Applying more than 50 volts across a droplet of weak hydrochloric acid causes the drop to rise into the air above a glowing plasma layer
Researchers in France have discovered a new way to levitate liquid droplets, which surprisingly also creates a mini light show, with the droplet sparking as it floats above a faint blue glowing gap.
Described this week in the journal Applied Physics Letters, from AIP Publishing, the work may offer an inexpensive new way to generate a freely movable microplasma, as well as yield insights into fundamental physics questions.
The floating effect is similar to Leidenfrost levitation -- in which droplets dance on a hot vapor cushion. But by creating the vapor with a strong jolt of electricity instead of heat, the researchers found they could ionize the gas into a plasma that glowed a soft blue light.
"This method is probably an easy and original way to make a plasma," said Cedric Poulain, a physicist at the French Alternative Energies and Atomic Energy Commission. Poulain speculates that the deformability of a liquid drop would let the researchers rig up a device to move the plasma along a surface, but he admits that such applications were far from his and his colleagues' minds when they first conceived the experiment.
At first, the researchers wanted to explore the limits of the analogy between the boiling phenomenon and water electrolysis, which is the breakup of water into hydrogen and oxygen gases by an electric current.
As an example of boiling behavior, Poulain described the case of a liquid droplet at the surface of a hot pan. If the pan temperature is just above 100 degrees Celsius, the drop spreads and water vapor bubbles grow at the pan surface. However, if the pan is very hot (more than 280 degrees Celsius), a cushion of vapor is formed between the drop and the pan, levitating the drop and preventing contact between the liquid water and the pan, a phenomenon called the Leidenfrost effect. "This is a classical ‘grandmother’ trick to test the temperature of a pan," Poulain said.
The team wondered if a similar transition exists in the case of water electrolysis. The analogy interested the authors, because they study an event called "boiling crisis" in nuclear power plant steam generators. If the core of a nuclear reactor gets too hot, bubbles in the cooling water can suddenly coalesce to form a vapor film that limits further heat transfer and leads to a dangerous increase in temperature.
A Cushion of Vapor from a Jolt of Electricity
In their lab, Poulain and his colleagues devised a set-up to run electricity through conductive droplets and film the droplets' behavior at high speed. They suspended a small drop of weak hydrochloric acid, which conducts electricity, above a metal plate and applied a voltage across the drop. When the drop touched the plate, electricity began to flow, and the water in the hydrochloric acid solution started to break down into hydrogen and oxygen gas.
Above 50 volts, the bottom of the droplet started sparking. It levitated, rising over the surface of the plate, and a faint blue glow emanated from the gap.
At first the researchers believed that the drop might be resting on a cushion of hydrogen gas from the breakup of water, but further analysis revealed that the gaseous cushion was in fact mostly water vaporized by energy from the electric current.
The blue light emission was unexpected and probably the most exciting feature of the experiment, the team said. Although fifty volts is a relatively low voltage, Poulain explained that the tiny gap between the droplet and the metal plate is what gives rise to the very high electric field necessary to generate a long-term and dense plasma with little energy.
Exploring the Blue Light
The researchers next plan to analyze the composition of the plasma layer. They say it appears to be a superposition of two types of plasma that is not well understood. They will also study the fast dynamics at the bottom of the drop just as the sparks begin to fly, which should yield additional insights into the plasma.
Although plasma dynamics may seem far removed from the problem of film boiling in nuclear reactors, Poulain is happy about the path the curiosity-driven research has taken the team.
"It's very exciting," he said of the team's foray into plasma levitation.
The article, "The plasma levitation of droplets," is authored by Cedric Poulain, Antoine Dugue, Antoine Durieux, Nader Sadeghi, and Jerome Duplat. It will be published in the journal Applied Physics Letters on August 11, 2015 (DOI: 10.1063/1.4926964). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/107/6/10.1063/1.4926964
The authors of this paper are affiliated with the French Alternative Energies and Atomic Energy Commission (CEA), Ecole Polytechnique, and the University of Grenoble Alpes.
ABOUT THE JOURNAL
Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org
Jason Socrates Bardi
Jason Socrates Bardi | newswise
New type of smart windows use liquid to switch from clear to reflective
14.12.2017 | The Optical Society
New ultra-thin diamond membrane is a radiobiologist's best friend
14.12.2017 | American Institute of Physics
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong
Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
14.12.2017 | Health and Medicine
14.12.2017 | Physics and Astronomy
14.12.2017 | Life Sciences