Amorphous glass state

In general, the rotational and vibrational motions of molecules are limited in the amorphous glass state. In the rubbery state, large-scale molecular motion, such as translational motion, is possible (Ubbink and Schoonman, 2003). Therefore, the encapsulated flavor or oil exists stably in the amorphous glassy state, but in the rubbery state some deterioration takes place. Since amorphous states are nonequilibrium states, thermodynamic driving forces tend to shift the amorphous state into a more stable crystalline state, resulting in time-dependent crystallization, solidification of powders, and caking. 

At high tanperatures the local icosahedral order in the liquid state is shortlived and the distorted (e.g., cubic) configurations at the equivalent minima of the APES are oriented arbitrarily with a complicated dynamics of transition between them. Below the critical tanperature an ordering of these distortions takes place due to their interaction, and the system transforms into a crystal with the symmetry determined by the local distorted configurations and their interaction, similar to phase transitions in crystals (see Section Vll). Another possibility is that the liquid state transforms into an amorphous (glass) state if, dependent on the interaction between the centers, a freeze of the randomly oriented distortions takes place before their ordering [67],... 

The writing process, that is, the transition crystalline — amorphous, is caused by briefly (<50 100 ns) heating up the selected storage area (diameter (( )) ca 0.5—1 Hm) by a laser pulse to a temperature above the melting point of the memory layer (Eig. 15, Record), such that the film locally melts. When cooled faster than a critical quench rate (10 -10 ° K/s), the formation of crystalline nuclei is suppressed and the melted area sohdifies into the amorphous (glass-like) state. 

Total sugar products are also produced by dehydrating hydroly2ate to a mixture of crystals and amorphous glass. This product is not produced in significant quantities in the United States or Europe but is popular in Japan and Korea where it represents 40—50% of total crystalline dextrose sold (14). 

Continuous transition of state is possible only between isotropic states it may thus occur between amorphous glass (i.e., supercooled liquid of great viscosity) and liquid ( sealing-wax type of fusion ), or between liquid and vapour, but probably never between anisotropic forms, or between these and isotropic states. This conclusion, derived from purely thermodynamic considerations, is also supported by molecular theory. 

FIG. 31 Schematic diagram illustrating the transition between a supercooled liquid state (rubber) and an amorphous solid state (glass). The glass transition event is typically caused by a decrease in water content and/or temperature. The reversibility of the transition, as indicated by the dotted arrow, is material dependent (see text for further discussion of the reversibility of the transition). 

In contrast, the flexibility of amorphous polymers above the glass state is decreased when stiffening groups (structures 2.10 through 2.13) are present in the polymer backbone ... 

As a result of the strong drive to equilibrium, it is usually difficult to quench the isotropic melt to an amorphous glass when liquid crystal formation is possible. Extraordinary quenching techniques may be needed. Once produced, the amorphous state loses its metastability on heating above the glass transition Tga. The melt is quite unstable, so that it may not be possible to keep the melt from changing to the mesophase 21. ... 

Some substances are, however, not able to crystallize, for instance normal glass, as a result of a too irregular molecular structure. When such a substance is cooled down from the liquid state, and follows the line AB, then from B to D it still remains a fluid, which solidifies at D without showing a jump in volume. The line then continues as DE, with about the same slope as CF the matter is, however, not in a crystalline condition, but in an unordered, amorphous, glassy state, and has, therefore, a greater volume. 

In 1931 Simon reported that small molecules in their amorphous solid state are not in thermodynamic equilibrium at temperatures below their glass transition u. Such materials are in fact supercooled liquids whose volume, enthalpy, and entropy are greater than they would be in the equilibrium glass. (See Fig. 1). 

Explain the differences between geometric frustration, the spin-glass state, and Simpson s amorphous antiferromagnetism. 

The physical state of starch during extrusion can be considered to change from a partially crystalline polymer to a polymer melt which is homogenized by shear. Extrusion may also decrease the molecular size of starch components, which is observed from decreased melt viscosity (Lai and Kokini 1991), and obviously a decreased molecular size results in a decreased glass transition temperature of the extmdate. The dramatic decrease of pressure that occurs as a viscous, plasticized melt exits the die may allow an extremely rapid loss of water, expansion of the melt and cooling to an amorphous solid state. 

Glass obtained by quenching a molten liquid to room temperature is an amorphous metastable state. 

Glasses and ceramics are inorganic materials that have been produced for thousands of years see Oxides Solid-state Chemistry and Noncrystalline Solids). Traditionally they are made from natural raw minerals such as clays or sand. Crystalline ceramics are shaped by adding water to clays in order to produce a plastic material and then heated in a furnace. Amorphous glasses are made from the melt and shaped by moulding near their softening temperatme. In both cases, high temperatmes are required. 

If a critical point solid-liquid exists, both phases would have the same equation of condition, analogous to Van der Waals equation for liquids and gases. From considerations based on the molecular theory, Tammann concludes that this is not the case. A liquid can change continuously into an amorphous glass-like sohd, but never into an anisotropic crystal. It is difficult to conceive of continuous transition from a state of disordered motion, such as we must assume in the liquid and gaseous states, to the ordered arrangement of the atoms and molecules in a crystal. 

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