Let’s make a water drop that’s rhythmic!

Ulsan Institute of Science and Technology (UNIST) announced that a research team led by Jeong Joon-woo, a professor of the physics department, found the synchronization phenomenon of small drops of water making beats in a fine oil tube (microfluid tube).

The research team also presented a theoretical model to explain the cause of this synchronization phenomenon.

According to the research team, if you put water in a microfluid tube that runs oil on both sides, the stream that does not mix with oil breaks itself and becomes a droplet of water.

Originally, the water droplets are supposed to be made in an offbeat form on both sides, but the research team captured a scene in which water droplets, which were first made under certain conditions, synchronized by beating themselves over time.

The research team explained this as a “physical principle of interaction between boundary surfaces.”

The vibrations that occur at the interface between water and oil are viewed as one vibrator, like a pendulum.

When several drops of water are created, vibrators are formed as many as water droplets, and the interaction between the different vibrators adjusts the water droplet production cycle.

Likewise, if you look at the cilia of cells floating in the water as a vibrator, you can explain the behavior of the cilia moving at the beat.

The research team changed the degree to which two droplet productions keep the beat by adjusting the distance of the interfaces, the speed of the liquid flow, and the viscosity.

This technology can be used to control the flow of liquid samples in Lab-on-a-chip (a type of biochip that diagnoses cancer or pathogens, meaning that a laboratory is placed on one chip).

“This is the first time we have observed synchronization of ‘simultaneous generation’ that previous studies on the creation of droplets using lap-on-chips have overlooked,” said Eom Yoo-jin, a professor of physics at Ulsan Science Institute, the first and the corresponding author.

“It is a textbook model system that can explain synchronization with intuitive principles,” Professor Chung said. “It will be useful as a futuristic lab-on-a-chip technology that can control fluids without complicated structural production.”

The research was carried out with the support of the research tasks of the Ministry of Science and ICT and the Korea Research Foundation and the Ulsan Science Institute, published in the online edition of the international journal Nature Communications earlier this year.


Um, E., Kim, M., Kim, H., Kang, J. H., Stone, H. A., & Jeong, J. (2020, October 15). Phase synchronization of fluid-fluid interfaces as hydrodynamically coupled oscillators. Retrieved December 24, 2020, from

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