Devitrification

About: Devitrification is a research topic. Over the lifetime, 2619 publications have been published within this topic receiving 41494 citations.

Electron microscopy of frozen water and aqueous solutions

Abstract: SUMMARY Thin layers of pure water or aqueous solutions are frozen in the vitreous state or with the water phase in the form of hexagonal or cubic crystals, either by using a spray-freezing method or by spreading the liquid on alkylamine treated films. The specimens are observed in a conventional and in a scanning transmission electron microscope at temperatures down to 25 K. In general, the formation of crystals and segregation of solutes during freezing, devitrification and evaporation upon warming, take place as foreseen by previous X-ray, thermal, optical and electron microscopical studies. Electron beam damage appears in three forms. The devitrification of vitreous ice. The slow loss of material for the specimen at a rate of about one molecule of pure water for every sixty electrons. The bubbling in solutions of organic material for doses in the range of thousands of e nm−2. We propose a possible model for the mechanism of beam damage in aqueous solutions. The structural and thermal properties of pure frozen water important for electron microscopy are summarized in an appendix.

Protic Ionic Liquids: Solvents with Tunable Phase Behavior and Physicochemical Properties

Abstract: The phase behavior, including glass, devitrification, solid crystal melting, and liquid boiling transitions, and physicochemical properties, including density, refractive index, viscosity, conductivity, and air−liquid surface tension, of a series of 25 protic ionic liquids and protic fused salts are presented along with structure−property comparisons. The protic fused salts were mostly liquid at room temperature, and many exhibited a glass transition occurring at low temperatures between −114 and −44 °C, and high fragility, with many having low viscosities, down to as low as 17 mPa·s at 25 °C, and ionic conductivities up to 43.8 S/cm at 25 °C. These protic solvents are easily prepared through the stoichiometric combination of a primary amine and Bronsted acid. They have poor ionic behavior when compared to the far more studied aprotic ionic liquids. However, some of the other physicochemical properties possessed by these solvents are highly promising and it is anticipated that these, or analogous protic s...

Chemistry of Glass

Abstract: Historical Development of Glass Chemistry. Freezing of a Melt to a Vitreous Solid. Structural Elements of Silicates. Classical Theories of Glass Structure. Methodology in Glass Research. Microphase Separation. Structure and Properties of Colorless Glasses. Structure and Properties of Colored Glasses. Crystallization of Glasses. Strength of Glass. Interaction Between High-Energy Radiation and Glass. Survey of the Physical Basis of Some Glass Properties.

The amount of immobilized polymer in PMMA SiO$_{2}$ nanocomposites determined from calorimetric data

Abstract: For semicrystalline polymers there is an ongoing debate at what temperature the immobilized or rigid amorphous fraction (RAF) devitrifies (relaxes). The question if the polymer crystals aremelting first and simultaneously theRAFdevitrifies or the RAF devitrifies first and later on the crystals melt cannot be answered easily on the example of semicrystalline polymers. This is because the crystals, which are the reason for the immobilization of the polymer, often disappear (melt) in the same temperature range as theRAF. For polymer nanocomposites the situation is simpler. Silica nanoparticles do notmelt or undergo other phase transitions altering the polymer–nanoparticle interaction in the temperature range where the polymer is thermally stable (does not degrade). The existence of an immobilized fraction in PMMA SiO2 nanocomposites was shown on the basis of heat capacitymeasurements at the glass transition of the polymer. The results were verified by enthalpy relaxation experiments below the glass transition. The immobilized layer is about 2 nm thick at low filler content if agglomeration is not dominant. The thickness of the layer is similar to that found in semicrystalline polymers and independent from the shape of the nanoparticles. Nanocomposites therefore offer a unique opportunity to study the devitrification of the immobilized fraction (RAF) without interference of melting of crystals as in semicrystalline polymers. It was found that the interaction between the SiO2 nanoparticles and the PMMA is so strong that no devitrification occurs before degradation of the polymer. No gradual increase of heat capacity or a broadening of the glass transitionwas found. The cooperatively rearranging regions (CRR) are either immobilized or mobile. No intermediate states are found. The results obtained for the polymer nanocomposites support the view that the reason for the restricted mobility must disappear before the RAF can devitrify. For semicrystalline polymers this means that rigid crystals must melt before the RAF can relax. 2007 Elsevier Ltd. All rights reserved.