Jamming and The Glass Transition

Eric Corwin, Physics
VoronoiIllustration-672x372The study of jammed systems began as a culinary curiosity in 1727, when the Reverend Stephen Hales studied how peas pack when compressed in an iron pot. Fill a pot with peas and you can run your hand through them. This is because they can flow out of the way much as a liquid would. But as pressure exerted on them, and thus their density, is increased, you will find that there is a critical point, above which the peas “jam” into a stable but amorphous solid. This behavior is very general.  Pretty much everything composed of discrete chunks can go through a jamming transition: colloids in solution, a pile of sand, a jar full of candies, even cars in a traffic jam. Even thermal systems can undergo this same sort of transition, most easily observed as molten glass cools into everyday window glass. Thus the thermal glass transition and the thermal jamming transition are really two sides of the same coin. Understanding these linked transitions will lead to revolutions in controlling, designing, and processing new materials: entire cars injection molded out of metallic glasses; optical band gap materials to enable photonics, rather than electronic computer chips; and new, more reliable pills for time-released drug delivery, to name just a few.  To this end, we will focus extensively on experimental, numerical, and theoretical studies of the jamming and glass transition(s), the collective behavior of granular materials, and complex macroscopic systems subject to chaotic forcing.