What is the best recipe for making soap bubbles?

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Emmanuelle Rio blowing bubbles in a bubble. Serge Guichard/CNRSEmmanuelle Rio blowing bubbles in a bubble. Serge Guichard/CNRS

A soap bubble attracts the attention of young and old. Who has never wondered the recipe of these fascinating bubbles or how to get the biggest one - In collaboration with artists, who have a great empirical knowledge of the recipes that work in their acts, a team from the Laboratory of Solid State Physics (CNRS/University of Paris-Saclay) has identified the main ingredients ensuring to get the best bubbles. The results of this study and a second one were published in December 2022 in theEuropean Physical Journal E and Physical Review Letters.

Both artists and scientists need stable bubbles. The former to design spectacular acts, the latter to study two-dimensional turbulence or surface undulations, for example. Bubbles are also a basic element for the study of foams.

Researchers at the Solid State Physics Laboratory have teamed up with artists to study their recipes by analyzing the contribution of each ingredient to bubble stability. Their laboratory experiments, conducted under controlled conditions, allowed them to quantify the stability and ease of bubble generation of different mixtures.

The results show that the perfect recipe should contain water with the addition of: 4% dishwashing liquid, between 0.05% and 0.1% polymer 1 and 10% glycerol. The polymer will allow the creation of stable bubbles, while the glycerol will increase the longevity of the bubbles without making them more difficult to blow.

In another study, the team also identified another major mechanism to consider in explaining the bursting of these giant bubbles: like any object that evaporates, soap bubbles are cold. The researchers measured this temperature to be up to 8 degrees colder than its surroundings, which represents a significant change. By decreasing evaporation, the concentration of glycerol in the recipe also decreases the cooling of the bubble.

New research will focus this time on the evolution of the thickness of giant soap films over time and their lifetime.

1 A polymer is a substance composed of macromolecules and derived from low molecular weight molecules. For example, for this research, scientists used guar gum and JLube which is a polyoxyethylene-based veterinary lubricant.

An optimized recipe for making giant bubble. Pasquet M, Wallon L, Fusier P-Y, Restagno F, Rio E. EPJE, 15 April 2021. https://link.springer.com/article/10.1140/epje/s10189’021 -00054-5

Measurement of the temperature decrease in evaporating soap films,F. Boulogne, F. Restagno, E. Rio. Physical Review Letters, December 19, 2022. https://link.aps.org/doi/10.1103/PhysRevLett.129.268001

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