A little lesson learned today: isopropanol blows stable bubbles more easily than pure water.

this is seen in the video below. The live shot, schematic diagram and English explanation video all have

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(video source: APS Physics)

the following is my additional explanation in Chinese.

if you blow air into a cup of pure water with a straw, this process also produces bubbles, but because of the high surface tension of the pure water, these bubbles are so unstable that they burst almost immediately.

if you want to blow more stable bubbles on the surface of a cylinder of liquid, the general idea is to add surfactants such as detergents. But you can actually get relatively stable bubbles without surfactant, so replace the water with a more volatile liquid, such as isopropanol.

the life of the bubbles floating on the surface of these volatile liquids is much longer than that of pure water, and it can be found that there is a very active liquid flow on the liquid film of the bubbles through the interference color of the thin film.

according to the flow of the liquid film and the volatilization of the liquid, the researchers give an explanation that the bubble is not easy to break:

first of all, the liquid surface, including the liquid film and the surrounding liquid, evaporates, which takes away some heat, which is more likely to lead to cooling for the liquid film.

as a result, the liquid film becomes a little cooler than the surrounding liquid, and the decrease in temperature will lead to an increase in surface tension.

next, the surface tension of the bubble liquid film is different from that of the surrounding liquid, and the unbalanced surface tension will lead to the flow of the liquid. The flow direction is the flow from the place with low surface tension to the place with high tension (as shown in the following figure).

this causes the surrounding liquid to be added to the liquid film of the bubble, so the liquid film is not easy to become too thin and break. Pure water not only volatilizes slowly but also has high surface tension, so bubbles are difficult to stabilize.

although I'm not sure what it's like to blow bubbles into isopropanol _ (: blowing "∠) _