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Colloidal crystals are three-dimensionally periodic
lattices assembled from monodispersed spherical colloids.
The ability to crystallize spherical colloids into spatially
periodic structures has enabled interesting and often
useful functionality not only from the constituent colloidal
particles, but also from the long-range order exhibited
by these periodic structures.
A variety of methods by which to assemble spherical
colloids into crystalline lattices have been successfully
demonstrated, with notable examples including sedimentation
in a gravitational field, crystallization through attractive
capillary forces caused by solvent evaporation, and
self-organization via entropic forces or repulsive electrostatic
interactions.
Similar to the diffraction of X-rays from atomic and
molecular crystals, crystalline lattices of spherical
colloids diffract light according to the Bragg equation.
These periodic structures have also been actively explored
as functional components in fabricating new types of
diffractive devices such as filters and switches, smart
optical sensors, and photonic bandgap structures. Recent
studies on the unique optical properties of these materials,
often referred to as photonic bandgap crystals, have
lead to a new and exciting field of research.
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