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L’X and Nestlé invent the bubbles of the future

A team of researchers from the Hydrodynamic Laboratory (École Polytechnique / CNRS) and from the Nestlé Group have been working together for several months as part of a research contract. The results of their work on the stability of bubbles were published in the journal Physical Review X.

Their paper has just been published in Physical Review X, one of the most prestigious scientific publications in the field of physics. After two years of work, Charles Baroud, Associate Professor at École Polytechnique, Nicolas Taccoen, PhD student at the Hydrodynamic Laboratory (École Polytechnique / CNRS) and Deniz Gunes, a scientist at the Nestlé Research Center in Lausanne (Switzerland), identified the conditions that prolong the "life" of the bubbles in foams, using a microfluidic modeling.

"Foams are everywhere: in food like chocolate mousse, in cosmetics with shaving foam or in architecture with foam insulation used in the walls of a house," says Charles Baroud, microfluidics specialist who works on the ways to handle fluids at micron scales. Indeed, a foam is made of bubbles that are dynamic structures that can merge together, but also grow or shrink and disappear within a few seconds. The goal of the research conducted by the scientists is to stabilize the bubbles in time so that the foam retains its appearance and initial properties as long as possible.

Covering the surface of bubbles with small solid particles

"The most common way to stabilize foam is to add a molecular surfactant, an essential component in aerated desserts, that stabilizes the bubbles so that they do not fuse together," says Charles Baroud. However, an alternative solution, which had already been demonstrated, is to coat the surface of the bubbles with small solid particles, such as globular proteins, for a food foam. But the physical equilibria underlying this phenomenon had not been explained until the work conducted by the team of researchers from École Polytechnique and Nestlé.

The scientists set up a unique experimental technique based on microfluidics to examine the stability of bubbles under different values of stress, and to identify the conditions that can extend the "life" of bubbles in foams. "This approach helps to identify and understand the conditions that lead to the collapse of bubbles in aerated food products, through measures of the strength of a bubble which is covered with particles," explains Charles Baroud. Another important contribution of their work is that these measurements are associated with a theoretical model - developed in collaboration with François Lequeux, Scientific Director at ESPCI Paris Tech - which is used to predict the overall evolution of a foam, composed of a large number of interacting bubbles.

Potential applications in many areas

These research findings could be applied to food products under the research contract between the Nestlé Group and École Polytechnique. "We will work together on the use of particles that exist naturally in foods to stabilize foams," says the professor. These results could also help increase the life of foams and potentially reduce the amount of fat used in the products.

More broadly, the foams are present in many areas so potential applications in cosmetics, pharmaceuticals, or architecture could emerge. In the construction sector, cellular concrete, composed of air bubbles in the cement matrix, could particularly benefit from these findings. According to Florent Dalas, engineer at LafargeHolcim Research Center, the Franco-Swiss group in the building materials industry, this research could be revolutionary: "With more stable bubbles, the use of cellular or foam concrete could be reduced while retaining its strength, and one could imagine materials that do not exist today with a smaller carbon footprint."

> Read the article in Physical Review X