Many of the industrial applications involve controlling the interaction between particles. Materials consisting of linked colloids could have interesting properties. For example, researchers are discussing making photonic crystals, materials that act as semiconductors for light, out of colloids. To do so, they must arrange colloidal particles of a particular size to filter light in a prescribed way. Accordingly, Grier and other researchers around the world have focused their attention on the physics of colloidal crystals.
Some groups use gold or silica clusters for their work.
The beads are so uniform, says Cherry A. Murray, head of the semiconductor physics research department at Lucent Technologies in Murray Hill, N.J., that scientists use them to calibrate the magnification of electron microscopes. In addition to uniform size, other properties make the beads attractive to colloid researchers. The beads are manufactured with a surface coating of thousands of sulfate salt groups, which dissociate into ions when the beads are placed in water. The positively charged ions float away, leaving a host of negative charges on the beads. In other words, they melt.