Exploring Nucleation Pathways and Solid-solid Transitions in Two-dimensional Colloidal Crystallization

Crystallization, which is found in many natural and manmade systems, describes a phase transition between a disordered and an ordered state, or a pathway on a phase diagram. Although the final crystal structures that emerge are often well understood, the microscopic pathways, which could go through a number of metastable intermediates, are difficult to observe or predict. Do the particles form the final crystal structure directly? Do they form metastable structures first and then transform? And do the pathways they follow influence their final symmetry or order? In this talk, I will present a combination of computer simulations and video microscopy experiments investigating the crystallization pathways of DNA-coated colloids. We explore the role of the relative strengths of interactions in determining the pathway, symmetry, and compositional order in crystallization of a binary suspension. We observe a rich diversity of behavior, including both one- and two-step nucleation pathways, as well as solid-solid transitions between crystal phases. These results may help shed light on the fundamental nature of crystallization, as well as provide new methods for controlling the self-assembly of materials made from colloids.