Ordering and disordering of molecular solids upon mechanical milling: the case of fananserine

In this article, we study the physical transformations of the forms III and IV of fananserine upon mechanical milling. The investigations have been performed through X-Ray powder diffraction and differential scanning calorimetry experiments. The results indicate that both forms undergo a polymorphic transformation toward the metastable form I upon milling at room temperature (25 degrees C) while an amorphization is observed upon milling at 0 degrees C. It thus appears that the nature of the transformation induced by milling does not depend on the initial polymorphic state, but strongly depends on the milling temperature. Interestingly, the change in the nature of the transformation with the milling temperature occurs in a short temperature range around the glass transition temperature (T(g) = 19 degrees C). The implication of T(g) in the duality "amorphisation/polymorphic transformation" generally observed upon milling is thus discussed. The physical stability of the end products is also investigated and discussed with respect to the storage temperature of the material.