Two-dimensional colloid crystals obtained by coupling of flow and confinement.

This Letter describes the generation of 2D colloidal lattices in microchannels by coupling the laminar flow of dispersions of spherical colloids and geometrical confinement. We describe a nonequilibrium, convective, mechanism leading to formation of ordered 2D structures of both closed-packed hexagonal and non-closed-packed rhombic symmetries. The number and types of possible lattices is determined by the ratio of the width of the channel to the diameter of the particle. The structures tend to return to a regular lattice after a defect is introduced; that is, for example, they tend to self-repair disorder induced by particle polydispersity, contaminants, and flow instabilities. The stability of different lattices is analyzed numerically for particles with different polydispersity.