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An ordered arrangement of colloidal particles. Nearly monodisperse hard-sphere-like particles can order through packing entropy at sufficient concentration, while weak reversible attractions or templates can guide ordering. An irreversibly aggregated solid is not necessarily a colloidal crystal.

An experimental physicist who coauthored the self-assembly of ordered colloidal crystals in a thin nematic liquid crystal. Particles distort the surrounding orientational order and create topological defects; sharing those distortions can bind neighboring particles. The observed structures depended on the type of local ordering, showing how a host material's defects can organize suspended particles into larger patterns.^[ref]

For this self-assembly into a colloidal crystal, four useful elements are building blocks, interactions, environment and reversible dynamics. The building blocks here are nearly monodisperse polymer spheres; their shape and size distribution constrain the accessible packing. Their interactions include excluded volume, Van der Waals forces and electrostatic or steric stabilization, which set the free energy landscape. The aqueous environment supplies temperature, viscosity, ionic strength, confinement and concentration controls. Finally, Brownian motion and rotation must let particles encounter one another and rearrange or detach from incorrect contacts. Attractions that bind every collision irreversibly favour an amorphous aggregate rather than an annealed colloidal crystal. These four categories include both thermodynamic selection and the transport/kinetic access needed to realize it.