Reasons for studying phase diagrams

The dependence of the transition temperatures on concentration shows, as has already been described, whether there is miscibility in multicomponent systems. Partial miscibility in a glassy or crystalline phase may be useful for compatabilization of two components. Eutectic blends may be desired to obtain a certain morphology of the crystalline regions of a blend. 

Classical thermodynamics gives the criteria for miscibility with equations (9.5) and (9.6). The most important property that affects miscibility of polymer systems compared with other systems is the large molar mass of the components. The Gibbs free energy of mixing is given by 

At present, the most common way to gain information about the phase behavior of polymer systems is first to obtain experimental data about the temperature and composition dependence of phase transitions and then to interpret them by applying thermodynamic principles. Following this semi-empirical method, the observation of glass transition(s) is commonly used to study miscibility in amorphous and semicrystalline mixtures. 

There are several equations to describe Tg-composition dependence in miscible blends, for example the Gordon-Taylor, Fox, Kelley-Bueche or Kanig equations [60-63] however, there are systems that do not fit to any of them. The Gordon—Taylor equation may serve here as an example of the relations mentioned above  

Tg is the glass transition temperature of the blend, Tg is the glass transition temperature of the pure polymer 1, Tg is the glass transition temperature of the pure polymer 2, K is the ratio of the difference between the expansivities above and below the glass transition of polymer 2 and polymer 1, and volume fraction of polymer 2. 

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Reasons for studying phase diagrams 9.6 REASONS FOR STUDYING PHASE DIAGRAMS... 

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