The University of Chicago has received a $1.8 million grant from the W.M. Keck Foundation to launch a new research program on the sudden and dramatic transformations that occur in processes where small-scale structural rearrangements result in rapid and far-reaching outcomes. These include the breakup of splashing water droplets, the sudden motion of landslides and the extreme shape changes that occur in a dividing cell.
The University has allocated an additional $1.2 million to the project team, which will include Margaret Gardel, Assistant Professor in Physics; Heinrich Jaeger, Professor in Physics; Sidney Nagel, the Stein-Freiler Distinguished Service Professor in Physics; and Wendy Zhang, Assistant Professor in Physics. Together they will analyze various aspects of catastrophic deformation, a class of what physicists call “far-from-equilibrium behavior.” This type of physical behavior, they say, is one of the most important but also least understood issues in physics, materials science and biology.
A major component of the research will be to evaluate the phenomena of jamming, memory and singularities as a means of better understanding catastrophic deformation.
“Physics has discovered over many years of research that there are at least three categories that give unified behavior within each category: liquid, gas or solid,” Jaeger said. “What’s exciting for us now is this question of whether or not there are equally universal new categories beyond these three established categories. And one of those is a configuration that is neither quite solid nor quite a liquid. It is what we would call ‘jammed.’”
Memory, in the physics sense, refers to whether the recent movement of a molecule is connected to what it will do next. Constant collisions between molecules contained in gases, liquids and solids in their normal states sever any such connection. But memory comes into play in materials, including ordinary window glass, which form glassy states.
“One of the remarkable things that people see in glassy systems is that they often seem to have a memory,” Zhang said. “There’s a difference between how the material behaves if you simply cool it versus you cool it, reheat it and cool it again. It seems to remember what you’ve done to it, and we’re not quite sure how.”
Along with jamming and memory, singularities also can control the dynamics, shape and overall evolution of catastrophic deformation processes. Where singularities occur, scientists encounter great difficulty in using equations to describe the behavior of fluid motion.
“The governing equations for these are inexcusably horrible,” Nagel said. And yet they govern the behavior of fluids on Earth, gases in outer space and perhaps even the internal dynamics of the atom. “It’s these kinds of equations that govern the texture and form of our lives,” he said.
The researchers have applied $1 million of the total funding to developing instruments that will advance current capabilities in ultrafast imaging. They will develop a high-speed imaging apparatus using X-rays produced at the Advanced Photon Source at Argonne National Laboratory to study granular materials.
The team also will combine new camera technology with a confocal microscope, an instrument for producing enhanced images in a narrow field of view. The setup will allow the Chicago team to take images at near-video rates of approximately 30 frames each second, which is critical for studying the properties and dynamics of proteins and cells. The previous state-of-the-art of confocal microscopy limited the image rate to approximately one frame every second.
“Different timescales tell you different things about the behaviors of materials,” Gardel said. Silly Putty, for example, will break like a solid when slammed against a tabletop. But when pulled apart slowly, it deforms like a liquid. Scientists observe the same sort of behavior in the cystoskeleton, which provides structural support for cells. Precise new measurements may yield a better understanding of the cytoskeleton’s structural rearrangements.
“At long timescales, there is flow, there are structural rearrangements occurring. But then at the faster timescales, you’re able to see its more solid-like properties,” Gardel said. “By looking at the dynamics of those short timescales, you can extract information about how rigid the cytoskeleton is.”