Confinement effects in surfactant-driven Marangoni flows

Recently, we have observed that surfactants deposited on liquid films can cause complex flows in confined environments. Surfactants are molecules typically found in soaps, but also in other substances. They can alter the surface tension between two phases, such as a liquid phase (water) and a gas phase (air). When the concentration of surfactants at an air-water interface is non-uniform, this creates a Marangoni tension, which leads to the spreading of the surfactants to even out their concentration. In most liquids, there is a trace of endogenous surfactants at very low concentrations, due to natural contamination. These endogenous surfactants can interact with exogenous surfactants locally deposited on the interface and alter the Marangoni-driven spreading. This can lead, for example, to flows capable of solving a maze (photo on the left and our award winning video, Temprano-Coleto et al. Phys. Rev. Fluids, 2018), or it can be at the origin of the Japanese art of Suminagashi (right picture, also Mcnair et al. J. Fluid Mech. 2024). There are also important applications in medicine. Surfactant therapies are used to treat lung diseases, in order to transport therapeutic drugs down to the lung alveoli, where gravity does not play a role. Our preliminary work (Mcnair et al. Phys. Rev. Lett., 2025) has showed that interactions between an external surfactant and internal surfactant naturally produced by the lung can alter the propagation of the therapeutic surfactant in some parts of the lungs, which may explain the mixed efficacy of these treatments.

The aim of this doctoral thesis is to validate experimentally existing theoretical models and develop them further in order to understand the interaction between endogenous and exogenous surfactants in complex confined geometries. Simple and advanced imaging techniques with dyes and tracers, such as particle tracking and PIV, will be used to obtain experimental data. Theoretical and numerical tools will be used to develop the models for their experimental validation.

The LMFA is an internationally recognized research laboratory in fluid mechanics, and part of a dynamic research and industrial environment in the Metropole of Lyon. The candidate will benefit from strong support within this lab, which hosts a large international community of PhD students each year. It is located in the heart of the city of Lyon, which offers a dynamic and stimulating environment for research and student life.

The project will take place in one of the laboratories of the Université Claude Bernard Lyon 1: the Fluid Mechanics and Acoustics Laboratory (LMFA: http://lmfa.ec-lyon.fr/). The LMFA is an internationally recognized research laboratory in fluid mechanics, and part of a dynamic research and industrial environment in the Metropole of Lyon. The candidate will benefit from strong support within this lab, which hosts a large international community of PhD students each year. It is located in the heart of the city of Lyon, which offers a dynamic and stimulating environment for research and student life.

Profile

Candidates must hold a master-level degree, or an equivalent degree, and have an excellent academic record in fluid mechanics, mechanics, physics or any related discipline. They must show strong motivation for research in fundamental science with an interdisciplinary nature, some laboratory experience, and skills in coding and developing numerical simulations. Fluent English is required (level C1). Fluent French is not mandatory but recommended (level B1).

Eligibility

Only Chinese citizens are allowed to apply for this doctoral thesis funding offer, due to the nature of the funding source: the China Scholarship Council. Candidates must not be working (outside China) at the time of application, but applicants registered in an awarding-degree institution outside China are eligible.