The Inverse Leidenfrost Effect

The Leidenfrost effect occurs when a volatile droplet like water levitates over a hot surface because it floats on a cushion of its own vapor.

The inverse Leidenfrost effect levitates a droplet on a bath of liquid nitrogen, where the nitrogen bath creates the vapor rather than the droplet itself.

Recent papers have documented this phenomenon, prompting the host to contact a scientist to learn how to replicate and understand the effect.

• Polystyrene box approximately 20 by 20 centimeters with good insulation • Two beakers of different sizes • Liquid nitrogen

A styrofoam piece with a cylindrical cutout filled with liquid nitrogen to keep the outer space cold and insulated; a large beaker boiling with liquid nitrogen; and an inner beaker with non-boiling liquid nitrogen where the experiment occurs.

100 microliters of silicone oil dropped onto the liquid nitrogen bath produces multiple levitating droplets, but the experiment fails because the nitrogen in the middle beaker begins boiling.

The boiling in the outer beaker creates instability that interferes with proper observation of the effect.

With clean beakers and fresh liquid nitrogen, a droplet of silicone oil successfully bounces back and forth, demonstrating the inverse Leidenfrost effect.

The effect can continue almost indefinitely, lasting tens of minutes, unlike the classic Leidenfrost effect where the droplet is consumed creating its own vapor cushion.

Heat required to evaporate the bath comes from both the droplet and the warm atmosphere around the experiment, allowing the supporting vapor to persist even after the drop freezes.

Instability in the experimental setup causes the outer beaker boiling to shake the inner beaker, interfering with droplet motion; professional setups show the drop moving in straight lines.

Many people observed droplets moving on a bath but nobody had explained the mechanism until recent research addressed this phenomenon.

A thin vapor layer exists between the floating drop and the bath, but this layer is not uniformly thick; capillary waves grow underneath creating instability.

• Droplets cannot be deposited perfectly, creating tiny waves that return beneath the drop • These waves cause asymmetry underneath the droplet where one side is higher than the other • More nitrogen gas escapes from the higher side

Gas escaping from the asymmetrical sides drags the droplet along, similar to how wind pushes raindrops across a windshield, rather than pushing in the opposite direction.

When the droplet approaches a wall, a small liquid nitrogen meniscus forms, causing the drop to climb it; the propelling force reverses and pushes it back, creating a star-shaped motion pattern that is self-propelled and self-repelling from walls.

Very young embryos (approximately 10 cells) can be placed in cryopreservation liquid and frozen in liquid nitrogen; fast freezing prevents ice crystal growth, preserving the embryo structure.

Embryos with cryopreservant can be placed on the liquid nitrogen bath to create self-propelled droplets that move in controlled directions without manual contact.

• Cells or chemicals can be simultaneously frozen and moved • No contamination occurs because the droplets are never directly touched • Self-propulsion eliminates need for external manipulation

This technology could enable systematic freezing and movement of cells or biological materials in a completely contactless manner, opening possibilities for improved cryopreservation procedures.