Mechanisms for the Formation of Hierarchical Architectures

Crystallization often does not follow the monomer-by-monomer addition pathway described by classical nucleation theory. Instead, the initial steps may involve the formation of larger building blocks, such as crystalline or amorphous nanoparticles, droplets, clusters, complexes, or oligomers, that subsequently undergo assembly into a crystal. These multistep crystallization processes are ubiquitous in mineral formation and biomineralization. In materials synthesis, using non-classical crystallization pathways is particularly attractive, because in a multistep crystallization process, the restriction on which crystalline faces can grow is lifted adding to the versatility of materials architectures that can be obtained. Predicting the outcomes of non-classical crystallization by understanding the control parameters that influence crystallization pathways is an important and challenging task. Advancing this understanding is essential for realizing the full potential of non-classical crystallization in the design of functional materials. The status of the development of a predictive theoretical framework for modeling particle-based crystallization will be reviewed.