Fluid dynamics: A recipe for the perfect soap bubble
Soap bubbles fascinate not only children. But how do they become particularly large, long-lasting and stable? French physicists have systematically investigated this.
There is hardly a child who does not stop in fascination when street artists blow giant soap bubbles into the sky. One of the earliest artistic depictions of soap bubbles is found in Pieter Bruegel's painting "The Children's Games" from 1560, leading historians to conclude that soap bubbles have been used to entertain children for at least 500 years, possibly much longer. But soap bubbles are also a subject of research and a tool in physics, architecture and mathematics. The appearance and statics of the Olympic Stadium in Munich, for example, are based on experiments with soap bubbles. Physicists at the Université Paris-Saclay recently set out on a systematic search for a recipe for the largest possible stable soap bubbles. They published their results - not without a humorous passage or two - on the preprint server "ArXiv".
They went on to first determine the best concentration of dishwashing liquid, then gradually add the other ingredients, such as glycerine, and observe how they affect the quality of the bubbles. For their research, they used different cameras and automated bubble generation techniques. "Our main findings are that the surfactant concentration must not be too high, the solution must contain some long, flexible polymer chains to allow easy bubble formation, and the addition of glycerol allows for better bubble stability by preventing evaporation," the team wrote in the paper.
Concretely, the result is: Take the desired amount of water and add four per cent by volume of dishwashing detergent (compromise between stability and good bubble formation), 0.1 per cent by volume of guar gum (increases extensional viscosity(increases stretch viscosity), ten percent by volume glycerine (increases durability) and a few dashes of citric acid to lower the pH (has no effect on bubble formation, but increases the durability of the mixture).
Once again, leaving aside the fact that word of the results must first get around among the soap blowers of the world, the researchers caveat: "Of course, we have not provided any proof here that this recipe is the best possible, but it is based on systematic studies and clear physical arguments." All that remains is to prove that this recipe can beat the current world record set by Gary Pearlman in 2015: He created a free-floating soap bubble with a volume of 96.27 cubic metres.
Spectrum of Science
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