The Immense Power of Tiny Bubbles

Koichi Terasaka (Professor, Department of Applied Chemistry)

If you look closely around you, you will see many bubbles. Bubbles are constantly forming in hot springs, goldfish bowls, and carbonated drinks. If you look even closer, you'll find that Styrofoam, hair mousse, and soft-serve ice cream also contain tiny bubbles. Why are there bubbles in them? Are bubbles necessary? What are bubbles?

The bubbles you often see are cavities floating in water. They contain air inside. The boundary between water and air reflects light well, which is why bubbles sparkle. What properties do bubbles have? Bubbles have a much lower specific gravity than water and are good insulators. Bubbles have a surface that easily attracts impurities in the water. The smaller the bubble, the more easily air dissolves in the water. For goldfish to live comfortably, they need water with plenty of dissolved oxygen. If you remove the bubbles from mousse or soft-serve ice cream, they turn into liquid and flow away. Flat carbonated water is not tasty. A box made of styrene resin without bubbles cannot provide sufficient insulation.

Have you ever seen "microbubbles"? Microbubbles are bubbles much smaller than one millimeter, created using a special method. At the Koichi Terasaka Laboratory in the Faculty of Science and Technology at Keio University, we are actively conducting applied chemistry research using microbubbles.

Video 1 shows the generation of microbubbles using the pressurized dissolution method. Microbubbles mix into the water in the tank, making it look like milk. The video includes observations through a microscope. The tiny microbubbles are finely dispersed, convect very slowly, and remain in the water for a much longer time than ordinary bubbles. This is very effective for dissolving air into water and for applications in chemical reactions.

Video 2 shows a water purification experiment using microbubbles. A blue waste liquid was poured into a tank with the Keio emblem on the opposite side. Next, air was turned into microbubbles and introduced from the bottom of the tank. The microbubbles attached to the fine particles of the waste liquid and slowly rose. In about one hour, the waste liquid became almost transparent, and the Keio emblem could be seen clearly. Under the right conditions, microbubbles have the property of adsorbing fine particles. Because they rise slowly, the particles do not detach. This technology is very useful for improving the water environment.

Video 3 shows an experiment observing the formation of solid crystals using microbubbles. Microbubbles have the property of dissolving and shrinking much faster than ordinary bubbles. When a single microbubble is placed in a very dilute saltwater solution on a slide glass and observed under a microscope, solid crystals form because the gas inside the microbubble rapidly dissolves into the surrounding liquid. If crystals that normally can only be formed in a concentrated solution exceeding its solubility can be created in a dilute solution, it will greatly contribute to resource conservation and cost reduction, enabling the realization of environmentally friendly factories.

Japan is currently at the forefront of microbubble research in the world. To continue leading the world, we need the power of your youth. Why not join us in creating environmental technologies and functional materials using microbubbles?