A new recipe for making eternal bubbles

To believe that French researchers like to wedge the bubble. In January, a team from the University of Lille inflated soap bubbles which do not burst into the air for several months. Six months later, colleagues from the ENS de Lyon are doing better with bubbles for years, but this time trapped in a liquid and not in the air. “I still have these microballoons, as they are called, dating back more than ten years! »underlines Stéphane Santucci, CNRS researcher who describes this performance in Physical Review Applied.

Wedging so many particularly stable bubbles in a liquid is of interest to cosmetics manufacturers (L’Oréal financed part of the work, covered by several patents) or the food industry to encapsulate various oils or aromas.

“It can also be used to protect plants from frost. These bubbles are sprayed on the sheets to serve as insulation. The rain will wash away these non-polluting clay-based particles”suggests Vance Bergeron, CNRS researcher and other co-author.

A shell around the bubbles

The performance is actually worth not by the incredible longevity of this material, as other methods already did, but by the recipe, “simple, inexpensive and deployable on a large scale”notes Stéphane Santucci.

Everything typically starts with mixing the liquid with a surfactant, that is to say a soap which stabilizes the interface between the liquid and the air (for a bubble) or between two liquids (for drops). Many bubbles of a few tens of micrometers appear, but they are fragile: the surfactant does not resist the pressure in the bubble, which eventually disappears. Hence the subsequent addition of particles 0.25 micrometers in diameter, such as silica, to form a shell around the bubbles, which will be robust, even eternal.

“Their simple method could make large quantities of bubbles or foam, and at low cost” – Wiebke Drenckhan, CNRS researcher

Problem, you have to force these balls to stick to the bubbles. This is where the main innovation of the Lyonnais lies, even the change of paradigm that they introduce, compared to other methods. They use negatively charged soaps and positively charged particles (or vice versa) so that these two species attract each other at the surface of the bubbles.

And it works ! “Their simple method could make large quantities of bubbles or foam, and at low cost, notes Wiebke Drenckhan, CNRS researcher at the Charles-Sadron Institute in Strasbourg (and columnist at the World). The problem is that not everyone agrees on their interpretation of what is happening! »

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