A holistic view of nucleation and self-assembly

Nucleation is the seminal process in the formation of ordered structures ranging from simple inorganic crystals to macromolecular matrices. Observations over the past 15 years have revealed a rich set of hierarchical nucleation pathways involving higher-order species ranging from multi-ion clusters to dense liquid droplets, as well as transient crystalline or amorphous phases. Despite this complexity, the pathways that lead to nucleation can be described by a holistic framework that is rooted in classical concepts, but which takes into account the coupled effects of perturbations in free-energy landscapes and the impact of dynamical factors. This article describes that framework using a series of in situ transmission electron microscopy and atomic force microscopy studies on inorganic, organic, and macromolecular systems to illustrate the evolution in nucleation processes as these perturbations and dynamical factors come into play. The results provide a common basis for understanding development of order in systems as diverse as simple salt crystals, branched semiconductor nanowires, and microbial membranes.