Using molecular simulation, we shed light on the molecular mechanisms underlying the crystallization process. We first examine the formation of liquid precursors prior to the formation of the crystal nucleus. For substances able to exist in more than one liquid phase (i.e. exhibiting liquid polymorphs), we observe the formation of a nanosized droplet of a metastable liquid polymorph, which later gives rise to a crystal nucleus. This result suggests that liquid polymorphs provide additional metastable states, that the system uses to find a more favorable crystallization pathway. We then examine the selection of a specific crystalline polymorph during nucleation and growth. We show how the conditions of crystallization influence the outcome of polymorph selection, but also how fast this selection proceeds. We finally rationalize these findings in terms of the phase diagrams, including the domains of occurrence of the metastable polymorphs, for the systems studied.

How the relative stability of different polymorphs influence the crystallization process: insights from molecular simulation

243rd National Meeting (2012)

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