Fragile, short-lived, fascinating, soap bubbles and in particular giant ones are often used by artists to accompany their acts. Each artist has a recipe that allows him to optimize his act and to obtain bigger, more beautiful, more stable bubbles.
The Soft Interfaces group (MMOI) at the Laboratoire de Physique des Solides has just published a popularization article in The Conversation to summarize the current understanding on how to blow giant soap bubbles. This work is the result of several years of research by the team but also by the scientific community working on foams and soap bubbles. It is at the core of Marina Pasquet’s thesis, in which she collaborates with bubble artists (Figure 1) to better understand the role of the different ingredients in the stabilization of giant bubbles. A bubble is formed by dipping an object in a soap solution, which creates a film of soap when the object is removed. The first question is to understand what determines the size of the bubbles blown. In the literature there are essentially two situations. When blowing hard into a soap film, the size of the bubbles obtained is fixed by the size of the film. On the other hand, if you blow very gently on the film, you can produce significantly larger bubbles. To understand why the recipe for “bubble soap” is so important, we need to look at the mechanisms that allow the film to thin as the bubble forms, and those that slow down the softening process. To do this, we explain the role of the different ingredients found in giant bubble recipes:
– The soap itself, which gives the film some resistance to stretching
– Polymers that impart elongational viscosity to the liquid and prevent it from breaking when it thins as the bubble is closes up on itself to detach
– Glycerol that slows down the evaporation of the liquid
The article concludes with a recipe proposal approved by professional bubble artists and whose composition is understood by scientists.
Figure. Phototograph of Marina Pasquet and Pierre-Yves Fusier (Slash Bubble on stage) taken by Serge Guichard ©.
Comment faire des bulles de savon géantes.
M. Pasquet, A. Salonen, E. Rio
The Conversation (16 septembre 2021)