The recipe for a perfect soap bubble
The perfect formula exists!
To form a soap bubble, we immerses an object in a soapy solution, which creates a soapy film when the object is removed. It will then need to be stretched, which requires thinning it while avoiding the bubble [n’éclate]». This process has been validated by Paris-Saclay researchers. Indeed, in April 2021, the Solid State Physics Laboratory team found the optimal recipe. In an article published on The European Physical Journal E, The CNRS researchers, Sandrine Mariot, Marina Pasquet, Vincent Klein, Frédéric Restagno and Emmanuelle Rio have listed the ingredients: water, to which 4% dishwashing liquid is added, between 0.05% and 0.1% of polymer and 10% glycerol.
As for the instructions: first mix 20mm of water, then the washing up liquid, followed by the polymer, finishing with 100mm of glycerin before adding the remaining 40mm of water. It would therefore require at least 60 millimeters of water.
The soap bubble, which is made up of air surrounded by a very thin film of liquid, which is itself surrounded by air, requires a minimum of soap, ” but not too much “, explain the researchers Rio, Salonenn and Pasquet. The main function of the polymer is to allow the creation of stable bubbles, while the glycerol increases their longevity, without making them more difficult to blow. Experiments conducted under controlled conditions allowed to quantify the stability and ease of generating it, from different mixtures.
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A good bubble is a stable soap film
Until 2021, scientific studies on soap films generated in a controlled environment concerned only those of a few square centimeters. Paris-Saclay’s new experiments broaden the field of possibilities with a new setup for generating and characterizing giant bubbles (2m x 0.7m).
In principle, their size depends on that of the soapy film formed and on the flow with which you blow on it. However, the soapy solution, by itself, is important.
With an initial thickness of a few micrometres, the film naturally tends to thin out, up to the fateful breaking stage. The bigger the bubble, the thinner the film. The soap molecules help stabilize them in several ways.
They allow, in particular, to resist its thinning thanks to the Marangoni effect, the process of transporting material along an interface under the effect of a surface tension gradient. A phenomenon also observed in wine. In the case of bubbles, the presence of soapy molecules, without abusing them, would favor their effect.
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The temperature, an essential element for their stability
Fragile, ephemeral, these suspended fragments of air often cause a twisted charm of sadness when they explode.
More recently, in December 2022, a team from the same laboratory, specializing in the study of condensed matter physics, in Paris-Saclay, provided new keys to make visual pleasure last. The results published in Physical Review Letters, demonstrate that evaporation plays an important role on the stability of the soap film. Neglected until then, they establish that evaporation would lead to a thinning of the latter, but also to its cooling. And poof!
The temperature variation of said film, in evaporation, for different relative humidity values and glycerol concentrations, would give the following conclusion: [leur] the temperature can decrease after their creation up to 8° C according to this recent document.
This recent advance combines with the conclusions of 2021, postulating that to slow the thinning it would be necessary to increase the “stretching viscosity “. A strong viscosity stretched it would allow the films to be stretched considerably, without rushing them, to prevent them from breaking. To put the odds on his side, the addition of polymers rounds out the formula, because, as macromolecule-based substances, they will tend to line up during flow and generate friction, slowing flow, thinning and potential cracking.
Now you know everything about creating the perfect bubble.
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Sources:
How to make giant soap bubbles. Marina Pasquet, Anniina Salonen, Emmanuelle Rio, The conversationSeptember 16, 2021. https://theconversation.com/comment-faire-des-bubles-de-savon-geantes-167600
An optimized recipe for making giant bubbles. Pasquet M, Wallon L, Fusier PY, Restagno F, Rio E. EPJ extensionApril 15, 2021. https://link.springer.com/article/10.1140/epje/s10189-021-00054-5
Measurement of temperature decrease in evaporating soap films,F. Boulogne, F. Restagno, E. Rio. Physical Review LettersDecember 19, 2022. https://link.aps.org/doi/10.1103/PhysRevLett.129.268001
