Epitaxial 2D
nucleation of the stable polymorphic form of the steroid 7αMNa on the
metastable form: Implications for Ostwald's rule of stages
C. Stoica, P. Verwer, H. Meekes, , , E. Vlieg, P.J.C.M. van Hoof and
F.M. Kaspersen
Int. J. of Pharmaceutics 309 (2006) 16-24
Abstract
This paper presents in situ observations of the epitaxial nucleation
and growth of the stable polymorph of a steroid, 7αMna, on a specific
face of the metastable form at low supersaturation, using optical
microscopy and in situ Raman spectroscopy. The presence of the
metastable polymorph is essential for the nucleation and growth of the
stable one. The order of the metastable zones of the stable and
metastable polymorphs is reversed for the epitaxial growth process as
compared to the case of 3D nucleation. The rate of transformation of
the metastable polymorph to the stable one can be controlled by the
supersaturation.