The presence of a gas in a liquid is usually called an air bubble. The formation of air bubbles occurs in many processes in nature. When a gas is subjected to a shear force in a liquid, bubbles of different sizes and shapes will be formed. At present, the classification and definition of bubbles is not very strict. They can be divided into centimeter bubbles (CMB), millimeter bubbles (MMB), micron bubbles (MB), micro and nano bubbles (MNB), and nano bubbles (NB) in order from large to small. The so-called micro nano bubbles refer to bubbles with a diameter of about 10 microns to hundreds of nanometers when they occur. This kind of bubble is between micro and nano bubble and has physical and chemical characteristics that conventional bubbles do not have.
Micro nano bubble technology was developed in the late 1990s, and it took off in Japan in the early 2000s. The manufacturing methods such as cycle shearing, pressure dissolution, electrochemistry, micropore pressure and mixed jet can produce micro nano bubbles under certain conditions.
Micro nano bubble technology is not only a technology, but also a theoretical problem. In the past many years, it was theorized that micro nano bubble could not survive in a solution for a long period because according to a traditional theory, the smaller the bubble size is, the greater the internal pressure is caused by surface tension, and the calculated value of such pressure can be very high. According to Henry's law of gas dissolution, the higher the pressure is, the greater the amount of dissolution is and the faster the dissolution rate is. Therefore, as the bubble shrinks, the life of the bubble will decrease exponentially. However, this is not the case in practice. Nano bubbles can exist in the solution for a long time, which provides important support for the application of this technology, but the theoretical explanation for the long existence of bubbles is still incomplete.
In essence, micro nano bubble technology is a highly efficient gas dissolution technology, which can not only improve the dissolution rate, but also effectively improve the apparent solubility of gas, and that is an important basis for the biological effect of the gas. Therefore, nano bubble technology is a perfect match for hydrogen biology, and it is important for researchers engaged in the development of hydrogen medical technology to understand and master this concept and technology.