Pressure-temperature parameters amorphous solids

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. 

Thus the simulation of quenching may not necessarily be an adequate model of the real process. This is an important fact if we take into consideration the fact that an amorphous state is generally metastable so that its structural characteristics depend upon the history of its formation. This distinguishs the amorphous state from the stable crystalline state whose structure is in principle determined by the thermodynamic parameters, e.g., pressure and temperature, and not upon the history of its formation. To be more specific, let us consider the simple case when a crystalline structure of a solid may be determined... 

The morphology of the resulting solid material depends both on the material structure (crystalline or amorphous, composite or pure, etc.) and on the RESS parameters (temperature, pressure drop, distance of impact of the jet against the surface, dimensions of the atomization vessel, nozzle geometry, etc.)[ l It is to be noticed that the initial investigations consisted of pure substrate atomization in order to obtain very line particles (typically of 0.5-20 m diameter) with narrow diameter distribution however, the most recent publications are related to mixture processing in order to obtain microcapsules or microspheres of an active ingredient inside a carrier. 

Abstract Supercritical antisolvent technology can precipitate polyvinylpyrrolidone (PVP) particles and crystallize paracetamol (PCM) crystals first separately and then together in the form of a solid dispersion. Supercritical carbon dioxide (SCCO2) is used as an antisolvent. For PVP particle generation, ethanol, acetone, and mixtures of ethanol and acetone are used as solvents. The initial concentration of PVP in the solution was varied between 0.5 and 5 wt%, the operation pressure between 10 and 30 MPa, and the composition of ethanol/acetone solvent mixtures between 100 and 0 wt% of ethanol at a constant temperature of 313 K. An increase in the content of the poor solvent acetone in the initial solution leads to a significant decrease in mean particle size. Fully amorphous PVP powder always precipitates for all the parameters investigated. 

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