Assembling colloidal devices by controlling interparticle forces

In recent years the concept of "colloidal devices" has emerged. These include colloidal crystals with photonics properties, as well as displays, machines, and other assemblies having a particular purpose. The assembly of colloidal devices, or even simpler assemblies, can proceed with top-down approaches, applied fields, bottom-up approaches, or combinations of these. Bottom-up assembly, in which the particles have "colloidal force information" encoded chemically on their surfaces and interiors, appears to be especially suited for larger-scale production. The encoded information directs how the particles assemble and function, and a simple example is a colloidal crystal that has purely repulsive forces between all the particles. A richer assembly process can occur with site-specific chemistry, which sometimes occurs naturally on particles, such as when a particle has two different crystal faces. And in recent years, researchers have developed techniques for intentionally placing site-specific chemistry on particles, enabling assembly to proceed through localized electrostatic, van der Waals, depletion, hydrophobic, and receptor-ligand forces. Site-specific colloidal forces are useful in effecting colloidal and nanocolloidal assembly for state-of-the-art and future structures and devices.