Amorphous glassy state

Food materials (ingredients or whole systems) can be composed of matter in one, two, or all three physical states solid (crystalline or amorphous or a combination of both), liquid, and gas. The crystalline state is an equilibrium solid state, whereas the amorphous glassy state is nonequilibrium solid state. The main transitions that occur between the physical states of materials of importance to foods are summarized by Roos and Karel (1991) and Roos (2002). The most important parameters affecting the physical state of foods, as well as their physicochemical properties and transition temperatures, are temperature, time, and water content (Slade and Levine, 1988 Roos, 1995). Pressure is not included in this list, as food materials usually exist under constant pressure conditions. 

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. 

Estimate the solubility and the heat of solution (sorption) of oxygen in poly(ethylene terephthalate) (PETP), both in the quenched amorphous glassy state and in the semicrystalline state (xc = 0.45). 

In previous examples of substituted polysiloxanes, the relaxation of the side chains with the rigid backbone was assumed to describe the polymer chain in the amorphous glassy state. This assumption, relaxation of side chains only, can be used to study the crystalline states of PDES. Certainly, this simplification is extreme, but it can be usefiil to understand the available orientation of the pendant groups when the polymer chains undergo transition from one crystalline form to another. The present approach does not address the chain reorientation or the interchain interactions in the crystalline state. 

In general, the rotational and vibrational motions are limited in the amorphous glassy state. In the rubbery state, on the other hand, large-scale molecular motion, such as translational motion, is possible (Ubbink and Schoonman, 2003). Therefore, the encapsulated flavors or oils exist stably in the amorphous glassy state, but in the rubbery state some deterioration may take place. Since an amorphous state is not an equilibrium state, a thermodynamic driving force tends to shift the amorphous state to a more stable crystal state, resulting in a time-dependent crystallization, solidification of powders, and caking. 

Although the amorphous, glassy state can confer a degree of kinetic stability upon an otherwise unstable system, a glassy state alone does not... 

Many crystallizable polymers can be prepared in the amorphous glassy state by rapid quenching as films. Measurements of Aglass transition temperature determined. Such results are shown for amorphous polyethylene terephthalate (PET) in Figure 13 (17). The Brillouin splittings change slope at 70°C. If both Aa>(i) and Awt can be measured, the Poisson ratio (T can be determined according to ... 

This is used when polymers are readily melted without degradation and the molten polymer is forced through a spiimeret comprising 50 to 1000 fine holes. On emerging from the holes, the threads sohdify, often in an amorphous glassy state, and are wound into a yam. Orientation and crystallinity are important requirements in fibers, and the yam is subjected to a drawing procedure that orients the chains and strengthens the fiber. This technique is applied to polyesters, polyamides, and polyolefins. 

Vleeshouwers, S., Modeling and predicting properties of polymers in the amorphous glassy states, Thesis, Eindhoven Technical University, 1993. 

Among the manufacturers are American Cyanamid (Dexon), DuPont (Vicryl) and Kureha (Kuredux). The biodegradation of the PGA is usually faster than that of PL A, although an initial stage of abiotic hydrolysis appears to be necessary, since the pol3rmer has a phase in the crystaUine state and another in the amorphous glassy state [61]. 

In contrast to PDES, it is impossible to obtain PDFS in the completely amorphous glassy state even by quenching its melt with liquid nitrogen. For PDFS, due to a large interval between the temperature of the mesophase formation from the melt and crystallization (see Fig. 4) at any cooling rates, the mesophase is already formed before crystallization occurs. Hence, the presence of the mesophase in the temperature interval of crystallization leads to such fast crystallization rates that the possibility to reach the amorphous state or even obtain the mesomorphic glassy state is excluded. In PDES, amorphization seems to be possible because of a small temperature range of existence for the mesophase. The behaviour of PDFS also supports the fact that the formation of the mesophase from the isotropic melt is controlled by... 

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