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Polymorphism in Pharmaceutical Solids by Harry G. Brittain download in pdf, ePub, iPad

Ostwald suggested that the solid first formed on crystallisation of a solution or a melt would be the least stable polymorph. This can be explained on the basis of irreversible thermodynamics, structural relationships, or a combined consideration of statistical thermodynamics and structural variation with temperature. Solid phase transitions which transform reversibly without passing through the liquid or gaseous phases are called enantiotropic. In contrast, if the modifications are not convertible under these conditions, the system is monotropic. Various conditions in the crystallisation process is the main reason responsible for the development of different polymorphic forms.

Ostwald suggested that the solidThis can be explained

The most stable form is monoclinic form I. This experiment shows that additives can induce the appearance of polymorphic forms. Polymorphs have different stabilities and may spontaneously convert from a metastable form unstable form to the stable form at a particular temperature. For an enantiotropic system, a plot of the free energy against temperature shows a crossing point threshold before the various melting points.