Thermodynamics of Mesophase Transitions

Flexible, linear macromolecules frequently show on cooling only partial crystallization. Such materials can often be described by the crystallinity model (typical crystallinities of 30-90%) 18-19). Two of the questions in the description of macro-molecular mesophases must thus be what is the crystallinity of the sample and which phases are present  

The formation of macromolecular liquid crystals usually seems to be virtually complete. Also, when the mesogenic group is sufficiently mobile, there is only little supercooling of the transition to the liquid crystalline state. Plastic and condis crystals, on the other hand, are expected to behave more like the fully ordered, macromolecular crystals, i.e., partial crystallinity is expected in these cases. 

Liquid crystal forming materials have thus five possible pure phases (fully ordered -crystal, LC-glass, amorphous glass, liquid crystal, and isotropic melt). In addition, there may be four two-phase materials (fully ordered crystal and LC-glass, fully ordered crystal and amorphous glass, fully ordered crystal and isotropic melt, and fully ordered crystal and liquid crystal). The correlations between these phases are shown in Fig. 3. 

Each of the glass transitions has the appearance as given in Fig. 1. From the magnitude of the increase in heat capacity at the transition it should be possible to obtain information on the total amount of mobility gained, as outlined in Sect. 2. For well characterized systems, the glass transitions can also be used for the approximate determination of the weight fraction of crystallinity wc 

CRYSTAL TO LIQUID CRYSTAL TRANS I T I OIM CRYST - TO. LC TRANS.  

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