects, related to a chemical stratification of the solution from the surface to the cavity center. From a thermodynamics point of view, confined water and water in the interphase appear more reactive than bulk water: these measurements offer perspectives for the solid-solution interaction interpretation in the natural media. Some applications of the observations are discussed.

Le travail présenté dans cette thèse est consacré à la précipitation interphase dans les aciers microalliés au vanadium. Il s’agit principalement de mieux comprendre l’évolution des microstructures et des propriétés mécaniques résultantes à partir d’une double approche expérimentale et de modélisation. Les analyses effectuées conjointement en Microscopie Electronique en Transmission et en nanoindentation ont permis de mieux cerner les relations qui existent entre les paramètres microstructuraux de la précipitation interphase (taille moyenne des carbures, distances moyenne entre carbures et entre feuillets, morphologie des carbures) et les modifications de propriétés mécaniques locales induites dans les aciers à très haute résistance. Par ailleurs, nous avons développé un modèle original qui couple les cinétiques de transformation de phases à celle de la précipitation interphase. Ce modèle permet de décrire l’évolution des paramètres microstructuraux et les résultats obtenus sont en très bon accord avec les résultats expérimentaux. / The present thesis gives an overview of carbide aggregates (interphase precipitation and carbide fiber) in vanadium-alloyed steels, covering the aspects of microstructure, modeling, and mechanical properties. The microstructural features of different carbide aggregates by the use of microscopies, and the transition of carbide morphologies is discussed. A new model considering the ledge mechanism as well as austenite decomposition is subsequently proposed according to the observed microstructure. The sheet spacing, particle spacing, and interface velocity, can be calculated and show good agreements with experimental data. Finally, the effect of interphase-precipitated carbide distribution (sheet spacing, particle spacing, and carbide radius) on Orowan strengthening contribution is examined by nano-indentation. By the virtue of small indenter, the mechanical properties of single ferrite grain are able to be extracted.Keyword: