TITLE: "The physics of the colloidal glass transition"

SPEAKER: Professor Eric Weeks,

TIME: Thursday Oct. 4, 2001 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

Are glasses merely extremely slow liquids, and if so, why are they many orders of magnitude more viscous than conventional liquids? We study highly concentrated colloidal suspensions, a model system which has a glass transition. By using a confocal microscope to follow the three-dimensional motion of colloidal particles, we can directly observe the microscopic behavior responsible for the macroscopic viscosity divergence of glasses. For metastable "super-cooled" colloids, we find that structural rearrangements involve only a few, anomalously mobile particles at any given time. These mobile particles move in cooperative regions, and the size of the regions grows as the glass transition is approached. This is the first direct experimental evidence for a growing dynamic length scale at the glass transition, which might explain the viscosity divergence. We also study the non-equilibrium behavior of the colloidal glasses themselves, which have properties which change over time ("aging").