Amorphous polymorphism
نویسنده
چکیده
Recent studies of amorphous solid materials have revealed the possibility that more than one distinct amorphous phase may be formed from the same substance. In analogy with the phenomenon of crystalline polymorphism, this behavior has been termed “amorphous polymorphism”. We review the experimental manifestation of amorphous polymorphism, especially in tetrahedrally coordinated materials such as Hz0 and SiO2. Guided by computer simulation results on these substances we show how a thermodynamic explanation of these phenomena is possible, specifically that amorphous polymorphism occurs in substances where the thermodynamic behavior of the liquid state exhibits liquid-liquid phase separation, or a tendency toward it. We identify a number of systems which may also display amorphous polymorphism, and emphasize the central role to be played by computer simulation in the elucidation of this phenomenon.
منابع مشابه
Improvement of Physico-mechanical Properties of Partially Amorphous Acetaminophen Developed from Hydroalcoholic Solution Using Spray Drying Technique
Objective(s): This study was performed aiming to investigate the effect of particle engineering via spray drying of hydroalcoholic solution on solid states and physico-mechanical properties of acetaminophen. Materials and Methods: Spray drying of hydroalcoholic solution (25% v/v ethanol/water) of acetaminophen (5% w/v) in the presence of small amounts of polyninylpyrrolidone K30 (PVP) (0, 1...
متن کاملStructural modification of swift heavy ion irradiated amorphous germanium layers
Swift heavy ion (SHI) irradiation of conventional glasses results in non-saturable plastic flow as a consequence of the ion hammering effect [1]. SHI irradiation of amorphous Si (a-Si) at non-perpendicular incidence also leads to unsaturated plastic flow, which shows a linear dependence on the ion fluence. The positive direction of flow suggests that a liquid phase with density similar to that ...
متن کاملCalcium carbonate polyamorphism and its role in biomineralization: how many amorphous calcium carbonates are there?
Although the polymorphism of calcium carbonate is well known, and its polymorphs--calcite, aragonite, and vaterite--have been highly studied in the context of biomineralization, polyamorphism is a much more recently discovered phenomenon, and the existence of more than one amorphous phase of calcium carbonate in biominerals has only very recently been understood. Here we summarize what is known...
متن کاملPolymorphism and polyamorphism in bilayer water confined to slit nanopore under high pressure.
A distinctive physical property of bulk water is its rich solid-state phase behavior, which includes 15 crystalline (ice I-ice XIV) and at least 3 glassy forms of water, namely, low-density amorphous, high-density amorphous, and very-high-density amorphous (VHDA). Nanoscale confinement adds a new physical variable that can result in a wealth of new quasi-2D phases of ice and amorphous ice. Prev...
متن کاملPreparation and Crystallographic Analysis of Gliclazide Polymorphs
Since the introduction of gliclazide in the pharmaceutical industry, a large number of research groups have been engaged in various investigations aiming to enhance its biomedical application. But, very limited efforts have been made to study polymorphism of gliclazide. Therefore, this study focuses on solvent-induced polymorphism of gliclazide and its characterization by thermal methods. Three...
متن کامل