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Why "10 metres water-resistant" is not enough for swimming with a watch
by David Lee
The perfect soap bubble
2.4.2020
Translation: machine translated
If you want to create giant soap bubbles, you need to add a special ingredient to the soapy water. Researchers now present the ultimate recipe.
If you want to create a perfect soap bubble, you need more than just soap and water. Enthusiasts have known this for a long time and share their knowledge with the help of an online wiki. Among other things, they swear by the food additive guar gum, also known as E 412. If you add it to soapy water in the right concentration and pay attention to a few other things, you can create huge bubbles with the mix. The current record holder, for example, had a volume of 96 m3 and would even have been able to fit a small lorry.
A team of researchers led by Justin C. Burton has now set out in search of the physical background. The fluid dynamicists from Emory University in the US state of Atlanta tested various mixtures and pulled them up with a kind of rope sling. The researchers then measured the soap walls, which were just a few micrometres thick, using an infrared laser, as they report in the journal Physical Review Fluids.
According to the study, it is actually substances such as the plant gum E 412 or the polymer polyethylene glycol that make gigantic soap bubbles possible. When dissolved in water, they form long chains of polysaccharides, which cross-link with each other on the surface and thus stabilise it. According to the tests, the best results are obtained when several polymer sizes are mixed. These can then interlock in a variety of ways, which makes the soap bubbles more elastic.
According to the researchers, the best possible soap bubbles are obtained by mixing two to three grams of guar gum with 50 millilitres of alcohol and then allowing the mixture to rise in one litre of water for ten minutes. Then add two grams of baking soda and 50 millilitres of a special washing-up liquid; the researchers recommend the Dawn Professional brand, which is available in the USA. Emory University has published detailed instructions on its homepage.
What you should bear in mind when making your own: It's not just the recipe that determines the perfect bubble, but also the environmental conditions. Moderate temperatures and high humidity seem to have a positive effect on the life of the bubbles, as less liquid can then evaporate.
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