With the onslaught of the COVID-19 pandemic, understanding the nature of airborne viruses and microorganisms has become more important than ever. Experts have been constantly searching for better ways of studying these entities and developing effective strategies to prevent them from spreading. One such technique that has gained the attention of scientists is droplet levitation.
What is Droplet Levitation?
Droplet levitation is a method where sound waves suspend tiny droplets in the air. It involves placing a droplet on a small platform and emitting sound waves at a certain frequency using an ultrasonic transducer. The sound waves form a pressure field that resists gravity and suspends the droplet mid-air.
A group of researchers from Tyumen State University in Russia discovered self-sustained levitation of tiny droplets while experimenting with the combinations of immiscible liquids. Researchers Natalia Ivanova and Denis Klyuev noticed that after detaching from the syringe needle, butyl alcohol levitated above the surface of a liquid layer without collapsing onto it.
The noncoalescence of droplets without an underlying liquid is well-known in the scientific community. Still, in the natural setting, a droplet can only levitate above a liquid pool in milliseconds. Keeping the droplets levitating for a long period requires the continuous generation of excess pressure inside the gap between a droplet and the surface of the liquid under it. Such events can be made possible using various methods like vibrations, creating air flows within the ultrathin gap under the droplet, magnetism, or acoustic levitation. These methods require external work on the system or the creation of non-equilibrium conditions.
In the experiment performed by Ivanova and Klyuev, they achieved self-sustaining and long-term levitation of millimeter-sized droplets of various liquids without the need for any external force. They reported to have witnessed the levitation of droplets for tens of minutes. The researchers used solutocapillary convection within a pool of silicone liquid. Solutocapillary convection occurs when the non-uniform distribution of vapor molecules from the droplet in the pool surface forms a surface tension gradient.
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Harnessing the Potential Self-Sustained Droplet Levitation
Droplet levitation is found to have several important scientific applications. The effect of long-term self-sustained droplet levitation can help in developing tools for understanding the nature of heat and mass transfer within a vapor film.
This technique also has a lot of advantages over the traditional approaches to studying airborne particles. Microorganisms can be spread in the air through tiny droplets called aerosols. In biology, aerosols provide an ideal environment for prebiotic transformation that could support life. This was particularly observed during the COVID-19 pandemic, where the SARS-CoV-2 virus was transmission between each person via aerosols.
Since the researchers can study the droplets without physical contact, they are free from the risks of contamination by the microorganisms in the droplets. This technique also allows the study of individual droplets, providing more accurate information regarding the behavior of airborne particles. Moreover, droplet levitation can be used in exploring a large variety of microorganisms, such as viruses, bacteria, and fungi.
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