New method uses heat flow to levitate variety of objects

New method uses heat flow to levitate variety of objects
February 15, 2017 by Greg Borzo
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https://phys.org/news/2017-02-method-levitate-variety.html

Although scientists have been able to levitate specific types of material, a pair of UChicago undergraduate physics students helped take the science to a new level.

Third-year Frankie Fung and fourth-year Mykhaylo Usatyuk led a team of UChicago researchers who demonstrated how to levitate a variety of objects—ceramic and polyethylene spheres, glass bubbles, ice particles, lint strands and thistle seeds—between a warm plate and a cold plate in a vacuum chamber.

"They made lots of intriguing observations that blew my mind," said Cheng Chin, professor of physics, whose ultracold lab in the Gordon Center for Integrative Science was home to the experiments.

In their work, researchers achieved a number of levitation breakthroughs, in terms of duration, orientation and method: The levitation lasted for more than an hour, as opposed to a few minutes; stability was achieved radially and vertically, as opposed to just vertically; and it used a temperature gradient rather than light or a magnetic field. Their findings appeared Jan. 20 in Applied Physics Letters.

"Magnetic levitation only works on magnetic particles, and optical levitation only works on objects that can be polarized by light, but with our first-of-its-kind method, we demonstrate a method to levitate generic objects," said Chin.

In the experiment, the bottom copper plate was kept at room temperature while a stainless steel cylinder filled with liquid nitrogen kept at negative 300 degrees Fahrenheit served as the top plate. The upward flow of heat from the warm to the cold plate kept the particles suspended indefinitely.

"The large temperature gradient leads to a force that balances gravity and results in stable levitation," said Fung, the study's lead author. "We managed to quantify the thermophoretic force and found reasonable agreement with what is predicted by theory. This will allow us to explore the possibilities of levitating different types of objects." (Thermophoresis refers to the movement of particles by means of a temperature gradient.)

"Our increased understanding of the thermophoretic force will help us investigate the interactions and binding affinities between the particles we observed," said Usatyuk, a study co-author. "We are excited about the future research directions we can follow with our system."