Figure 1
APS/Alan Stonebraker

Figure 1: An evaporating drop of liquid, laden with micron-size spherical particles, leaves a ringlike stain on the underlying surface. Light and electron microscopy reveal variations in the structure of the ring—crystalline near the outer edge and disordered toward the inner part—that occurs during evaporation. The high-zoom image in the upper right shows the succession of hexagonal and square packing arrangements characteristic of a layer of colloidal particles confined to a wedge.