Frozen microvoids

Above the glass transition temperature, i.e. in the rubbery state, the mobility of the chain segments is increased and frozen microvoids no longer exist A number of physical parameters change at the glass transition temperanire and one of these is the density or specific volume. This is shown in figure V - 26 where the specific volume of an amorphous polymer has been plotted as a function of the temperature. 

The parameter C/j of the equation (4) is believed to correlate with the volume of the frozen microvoids [45], i.e. the part of the polymer free volume also called excessive free volume . The existence of the intermolecular gaps (microvoids) in glassy polymers is widely recognized and has been analyzed in numerous studies [e.g. 40, 46-55]. 

Most food products and food preparations are colloids. They are typically multicomponent and multiphase systems consisting of colloidal species of different kinds, shapes, and sizes and different phases. Ice cream, for example, is a combination of emulsions, foams, particles, and gels since it consists of a frozen aqueous phase containing fat droplets, ice crystals, and very small air pockets (microvoids). Salad dressing, special sauce, and the like are complicated emulsions and may contain small surfactant clusters known as micelles (Chapter 8). The dimensions of the particles in these entities usually cover a rather broad spectrum, ranging from nanometers (typical micellar units) to micrometers (emulsion droplets) or millimeters (foams). Food products may also contain macromolecules (such as proteins) and gels formed from other food particles aggregated by adsorbed protein molecules. The texture (how a food feels to touch or in the mouth) depends on the structure of the food. 

These results, combining the widely known instability (and dissipative structure ) phenomenon of melt fracture with the new non-equilibrium description of multiphase polymer systems, will hopefully stimulate more experimental and theoretical work devoted to these (frozen) dissipative structures. Up to now, it remains open which property of the melt may be responsible for its suddenly occurring capability to disperse fillers (pigments, carbon-black, etc.) or other incompatible polymers above melt fracture conditions. We can only speculate that the creation of microvoids ( = inner surfaces) in particular and a sudden increase of gas solubilisation capability at and above melt fracture allows the polymer melt to wet the surface of the material to become dispersed. This means that a polymer melt might have completely different (supercritical) properties above melt fracture, than we usually observe. 

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