Crystallization under far-from-equilibrium conditions is investigated for two different scenarios: crystallization of the metallic glass alloy Cu50Zr50 and solidification of a transparent organic compound, o-terphenyl. For Cu50Zr50, crystallization kinetics are quanti ed through a new procedure that directly fits thermal analysis data to the commonly utilized JMAK model. The phase evolution during crystallization is quantified through in-situ measurements (HEXRD, DSC) and ex-situ microstructural analysis (TEM, HRTEM). The influence of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined. For o-terphenyl, the relationship between crystal growth velocity and interface undercooling is systematically studied via directional solidification.
“This book contains overviews on technologically important classes of glasses, their treatment to achieve desired properties, theoretical approaches for the description of structure-property relationships, and new concepts in the theoretical treatment of crystallization in glass-forming systems. It contains overviews about the state of the art and about specific features for the analysis and application of important classes of glass-forming systems, and describes new developments in theoretical interpretation by well-known glass scientists. Thus, the book offers comprehensive and abundant information that is difficult to come by or has not yet been made public.” Edgar Dutra Zanotto (Center for Research, Technology and Education in Vitreous Materials, Brazil) Glass, written by a team of renowned researchers and experienced book authors in the field, presents general features of glasses and glass transitions. Different classes of glassforming systems, such as silicate glasses, metallic glasses, and polymers, are exemplified. In addition, the wide field of phase formation processes and their effect on glasses and their properties is studied both from a theoretical and experimental point of view.
“This book contains overviews on technologically important classes of glasses, their treatment to achieve desired properties, theoretical approaches for the description of structure-property relationships, and new concepts in the theoretical treatment of crystallization in glass-forming systems. It contains overviews about the state of the art and about specific features for the analysis and application of important classes of glass-forming systems, and describes new developments in theoretical interpretation by well-known glass scientists. Thus, the book offers comprehensive and abundant information that is difficult to come by or has not yet been made public.” Edgar Dutra Zanotto (Center for Research, Technology and Education in Vitreous Materials, Brazil) Glass, written by a team of renowned researchers and experienced book authors in the field, presents general features of glasses and glass transitions. Different classes of glassforming systems, such as silicate glasses, metallic glasses, and polymers, are exemplified. In addition, the wide field of phase formation processes and their effect on glasses and their properties is studied both from a theoretical and experimental point of view.
Pressure is one of the essential thermodynamic variables that, due to some former experimental difficulties, was long known as the “forgotten variable.” But this has changed over the last decade. This book includes the most essential first experiments from the 1960's and reviews the progress made in understanding glass formation with the application of pressure in the last ten years. The systems include amorphous polymers and glass-forming liquids, polypeptides and polymer blends. The thermodynamics of these systems, the relation of the structural relaxation to the chemical specificity, and their present and future potential applications are discussed in detail. The book provides (a) an overview of systems exhibiting glassy behavior in relation to their molecular structure and provides readers with the current state of knowledge on the liquid-to-glass transformation, (b) emphasizes the relation between thermodynamic state and dynamic response and (c) shows that the information on the pressure effects on dynamics can be employed in the design of materials for particular applications. It is meant to serve as an advanced introductory book for scientists and graduate students working or planning to work with dynamics. Several scientific papers dealing with the effects of pressure on dynamics have appeared in leading journals in the fields of physics in the last ten years. The book provides researchers and students new to the field with an overview of the knowledge that has been gained in a coherent and comprehensive way.
Glassy phases play an important role in our daily life and in many industries such as the food, pharmaceutical, and construction and are responsible for certain vital mechanisms in living species. Whereas crystals are solid phases that show periodicity of the constituent atoms or molecules, glasses are disordered solids that lack long-range positional order but behave mechanically like solids. Chapter 1 of the current thesis presents an introduction to the characteristics and dynamics of glassy phases. How they are derived from the liquid phase, and how they transform into the crystalline solid phase, thermodynamically more stable. The temperature at which a liquid transforms to the amorphous (glassy) phase is called the glass transition temperature, Tg. Along this thesis the relaxation dynamics of prilocaine (PLC) and stiripentol (STP), and the isothermal crystallization process of the latter have been experimentally studied. Both PLC and STP are drugs used in medical applications mainly as anesthesia and for the treatment of epilepsy, respectively. The studied materials have been analyzed by Broadband Dielectric Spectroscopy (BDS), Differential Scanning Calorimetry, X-Ray diffraction, Raman and I.R spectroscopy and confocal microscopy. The physical principles of BDS, the main experimental tool employed, are presented in Chapter 2. The details of the experimental set-ups are stated in Chapter 3. In the case of a pharmaceutical product, being able to control and foresee the aggregation phase and dissolution rate of the substance is vital. Many drugs are poorly soluble in water and thus, in biological media. The glass state of a drug is a non-equilibrium state that presents higher free energy than the crystal. This implies, that a glassy drug dissolves more rapidly and can be absorbed in larger amounts. Nevertheless, the higher free energy of glassy phases represents at the same time a major problem for shelf-life, since metastable phases are prone to spontaneously transforming into the stable crystalline state. This is a major problem, since wrong dosage or agglomeration of a drug could render it useless or toxic for the human body. Understanding the glass and crystallization dynamics of drugs, and their interaction with water is key to develop more efficient products. Water is the universal biological solvent. For most materials the addition of water leads to a decrease in viscosity, or equivalently, an increase of molecular mobility, resulting in a lower glass transition temperature Tg (the higher the water content the lower the Tg). This is referred to as the plasticizing effect of water. Chapter 4 presents a detailed analysis of both pure and hydrated prilocaine. Results show that the addition of water to PLC leads to the formation of PLC-water complexes, possibly water-bridged monomers or dimers that increase Tg. This antiplasticizing effect of water on the molecular mobility of a simple glass former represents a significant exception to the alleged universality of water as drug plasticizer. The physico-chemical origins of this behavior have been confirmed by studying the effect of confinement of the pure and hydrated drug in the pores of a nonporous structure (Chapter 5). In the case of STP, not only the glassy dynamics were studied, but also the crystallization process (Chapter 6). A sublinear correlation between the characteristic crystal-growth time and the relaxation time of the cooperative relaxation dynamics of stiripentol was found. This correlation was observed also in other substances, which suggests that it is a general correlation at temperatures above Tg. This may allow predicting a substance's crystallization time as a function of temperature. The results of this thesis provide valuable insight into the kinetics and relaxation dynamics, as well as the phase stability, of both studied drugs that could be general to other amorphous drugs. Global conclusions are outlined in Chapter 7.
The present book describes the fundamental features of glassy disordered systems at high temperatures (close to the liquid-to-glass transition) and for the first time in a book, the universal anomalous properties of glasses at low energies (i.e. temperatures/frequencies lower than the Debye values) are depicted. Several important theoretical models for both the glass formation and the universal anomalous properties of glasses are described and analyzed. The origin and main features of soft atomic-motion modes and their excitations, as well as their role in the anomalous properties, are considered in detail. It is shown particularly that the soft-mode model gives rise to a consistent description of the anomalous properties. Additional manifestations of the soft modes in glassy phenomena are described. Other models of the anomalous glassy properties can be considered as limit cases of the soft-mode model for either very low or moderately low temperatures/frequencies.
When a liquid is cooled below its melting temperature under conditions that prevent it from crystallizing, it forms an amorphous solid, or "glass." Glass-forming materials are ubiquitous, ranging from familiar silica glasses of which everyday windows are composed, to liquid water. While structurally indistinguishable from high-temperature liquids, supercooled liquids exhibit rich and complex dynamics. For instance, as the temperature is lowered, structural reorganization within supercooled liquids occurs over increasingly long time scales. Inspecting atomistic mobility over an interval of time reveals that dynamics is "heterogeneous," with distinct regions of mobility and immobility in space-time. In this dissertation, we characterize glassy dynamics in experimental systems and in coarse-grained lattice models. We show how the characteristic dynamics of atomistic glass-forming materials can be reproduced using a kinetically constrained lattice model referred to as the Arrow model, and thus present glassy dynamics "on a lattice." We then show that combining the Arrow model with a second lattice model that undergoes a thermodynamic phase transition captures the competition between crystallization and glass formation experienced by a material cooled below its melting temperature. With this combined model, we demonstrate how specific cooling protocols influence polycrystalline structure, and we qualitatively reproduce the non-monotonic temperature dependence of crystallization time scales. Finally, we explore glassy dynamics "in nature" by applying many of the same tools and ideas used to characterize glasses to study dynamical features of protein side-chains. We demonstrate the presence of supercooled liquid-like dynamics in a biomolecular system.
