Liquid Droplets That Levitate On a Blue Light Pad

Scientists in France have found a novel technique to levitate liquid droplets on a cushion or pad of blue light. The effect sets off a striking light show with the droplets generating sparks as they drift over the blue gap.

The effect is quite like the Leidenfrost Levitation in which a liquid drop is made to levitate on its vapor layer created over a hot surface. However, while in the Leidenfrost effect, the temperature is the initiating factor, here it is electricity creating the interesting spectacle.

Plasma creation

The researchers discovered that a high pulse of electricity applied to a gas could vaporize it so the gas glows with a bluish light. This remarkable find may present an economical technique to produce movable micro plasma layers. Furthermore, the study yields remarkable insights into basic principles of physics.

Physicist Cedric Poulain of French Alternative Energies and Atomic Energy Commission explains that the technique is a simple and an innovative way to create plasma.

In the experiment tried out by the research workers, over 50 volts of electric power was applied across a droplet of dilute hydrochloric acid suspended above a metallic plate. This made the droplet levitate over a region radiating a light blue glow.

Cushion of vapor

At voltages above 50V, the base of the acid droplet started to produce sparks. The drop rose, increasing the gap above the metal plate and a blue light filled up the gap. The scientists first assumed that the droplet was lying on a cushion of gaseous hydrogen produced by the electrolysis of the acidified water. Further scientific analysis established that the gas cushion primarily consisted of water vapor.

Poulain explained that extremely small space between the metal plate and the droplet makes it easy to set up the high electric field needed to produce the plasma layer, even with moderate electric voltages.

Contrasting boiling with electrolysis of water

The team compared the electrolytic dissociation of water with boiling. Poulain brought forward the example of a water drop placed on the surface of a heated vessel. He pointed out that at temperatures higher than 100 degrees Centigrade, the drop spreads out and bubbles form on the surface. At temperatures exceeding 280 degrees Centigrade, a vapor cushion can be seen forming in between the drop and the vessel surface. This makes the water drop levitate so that there is no contact between the drop and the vessel surface.

The team described the transition in electrolysis as somewhat similar.

Figuring out the blue light phenomenon

According to the team of researchers working on the project, the emission of blue light was the most striking feature of the study. For a proper conception of the phenomenon, the scientists plan to explore the makeup of the plasma layer. They believe that two types of plasma are superposed, though they cannot yet understand the effect.

The scientists also intend to scrutinize the liquid dynamics at the lower surface of the droplet when the sparks just start to fly out. This should give further information regarding the nature of the plasma layer.