Assembly and phase transitions of colloidal crystals

Micrometre-sized colloidal particles can be viewed as large atoms with tailorable size, shape and interactions. These building blocks can assemble into extremely rich structures and phases, in which the thermal motions of particles can be directly imaged and tracked using optical microscopy. Hence, colloidal particles are excellent model systems for studying phase transitions, especially for poorly understood kinetic and non-equilibrium microscale processes. Advances in colloid fabrication, assembly and computer simulations have opened up numerous possibilities for such research. In this Review, we describe recent progress in the study of colloidal crystals composed of tunable isotropic spheres, anisotropic particles and active particles. We focus on advances in crystallization, melting and solid–solid transitions, and highlight challenges and future perspectives in phase-transition studies within colloidal crystals. Colloidal crystals composed of isotropic spheres are powerful model systems for the studies of crystallization, melting and solid–solid transitions at the single-particle level. Tunable, anisotropic or active particles provide greater opportunities to study crystal assembly and phase transitions.