French researchers have found a new way to levitate liquid droplets by using a stream of electricity to create a tiny cushion of plasma. In doing so, they may have also found a cheap and easy method to generate freely movable microplasma - and put on a very pretty blue light show to boot.
While levitation may sound like it belongs in the realm of fantasy, scientists have actually become quite skilled at levitating small objects using sound waves and magnets. But researchers from the French Alternative Energies and Atomic Energy Commission have now devised a new method, managing to float liquid droplets using plasma.
More than just a cool party trick, the new technique provides some important insight into the production of plasma. It works in a very similar way to something called the Leidenfrost effect, where liquid droplets sitting on an incredibly hot surface begin to levitate on a hot cushion of vapour. Although you may not have heard of it before, you've probably used it without realising when you sprinkle water on your pan to see if it's hot enough to cook with - if the water droplets skitter across the pan, you're good to go, and that's the Leidenfrost effect in action.
But in this experiment, instead of using a hot surface, the French team dropped watered-down hydrochloric acid, which is known for its conductive abilities, onto a metal plate and then began to run an electrical charge through it.
Immediately the water in the acid solution began to break down into hydrogen and oxygen gas. At 50 volts, the bottom of the droplet began to spark and levitate slightly off the surface, with an incredibly beautiful blue glow emanating from the tiny gap in between.
The researchers initially thought that the drop might be floating on top of the hydrogen gas from the breakup of the water. But after further research, they found that by using electricity to make the vapour cushion instead of heat, they'd actually managed to ionise the gas into plasma.
"This method is probably an easy and original way to make a plasma," lead researcher and physicist Cedric Poulain said in a press release. But he admits that this was far from the original reason for the experiment, which was more to do with simple scientific curiosity.
"We were interested in a better understanding of the boiling mechanism," Poulain told Chuck Bednar over at redOrbit. "Namely, the formation of bubbles (nucleation), as well as what happens at high heat flux when suddenly all the bubbles coalesce, leading to the well-known film boiling."
Although they weren't expecting to generate plasma at all, what surprised the team most of all was the blue light emission, seeing as they were only using a relatively low 50 volts. Poulain explains that this was caused by the tiny gap between the droplet and the metal plate, which gave rise to the very high electric field necessary to generate a long-term and dense plasma with little energy.
The next step is for the team to analyse the composition of the plasma cushion, which appears to be a superposition of two types of plasma - something that scientists known very little about.
"It's very exciting," said Poulain of the research's unexpected turn. Even though it wasn't what they set out to do, their results could could provide some fascinating insight into the physics of plasma and potentially lead to new, inexpensive ways to form it. And if that fails, they could always just put a grape in a microwave.