Condensed-Matter Physics & Materials Science Seminar

A sphere is a simple shape, but the geometry and statistical mechanics of a collection of spheres are not simple subjects. Understanding how spheres pack when they are confined or when they attract one another is a fundamental problem in condensed matter science, where
collections of spherical particles serve as model systems for studying phase behavior and non-equilibrium phenomena such as the glass transition. And controlling the packing of spheres is now a practical concern in engineering, where spherical colloidal particles serve as building blocks for photonic crystals and other new materials. How can we learn to understand and control the microstructure of matter
and materials made from spheres? Our approach is to study the structures of confined, few-sphere colloidal systems. Although bulk colloidal spheres are known to form face-centered cubic (FCC) crystals, our experiments show that under compression small groups of hard spheres form specific, reproducible clusters with a variety of non-FCC symmetries. These structures, which range from sphere
doublets, triangles, and tetrahedra to more exotic polyhedra, may provide a way to control the coordination in bulk sphere packings and colloidal materials.