Дисертації з теми "Soft glass"

Envisioning novel fully monolithic fiber-optical devices, this dissertation investigates four fiber optical devices both, active and passive, that contribute to the goal of further integrating and miniaturizing fiber optics. An all phosphate glass fiber laser was designed in an effort to reduce laser intensity noise by reducing cavity losses and low mechanical strength that arise from intra-cavity fusion splices between silica fiber Bragg gratings (FBG) and phosphate active fiber in state of the art phosphate single frequency fiber lasers. Novel phosphate glass based FBGs have been fabricated utilizing high intensity laser pulses at 193 nm and a phase-mask. Net reflectivities of up to 70 % and a bandwidth of 50 pm have been achieved in the FBGs. The laser design comprised two of the novel FBGs and a short section of Er³⁺Yb³⁺ phosphate fiber to form a distributed Bragg reflector (DBR) laser. The performance of the new laser has been compared to a conventional phosphate fiber laser. Particular focus was put on the laser intensity noise due to its dependence on intra-cavity losses. Relative intensity noise (RIN) amplitudes of -80 dB/Hz have been measured for both lasers when operating at comparable output powers. For similar levels of absorbed pump power the relaxation oscillation frequencies (ROF) were shifted towards lower frequencies in the new laser. ExcessFBG scattering losses and mode-field miss-match between the active and passive fiber limited the output power of the new laser to 16 mW compared to 140 mW in the conventional laser. A monolithic all-phosphate glass fiber laser with up to 550 mW output power that is operating at a single longitudinal mode and exhibiting narrow linewidth is presented. The laser cavity has been formed by inscribing FBGs directly into heavily Er³⁺Yb³⁺ doped phosphate glass fiber using femtosecond laser pulses and a phase mask, completely eliminating the need for intra-cavity fusion splices. A linewidth of less than 60 kHz and relaxation oscillation peak amplitudes below -100 dB/Hz without active suppression of RIN have been measured. The compact form factor and higher output power combined with the low noise and narrow linewidth characteristic make this laser an ideal candidate for ranging, interferometry and sensing applications. Strong and robust Bragg gratings in optical fiber fabricated from highly photosensitive photo-thermo-refractive (PTR) glass are demonstrated. The fibers were drawn at 900 °C from a machined PTR-glass preform. A low power two beam interference pattern from a continuous wave (cw) He-Cd laser with a wavelength of 325 nm was used to write gratings into the fibers, achieving peak grating strengths of 20 dB and a spectral width of 45 pm. The gratings showed no sign of degradation when exposed to a high temperature environment of 425 °C for several hours. This is significantly higher when compared to standard Telecom FBGs which are rated for operation temperatures below 200 °C. A detailed study of novel mode-field adapters (MFA) based on multi-mode interference in graded index multi-mode fibers (GIMF) is presented. MFAs are often used in cases when low coupling losses between single mode fibers with very different mode-field diameters are needed. Here a new type of MFAs has been fabricated and characterized from a selection of commercially available single mode and graded index fibers. Compared to existing techniques the presented MFAs can be fabricated very quickly and are not limited to certain fiber types. Insertion losses of 0:5 dB over a spectral range of several hundred nm have been obtained with an ultra compact MFA with a length of 275 μm.

This thesis focuses on the potential of compound-glass, highly nonlinear, small-core fibres for use in nonlinear applications. Both fibres with a conventional step-index design and small-core holey fibres are considered. While the former technology is more mature, the latter represents the ultimate candidate, since it offers the flexibility of combining novel dispersion properties with a very high nonlinearity. With regard to holey fibre designs, small-core, compound-glass holey fibres with different core diameters and designs are considered for two different background materials: a commercially available lead-silicate glass and a bismuth-oxide based glass. Firstly, characterization measurements are performed on the fabricated holey fibres. The measurements reveal the advantages of each glass type and each fibre design, the ultra-high nonlinearity that can be achieved in such fibres and the potential of achieving simultaneously a novel dispersion profile and high nonlinearity. Nonlinear applications are then demonstrated for some of the fibres presented. In particular, the use of a lead-silicate holey fibre, having a dispersion-shifted profile, with a zero-dispersion wavelength lying close to the C-band is demonstrated in cross-phase modulation based wavelength conversion and switching applications in the 1.55 μm window. Both a co-polarized pump and probe scheme and a Kerr-shutter configuration are considered. For the same fibre, the stimulated four-wave mixing process for amplification and wavelength conversion applications in the C-band is thoroughly studied. Numerical simulations and experimental findings are combined to study the fibre performance, demonstrate its applicability to nonlinear wavelength conversion applications and identify future improvement objectives. The suitability of compound-glass holey fibres is also examined for the generation of correlated photons, through spontaneous four-wave mixing, and the generation of a broad supercontinuum by pumping at the convenient in terms of high power laser availability wavelength regions of 1.0 μm and 1.5 μm. The experiments presented in this thesis constitute the first nonlinear applications ever reported for dispersion-tailored, compound-glass holey fibres, clearly revealing their potential in fibre-based nonlinear applications. Nonlinear applications are also demonstrated for a commercially available, fiberised, bismuth-oxide based fibre with a step-index design. Using this fibre, an all-optical regenerator of Return-to-Zero picosecond pulses is realized at repetition rates of 10 and 40 Gb/s. The same fibre is also employed in an all-fiberised pulse compression scheme, which relies on nonlinear pulse propagation in the normal dispersion regime and enables the compression of picosecond pulses down to the femtosecond scale. In both applications, the ultra high nonlinearity of the compound-glass, step-index fibre results in reduced fibre-length and peak power requirements. The thesis concludes by addressing the issues concerning the practicality of compound-glass fibres and proposing potential future directions.

Les matériaux constitutifs des seringues destinées à l'industrie pharmaceutique peuvent entraîner des interactions indésirables avec les solutions médicamenteuses qu'elles contiennent. Lors du glissement d'un joint de piston dans le corps d'une seringue, les matériaux utilisés, la géométrie des différents éléments ainsi que les conditions expérimentales déterminent la mécanique du glissement. L'étude du glissement d'un joint de piston en élastomère mou dans un corps de seringue en verre lubrifié a été réalisée. L'influence de différents paramètres sur les forces de frottement tels que la viscosité et la quantité du lubrifiant et la nature de l'élastomère, a été étudiée. Cette étude couplée à une modélisation a permis de mettre en évidence des paramètres clés qui gouvernent la forme générale d'une courbe de glissement tels que la déformation du joint de piston et le cisaillement de l'huile. De plus, la condition nécessaire pour obtenir un pic d'activation sur les courbes de glissement est d'avoir une variation du coefficient de frottement qui suit une courbe de Stribeck
Prefillable syringes for the pharmaceutical industry are made of different kinds of materials which can have undesirable interactions with the medicinal solutions present inside the syringe barrel. When a plunger stopper glides inside a syringe barrel, the materials used and the geometry of the different elements influence the gliding mechanics. The study of the gliding of a wavy elastomeric plunger stopper inside a siliconized glass barrel has been done. The influence of various parameters on the gliding forces, as the viscosity and the quantity of the lubricant, and the nature of the elastomer has been studied. This experimental study has been coupled to a modelization which has enabled to emphasize some critical parameters that govern the general shape of a gliding curve as the deformation of the stopper and the shear of the silicone oil. A necessary condition to obtain an activation peak for the gliding curves is to have a friction coefficient that follows a Stribeck-like variation

In this thesis Moore and Yeo's proposed mapping of the structural glass to the Ising spin glass in a random field is presented. In contrast to Random First Order Theory and Mode Coupling Theory, this mapping predicts that there should be no glass transition at finite temperature. However, a growing correlation length is predicted from the size of rearranging regions in the supercooled liquid, and from this a growing structural relaxation time is predicted. Also presented is a study of the propensity of binary fluids (i.e. fluids containing particles of two sizes) to phase separate into regions dominated by one type of particle only. Binary fluids like this are commonly used as model glass formers and the study shows that this phase separation behaviour is something that must be taken into account.The mapping relies on the use of replica theory and is therefore very opaque. Here a model is presented that may be mapped directly to a system of spins, and also prevents the process of phase separation from occurring in binary fluids. The system of spins produced in the mapping is then analysed through the use of an effective Hamiltonian, which is in the universality class of the Ising spin glass in a random field. The behaviour of the correlation length depends on the spin-spin coupling J and the strength of the random field h. The variation of these with packing fraction and temperature T is studied for a simple model, and the results extended to the full system. Finally a prediction is made for the critical exponents governing the correlation length and structural relaxation time.

La compréhension du mécanisme de la formation du verre est l'un des importants problèmes ouverts en recherche sur la matière condensée. De nombreuses questions restent sans réponse, en raison d'une énorme augmentation des temps de relaxation pendant le processus de refroidissement qui ne permet pas l'exploration des propriétés d'équilibre des liquides surfondus à très basses températures. Les simulations numériques des liquides surfondus sont actuellement en mesure d'atteindre l'équilibre à des températures comparables à la température du crossover de la théorie de couplages de modes, qui est bien supérieure à la température de transition vitreuse expérimentale. En conséquence, les simulations plus lentes que les expériences pour équilibrer un liquide surfondu par un facteur d'environ huit ordres de grandeur. Les progrès réalisés pour combler cet écart ont été lents et résultent essentiellement d'améliorations de l'architecture des ordinateurs. Dans cette thèse, nous résolvons en partie le problème de la thermalisation à basse température de liquides surfondus dans des simulations numériques. Nous combinons l'utilisation d'un algorithme Monte Carlo, connu sous le nom d'algorithme de swap, avec la conception de nouveaux modèles de formateurs de verre. Nous examinons systématiquement des nombreux systèmes, à la fois des mélanges discrets de particules, ainsi que des systèmes a polydispersité continue. Nous discutons le rôle que la polydispersité et la forme du potentiel entre particules jouent pour éviter la cristallisation et parvenir efficacement à des régimes de température inexplorés. De plus, nous étudions les processus dynamiques à l’œuvre pendant une simulation de swap Monte Carlo. Nous démontrons que, dans certains cas, notre technique permet de produire des configurations équilibrées à des températures inaccessibles même dans des expériences. Dans ce régime de température complètement nouveau, nous examinons plusieurs questions ouvertes concernant la physique de la transition vitreuse. Nous montrons qu'un fluide de sphères dures peut être équilibré jusqu'à la densité critique du jamming, et même au-delà. Nous mesurons l'entropie configurationelle dans un liquide refroidi à très basse température. Nous mettons en évidence une forte dépendance dimensionnelle, qui suggère l'existence d'une transition vitreuse idéale à une température finie en trois dimensions et à son absence en deux dimensions. Nous détectons l'augmentation de l'ordre amorphe quantifié par une longueur statique point-to-set pendant la formation du verre. Nous mesurons les exposants critiques introduits dans la théorie de champ moyen des verres beaucoup plus proche de la température critique prédite dans la théorie. Enfin, nous révélons l'absence de transition géométrique caractérisant le paysage d’énergie potentiel au travers de la température du crossover de la théorie de couplages de modes.Les modèles et les algorithmes développés dans cette thèse déplacent les études des liquides surfoundus vers un territoire entièrement nouveau, en réduisant l'écart entre la théorie et les expériences, ce qui nous amène plus proche de la solution du problème de la transition vitreuse
Understanding the mechanisms that lead to glass formation is one of the open problems for the condensed matter research. Numerous questions remain unanswered, because the tremendous increase of relaxation times during the cooling process prevents the exploration of equilibrium properties of supercooled liquids at very low temperature. Computer simulations of glass-forming liquids are nowadays able to reach equilibrium at temperatures comparable to the Mode-Coupling crossover temperature, which is well above the experimental glass transition temperature. As a consequence, simulations lag eight orders of magnitude behind experiments in terms of equilibration times. Progress to close this gap has been slow, and stems mostly from hardware improvements.In this thesis we make an important step to close this gap. We combine the use of a Monte Carlo algorithm, known as the swap algorithm, with the design of novel glass-forming models. We systematically test numerous models using both discrete mixtures and polydisperse systems. We discuss the role that polydispersity and particle softness play in avoiding crystallization and in efficiently reaching previously unexplored regimes. We study the dynamical processes taking place during swap Monte Carlo simulations. We demonstrate that in some cases our technique is able to produce thermalized configurations at temperatures inaccessible even by experiments.In this newly accessible regime, we investigate some open questions concerning the glass transition. We show that a hard sphere fluid can be equilibrated at, and even beyond, the jamming packing fraction. We measure the configurational entropy in extremely supercooled liquid, finding a strong dimensional dependence that supports, on the one hand, the existence of an ideal glass transition at a finite temperature in three dimensions and, on the other hand, its absence in two dimensions. We detect the increase of amorphous order quantified through a static point-to-set length throughout the glass formation. We measure the critical exponents introduced in the mean-field theory of glasses much closer to the supposed ideal glass transition. Finally, we reveal the absence of a sharp geometric transition in the potential energy landscape across the Mode-Coupling crossover.The models and the algorithms developed in this thesis shift the computational studies of glass-forming liquids to an entirely new territory, which should help to close the gap between theory and experiments, and get us closer to solve the long-standing problem of the glass transition

This work investigated the biocompatibility of soluble phosphate based glasses as scaffolds for supporting the in vitro morphogenesis the hard-soft tissue interface (enthesis) as an approach dealing with ligaments and tendons clinical problems. The short term response of human oral osteoblasts (HOB), oral fibroblasts (HOF) and flexor tendon fibroblasts (HTF) was assessed on glass discs of various compositions, and different dissolution rates, of the generic ternary form (CaO)o.ox-(Na2O)o.oy-(P20s)o5 through evaluating the maintenance of the seeded cell attachment, survival, proliferation and phenotype by using SEM, immunocytochemistry and the CyQUANT cell density kit. Subsequently, the most biocompatible ternary glass compositions were utilised for fibre production. The effect of fibre diameter of cell adhesion and survival was determined and quaternary glass fibres, of the generic composition (CaO)o.46-(Na20)o.ox-(Fe203)o.oy-(P2C>5)o.5o, where characterised in terms of diameter and solubility profiles. Three-dimensional scaffolds were produced from these fibres and the long term viability, morphology and population growth of the seeded HOB and HOF cells were determined using immunocytochemistry and direct cell count. This was coupled with application of qPCR experiments to evaluate the maintenance of differentiation of the seeded cell population. The role of extrinsic factor inclusion in enhancing in vitro, scaffold associated, tissue morphogenesis was also investigated by stimulating osteogenic differentiation in the seeded HOB cell population. An open lamellar flow bioreactor providing nutrients, oxygen and waste perfusion to the cell-scaffold culture was deigned and assessed. The feasibility of simulating the anatomical architecture of the enthesis has also been addressed as cells were seeded in co-culture on a continuous fibre arrangement. In this study, quaternary phosphate based glass fibre scaffolds containing 3 mol% iron oxide (Fe203), of approximately 30 microm in diameter, and of the composition (CaO)o.46-(Na20)o.oi-(Fe203)o.o3-(P205)o.5o have been shown to support HOB and HOF attachment, well spread morphology, survival and proliferation with no negative impact of cell differentiation. Induction of osteogenesis in the scaffold culture has resulted in up-regulating HOB related gene transcription and the flow culture system, at certain flow rates, has been verified for future use. The Co-culture system design has been successfully implemented as HOB and HOF cells were seeded with an acellular separation zone across the fibre scaffold arrangement.

Cette thèse est dédiée à l’étude de la génération de supercontinuum (SCG) deforte puissance moyenne dans le domaine spectral entre 2 mm et 5,5 mm. Un laser à fibredopée thulium (Tm3+) opérant dans un régime simultanément déclenché et à verrouillage demodes (QML) a été développé. En régime continu ce laser a délivré 70 W et en régime QML,26Wmoyens ont été obtenus pour des taux de répétition en QS de 180 kHz ou plus. L’énergiela plus élevée contenue dans une enveloppe QS a été évaluée à 166 mJ avec 66 mJ contenuedans la sous-impulsion à verrouillage de mode la plus énergétique. L’émission du laser àfibre correspondait toujours à un facteur de qualité M2 excellent, entre 1,1 et 1,2. La SCGcouvrant la plage spectrale de 2 mm à 5,5 mm a été réalisée en implémentant différentes fibresen cascade. Des supercontinua jusqu’à environ 4 mm ont été générés dans des fibres en fluorurepuis pour la plage spectrale complémentaire entre 4 mm et 5,5 mm, des fibres en chalcogénureont été utilisées.La puissance moyenne maximale de 7,8 W a été démontrée pour un supercontinuum dans unefibre en ZBLAN. Le spectre s’étend jusqu’à 4,2 mm. Au total, 69%/43%/30%/16,5% de lapuissance totale ont été mesurés au-delà de 2,15 mm/2,65 mm/3,1 mm/3,5 mm respectivement.La fibre en InF3 a permis d’atteindre une puissance moyenne de 0,8 W et le supercontinuums’étend jusqu’à 2,95 mm.Pour les essais d’élargissement spectral complémentaire, trois fibres en chalcogénure ont étéutilisées. L’élargissement spectral a été démontré pour toutes les fibres en chalcogénure.Jusqu’à 20 mW de puissance ont été obtenus avec une fibre As2Se3. Le spectre a été étendujusqu’à 4,9 mm
This thesis reports about the investigation of high power supercontinuum (SC)generation between 2 mm and 5.5 mm. A Q-switched mode-locked (QML) thulium (Tm3+)-doped fiber laser has been developped to pump different nonlinear fibers. The fiber laserprovided in continuous wave regime an output power of 70 W. In QML operation, 26 W havebeen obtained with Q-switched repetition rates of 180 kHz or higher. The highest energy of theQS envelopes has been 166 mJ with 66 mJ contained in the most-energetic ML pulses, whichhave been surrounded by Gaussian-like pedestals with temporal widths around 2.5 ns. On topof these pedestals, very short temporal peaks with pulse durations around 15 ps appeared. Thehighest achieved peak power of a pedestal has been 25 kW. The beam parameter product M2of the fiber laser has been measured in different operational regimes and resulted always in anexcellent value around 1.2.The highest SC output power level from a ZBLAN fiber has been 7.8 W. In total, 69%/43%/30%/16.5% of the transmitted SC output radiation could be converted beyond the wavelengthof 2.15 mm/2.65 mm/3.1 mm/3.5 mm, respectively, with the broadest output spectrum from theZBLAN fiber exceeding 4.2 mm. The InF3 fiber provided a total output power of 0.8 W withan output spectrum up to 2.95 mm.Successful broadening of the wavelength-limited SC output from the ZBLAN fibers has beenachieved with all three investigated chalcogenide fibers with as much as 20 mW of outputpower by using an arsenic selenide fiber. The output spectrum exceeded 4.9 mm

This thesis, which contains fourteen chapters in two parts, presents theoretical and computer simulation studies of dynamics in supercooled liquids and thermotropic liquid crystals. These two apparently diverse physical systems are unified by a startling similarity in their complex slow dynamics. Part I consists of six chapters on supercooled liquids while Part II comprises seven chapters on thermotropic liquid crystals. The fourteenth chapter provides a concluding note. Part I starts with an introduction to supercooled liquids given in chapter 1. This chapter discusses basic features of supercooled liquids and the glass transition and portrays some of the theoretical frameworks and formalisms that are widely recognized to have contributed to our present understanding. Chapter 2 introduces a new model of binary mixture in order to study dynamics across the supercooled regime. The system consists of an equimolar mixture of the Lennard-Jones spheres and the Gay-Berne ellipsoids of revolution, and thus one of its components has orientational degrees of freedom (ODOF). A decoupling between trans-lational diffusion and rotational diffusion is found to occur below a temperature where the second rank orientational correlation time starts showing a steady deviation from the Arrhenius temperature behavior. At low temperatures, the optical Kerr effect (OKE) signal derived from the system shows a short-to-intermediate time power law decay with a very weak dependence on temperature, if at all, of the power law exponent as has been observed experimentally. At the lowest temperature investigated, jump motion is found to occur in both the translational and orientational degrees of freedom. Chapter 3 studies how the binary mixture, introduced in the previous chapter, explores its underlying potential energy landscape. The study reveals correlations between the decoupling phenomena, observed almost universally in supercooled molecular liquids, and the manner of exploration of the energy landscape of the system. A significant deviation from the Debye model of rotational diffusion in the dynamics of ODOF is found to begin at a temperature at which the average inherent structure energy of the system starts falling as the temperature decreases. Further, the coupling between rotational diffusion and translational diffusion breaks down at a still lower temperature, where a change occurs in the temperature dependence of the average inherent structure energy. Chapters 4-6 describe analytical and numerical approaches to solve kinetic models of glassy dynamics for various observables. The β process is modeled as a thermally activated event in a two-level system and the a process is described as a β relaxation mediated cooperative transition in a double-well. The model resembles a landscape picture, conceived by Stillinger [Science 267, 1935 (1995)], where the a process is assumed to involve a concerted series of the β processes, the latter being identified as elementary relaxations involving transitions between contiguous basins. For suitable choice of parameter values, the model could reproduce many of the experimentally observed features of anomalous heat capacity behavior during a temperature cycle through the glass transition as described in chapter 4. The overshoot of the heat capacity during the heating scan that marks the glass transition is found to be caused by a delayed energy relaxation. Chapter 5 shows that the model can also predict a frequency dependent heat capacity that reflects the two-step relaxation behavior. The high-frequency peak in the heat capacity spectra appears with considerably larger amplitude than the low-frequency peak, the latter being due to the a relaxation. The model, when simplified with a modified description of the a process that involves an irreversible escape from a metabasin, can be solved analytically for the relaxation time. This version of the model captures salient features of the structural relaxation in glassy systems as described in chapter 6. In Part II, thermotropic liquid crystals are studied in molecular dynamics simulations using primarily the family of the Gay-Berne model systems. To start with, chapter 7 provides a brief introduction to thermotropic liquid crystals, especially from the perspective of the issues discussed in the following chapters. This chapter ends up with a detail description of the family of the Gay-Berne models. Chapter 8 demonstrates that a model system for calamitic liquid crystal (comprising rod-like molecules) could capture the short-to-intermediate time power law decay in the OKE signal near the isotropic-nematic (I-N) phase transition as observed experimentally. The single-particle second rank orientational time correlation function (OTCF) for the model liquid crystalline system is also found to sustain a power law decay regime in the isotropic phase near the I-N transition. On transit across the I-N phase boundary, two power law decay regimes, separated by a plateau, emerge giving rise to a step-like feature in the single-particle second rank OTCF. When the time evolution of the rotational non-Gaussian parameter is monitored as a diagnostic of spatially heterogeneous dynamics, a dominant peak is found to appear following a shoulder at short times, signaling the growth of pseudonematic domains. These observations are compared with those relevant ones obtained for the supercooled binary mixture, as discussed in chapter 2, in the spirit of the analogy suggested recently by Fayer and coworkers [J. Chem. Phys. 118, 9303 (2003)]. In chapter 9, orientational dynamics across the I-N transition are investigated in a variety of model systems of thermotropic liquid crystals. A model discotic system that consists of disc-like molecules as well as a lattice system have been considered in the quest of a universal short-to-intermediate time power law decay in orientational relaxation, if any. A surprisingly general power law decay at short to intermediate times in orientational relaxation is observed in all these systems. While the power law decay of the OKE signal has been recently observed experimentally in calamitic systems near the I-N phase boundary and in the nematic phase by Fayer and coworkers [J. Chem. Phys. 116, 6339 (2002), J. Phys. Chem. B 109, 6514 (2005)], the prediction for the discotic system can be tested in experiments. Chapter 10 presents the energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals by determining the inherent structures of a family of one-component Gay-Berne model systems. This study throws light on the interplay between the orientational order and the translational order in the mesophases the systems exhibit. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures. The inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the I-N transition and this breakdown is found to occur at a temperature below which the system explores increasingly deeper potential energy minima. There exists a remarkable similarity in the manner of exploration of the potential energy landscape between the Gay-Berne systems studied here and the well known Kob-Andersen binary mixture reported previously [Nature, 393, 554 (1998)]. In search of a dynamical signature of the coupling between orientational order and translational order, anisotropic translational diffusion in the nematic phase has been investigated in the Gay-Berne model systems as described in chapter 11. The translational diffusion coefficient parallel to the director D// is found to first increase and then decrease as the temperature drops through the nematic phase. This reversal occurs where the smectic order parameter of the underlying inherent structures becomes significant for the first time. The non-monotonic temperature behavior of D// can thus be viewed from an energy landscape analysis as a dynamical signature of the coupling between orientational and translational order at the microscopic level. Such a view is likely to form the foundation of a theoretical framework to explain the anisotropic translation diffusion. Chapter 12 investigates the validity of the Debye model of rotational diffusion near the I-N phase boundary with a molecular dynamics simulation study of a Gay-Berne model system for calamitic liquid crystals. The Debye model is found to break down near the I-N phase transition. The breakdown, unlike the one observed in supercooled molecular liquids where a jump diffusion model is often invoked, is attributed to the growth of orientational pair correlation. A mode-coupling theory analysis is provided in support of the explanation. Chapter 13 presents a molecular dynamics study of a binary mixture of prolate ellipsoids of revolution with different aspect ratios interacting with each other through a generalized Gay-Berne potential. Such a study allows to investigate directly the aspect ratio dependence of the dynamical behavior. In the concluding note, chapter 14 starts with a brief summary of the outcome of the thesis and ends up with suggestion of a few relevant problems that may prove worthwhile to be addressed in future.

For decades, Metallic Glass, with its isotropic featureless structure while exhibiting outstanding mechanical properties was possible only at a high rate of quenching and with at least one dimension in the submicron regime.  This limitation was overcome with the discovery of Bulk Metallic glasses, BMGs, containing three or more elements following the additional two empirical rules of optimum geometric size differences and negative energy of mixing among the constituent elements. Since then thousands of Fe-, Ni-, Al-, Mg-, Ti- based BMGs have been discovered and comprehensively investigated mainly by groups in Japan and USA. Yet the discovery of new combinations of elements for BMGs is alchemy. We do not know with certainty which element when added will make possible a transition from being a ribbon to a bulk rod.    In this thesis we report a discovery of castable BMGs rods on substitution of Fe by nickel in an alloy of FeBNb which could otherwise have been only melt-spun into ribbons.  For example, we find that substitution of just 6 at.% of Fe raises the glass forming range, GFA, to as much as ∆Tx =40K while the other parameters for GFA like Trg, γ, and δ reach enhanced values 0.57, 0.38, and 1.40 respectively.  Furthermore, the electrical conductivity is found to increase by almost a factor of two.  Magnetically it becomes softer with coercivity 260mOe which further reduces to much lower values on stress relaxation.  Ni does not seem to carry a magnetic moment while it enhances the magnetic transition temperature linearly with Ni concentration. We have investigated the role of Ni in another more stable BMGs based FeBNbY system in which case ∆Tx becomes as large as 94K with comparable enhancement in the other GFA parameters. Due to the exceptional soft magnetic properties, Fe-based bulk metallic glasses are considered potential candidate for their use in energy transferring devices. Thus the effect of Ni substitution on bulk forming ability, magnetic and electrical transport properties have been studied for FeBNb and FeBNbY alloy systems. The role of Ni in these systems is densification of the atomic structure and its consequence. We have exploited the superior mechanical properties of BMGs by fabricating structures that are thin and sustainable.  We have therefore investigated studies on the thin films of these materials retaining their excellent mechanical properties. Magnetic properties of FeBNb alloy were investigated in thin films form (~200-400nm) in the temperature range of 5-300K. These Pulsed Laser deposited amorphous films exhibit soft magnetism at room temperature, a characteristic of amorphous metals, while they reveal a shift in hysteresis loop (exchange anisotropy, HEB=18-25Oe), at liquid helium temperature. When thickness of films is reduced to few nanometers (~8-11nm), they exhibit high transparency (>60%) in optical spectrum and show appreciably high saturation Faraday rotation (12o/μm, λ= 611nm). Thin films (~200-400nm) of Ni substituted alloy (FeNiBNb) reveal spontaneous perpendicular magnetization at room temperature. Spin-reorientation transition was observed as a function of film thickness (25-400nm) and temperature (200-300K), and correlated to the order/disorder of ferromagnetic amorphous matrix as a function of temperature. These two phase films exhibits increased value of coercivity, magnetic hardening, below 25K and attributed to the spin glass state of the system.    Using the bulk and thin films we have developed prototypes of sensors, current meters and such simple devices although not discussed in this Thesis.                                         Ti-based bulk metallic glasses have been attracting significant attention due to their lower density and high specific strength from structural application point of view. High mechanical strength, lower values of young’s modulus, high yield strength along with excellent chemical behaviors of toxic free (Ni, Al, Be) Ti-based glassy metals make them attractive for biomedical applications. In the present work, toxic free Ti-Zr-Cu-Pd-Sn alloys were studied to optimize their bulk forming ability and we successfully developed glassy rods of at least 14mm diameter by Cu-mold casting. Along with high glass forming ability, as-casted BMGs exhibit excellent plasticity. One of the studied alloy (Ti41.5Zr10Cu35Pd11Sn2.5) exhibits distinct plasticity under uniaxial compression tests (12.63%) with strain hardening before failure which is not commonly seen in monolithic bulk metallic glasses.

QC 20120906

Hero-m

Les colloïdes déformables sont largement utilisés comme additifs rhéologiques dans de nombreuses formulations, allant des peintures et des revêtements aux cosmétiques. Dans ce travail, nous présentons une nouvelle classe de microgels colloïdaux stimulables par le pH, dont la déformabilité et les interactions attractives inter-particulaires sont ajustables. Les microgels sont constitués d'un réseau de polyélectrolyte réticulé gonflé par l'eau, dont l'élasticité est ajustée à volonté en faisant varier la quantité de monomère réticulant pendant la synthèse. L'introduction de groupes alkyle induit des attractions de courte portée entre les microgels, dont la force dépend de la composition et de l'architecture des chaînes hydrophobes. Ce système est donc un bon candidat pour étudier les conséquences macroscopiques de la variation du potentiel d'interaction de répulsif à associatif et un modèle pour des matériaux plus complexes tels que les gels réversibles, les gels protéiques, etc. Nous avons utilisé la rhéologie non linéaire, la diffusion statique et dynamique de la lumière couplée à la vélocimétrie par images de particules (PIV) pour relier les propriétés à l'échelle des particules au comportement macroscopique des suspensions dans les régimes liquide, de verre entropique et de verre encombré.Dans une première partie, le potentiel inter-particulaire est purement répulsif mais son intensité est variée en utilisant la densité de réticulation comme paramètre de contrôle. Lors de l'augmentation de la fraction volumique des colloïdes, les suspensions de microgels fortement réticulées se comportent successivement comme des suspensions liquides, des verres entropiques et des verres encombrés. Dans ce dernier, les propriétés rhéologiques suivent les prédictions récentes pour des sphères élastiques idéales à des fractions volumiques élevées. De plus, la structure vitreuse des suspensions qui possèdent des corrélations spatiales à courte distance est responsable des couleurs structurales non iridescentes qui passent continuellement du rouge au bleu en augmentant la concentration. En revanche, les microgels faiblement réticulés présentent des propriétés mécaniques et d’écoulements décrites par des lois d’échelle nouvelles, ce qui suggère qu'ils appartiennent à une classe différente de matériaux désordonnés que nous avons appelés « colloïdes ultra-moux».La deuxième partie a été consacrée à l'étude des effets des attractions de courte portée sur les propriétés statiques et dynamiques des microgels. La comparaison avec des microgels purement répulsifs ayant exactement la même composition, la même densité de réticulation et la même taille de particule met en évidence les spécificités des microgels associatifs, qui ont un potentiel d'attraction inter-particulaire variable. Dans le régime du verre encombré, des interactions attractives sont responsables des hétérogénéités d’écoulement - une compétition entre le glissement de paroi et / ou les bandes de cisaillement - contrôlées par la force des interactions attractives. Pour rationaliser la rhéologie de ces systèmes, nous proposons un modèle à deux états impliquant deux temps caractéristiques associés à la relaxation des associations et à l'ouverture de la cage, respectivement. Ces résultats établissent un lien entre la force des attractions à courte portée et les instabilités d'écoulement macroscopiques. Enfin, nous présentons deux applications où des microgels associatifs sont utilisés dans de nouvelles formulations comme des mélanges avec des microgels non associatifs et comme stabilisants d’émulsions
Soft colloids are widely used as rheological additives in formulations as diverse as paint, coatings, and cosmetics. In this work we present a novel class of pH responsive colloidal microgels with controllable softness and tunable attractive interparticle interactions. Microgels are crosslinked polyelectrolyte networks swollen by water. The elasticity of individual microgels is tuned at will through the crosslink density which depends on the amount of multifunctional monomers introduced during the synthesis. Alkyl groups induce short range attractions between microgels, whose strength depends on the composition and the architecture of the hydrophobic chains. This system is thus a valuable candidate to elucidate the relation between the macroscopic properties and the strength of the interaction potential when it is varied from soft repulsive to soft attractive. This question is central to the behavior of materials like reversible gels or protein gels. We use non linear rheology, static and dynamic light scattering and video microscopy coupled to high speed Particle Image Velocimetry (PIV) to connect the particle scale properties to the macroscopic behavior of the suspensions in the liquid, glass and jamming regime.In a first part, the interparticle potential is purely repulsive and its strength is varied using the crosslink density as a control parameter. Upon increasing the polymer concentration, highly crosslinked suspensions successively encounter well defined glass and jamming transitions, which delimit the dilute, entropic glass, jammed glass, and dense glass regimes. In the jammed regime the rheological properties support recent predictions and simulations for ideal elastic spheres randomly packed at high volume fraction. The glass-like structure of the suspensions with short range spatial correlations is responsible for non-iridescent structural colors which shift continuously from red to blue when the concentration is increased. In contrast, weakly crosslinked microgels exhibit novel mechanical and flow properties with unprecedented scaling properties, which suggest that they belong to a different class of disordered materials that we termed ‘ultrasoft’ colloids.In the second part we investigate the effects of short range attractions on the static and dynamic properties of soft microgels. The comparison with purely repulsive microgels with exactly the same composition, crosslink density, and particle size highlights the specificities of associative microgels which have different interparticle attractive potential. In the jammed glass regime, attractive interactions are responsible for flow heterogeneities -a competition between wall slip and/or shear-banding- controlled by the strength of attractive interactions. To rationalize the rheology of associative suspensions, we propose a two-state model involving two characteristic time scales associated to the relaxation of the associations and cage opening, respectively. These results establish a link between the strength of short-range attractions and the macroscopic flow properties. Finally, we present two applications where associative microgels are used as in novel formulations as blends with the non associative and as emulsions stabilizers

Les suspensions colloïdales de particules sphériques présentant des interactions de type sphères dures font partie des systèmes les plus simples et les plus largement étudiés en Matière Molle. Elles peuvent être considérées comme systèmes modèles pour tester des théories plus générales, par exemple en ce qui concerne la cristallisation [1] ou la transition vitreuse [2]. Malgré de nombreux résultats théoriques et expérientaux dans ce domaine, le comportement dynamique des suspensions de sphères dures n'a pas été complètement élucidé.La spectroscopie à corrélation de photons X (XPCS) est une technique de diffusion cohérente équivalente à la Diffusion Quasi-Elastique de la Lumière [3], qui est un des principaux outils d'investigation de la dynamique colloïdale [4]. Comparée à la luière visible, l'utilisation de rayons X procure des rensignements sur les transferts de moment de plus haute énergie, et évite les diffusions multiples - phénomène qui complique sensiblement les études en DQEL pour les échantillons concentrés. De plus, l'utilisation du détecteur 2D compteur de photons (MAXIPIX) disponible sur la ligne ID10 (ESRF) donne des renseignements sur l'évolution de la dynamique de l'échantillon au cours de l'exposition, via les fonctions de corrélation à deux temps.Dans ce travail, nous avons étudié une suspension de spheres colloïdales de PMMA (poly(méthylmétacrylate)) stériquement stabilisées. La distribution en taille des particules et leur concentration ont été obtenues par diffusion de rayons X aux petits angles (SAXS). Les expériences de XPCS effectuées aux plus grandes fractions volumiques en particules (>0.5) mettent en évidence à la fois des temps de diffusion courts et des temps longs autour des pics de Bragg. Une comparaison avec une précédente étude [5] montre, pour une petite gamme de fractions volumiques, une modification drastique de la loi d'échelle entre les temps de relaxation courts et les temps longs qui avait été initialement proposée par Segrè et Pusey [6]. L'analyse des fonctions de corrélation à deux temps révèle un comportement dynamique complexe des échantillons légèrement au-dessus de la transition vitreuse, alors qu'on n'observe aucun signe de modifications structurales via diffusion statique. Utiliser la XPCS sur des suspensions en écoulement dans des canaux cylindriques avait fait ses preuves pour renseigner à la fois sur les propriétés dynamiques et d'écoulement de suspensions diluées [7]. Ici, nous discutons les potentialités et les limites de cette méthode, en étudiant l'interaction entre les propriétés rhéologiques et dynamiques dans ces systèmes complexes modèles que sont les verres colloïdaux.[1] P. N. Pusey and W. van Megen. In: Nature 320.6060 (Mar. 1986), pp. 340-342 [2] P. N. Pusey and W. van Megen. In: Phys. Rev. Lett. 59 (18 1987), pp. 2083-2086.[3] V. A. Martinez et al. In: The Journal of Chemical Physics 134.5, 054505 (2011), p. 054505.[4] B. J. Berne and R. Pecora. Dynamic Light Scattering with application to chemistry, biology and physics. Dover Publications, New York, 2000. [5] D. Orsi et al. "Dynamics in dense hard-sphere colloidal suspensions". In: Phys. Rev. E 85 (1 2012), p. 011402. doi: 10.1103/PhysRevE.85.011402. url: http://link.aps.org/doi/1 0.1103/PhysRevE.85.011402. [6] P. N. Segrè and P. N. Pusey. In: Phys. Rev. Lett. 77.4 (1996), pp. 771-774.[7] A. Fluerasu et al. In: New Journal of Physics 12.3 (2010)

Les matériaux vitreux mous (émulsion concentrée, mousse, suspension concentrée...) présentent un comportement rhéologique entre solide et liquide. Aux petites contraintes le système reste élastique, mais au-dessus d’une contrainte seuil, le système s’écoule comme un liquide visqueux. Ce comportement se trouve dans de nombreux fluides industriels comme dans les cosmétiques, l’agro-alimentaire ou encore le béton. Une contrainte seuil n’apparait que au dessus d’une certaine fractions volumique. Au dessus de cette fraction les particules se bloquent entre elle, la relaxation n’est plus possible et l’écoulement devient fortement coopératif.Cette coopérativité influe sur la rhéologie à petite échelle, Quand le confinement devient de l’ordre de quelques particules, la viscosité ne dépend plus uniquement, comme habituellement, de la contrainte locale mais aussi de la contrainte au voisinage. C’est ce qu’on appelle rhéologie non-localeJ’ai étudié expérimentalement ce comportement en utilisant les outils de micro fluidiques. J’ai étudié une micro-émulsion concentrée s’écoulant dans un microcanal en observant directement l’écoulement des gouttes avec un microscope confocal. Les résultats sont comparés au model “Kinetic-Elasto-Plastic” de Bocquet et al. 2009 et à des simulations de dynamique moléculaire
Soft glassy materials (concentrated emulsion, foams, concentrated suspension…) present rheological properties between solids and liquid. Under small stress they stay elastic but at stress higher than a yield stress they begin to flow as a liquid. Those fluids are used in cosmetics, food industry or building materials as concrete. The yield stress behavior only appears when the volume fraction is high enough, where the particles are blocked by their neighbors. So the systems cannot relax and the flow become highly cooperative.This cooperativity impacts the rheology at small scale. When the confinement is of the order of few particles, the viscosity does not only depend on the local stress as usually but also on the stress in the neighborhood. This is called non-local rheology.I studied experimentally this behavior by flowing concentrated emulsion in a microchannel and observing directly the flow of the droplet with a confocal microscopy. The results from these microfluidics experiments are compared to predictions of the Kinetic Elasto Plastic model of Bocquet et al. 2009 and molecular dynamic simulation of jammed soft particles

Dans de nombreux cas, le développement de surfaces aux propriétés adhésives spécifiques fait appel à l’utilisation « d’interfaces décorées ». Ces interfaces sont composées d’un substrat solide sur lequel des chaînes de polymère sont plus ou moins bien ancrées. Ces chaînes se couplent mécaniquement au matériau environnant et contrôlent la transmission des contraintes de friction et d'adhésion aux interfaces. Ce couplage dépend en particulier de la pénétration des chaînes de surface dans la matrice et de leur dynamique. Dans cette thèse, les systèmes que nous avons étudiés sont constitués d’une couche de chaînes de polymère dont une extrémité est liée de manière covalente à un substrat solide. Ces brosses de polymère, constituent un système modèle pour des interfaces décorées. Notre objectif a été d’étudier la conformation et la dynamique de ces chaînes greffées lorsque ces dernières sont soumises à différents types de sollicitations afin de comprendre les mécanismes moléculaires régissant les propriétés d’adhésion et de friction de ce type d’interface. Dans un premier volet, nous avons étudié par réflectivité de neutrons la cinétique de cicatrisation d'une interface composée initialement de chaînes greffées recroquevillées sur un substrat et en contact avec un fondu. Lorsque le système est amené à une température supérieure à la température de transition vitreuse, les chaînes de polymère retrouvent une mobilité non nulle permettant ainsi la pénétration des chaînes greffées dans le fondu de polymère. La réflectivité de neutrons nous a permis d'une part de sonder à l'échelle moléculaire la cinétique de cicatrisation de ce type d’interface et d'autre part de la quantifier. L'influence des paramètres moléculaires sur cette cinétique de cicatrisation a pu être observée, ce qui nous a permis de proposer un modèle en loi d'échelle permettant d'apporter une interprétation physique au phénomène étudié. La deuxième partie de ce travail de thèse a consisté en l'élaboration d'un dispositif expérimental permettant de cisailler un système brosse/fondu au-dessus de la température de la température transition vitreuse et de geler la conformation des chaînes greffées dans leur configuration cisaillée. L'inversion des spectres de réflectivité neutrons associés a permis de mettre en évidence l'influence du cisaillement sur le degré d'interpénétration entre la brosse et le fondu qui régit la transmission des contraintes de friction sur ce type d'interface. De plus, nous avons pu mesurer la cinétique de relaxation de chaînes greffées, cisaillées au préalable, et la comparer aux expériences d’interdigitation simple. Cette comparaison a permis de divulguer l’importance du type de sollicitation sur la cinétique de relaxation d’une interface brosse / fondu.Nous avons également observé que la cinétique de relaxation et la conformation de chaînes greffées peuvent être altérées lorsque ces dernières sont confinées dans un film d'épaisseur comparable au rayon de giration des chaînes. Une étude systématique par réflectivité de neutrons a permis de mettre en évidence une accélération de la cinétique de relaxation du système en dessous d'une épaisseur critique qui pourrait être interprétée en termes de déplacement de la température de transition vitreuse. Dans un deuxième temps, nous avons étudié le glissement de solutions de polymères sur une surface greffée. La fraction volumique en chaînes libres dans la solution est un paramètre supplémentaire aux trois cas précédents qui contrôle ici le degré d'interpénétration entre chaînes libres et chaînes greffées. Une première approche théorique a permis de dissocier différents régimes de glissements à la paroi en fonction de fraction volumique. Nous avons entrepris une première série d'expériences de vélocimétrie laser après photolyse afin de mesurer le glissement à la paroi de solutions de polymère et de confronter les résultats expérimentaux avec notre approche théorique
In many cases, the development of surfaces with specific adhesive properties involves the use of "decorated interfaces." These interfaces consist of a solid substrate on which polymer chains are more or less well anchored. These chains are mechanically coupled to the surrounding material and control the transmission of friction and adhesion stresses at the interfaces. This coupling depends particularly on the penetration of the surface chains within the matrix and on their own dynamics. In this thesis, the systems we investigated are composed of a layer of polymer chains whose end is covalently linked to a solid substrate. These, so called, polymer brushes, provide a model system for decorated interfaces. Our objective was to study the conformation and dynamics of these grafted chains when they are subjected to different types of stress in order to understand the molecular mechanisms governing the adhesion and friction properties of this type of interface.In the first part, we investigated the healing kinetics of an interface composed initially of grafted chains collapsed on a substrate and in contact with a molten by using neutron reflectivity. When the system is brought above the glass transition temperature, the polymer chains mobility is high enough to allow the penetration of the grafted chains within the polymer melt. Neutrons reflectivity allowed us to probe at the molecular scale and to quantify the healing kinetics of this type of interface. The influence of molecular parameters on this healing kinetics was observed, which allowed us to propose a scaling law model to give a physical interpretation to the phenomenon studied.The second part of this thesis consisted in the development of an experimental setup which is able to shear a brush / melt interface above the glass transition temperature and to freeze the conformation of chains grafted in their sheared conformation. The inversion of the associated neutron reflectivity spectra made it possible to demonstrate the influence of shear on the degree of interpenetration between the brush and the melt which governs the transmission of stresses. In addition, we measured the kinetics of relaxation of grafted chains previously sheared and we compared it to the interdigitation experiments. This comparison highlighted the influence of the kind of solicitation on the relaxation kinetics of a brush/melt interface.We also observed that the relaxation kinetics and the conformation of the grafted chains may be altered when they are confined in a film which thickness is comparable to the radius of gyration of the chains. A systematic study using neutron reflectivity was conducted and highlighted an acceleration of the relaxation kinetics of the system below a critical thickness which could be interpreted in terms of a shift in the glass transition temperature.Secondly, we studied the slip of polymer solutions onto a grafted surface. The volume fraction of free chains in solution is an additional parameter which controls the degree of interpenetration between free chains and grafted chains. A first theoretical approach showed that different slip regimes can occur as a function of volume fraction. We have undertaken a first series of experiments using laser velocimetry after photobleaching to measure the surface velocity of flowing polymer solutions and to compare the experimental results to our theoretical approach

This thesis studies non-equilibrium dynamics in disordered "glassy" systems, focusing particularly on the response to such systems to external driving and loading. Its primary motivation is a body of experimental data suggesting that glassy dynamics underlie the mechanical properties (rheology) of a wide variety of disordered soft materials (e.g. foams, dense emulsions and dense colloidal suspensions): typically, such materials show pronounced non-linearity in their stress response to slow steady shear (often with a yield stress in the limit of zero shear) and a loss modulus which curves upwards slightly to low frequencies (in apparent violation of linear response theory). In what follows, can, when rheologically driven, broadly capture this behaviour. We also show that they predict ageing at small loads, in qualitative agreement with the results of recent ageing experiments. Beyond this rheological motivation, we also use the models to study more general concepts of glassy dynamics, such as the use of fluctuation-dissipation theorems (FDTs) for defining effective non-equilibrium temperatures. As a preliminary step, we extend the existing rheological formalism to include ageing materials in which time-translational invariance (TTI) is lost. Within this generalized framework, we then analyze the rheologically driven trap model - the "soft glassy rheology" (SGR) model - which considers an ensemble of elastic elements undergoing activated local yielding dynamics, with distributed yield thresholds, governed by a noise temperature x. (Between yields, each element follows affinely the applied shear). We review the model's exact constitutive solution and discuss its mapping, in the undriven limit, to Bouchaud's trap model. We exploit this mapping to demonstrate the existence (in linear rheology at least) of an ageing glass phase (x < 1), in which the relaxation time is always of order the sample age.

Paul Auster’s City of Glass contains a jumble of identities. In fact, the identities are more numerous than the characters, and consequently, characters have several different identities. Some of these identities are obvious constructs, but with others the degree of construction is less evident. Poststructuralist theory, however, puts forward the idea that these seemingly original identities are in fact constructs to the same level as all others. Thus, this essay argues that there are no original identities; identities are constructed by outer factors. This essay discusses three outer factors contributing to the construction of identities, factors commonly discussed in poststructuralist criticism, these three being language, cultural codes and chance.

This thesis is a study of tailoring amorphous Fe-B-Si based alloy to produce bulk glassy rods by adding Nb. We have prepared rapid quenched thin ribbons (thickness ~12 µm) by melt spinning, and glassy rods of diameter ~1mm by Cu-mold casting based on compositions (Fe0.78B0.13Si0.9)100-xNbx (x=0, 4, 8, 12), and studied their different physical properties. The melt-spun ribbons are found to be X-ray amorphous, whereas some nano-crystallinity is observed in the case of rods. All the ribbons show high saturation magnetization and low coercivity, which are the desirable characteristics of a soft ferromagnet. These ribbons are thus suitable for designing high frequency transformers, and sensors from an applications point of view. With increasing Nb content their saturation magnetization, ferromagnetic Curie temperature, and resistivity are found to decrease as expected. The temperature dependence of electrical resistivity shows small positive temperature co-efficient that is expected for a metallic disordered material. We have also studied the modification of the properties on thermal annealing the (Fe0.78B0.13Si0.9)96 Nb4 ribbon at different temperatures in a neutral atmosphere.

The ferromagnetic bulk metallic glasses (BMGs) started to be investigated only in the last 10 years.They are difficult to cast, but their properties are uniques. The work deals with casting, mechanical and soft magnetic properties of new Fe-based BMGs. Such alloys can be cast directly in samples with various geometries and they can be use as magnetic parts in different devices.

O desenho planar para as células a Combustível de Óxido Sólido (SOFC) é melhor do que o tubular devido a sua maior densidade de corrente e menor custo de fabricação. No entanto, o projeto de SOFC planar requer selantes para evitar o vazamento de combustível e a mistura de gases em altas temperaturas. Os vidros e os vitrocerâmicos têm demonstrado serem os mais adequados por apresentarem boa compatibilidade com outros componentes da célula nas temperaturas de trabalho das SOFCs (700-1000°C). No presente estudo, uma série de composições pertencentes ao sistema BaO-Al2O3-SiO2 (BAS) com a adição de B2O3 foram sintetizados tomando as proporções apropriadas de cada óxido constituinte. Propôs-se melhorar este sistema utilizando-se formadores e teores relevantes de modificadores estruturais, de forma a compatibilizar tanto o desempenho térmico por meio do coeficiente de expansão térmica (CET) como a compatibilidade química com os demais componentes da célula. A originalidade deste estudo está na busca destas características em regiões de composições ainda não exploradas, localizadas dentro do triangulo de compatibilidade BS-B2S-BAS2 na região rica em bário do sistema ternário. Entre estes vidros sintetizados quatro composições (BAS-4, BAS-5, BAS-6 e BAS-7) foram escolhidas porque são as mais adequadas às solicitações termomecânicas exigidas para um material vítreo atuar como selante em SOFC.
The design for planar cells Fuel Solid Oxide (SOFC) is better than the tubular due to its higher current density and lower manufacturing cost. However, the design of planar SOFC requires sealant to prevent leakage of fuel and the mixture of gases at high temperatures. Glasses and glass-ceramics have proven to be the most suitable because they have good compatibility with the other components of the cell at working temperature (700-1000°C). In the present study, a series of compositions belonging to the BaO-Al2O3-SiO2 (BAS) system with the addition of B2O3 were synthesized having the appropriate proportions of each component oxide. It was proposed to improve this system using relevant levels of formers and structural modifiers oxides, in order to match both the thermal performance of thermal expansion coefficient (TEC) and chemical compatibility with other components of the cell. The originality of this study is to search for these characteristics in regions of compositions not yet explored, located inside the compatibility triangle BS-B2S-BAS2 at the barium rich part of the ternary diagram. Among the synthesized glasses four batch compositions (BAS-4, BAS-5, 6-BAS, BAS-7) were chosen because best matched the thermo-mechanical required for a glassy material to act as SOFCs sealant.

À la différence des liquides simples, les solides amorphes, une vaste catégorie de matériaux allant des verres métalliques aux émulsions concentrées, ne se mettent à s'écouler qu'au-delà d'une contrainte finie. Notre thèse a pour objet la modélisation de cet écoulement, dans un cadre général et avec un accent mis sur les hétérogénéités. En premier lieu, notre travail a porté sur l'inclusion d'inhomogénéités dans le cadre de la théorie de couplage de modes appliquée à la rhéologie et nous avons notamment obtenu une équation générale d'évolution des inhomogénéités de densité. À basse température, l'écoulement est en effet fortement hétérogène : des phases de déformation élastique sont entrecoupées de réarrangements de particules, brusques et localisés, qui interagissent par le biais des déformations élastiques qu'ils génèrent. En second lieu, nous avons donc considéré un modèle calqué sur ce scénario et affiné ses éléments constitutifs pour rendre compte de la compétition entre cisaillement appliqué et réarrangements locaux, à l'origine de la courbe d'écoulement des matériaux athermiques. Cette dernière a été reproduite de manière satisfaisante. Pour ce qui est des corrélations spatiales dans l'écoulement, nous avons montré qu'il n'existe pas de loi d'échelle universelle dans les modèles élasto-plastiques, malgré la présence d'une classe de longueurs de corrélation décroissant comme dot{gamma}^{ icefrac{-1}{d}} en d dimensions, dans le régime dominé par le cisaillement. Par ailleurs, dans diverses variantes du modèle, le cisaillement se trouve localisé dans une région du matériau. Ce phénomène apparaît dès lors que les blocs élasto-plastiques sont durablement fragilisés à la suite d'un événement plastique. Enfin, les prédictions du modèle ont été directement mises en regard avec des expériences sur l'écoulement en microcanal d'émulsions concentrées et des simulations de dynamique moléculaire à température nulle. Les écarts observés nous ont poussé à développer et implémenter un code plus flexible, qui s'appuie sur une routine simplifiée d'Éléments Finis et rend mieux compte du désordre structurel et des effets inertiels
Contrary to the case of simple fluids, a finite stress is required to initiate the flow of amorphous solids, a broad class of materials ranging from bulk metallic glasses to dense emulsions. The objective of this thesis is to model the flow of these materials in a general framework, with an emphasis on heterogeneities. In a first approach, using the liquid regime as a starting point, I have investigated to what extent inhomogeneities can be accommodated in the framework of the mode-coupling theory of rheology. A generic equation for the evolution of density inhomogeneities has been derived. At low temperatures, the flow is indeed quite heterogeneous: it consists of periods of elastic deformation interspersed with swift localised rearrangements of particles, that induce long-range elastic deformations and can thereby spark off new rearrangements. In a second approach, a model rooted in this scenario has been refined so as to reflect the interplay between the external drive and the localised rearrangements, which is at the origin of the flow curve of athermal solids. The latter has been reproduced satisfactorily. Turning to spatial correlations in the flow, we have shown that there exists no universal scaling for these correlations in elastoplastic models, although a broad class of correlation lengths scale with dot{gamma}^{ icefrac{-1}{d}} in the shear-dominated regime in d dimensions. Besides, shear localisation has been observed in diverse variants of the model, whenever blocks are durably weakened following a plastic event. Finally, we have directly compared model predictions to experimental results on the flow of dense emulsions through microchannels and to athermal molecular dynamics simulations. Spurred on by the observation of some discrepancies, we have developed and implemented a more flexible code, based on a simplified Finite Element routine, which notably provides a better account of structural disorder and inertial effects

Planare keramische Hochtemperaturbrennstoffzellen liefern aufgrund ihres hohen Wirkungsgrades sowie einer hohen Variabilität geeigneter Brennstoffe einen wertvollen Beitrag zur ressourcenschonenden Stromproduktion. Für einen sicheren Betrieb dieser Brennstoffzellen sind hermetisch dichte und elektrisch isolierende Dichtungen unabdingbar. Aufgrund ihrer chemischen Stabilität sowie der Anpassung relevanter Fügeeigenschaften wie Viskosität und thermischem Ausdehnungsverhalten eignen sich insbesondere teilkristalline Glaslote als Dichtungs- und Fügewerkstoffe für diese Aufgabe. Für einen zuverlässigen Langzeitbetrieb von Brennstoffzellensystemen ist neben der Anpassung der Fügeparameter ein umfassendes Verständnis der Alterungsprozesse von Glasloten im Fügeverbund unter Betriebsbedingungen hinsichtlich Gasdichtheit und elektrischem Iso-lationsvermögen von entscheidender Bedeutung. In grundlegenden Untersuchungen zeigt diese Arbeit auf, welche vielschichtigen Degradationsprozesse in teilkristallinen Glasloten unter simulierten Einsatzbedingungen ablau-fen. Durch geeignete Versuchsabläufe gelang es, diese Einflüsse hinsichtlich ihrer Auswirkungen auf Degradationsprozesse zu separieren und zu bewerten. Die daraus gewonnenen Erkenntnisse flossen in eine Glaslotentwicklung ein, mit der die Degradationsstabilität teilkristalliner Glaslote unter den gegebenen Einsatzbedingungen deutlich erhöht werden konnte. Besondere Berücksichtigung fand hierbei der Einfluss der Glaszusammensetzung auf Degradationsprozesse im Verbund mit den metallischen Fügepartnern sowie die Porenbildung in gesinterten glaskeramischen Gefügen unter brennstoffzellentypischen Betriebsbedingungen. Im Gesamtergebnis zeigt die vorliegende Arbeit, dass zur Erfüllung von Fügeaufgaben neben der Anpassung intrinsischer Glasloteigenschaften auch das langfristige Verhalten teilkristalliner Glaslote im Fügeverbund Berücksichtigung finden muss.

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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Ce travail propose une étude expérimentale visant à caractériser les processus dynamiques se produisant au sein de matériaux vitreux mous. La première partie présente des mesures de diffusion de traceurs nanométriques dans la Laponite (une suspension colloïdale) obtenues par une méthode de recouvrement de fluorescence (FRAP). Cette étude montre que la diffusion varie avec la concentration de Laponite et la taille du traceur. Un modèle hydrodynamique de diffusion confinée permet de décrire quantitativement les données expérimentales. Une deuxième partie concerne l'étude expérimentale du vieillissement de matériaux vitreux. Nous testons en pratique le concept théorique de température effective. Celle-ci est obtenue grâce à la technique de FRAP par la mesure simultanée de la diffusion et la convection de sondes fluorescentes dans la Laponite en cours de prise. Contrairement à certaines mesures de la littérature, le système est bien gouverné par la température ambiante. Nous présentons ensuite une étude visant à caractériser le comportement de la Laponite cisaillée. Nous avons pour cela mis au point un dispositif permettant d'appliquer un champ électrique au système, et ainsi créer des déformations locales. L'effet obtenu s'est révélé trop faible, avec d'assez grandes incertitudes (probablement liées à la complexité du système), pour être considéré comme significatif. Enfin, nous avons étudié les propriétés du Carbopol, un fluide à seuil, en mesurant sa dynamique d'ascension par capillarité. La rugosité de surface des capillaires influe énormément sur la montée du fluide. Nous montrons aussi que l'ascension est pilotée par la rhéologie du système, notamment par le seuil d'écoulement.

As the appetite for data use across telecommunications networks is predicted to continue to grow rapidly in the coming years, there is an increasing need to address the bandwidth gap that exists between the optical links that underpin high speed networks and the electronic layer typically used for processing signals at the endpoints. Nonlinear fibre optics is a potential avenue to addressing this bandwidth bottleneck, where nonlinear optical phenomena can be exploited to perform signal processing tasks, thereby allowing the broad bandwidth of optical media to be used for signal processing as well as transmission. Indeed the development of such optical signal processing devices is crucial to moving towards the next generation of communications technology - where ultra fast telecommunication networks with speeds approaching 1 Tb/s are required. This work explored the use of the enhanced optical nonlinearity and dispersion engineering possible in soft glass microstructured fibres as a basis for developing devices for broadband telecommunications applications at 1.55 μm. Two applications were considered in this research, namely multicasting and phase sensitive amplification - both of which are signal processing applications that are important to the realisation of all optical networks. A number of soft glass materials were studied in this research, primarily those with high nonlinear refractive indices such as chalcogenides, tellurites, bismuth oxide based glasses and germanates. During the course of this work a novel lead germanate glass was also developed. This glass was shown to have a high nonlinear index and relatively high mechanical strength when compared to tellurite glasses of similar refractive indices. Dispersion tailored, soft glass fibre designs were developed for both multicasting and phase sensitive amplification. The design geometry, referred to as a ‘hexagonal wagon wheel design’, was a hybrid model combining a hexagonal array geometry for dispersion engineering with a suspended core or ‘wagon wheel’ geometry for high nonlinearity. The fibre designs were optimised for each application by using a genetic algorithm based optimisation technique to achieve high and broad gain suitable for efficient signal processing at extremely high bit rates. Each fibre design was modelled for its intended application to demonstrate, numerically, that the designs were indeed capable of performing their intended application over a broad band. The modelling work used a numerical beam propagation model and demonstrated that the designs were capable of operating at the extremely high bit rate of 640 Gb/s. Advances were made to fabrication techniques during the fabrication trials of these novel designs due to the complex nature of the designs and, in some cases, the use of novel materials. A first generation, simplified hexagonal wagon wheel fibre was fabricated in the novel germanate glass developed earlier. A number of characterisation experiments were also performed on fabricated microstructured fibres, including a measurement of the dispersion profile for a tellurite fibre (that was shown to be in good agreement with modelling results) and the measurement of the nonlinear index for a fibre fabricated with the novel germanate glass - one of the few such measurements in the literature for this family of glasses. In addition to these fabrication advances and characterisation experiments, a study of dispersive waves was performed on previously fabricated hexagonal wagon wheel fibres in collaboration with colleagues at the University of California, Merced. These experiments were used to study soliton propagation in these fibres at near infrared wavelengths. Comparison of experimental data to theoretical models is shown to have good agreement - an important validation of the modelling technique.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2015.

The objective of this thesis is to explore the potentials of using soft-glass (non-silica) based microstructured optical fibres (MOFs) for nonlinear optical applications. The high linear and nonlinear refractive indices of soft glasses and the ability to tailor the dispersion properties of MOFs have made them an ideal platform for developing nonlinear optical applications. Soft glasses also provide the possibilities of developing waveguides with mid-infrared transmission capability. In addition, the advances in fabricating MOFs with sub-wavelength structures and high refractive index contrast mean that nonlinear processes in these fibres can no longer accurately explored using conventional theories (namely scalar theories). A full vectorial theory is thus required, and this thesis drives forward some applications of recently developed generalised nonlinear theory. In this work, the author studies soft-glass MOFs from two aspects. The first aspect is to develop soft-glass MOFs for new frequency light generation using the scalar theories. The second aspect is to explore new nonlinear phenomena in sub-wavelength scale high-index-contrast waveguides, which includes soft-glass MOFs, using a full vectorial theory. The goal of studying these two aspects is develop a general theory that can explain and accurately predict all nonlinear effects in all types of waveguides. Progress towards two novel nonlinear light sources is described, namely a femtosecond near-transform-limited tunable light source based on a fibre optical parametric oscillator (FOPO) and a broadband highly coherent supercontinuum (SC) source in the mid-infrared. The advantages of soft-glass MOFs have never previously been employed to enhance the performance of FOPOs. Also the bandwidth and coherence of SC sources have never been optimised simultaneously, utilising the advantages of soft-glass MOFs. In this work, a genetic algorithm based fibre design approach is developed and applied to design and optimise fibres for these devices. The extrusion technique is used to fabricate fibre preforms. Simulations and experiments are performed to demonstrate SC generation and new frequency light generation in the final fibre. The Kerr nonlinearity and nonlinear polarisation interactions are studied in a full vectorial framework. A continuous self-phase-modulation method was used to measure the Kerr nonlinearity of soft-glass MOFs, which confirmed the validity of the full vectorial theory. After that, new polarisation behaviours including polarisation self-switching were discovered and studied. The outcomes of the works demonstrate the efficiency of using soft-glass MOFs for nonlinear applications. As described in Part I, for the FOPO, only a few millimetres of fibres were used to achieve near transform limited output with high conversion efficiency across a large frequency separation. For the supercontinuum source, a broadband continuum spectral output that was only limited by the transmission window of the glass and highly coherent was obtained. The supercontinuum experiments indicated the fabricated fibres had behaved as expected with the consideration of fabrication distortion. As described in Part II, the work on the nonlinear effects with the full vectorial theory indicates that the Kerr nonlinearities of soft-glass MOFs can be significantly larger than they were previous predicted. New nonlinear polarisation behaviours including polarisation self-switching can take place in soft-glass MOFs with milliwatt level of power which indicates significant differences in the nonlinear processes that involved in FOPO and SC light sources should be observed with soft-glass MOFs. Combining the full vectorial theory with FOPOs, supercontinuum sources and other nonlinear applications will lead to a better understanding the physics of the nonlinear processes behind these applications as well as further increase the efficiency of using soft-glass MOFs for these nonlinear applications and discover new applications.
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2012

This thesis contains a study of the suitability of tellurite glass for use in microstructured fibre lasers. This thesis looks into the possibility for lasing at around 3μm, where tellurite glass is transparent. To test the lasing potential of fabricated tellurite glass microstructured fibres, lasing at 1.5μm was demonstrated. The research contained within this thesis includes: The development and characterisation of the tellurite glass composition; including modifications made to this composition to match the refractive indices of the doped and undoped glasses, reducing the glass material loss, finding the glass crystallisation stability and density as well as measuring the temperature dependence of the glass melt viscosity, of which an understanding is required for its extrusion (Chapter 2). The fabrication of microstructured tellurite fibres which included large mode area fibres, motivated by the desire to fabricate a double clad fibre and the development of small core fibres which were used in the fibre laser experiments (Chapter 3). A spectroscopic study of the erbium III doped glass including lifetimes, absorption and emission measurements (Chapter 4) and a description of the laser modelling, experiments and results (Chapter 5).
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2011

碩士
國立臺北科技大學
材料科學與工程研究所
100
The glass forming ability and soft magnetic properties of Fe-Mn-Si-B-Cu were investigated in this study. Multi-component alloy ribbons with compositions of Fe75Mn3Si10B12-XCuX(x = 0, 1, 2, 3, 4 at.%) were synthesized by the single roller melt-spinning method. To examine the thermal properties, the as-cast ribbons was measured with differential scanning calorimetry(DSC). Microstructure were examined by X-ray diffractometer(XRD) and scanning electron microscopy(SEM). Alloying additions of Cu=0, 1, 2 at.% were confirmed amorphous by XRD and SEM images. When the additions came up to Cu=3, 4 at.%, α-Fe、Fe3Si、Mn2B0.98 phase were identified. Amorphous ribbons’ thermal properties were measured, supercooled liquid regions were 166.23 K and 54.73 K when additions of Cu=0, 1, at.% respectively. The saturation magnetization Ms was increased from 1.45 T to 1.57 T and coercivity Hc was decreased from 21.41 A/m to 5.41 A/m when annealing Fe75Mn3Si10B11Cu1 for 60s at 573 K and 673 K. It was verified that Cu alloying additions increased the nucleation rate can improve the soft magnetic properties of alloy ribbon.

碩士
國立臺北科技大學
材料及資源工程系研究所
100
The effect of minor Pd addition on glass forming ability and soft magnetic properties of Fe-Si-B metallic glass were investigated. The (Fe75Si10B15)100-xPdx (x = 0，0.5，1，2 at%) ingots via vacuum-arc-melting under argon atmosphere. A single roller melt-spinning method was employed to produce the alloy ribbons. Structural results show that:(Fe75Si10B15)100-xPdx amorphous alloy ribbons, 0 at%Pd and 1 at%Pd ribbons have a tendency to slightly crystalline by XRD analysis and SEM observation. When Pd addition of 1% and 2% alloy belong to the amorphous structure. DSC thermal analysis shows that Fe-Si-B amorphous alloy add Pd has a Tg of characteristic temperature. And when the addition of 1at% with the best GFA (glass forming ability), the results for the Tg is 767.8 K and Tx is 841.3K. Finally, Kissinger plot method to obtain 1 at% has the highest activation energy of crystallization reach 447.95 kJ/mol, that show it has high thermal stability. The magnetic measurements show the value of Ms is 1.28 T, 1.30 T,and the value of Hc is 33.0, 30.8 A/m for 1 at%, 2 at%. The Fe-Si-B amorphous ribbons with the highest Ms 1.52 T. The Fe-Si-B The alloy has the exist of microcrystals in the amorphous base, so that the value of Hc is as high as 49 A / m. Then, 1 at% alloy ribbons annealed at different temperatures for 10 minutes. The magnetic properties of the best improvements for the annealing temperature of 650K, Ms upgrade from 1.28 T to 1.34 T, Hc from 33.0 A/m down to 14.0 A/m. Therefore, The stress-relief annealed treatments really reduce the residual stress caused by the internal stress of the lattice strain and quench. Therefore, the annealing heat treatment to improve the magnetic losses caused by the addition of the Pd.

碩士
國立臺北科技大學
材料科學與工程研究所
97
The effects of glass forming ability and soft magnetic properties by Hafnium addition on Fe-Nb-B amorphous alloy was investigated in this study. The multi-component alloy ribbons with compositions of (Fe72Nb4B24)100-xHfx (X=0,1,2,3,4,5 and 6 at.%) were prepared by single roller melt-spinning method, and the alloy rods were prepared by inductance casting. Thermal properties were measured by a differential scanning calorimetry (DSC) and high-temperature differential scanning calorimetry (HTDSC) at a heating rate of 0.33 K/s. Microstructure was examined by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The soft magnetic properties, for instance, coercive force (Hc) and saturation magnetization (Ms) were examined by vibrating sample magnetometer (VSM). The thermal magnetometry analyzer (TMA) which at a heating rate of 0.33 K/s and in an applied magnetic field 110Oe was used to measured the Curie temperature (Tc) and the magnetic phase. In conclusion, the alloy ribbons showed amorphous structure in X=1 to 4, and the X=2 ribbon revealed the best glass forming ability. On the other side, the Ms decreased from 1.15 T to 0.65 T, the Tc decreased from 545 K to 417 K ,and the Hc has a minimum 12.81 A/m of the X=2 ribbon. In brief, the 2 at% Hf addition showed the best glass forming ability, and it revealed the best glass forming ability and still keep good soft magnetic properties. The addition of Hafnium could increase GFA and still maintain good soft magnetic properties.

碩士
國立臺北科技大學
材料及資源工程系研究所
100
In this investigation, we explored the effects of a small Niobium(Nb) addition in the glass forming ability and remained the soft magnetic properties of Fe-Mn-Si-B amorphous alloy. Multi-component alloy ribbons with compositions of Fe75Mn3Si10B12-xNbx (X=0、1、2、3 and 4 at.%) were synthesized by the single roller melt-spinning method. To examine the glass transition temperature(Tg), crystallization temperature(Tx) and Curie temperature(Tc), the as-cast ribbons was measured with a differential scanning calorimetry(DSC) at a heating rate of 0.33 K/s. Microstructure were examined by X-ray diffractometer(XRD) and scanning electron microscopy(SEM). The saturation magnetization(Ms) and coercive force(Hc) were examined by a vibrating sample magnetometer(VSM) in an applied magnetic field 7000 Oe. To examine the Curie temperature(Tc) and magnetic phase with a thermal gravimetric analyzer(TMA) at a heating rate of 0.33 K/s and in an applied magnetic field 110 Oe. We could observe that the broaden peaks appered when Nb addition were 0~4 at% by XRD and SEM results. The maximum ΔTx (= Tx-Tg) value was 97 K for the 2 at% Nb addition by DSC analysis. In addition, the Ms decreased from 1.45 T to 1.02 T, and the minimum Hc value was 5.89 A/m for the 2 at% Nb. In condition, the 2 at% Nb addition showed the best glass forming ability, and still keep good soft magnetic properties. Annealing the amorphous ribbons at 350℃ and 450℃, using VSM、XRD and SEM to analyze soft magnetic propertiesand microstructure. It was examined that addition of Nb could inhibit the growth of grain at 450℃. The small addition of Nb was very effective in improving glass-forming ability and remained the soft magnetic properties of Fe-Mn-Si-B alloys.

In models for networks of regulatory interactions in biological molecules, the sigmoid relationship between concentration of regulating bodies and the production rates they control has lead to the use of continuous time 'switching' ordinary differential equations (ODEs), sometimes referred to as Glass networks. These Glass networks are the result of a simplifying assumption that the switching behaviour occurs instantaneously at particular threshold values. Though this assumption produces highly tractable models, it also causes analytic difficulties in certain cases due to the discontinuities of the system, such as non-uniqueness. In this thesis we explore the use of 'ramp' functions as an alternative approximation to the sigmoid, which restores continuity to the ODE and removes the assumption of infinitely fast switching by linearly interpolating the focal point values used in a corresponding Glass network. A general framework for producing a ramp system from a certain Glass network is given. Solutions are explored in two dimensions, and then in higher dimensions under two different restrictions. Periodic behaviour is explored in both cases using mappings between threshold boundaries. Limitations in these methods are explored, and a general proof of the existence of periodic solutions in negative feedback loops is given.
Graduate

碩士
國立中正大學
物理學系暨研究所
101
Amorphous materials with excellent intrinsic properties, such as high thermal stability, high electrical resistivity, outstanding soft magnetic and mechanical properties, have been discovered. Consequently, ferromagnetic Fe-based bulk metallic glasses (BMGs) were considered as suitable candidates for replacing conventional crystalline Si-steel for motor applications. In this work, the effect of transition metals (M, M=Mo, V, Nb, Ta, Ti, Zr, and Hf) on the glass-forming ability (GFA) and soft magnetic properties of Fe76M3P10C4B3Si3 melt spun ribbons and BMGs sheets were studied. Among those transition metals, Mo exhibits the best GFA properties. Meanwhile, for Fe76Mo3P10C4B3Si3 ribbon, the supercooled region (∆Tx) of 62 K, reduced glass transition temperature (T¬rg) of 0.57, as well as the lowest Hc of 24.6 A/m, measured by vibrating sample magnetometer, were obtained. According to these results, the Mo content was modified in order to further improve GFA and soft magnetic properties of the samples. For Fe79-xMoxP10C4B3Si3 (x= 2.5, 3.0, 3.5, 4.0, 4.5) series ribbons, the best GFA properties and soft magnetic properties were achieved for x=3. In addition, the maximum thickness of amorphous sheet using Fe76Mo3P10C4B3Si3 can be as large as 2 mm which showed the optimal properties of ∆Tx= 62 K, T¬rg= 0.57, σ12 kOe= 1.09 T, Hc= 50.6 A/m (0.63 Oe) and TC= 535 K. Finally, amorphous ribbon and bulk samples were made by using Fe76-xCoxMo3P10C4B4Si3 (x= 0, 5, 10, 15, 20) alloys. The lowest coercivity was found in alloy ribbons with x= 10, it also showed the optimal properties of ∆Tx= 51 K, T¬rg= 0.58, σ12 kOe= 1.19 T, Hc= 15.2 A/m ( 0.19 Oe) and TC= 594 K.

This thesis presents an investigation into the direct CO₂ laser post processing of optical fibres, with a specific emphasis on soft glass compositions. It presents novel techniques for the fabrication of soft glass optical fibre based devices, novel techniques for the direct measurement of glass melt properties and the optical characterization of all fabricated devices, including a novel technique for measuring the evolution of ultra-short pulses along sub-wavelength tapered optical fibre. New photonic devices fabricated from soft glass optical fibres are of scientific interest due to the high non-linearity and high refractive index. However for the increased understanding and controlled fabrication of such devices, measured values of the physical properties of the glass melts are required, and for many new materials this information is either unavailable or must be obtained for the exact conditions that the devices are produced. This thesis presents new methods for the measurement of surface tension and viscosity at the same conditions as the fabrication of the optical devices presented, through the use of a scanning CO₂ laser. It also reports previously unpublished surface tension values for several glass compositions and investigates the effect the glass making environment had on the resulting surface tensions. Novel fabrication techniques for new soft glass optical devices are also presented, including the pressurised tapering of Bismuth MOF using an elliptical CO₂ laser beam control the rate of microstructure collapse or expansion such as to produce a photonic crystal device whereby the zero dispersion wavelength varies as a function of displacement along the taper length. The direct CO₂ laser tapering of silica and soft glass optical fibres to sub-wavelength diameters is also presented as well as the production of new high Q factor optical microsphere’s resonators of diameters <10μm, fabricated from Er-Yb co-doped tellurite glass, and attached to tapers situated near the un-tapered optical fibre for mechanical stability.
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2013

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand. partly in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg 2016
Non-renewable resources are becoming scarce and current Global Warming Potential (GWP) values are rising. In an effort to promote a successful shift towards a “greener’ planet, governments worldwide are developing policies, which enforce businesses to contribute to the effort. One such policy is the potential upcoming carbon tax (measured in weight of C02e) in South Africa. As a result, industries need to carefully analyse and understand their core processes and their impact on the environment to ensure that their operations have the lowest environmental cost possible. One such industry in South Africa is the fast growing Carbonated Soft Drinks (CSD) beverage packaging industry. CSD are packaged in both Returnable Glass Bottles/Glass (RGB) and PET containers. The Product Carbon Footprint (PCF) of the CSD packaging process for 300ml Glass and 500ml PET containers was of particular interest. Review of academic literature revealed that no similar research has been conducted previously in South Africa. International studies on PCF, which vastly use the (ISO 14040/14044, 2006) for their method, were found to have conflicting results and conclusions regarding the “greenness” of the two types of containers both with respect to the overall GWP of each and the percentage contribution of the packaging process life cycle stage to the total environmental impact. This is mainly because such studies are region and technology specific. A study was therefore required to understand the implications the business' Glass and PET CSD packaging process has on its GWP and hence carbon tax. The GHG (Green House Gas) Protocol PCF guideline (World Resource Institute, 2013) was used to construct the method for this research to ensure best practice, which would allow the study to be expanded into a full blown Fife Cycle Assessment (FCA) as future work. It was found that the 500ml PET packaging process draws 100% of its Cumulative Energy Demand (CED) from purchased electricity (generated by burning coal) and has a GWP of 65 147 gCCTe/hl (hectolitre), which is 4.5 times less than that for 300ml Glass (294 173 gCCEe/hl) which has 71% of its emissions resulting directly from coal fired boilers on site. A dynamic model analysis revealed that packaging in larger containers results in a significant GWP reduction per volume for both Glass and PET containers. It was recommended that short term the business needs to focus on optimising its packaging lines’ equipment, work with suppliers on reducing the weight of the raw materials used for the packaging containers manufacture and promote rate of return of its Glass.
MT 2018

Binary mixtures of polymers and soft nanocolloids, also called as polymer nanocomposites are well known and studied for their enormous potentials on various technological fronts. In this thesis blends of polystyrene grafted gold nanoparticles (PGNPs) and polystyrene (PS) are studied experimentally, both in bulk and in thin films. This thesis comprises three parts; 1) evolution of microscopic dynamics in the bulk(chapter-3),2) dispersion behavior of PGNPs in thin and ultra thin polymer matrices (chapter-4) 3) effect of dispersion on the glass transition behavior (chapter-5). In first part, the state of art technique, x-ray photon correlation spectroscopy is used to study the temperature and wave vector dependent microscopic dy¬namics of PGNPs and PGNP-PS mixtures. Structural similarities between PGNPs and star polymers (SPs) are shown using small angle x-ray scatter¬ing and scaling relations. We find unexpected (when compared with SPs) non-monotonic dependence of the structural relaxation time of the nanoparticles with functionality (number of arms attached to the surface). Role of core-core attractions in PGNPs is shown and discussed to be the cause of anomalous behavior in dynamics. In PGNP-PS mixtures, we find evidence of melting of the dynamically arrested state of the PGNPs with addition of PS followed by a reentrant slowing down of the dynamics with further increase in polymer frac¬tion, depending on the size ratio(δ)of PS and PGNPs. For higher δ the reen¬trant behavior is not observed with polymer densities explored here. Possible explanation of the observed dynamics in terms of the presence of double-glass phase is provided. The correlation between structure and reentrant vitrifica¬tion in both pristine PGNPs and blends are derived rather qualitatively. In the second part, the focus is shifted to miscibility between PGNPs and polymers under confinement i.e., in thin films. This chapter provide a compre¬hensive study on the different parameters affecting dispersion viz., annealing conditions, fraction of the added particles, polymer-particle interface and more importantly the thickness of the films. Changes in the dispersion behavior with annealing is shown and the need for annealing the films at temperatures higher than the glass transition temperature of the matrix polymers is clearly elucidated. Irrespective of the thickness of the films( 20 and 65 nm) studied, immiscible particle-polymer blends unequivocally prove the presence of gradi¬ent in dynamics along the depth of the films. To our knowledge for the first time, we report results on confinement induced enhancement in the dispersion of the nanoparticles in thin polymer films. The enhanced dispersion is argued to be facilitated by the increased free volume in the polymer due to confinement as shown by others. Based on these results we have proposed a phase diagram for dispersibility of the nanoparticles in polymer films. The phase diagram for ultra thin films highlights an important point: In ultra thin films the particles are dispersed even with grafting molecular weight less than matrix molecular weight. In the third part, we have studied the glass transition of the thin films whose structure has been studied earlier in the earlier part. Non-monotonic variation in glass transition with the fraction of particles in thin films has increased our belief on the gradient in the dynamics of thin polymer films. En¬hanced dispersion with confinement is captured with the enhanced deviation in glass transition temperature of ultra thin films. Effect of miscibility param¬eter on Tgis studied and the results are explained with the subtle interplay of polymer-particle interface and confinement.

Colloids and polymers are often used in industrial applications to obtain desired properties for formulations such as cosmetics, paints, household cleaners and adhesives. We have studied the rheological modifier laponite, a synthetic disc shaped clay with a diameter of 25 nm and thickness of about 1 nm. It carries a negative charge on the face, while the rim charge is pH dependent. For pH < 9 there is a positive charge along the rim, while at high pH the colloid has a net negative charge. The latter pH conditions lead to the formation of a colloidal glass. Low laponite concentrations (cl ≤ 2 wt%) initially have a viscoelastic liquid response. The storage modulus becomes frequency independent and escalates over time while the loss modulus shows an upturn at low frequency, both of which are well predicted by the soft glassy rheology (SGR) model. At low cl clusters form due to weak attractions and interact as the constitute elements via a long range repulsion to form the glass. Dynamic light scattering, neutron scattering and rheology were used to study the melting of the glass with the addition of low molecular weight poly(ethylene oxide) (PEO). Excess small polymer chains in solution cause a depletion force resulting in a low viscosity liquid with fast dynamics. Ultra small angle neutron scattering and rheology verify re-entrant behavior with the addition of high molecular weight PEO. We believe a viscoelastic solid is re-formed due to polymer chains bridging between laponite particles. This is the first evidence of re-entrant type behavior in anisotropic colloids. At high cl (3 wt%) the system is immediately frustrated and a glass is formed due to repulsive interactions between individual particles resulting in G' aging. The aging of G' can be suppressed and tuned with the addition of high molecular weight PEO. Above a critical ratio, ϕ, of the total polymer surface area to total laponite surface area, the PEO dynamics dominate at high frequencies. Thus, it appears that the only parameter needed to tune the rheology of these complex laponite-PEO systems is ϕ.

The thesis describes the study of slow dynamics of confined polymers and soft colloids. We study the finite size effect on the dynamics of glassy polymers using newly developed interfacial microrheology technique. Systematic measurement have been performed to address the issue of reduction of glass transition under confinements. Slow and heterogeneous dynamics are the underlined observed behavior for dynamics in confined glassy polymers. The slow relaxation dynamics and dynamical heterogeneity in polymer grafted nanoparticles (PGNPs) systems were studied using advanced X - ray photon correlation spectroscopy (XPCS) techniques. Our studies presented in this thesis on dynamics of polymer grafted nanoparticle systems in melts and solution are the first attempt to study them experimentally. Thus our work shed the light about new technique to study confined system more accurately and explore new soft colloidal system to study fascinating dynamics and interesting phase behavior. In Chapter 1, we provide the theoretical background along with brief review of the literature for understanding the results presented in this thesis. The details of the experimental set up and their operating principle along with the details of the experimental conditions are provided in Chapter 2. In Chapter 3 we present our newly developed technique (interfacial microrhelogy) and its consequences to study the complex fluids at interface. Chapter 4 discusses the concentration and temperature dependent glassy dynamics in confined glassy polymers. In Chapter 5 we provide the structural and dynamical study of polymer grafted nanoparticles in melts and solutions. We provide the summary of our result and the future prospective of the work in Chapter 6. Chapter-1 provides the ground work and theoretical aspects for understanding the results presented in this thesis. It starts with the discussion about the slow dynamics of complex fluids and transit to dynamic behavior of polymer in confinement, glassy dynamics in confinements . This also discusses the basic aspects of studying viscoelastic properties using rheology, interface rheology, microrheology, interface microrheology techinques. In continuation it discusses structure and dynamics of different soft colloids investigated for last decade and then theoretical aspects of XPCS is discussed. Towards the end of this Chapter, we discuss the procedure to explain and understand systems dynamical heterogeneity near glass like phase transition. Chapter-2 contains the details of the experimental techniques which has been used for the study of confined polymers and soft colloids. Brief introduction to basic principles of the measurements followed by details of the material and methods have been provided. Chapter-3 we discuss the interafacial microrheology of different complex fluids and advantages of the techniques is discussed in Chapter 3. This includes discussion about the technique sensitivity at the surface using quantum dots (QDs) as a probe and about the configuration of the QDs at/on monolayer. Later on establishment of the technique has been demonstrated through easurements on arachidic acid, poly(methylmethacrylate) (PMMA), poly(vinylacetate) (PVAc), poly(methylacrylate) (PMA) monolayers. The extracted subdiffusive nature of QDs in on monolayers through mean square displacement has been explained using fractional Brownian motion model. Towards the end of the chapter we discuss about the extraction of real and imaginary elastic modulus from mean square displacement data using generalized Stokes-Einstein relation for the quasi two dimensional systems and explains about the possible viscoelastic transition in the different monolayers. The concentration and temperature dependent glassy dynamics of confined polymers (PMMA) are discussed in Chapter-4. We demonstrate the microscopic nature of spatio-temporal variation of dynamics of glassy polymers confined to a monolayer of 2 3 nm thickness as a function of surface density and temperature. It illustrates the systems dynamical heterogeneity and explain the observed large reduction of glass transition temperature in confined system through finite size effect. In Chapter 5 we discuss the result based on systematic studies of dynamics of PGNPs in melts and solutions. In addition it also illustrates the structural anisotropy and anomalous dynamical transitions in binary mixture of PGNPs and homopolymers in good solvent condition. It provides temperature and wave vector dependent XPCS measurements on polymer grafted nanoparticles with the variation of functionality. The functionality ( f ) dependent nonmonotonic relaxation in melts of PGNPs and solvent quality dependent non monotonic relaxation of PGNPs system have been elaborated in the continuation. We present possible phase behavior of PGNPs system in good solvent with addition of homopolymer of two different molecular weight. Chapter 6 contains the summary and the future perspective of the work presented.

碩士
國立臺灣大學
材料科學與工程學研究所
96
Several formulations of the glass based on BaO-B2O3-SiO2-Al2O3 systems have been developed and accepted as an appropriate compliant sealing material for planar Solid Oxide Fuel Cells (SOFC) operated at 800oC. The sealing materials in this study are designed by considering lower Tg (glass transition temperature) slightly than the set operation temperature (600-650oC), small CTE mismatch, chemically and physically compatible with the other components, and good wettability with specified substrates. Three main subjects are investigated in this study. The first one is the synthesis and characterization of the glasses, including thermal properties and crystallization behavior. The second is the investigation on crystallization kinetics by using Kissinger equation and Piloyan plot. Third one is to analyze the interfacial stability of the glass with 8YSZ or SDC. Differential thermal analysis (DTA) and Thermal Mechanical Analysis (TMA) were applied to study the thermal properties of the glass. X-ray diffraction (XRD) analysis was conducted to study the crystallization behavior. Scanning and transmission electron microscopes (SEM and TEM) with energy dispersive spectroscopy (EDS) were employed to observe the microstructure and phase evaluation. The results show that 47BaO-21B2O3-27SiO2-5Al¬2O3 (G1A5) possess better glass forming ability (GFA) than other formulation, and has the matched working temperature range (547-694oC) close to the operation temperature 600-650oC of IT-SOFC . The major crystalline phases that would precipitate from the glass matrix during IT-SOFC operation were hexacelsian and BaSiO3. The activation energies for each crystalline phase are 423±38 kJ/mol and 363±19 kJ/mol. When it comes to sealing with 8YSZ, although G1A5 glass can not have a good bonding property with 8YSZ, but it can seal very well with SDC, even after long-term thermal treatment (100 hr at 650oC). On the other hand, in this study we also found out another glass formulation, 53BaO-12B2O3-34SiO2-1Al¬2O3 (G6) can have a good bonding behavior with 8YSZ.

Planare keramische Hochtemperaturbrennstoffzellen liefern aufgrund ihres hohen Wirkungsgrades sowie einer hohen Variabilität geeigneter Brennstoffe einen wertvollen Beitrag zur ressourcenschonenden Stromproduktion. Für einen sicheren Betrieb dieser Brennstoffzellen sind hermetisch dichte und elektrisch isolierende Dichtungen unabdingbar. Aufgrund ihrer chemischen Stabilität sowie der Anpassung relevanter Fügeeigenschaften wie Viskosität und thermischem Ausdehnungsverhalten eignen sich insbesondere teilkristalline Glaslote als Dichtungs- und Fügewerkstoffe für diese Aufgabe. Für einen zuverlässigen Langzeitbetrieb von Brennstoffzellensystemen ist neben der Anpassung der Fügeparameter ein umfassendes Verständnis der Alterungsprozesse von Glasloten im Fügeverbund unter Betriebsbedingungen hinsichtlich Gasdichtheit und elektrischem Iso-lationsvermögen von entscheidender Bedeutung. In grundlegenden Untersuchungen zeigt diese Arbeit auf, welche vielschichtigen Degradationsprozesse in teilkristallinen Glasloten unter simulierten Einsatzbedingungen ablau-fen. Durch geeignete Versuchsabläufe gelang es, diese Einflüsse hinsichtlich ihrer Auswirkungen auf Degradationsprozesse zu separieren und zu bewerten. Die daraus gewonnenen Erkenntnisse flossen in eine Glaslotentwicklung ein, mit der die Degradationsstabilität teilkristalliner Glaslote unter den gegebenen Einsatzbedingungen deutlich erhöht werden konnte. Besondere Berücksichtigung fand hierbei der Einfluss der Glaszusammensetzung auf Degradationsprozesse im Verbund mit den metallischen Fügepartnern sowie die Porenbildung in gesinterten glaskeramischen Gefügen unter brennstoffzellentypischen Betriebsbedingungen. Im Gesamtergebnis zeigt die vorliegende Arbeit, dass zur Erfüllung von Fügeaufgaben neben der Anpassung intrinsischer Glasloteigenschaften auch das langfristige Verhalten teilkristalliner Glaslote im Fügeverbund Berücksichtigung finden muss.:Einleitung Grundlagen von Brennstoffzellen Funktionsweise von Brennstoffzellen Einteilung von Brennstoffzellen Unterteilung keramischer Hochtemperaturbrennstoffzellen Planare Hochtemperaturbrennstoffzellen Aufbau und Werkstoffe Dichtungen für planare Hochtemperaturbrennstoffzellen Glimmerdichtungen Aktiv- und Reaktivlotdichtungen Glaslotdichtungen Verbunddichtungen Glaslotdichtungen in planaren Hochtemperaturbrennstoffzellen Eigenschaften von Glas und Glaskeramik Fügen keramischer Brennstoffzellenstapel mit Glasloten Degradation von Glasloten in SOFCs Stand der Technik – Literatur Motivation dieser Arbeit Material und Methoden Verwendetes Glaslotsystem Metallsubstrate Erhitzungsmikroskopie Dilatometrie Röntgenographische Phasenanalyse Qualitative Heißgasextraktion Chemische Analysen Ermittlung des elektrischen Widerstandes Versuchsaufbau kompakter Glasproben Versuchsaufbau für Auslagerung unter dualer Atmosphäre Ermittlung der Heliumleckrate Gefügeanalyse Ergebnisse und Diskussion Charakterisierung des Standardglaslotes S01 Auslagerung bei Verwendung inerter Elektroden an Luft Spannungsfreie Auslagerung zwischen Goldsubstraten Spannungsfreie Auslagerung zwischen Crofer 22 APU- und Gold-Substraten Auslagerung unter elektrischer Spannung, Kombination A: beide Elektroden aus Gold Auslagerung unter elektrischer Spannung, Kombination B: Anode Gold, Kathode Crofer 22 APU Auslagerung unter elektrischer Spannung, Kombination C: Anode Crofer 22 APU, Kathode Gold Auslagerung unter elektrischer Spannung, Kombination D: beide Elektroden aus Crofer 22 APU Auslagerungen unter relevanten Betriebsbedingungen Charakterisierung des Ausgangszustand des Gefüges Auslagerung unter dualer Atmosphäre ohne elektrische Spannung Auslagerung unter dualer Atmosphäre mit elektrischer Spannung Auswirkungen verzögerter elektrischer Spannung Beschleunigte Degradation durch erhöhte elektrische Spannung Langzeitauslagerungen unter dualer Atmosphäre Glaslotentwicklung für keramische Brennstoffzellen Mechanismen von Porenbildung im Glaslot Glaslote mit erhöhter Stabilität gegenüber Blasenbildung Erhöhung der Stabilität gegenüber metallischen Fügepartnern Untersuchung von Fügeeigenschaften ausgewählter Glaslote Auslagerungen neu entwickelter Glaszusammensetzungen Degradationsverhalten modifizierter ZnO-haltiger Glaslote Degradationsverhalten ZnO-freier Glaslote Zusammenfassung Ausblick Anhang Abkürzungen, Formelzeichen und Einheiten Abbildungsverzeichnis Tabellenverzeichnis Literaturverzeichnis