Exploring nucleation pathways and solid-solid transitions in two-dimensional binary colloidal crystallization

Crystals are prevalent in many natural and manmade systems, including metals, minerals, proteins, and colloids. Although the crystal structures themselves are often well understood, the microscopic pathways by which crystals form are difficult to observe or predict. We use a combination of simulations and microscopy experiments to investigate the crystallization pathways of DNA-coated colloids. We observe a rich diversity of behaviors, including one-step and two-step nucleation pathways, as well as a spontaneous solid-solid phase transition during the crystallization of two-dimensional binary mixtures. In this talk, I will present the results of free energy calculations which indicate that the two-step nucleation transition arises from a competition between the free-energy landscapes of two different structures. I will also explore the possibility that the critical size governing this transition can be tuned by changing the relative strengths of interactions. These results may help shed light on fundamental aspects of nucleation, as well as provide new methods for controlling the self-assembly of materials made from colloids.