Nonclassical pathways of crystallization in colloidal systems

Colloidal systems offer ideal conditions to study the nucleation process, both from an experimental viewpoint, due to their relatively large size and long time scales, and from a modeling point of view, due to the tunability of their interactions. In this article, we review recent studies on the process of colloidal crystallization from a microscopic perspective. In particular, we focus on nonclassical pathways to nucleation, where the appearance of solid crystals involves fluctuations of two or more order parameters. Nonclassical behavior is interpreted as a decoupling of positional and orientational symmetry breaking. We then consider how the nucleation pathway determines which polymorph is selected upon nucleation from the melt. The study of nucleation pathways not only sheds new light on the microscopic mechanism of nucleation, but also provides important information regarding its avoidance, suggesting a deep link between crystallization and vitrification.