Dense Packing and Symmetry in Small Clusters of Microspheres

When small numbers of colloidal microspheres are attached to the surfaces of liquid emulsion droplets, removing fluid from the droplets leads to packings of spheres that minimize the second moment of the mass distribution. The structures of the packings range from sphere doublets, triangles, and tetrahedra to exotic polyhedra not found in infinite lattice packings, molecules, or minimum–potential energy clusters. The emulsion system presents a route to produce newcolloidal structures and a means to study howdifferent physical constraints affect symmetry in small parcels of matter.