Jamming and Glassy Behavior in Granular and Soft Matter Systems

Granular and soft-matter systems, such as foams, colloids and emulsions, undergo a “jamming transition” from a liquid-like state to a rigid but disordered solid state as one varies system parameters. In athermal systems at low densities, jamming may occur via compression as one increases the packing fraction of the particles. At higher densities, jamming may occur when the applied shear stress decreases below a critical yield stress. At finite temperatures, jamming may occur as one lowers the temperature and freezes into a glassy state. A “jamming phase diagram” has been proposed as a means to unify these three different routes to jamming. Using numerical simulations of a simple model system of frictionless disks in two dimensions, we review the jamming behavior with respect to compression, shearing, and varying temperature. We find that while compression can give a range of jamming packing fractions depending on the initial state, shear driven jamming defines a unique packing fraction where the yield stress vanishes; critical scaling applies at this shear driven jamming transition. Adding finite temperature to our model we use dimensional analysis and numerical simulations to argue that, contrary to the jamming phase diagram conjecture, athermal jamming and the equilibrium glass transition appear to be distinctly different physical phenomena.

Work done in collaboration with Peter Olsson and Daniel Vagberg of Umea University.