Detail:

Abstract:
　　In recent years, research on nucleation and crystallization has revealed alternative pathways to the classical ones known from the textbooks of crystallization. These so called nonclassical pathways allow for a better understanding of so far difficult to understand crystallization processes as observed for example in Biomineralization. In addition, they open up entirely new possibilities for the control of crystallization processes and therefore crystals, which would be impossible to synthesize by classical methods.
　　The presentation will focus on nonclassical nucleation processes for the example of CaCO3. It can be shown that so called prenucleation clusters of ca. 40 ion pairs in size exist in equilibrium with the ions and ion pairs. These clusters are highly dynamic polymers which constantly form and dissociate. Their formation is entropically driven by the release of hydration water. Increasing the overall ion concentration leads to a decrease in their dynamics and a phase transition in form of binodal demixing to nanodroplets. These coalesce and form larger droplets which solidify and form amorphous CaCO3, which finally crystallizes. This multi-step nucleation scenario is not only relevant for CaCO3, but also other minerals like calcium oxalates or phosphates and also organic molecules like amino acids. For the example of glutamic acid, it will be shown that classical layer by layer growth can be initiated by nanodroplets which attach to the crystal surface from the solution phase.