APS Gallery of Soft Matter 2025 prize to Isabelle Eisenmann

Congratulations to Isabelle Eisenmann for winning the prize for the best video in the competition ‘Gallery of Soft Matter 2025’ from the APS Division of Soft Matter! She presents there part of her thesis work carried out at LPENS between 2020 and 2024 under the supervision of Raphaël Jeanneret and Nicolas Desprat in the “Multi-scale physics of living systems” team.

In this study, Isabelle demonstrated the formation of periodic branching patterns in suspensions of motile microalgae (Chlamydomonas reinhardtii) fleeing intense light sources. Trying to escape the brightest areas, the algae find themselves attracted by the shadows created by areas denser in algae, thus amplifying the stochastic density fluctuations initially present. In the cylindrical geometry used in the experiments, these interactions lead to the formation of an algae-dense phase in the form of a network of branches. By quantitatively studying the patterns that appear in the system as a function of algae concentration, light intensity and the viscosity of the medium, Isabelle and her colleagues were able to develop a simple analytical model for predicting the patterns. Isabelle has also demonstrated that the dense phase created by the algae provides them with protection against the potential dangers of intense light: by hiding behind each other, the algae see less light on average and are therefore protected. A scientific article reporting these results is currently being peer-reviewed.

Isabelle will have the opportunity to present this research at an invited seminar at the next APS Global Physics Summit in Denver, Colorado.

More:
– Her winning video
– Article in “Physics magazine”

Author affiliation:
Laboratoire de physique de L’École normale supérieure (LPENS, ENS Paris/CNRS/Sorbonne Université/Université de Paris)

Corresponding author: Raphaël Jeanneret
Communication contact: Communication team