According to a press release dated October 20, 2026. A consortium of scientists from Université Côte d’Azur and the CNRS—including members of the Institut de Physique de Nice, the Laboratoire de Physique at ENS de Lyon, the Laboratoire Interdisciplinaire de Physique in Grenoble, and several European partners—has uncovered a previously unknown mechanism for the relaxation of liquid foams after flow ceases. This research, published in October 2026 in Physical Review Letters, opens up new avenues for understanding and controlling soft materials. Thumbnail: A close-up photograph of a foam © AdaptaLux via Wikimedia Commons
What actually happens inside a foam when we stop manipulating it? While we might instinctively think that it “comes to a standstill,” the reality is more subtle: its bubbles continue to reorganize themselves, in a way that is invisible to the naked eye. This phenomenon applies to a wide range of materials—foams, emulsions, pastes, gels—whose internal structure continues to evolve even when at rest.
In this study, the researchers used an ultrastable liquid foam as a model for a disordered material. Using high-speed X-ray tomorheoscopy, an advanced synchrotron imaging technique, they were able to simultaneously track the evolution of mechanical stresses and the movements of the bubbles in space and time, thereby gaining direct insight into the internal dynamics after the flow had stopped.
The results shed new light on the subject. Contrary to what is often observed in complex systems, where relaxation follows slow, time-spread laws, the researchers show here that the foam relaxes in a simple and rapid manner, following an exponential law. Even more surprising: the rate of this relaxation does not depend on how the foam was set in motion beforehand. It is directly linked to a local phenomenon—on the scale of a few bubbles—corresponding to individual rearrangements.
This result highlights a regime that has been little documented until now: stress relaxation does not rely on large-scale collective effects, but on a succession of independent local events. This discovery challenges certain assumptions about the behavior of amorphous materials and opens up new avenues for better understanding and predicting their evolution.
Ultimately, this research could help improve control over the mechanical properties of many materials used in industry (cosmetics, agri-food, construction materials) or in technological applications. It also provides a new conceptual framework for analyzing the influence of mechanical history on the state and stability of these complex systems.
Read more on the Université Côte d'Azur website
Reference
F. Schott, B. Dollet, C. M. Schlepütz, C. Claudet, S. Gstöhl, R. Mokso, S. Santucci & C. Raufaste. Stress Relaxation Driven by Elementary Plastic Events in Nonaging Liquid Foams. Phys. Rev. Lett. 137(16), 168201 (2026)
DOI: https://doi.org/10.1103/3np8-ljj1