This grant supports theoretical and computational research on the properties of disordered systems. In particular, research will be done on the concept of jamming. Many systems with no quenched disorder can jam, i.e., develop a yield stress or an immeasurably long stress relaxation time in a disordered state. These systems include supercooled liquids, colloidal suspensions, granular materials, emulsions and foams. It has recently been suggested that the onset of jamming might lead to some degree of universality. This is the concept of jamming. Specifically, it has been suggested that different systems should show similar behavior as they jam, and that each system has a jamming phase diagram.
The concept of jamming will be explored using numerical simulations on two very different systems that both exhibit transitions to constrained dynamics. The first is a quiescent thermal system, namely a binary Lennard-Jones mixture. This model has been shown to jam as the temperature is lowered to the glass transition. The second system to be studied is a driven, athermal system that has been shown to jam as the shear stress is lowered to the yield stress or as the density of particles is raised above close-packing.
One objective of the proposed research is to exploit the idea of jamming to gain new insight into the glass transition by applying recent ideas from granular materials (namely force chains) to supercooled liquids. We will also test the idea of jamming by calculating the complete jamming phase diagram for a binary Lennard-Jones mixture. Finally, we will test whether shear-induced fluctuations can be described by an enhanced effective temperature in binary Lennard-Jones mixtures. The idea of an effective temperature is already widely used to describe unjammed granular materials and needs to be examined carefully.
At a minimum, we will learn much more about the behavior of two intriguing systems (supercooled liquids and sheared athermal packings), even if we discover that their connection is only superficial. If the concept of jamming is correct, however, it will be extremely powerful because ideas derived from one system will be applicable to another. The recognition that different systems can be viewed within a broader framework has revolutionalized a number of fields in the past. It is important to explore the avenue of jamming because it may lead to new and deeper understanding of long unsolved problems such as the glass transition. %%% This grant supports theoretical and computational research on the properties of disordered systems. In particular, research will be done on the concept of jamming. Jamming commonly occurs to most of us in the form of traffic jams. As too many vehicles try to pass through a constrained path, the smooth flow of traffic becomes stopped or jammed. Many physical systems comprised of many particles can also jam, i.e., develop a yield stress or an immeasurably long stress relaxation time in a disordered state. These systems include supercooled liquids, colloidal suspensions, granular materials, emulsions and foams. It has recently been suggested that the onset of jamming might lead to some degree of universality among these diverse systems. This is the concept of jamming. Specifically, it has been suggested that different systems should show similar behavior as they jam, and that each system has a jamming phase diagram. In this research the concept of jamming will be explored using numerical simulations on two very different systems that both exhibit transitions to constrained dynamics. ***
