When we pour a carbonated drink into a cup, we see small droplets popping over the surface. This happens because air bubbles float up in water and burst on the water surface, ejecting water particles into the air.

These water particles are called ‘aerosols.’ In general, aerosols are tiny particles whose size ranges from a few nanometers to several micrometers that freely float in the atmosphere. Water droplets, dust, smoke, and water haze are typical examples of aerosols. They may either act as cloud condensation nuclei stimulating cloud formation, or scatter and absorb solar light eventually affecting the earth’s climate on a major scale.

Professor Jung Ho Je of Department of Materials Science and Engineering and his research team, Research Professor Byung Mook Weon and PhD candidate Ji San Lee, have identified the fundamental mechanism of aerosol formation during bubble bursting in their paper, ‘Size limits the formation of liquid jets during bubble bursting.’ The paper was published as the Featured Image in Nature Communications on June 21, a new open-access sister journal of Nature.

In the ocean, a large number of bubbles are trapped inside water by the breaking waves. The aerosols generated from these bubbles may affect the formation of clouds and hurricanes. They also may cause a migration of hazardous organisms from the ocean, possibly resulting in human respiratory diseases and other public health problems.

This phenomenon was first identified in the 1950s, but the exact mechanism has long been a mystery. Last year, a research team at University published a paper in Nature about a bursting cascade from a large bubble into small bubbles, but provided no explanation about how the small bubbles generate aerosols.

Professor Je and his team successfully filmed the microsecondlevel dynamic evolution of a bubble shape inside liquids and identified the critical factors for the aerosol formation using ultrafast X-ray microscopy at the Advanced Photon Source in the United States. The most critical factor is the bubble size; there is a size threshold for the liquid jet formation which varies depending on liquid solution, compensating the surface energy (driving force) with the liquid viscosity (retarding force).

Thanks to their discovery, we now consider a bubble bursting process as a coalescence phenomenon between two bubbles. Professor Je commented, “We could eventually find out a basic mechanism that is applicable to many phenomena regarding bubbles and water droplets, contributing to bubble control in industrial processes and to improvement in climate change models.”

The research was supported by the Creative Research Initiatives (Functional X-ray Imaging) of the Korean Ministry of Education, Science, and Technology and the National Research Foundation of Korea.