PSD research in self-assembling granular matter to be highlighted at APS 2022

January 25, 2022

Two early career scientists from the Department of Physics will be presenting their research in granular matter at the American Physical Society meeting that will be held March 14-18 at McCormick Place Convention Center in Chicago. Over 12,000 physicists across subfields attend the annual meeting. 

The scientists will represent the soft matter research lab of Heinrich Jaeger, the Sewell Avery Distinguished Service Professor in the Department of Physics, James Franck Institute, and the College. 

Tabletop Asteroids

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Asteroids span kilometers and form over millions of years. But efforts to build tiny asteroids in the laboratory could open up their secrets in minutes. (Credit: M. Lim, B. VanSaders, A. Souslov, H. Jaeger)

Melody Lim, a sixth-year student, recently completed her dissertation defense. Her presentation explores the role of electrostatic attraction and self-gravity in driving the assembly of astrophysical systems like protoplanetary aggregates, rubble-pile asteroids, and the rings of Saturn. 

Lim was chosen as an invited speaker to give a talk entitled “Acoustically Levitated Granular Matter” on March 15, from 5:24-6:00 p.m., presenting a case for tabletop experiments that controllably test models of granular materials in low gravity environments. “Tabletop” refers to the small scale of these experiments that fit on a lab bench or in a modest-sized room. 

Melody Lim
Melody Lim

By levitating particles in an ultrasonic standing wave, Lim can record the substrate-free assembly, manipulation, and scattering of particles. She will explain two new insights into astrophysical phenomena: granular contact charging and the rotational disruption of rubble-pile asteroids. Her work points to a new path for experiment—“tabletop asteroids,” where astrophysical processes that take millions of years, on the scale of kilometers, can be observed and controlled in minutes.

“Melody’s research using acoustic levitation has introduced a whole new experimental platform for exploring the many-body physics of small, strongly interacting particles,” said Prof. Jaeger. “Her findings provide an amazing inside view on how clusters assemble, and disassemble, particle-by-particle.”

“Working with acoustically levitated granular matter has been exhilarating, surprising, and inspiring at every turn,” said Lim. “I’m incredibly grateful for this opportunity to share what we’ve been doing, and hope that I can share something of my excitement for the future of these experiments with the broader community.”

Sequence of granular particle clusters demonstrating how they can merge and split.
In an acoustic trap, granular particles levitate and form clusters and can split. (Credit: Melody Lim)


Under gravity, Granulobots shift their collective shape and switch from soft to stiff states by applying torques to their neighbors. 

Research staff scientist Baudouin Saintyves received his Ph.D. in physics at the Sorbonne University and joined UChicago after postdoctoral positions at MIT and Harvard. He is currently exploring new resilient and autonomous robotic approaches based on the physics of soft matter and self-organization in nature.

His talk, “Granulobot: From Granular Matter to Self-Assembling and Reconfigurable Robotics,” on March 15, from 5:00-5:12 p.m., will introduce a new shape shifting robotic system based on the rich physics of granular matter.

Baudouin Saintvyes
Baudouin Saintyves

“When building sandcastles on the beach,” he said, “we can all experience that wet sand can behave either as a solid or as a liquid. We rely on this property to eventually form complex shapes with our hands. We thought about a robotic system that would take the inverse stance: What if the grains themselves can produce the deformation, without human hands?” 

The system he proposes instead demonstrates that the process of forming a shape is now initiated by motions and stresses produced by the grains themselves, without human physical interaction. This robotic “pile of sand” is made of multiple centimetric identical units, with a single motor on each that can “push” their neighbors. Adhering to this simple principle allows the robotic assembly to self-assemble, shift its shape and mechanical behaviors in real-time, as well as to be controlled in a decentralized way. These features are particularly relevant when highly resilient and autonomous robots are needed, such as in space exploration, catastrophe management, or field exploration. 

“Baudouin’s Granulobot is the first example of a new, very exciting class of modular robots,” said Prof. Jaeger. “These robots can morph into different shapes, can assemble themselves autonomously, and can break themselves apart into smaller units that then can move on their own,” he said.

Look for other talks and posters at the APS meeting featuring field-defining faculty in the PSD, including Profs. David Awschalom, Cheng Chin, Juan de Pablo, and Guilia Galli, among others. A full schedule of the scientific program is available on the APS website. Attendees may also join online for the majority of programs.

This article was updated on March 7.

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