Story by Greg Borzo | Photo by Jean Lachat | Video by UChicago Creative
Deep in a basement lab of the Gordon Center for Integrative Sciences lies a sophisticated tangle of steel tubes, bolts and wires—a device so sensitive that a misalignment of one degree can greatly reduce its performance.
Since 2014, physics undergraduates at the University of Chicago have been drawn to the shiny device and the opportunity it presents to explore the phenomenon of levitation. Their results have included suspending ice crystals and small polyethylene spheres in midair for a few minutes at a time.
Last year, third-year Frankie Fung noticed something peculiar floating in the machine—material that wasn’t part of the experiment. “It took me awhile to realize I just levitated lint, which accidentally got into the levitation chamber. I was pretty excited. We had always wanted to levitate bigger and heavier objects,” he said.
His chance discovery set off months of work with fourth-year Mykhaylo Usatyuk to levitate larger and larger objects. The research provided new insights into levitation, with the findings published in the academic journal Applied Physics Letters.
“From this accidental observation, they realized the hidden potential of our levitation machine,” said Cheng Chin, the UChicago professor of physics whose lab housed the experiment. “This led to a new series of observations that I couldn’t have imagined in the beginning.”
It took a lot of measuring, speculating and tinkering with the device over hundreds of experiments, but Fung and Usatyuk eventually levitated a variety of other everyday objects, including ice particles, thistle seeds—in addition to lint. In doing so they achieved a number of levitation breakthroughs, in terms of duration (an hour-plus opposed to minutes), orientation (radially and vertically) and method (through a temperature gradient rather than light or a magnetic field).
“We managed to create a system where you can levitate objects for a long period of time,” Usatyuk said.
“We’re talking about hours, and perhaps even longer,” Fung added.
How it works
In the experiment, a copper plate at the bottom is kept at room temperature while a stainless steel cylinder is filled with liquid nitrogen kept at negative 200 degrees Celsius to cool the top plate. The upward flow of heat from the warm to the cold plate keeps the particles suspended indefinitely.
The key to obtaining high levitation stability is the geometrical design of the two plates: A proper ratio of their sizes and vertical spacing allows the warm air to flow around and efficiently capture the levitated objects when they drift away from the center.
The researchers managed to quantify the thermophoretic force and found reasonable agreement with what is predicted by theory, said Fung, the study’s lead author. (Thermophoresis refers to the movement of particles in the presence of a temperature gradient.) “This will allow us to explore the possibilities of levitating different types of objects,” he said.
“Our increased understanding of the thermophoretic force will help us investigate the interactions and binding affinities between the particles we observed,” Usatyuk said. “We’re excited about the future research directions we can follow with our system.”
Levitation of macroscopic particles in a vacuum is of particular interest due to its wide applications in space, atmospheric and chemical research. The apparatus offers a new ground-based platform to investigate the dynamics of astrophysical, chemical and biological systems in a microgravity environment.
‘The joy of discovery’
For Fung and Usayuk, the published research was the culmination of countless hours in the lab.
When he first came to the University, Fung was hoping to join Chen’s lab to conduct research on ultracold atoms, but Chen instead suggested Fung join a project in which undergrads were trying to levitate small particles.
“One of the best things about doing experiments as an undergrad is the joy of discovery, especially when you discover something yourself,” Fung said. “I feel really fortunate to get published as an undergrad, because in a sense, it signifies your research is valuable to the scientific community.”
Usatyuk said that being in Chin’s lab showed him how science works in the real world. “When you’re actually in the lab working on something that has no clear answer, you get a greater appreciation for how the whole process works,” said Usatyuk, who attributed his interest in science to a high school trip to Argonne National Laboratory, during which he saw a levitating superconductor cooled using liquid nitrogen.
Chin’s lab is now looking at how to levitate macroscopic substances greater than a centimeter, how these objects interact or aggregate in a weightless environment, and how levitating ice particles aggregrate into snowflakes. He said there are ample research opportunities for undergraduates to continue to contribute—each year since the project began in late 2014, two different undergrads work on the levitation experiments.
“It’s not guaranteed that research will work, so it’s not very often that undergraduates publish a research paper,” Chin said, “It’s risky, but it’s an opportunity for young students to be ambitious and explore the possibilities.”
Originally published on April 4, 2017.