Levitation of Macroscopic Particles by Thermophoretic Force

We demonstrate levitation of micron-sized ice, ceramic, glass and polyethylene particles at low pressure (1-10 Torr) in the presence of a temperature gradient. Under thermophoresis, collisions with more energetic gas molecules from below provide a net upward momentum transfer. Particles initially levitate a few millimeters above a cold plate due to the Knudsen Compressor effect. Particles are then accelerated upwards by the thermophoretic force in the direction from hot to cold in the rarefied gas. In the appropriate pressure regime this allows for stable levitation for up to two hours. Lately we have also succeeded in levitating other materials, including thistle seeds and lint. Our future goals are to levitate water droplets, push levitated particles with a laser, and examine the dynamics behind multi-particle levitation.

The Chicago Maroon reported on our levitation project: Physics Undergraduates Help Discover New Levitation Method.

Levitation of Ceramic Particles

Levitation of Thistle