Crystallization from the amorphous state: nucleation-growth decoupling, polymorphism interplay, and the role of interfaces

The physical stability of the amorphous state is governed by crystallization, which results from the complex interplay of nucleation and growth processes. These processes can be further complicated by the preferred initial nucleation of less-stable phases, and interpretation requires the evaluation of the relative roles of structure, dynamics, and thermodynamics on the kinetics of the recrystallization. As a contribution to this issue, we reanalyze data sets concerning recrystallization of two pharmaceutical compounds: L-arabitol and RS ibuprofen. These compounds share the property of being good glass formers and present monotropic polymorphism. In the present analysis, we are mainly focusing on the localization of nucleation and growth zones and the role of a transient crystallization of the metastable phase. On the basis of the elementary theories, the results offer the opportunity to discuss the impact of interfacial energies, molecular mobility, crystal disorder, liquid short-range order, and crack formation in the glass.