Multiple amorphous phases polyamorphism

It seems appropriate here to introduce the current topic of multiple amorphous phases even if little work has yet been carried out. The phase rule states that at equilibrium 

However the case of true polyamorphism, where there is a well-defined phase transition between amorphous phases, is more difficult to demonstrate in food materials. Polyamorphism is known in the case of several inorganic compounds and has been proposed in several pharmaceutical preparations. 

In addition to multiple amorphous states, Wunderlich [22] has proposed coexistent dual amorphism, where the dominant characteristics are those of a mobile amorphous phase and a so-called rigid amorphous fraction (RAF). The RAF is characteristic of semi-crystalline polymers, found in many food, pharmaceutical and polymer areas, where polymer chains, as they pass from crystalline to amorphous regions, are perturbed and have properties lying between the two extremes. A property of the RAF is that it does not contribute to the step in heat capacity at the main glass transition. In fact the method of calculating the fraction of the rigid amorphous phase cp is usually to measure the crystallinity by an independent method, such as density or possibly X-ray methods, and to estimate the mobile amorphous fraction from the difference between the heat capacity steps of the sample under consideration and a 100% amorphous-generated state. The RAF is then calculated as the difference between 1 and the sum of the content of the previous phases. 

It is obvious that such a measurement, in common with many such difference methods, will be subject to considerable error. 

The demonstration of small glass transitions in foods can be difficult however, it is possible under favourable circumstances to demonstrate the presence of the RAF directly in, for example, isotactic polystyrene. The presence of the RAF, which has a higher glass transition temperature in view of the restricted motion of the chains, is revealed by an enthalpic relaxation peak [23] and a very small shift in the baseline Cp value as the RAF 

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