JCJC SIMI 4 - JCJC - SIMI 4 - Physique des milieux condensés et dilués

From liquid films to solid foams – F2F

Submission summary

Solid foams are complex networks of bubbles tightly packed in a solid material. These bubbles can be interconnected, like in sponge (opened cells), or separated by a solid film (closed cells), giving very different properties for applications. Despite its importance, the pore connectivity of today’s materials tends to be controlled thanks to several decades of experience, rather than by scientific understanding of the governing processes. The aim of the project is to contribute to that fundamental understanding by investigating the properties of the initially liquid foam template and its behaviour under solidification. For this purpose, it is crucial to elucidate the competition between several mechanisms taking place at different timescales and controlling the dynamics and rupture of the thin liquid films separating bubbles. More specifically, foam generation has to be faster than solidification, which in turn has to be slower (or faster) than film rupture to obtain open (or closed) cells, respectively.

To compare these different time scales, we will perform experiments to determine the time for the rupture of a single film during generation and drainage. Even though the opening time of a hole inside a static soap film is at this stage well characterized, it is indeed not clear what controls the rupture time of a film, especially under dynamic conditions. Some of our preliminary results show that this rupture time is critically linked to the thinning time. It is therefore crucial to first understand the generation and drainage of a thin film, which is controlled by the hydrodynamic boundary condition at the liquid/air interface. This boundary condition is intrinsically viscoelastic and determines the mobility of the interface, ranging from fully mobile to rigid, depending on the specific surfactant properties. Several descriptions exist in the literature that parameterize the interfacial mobility in a way that is either ad-hoc (such as the slip length) or incomplete (such as the interfacial rheology). The main objective of this project is therefore to combine theory and experiments in order to propose a complete and coherent description of this boundary condition, in which the interfacial mobility is directly related to the specific nature of the surface-active agents. Since this is a complex task, we will start with the investigation of simplified model systems. We ultimately intend to predict the rupture time during generation and drainage of a polymer film and to compare it to its solidification time (by reticulation).

Since this project is very ambitious, E. Rio, the coordinator has chosen to gather a team with complementary skills. Having both a solid education in hydrodynamics and 5 years’ of experience in physical-chemistry, she noticed how important it is, for such a project, to put together people from both communities. E. Rio is perfectly placed in this respect, being presently part of D. Langevin’s team, who popularized the importance of physical-chemistry to understand foam physics. At the same time, leading the project would be a great opportunity for her to create an independent team around a subject, where she is already internationally recognised. The project will have a crucial need for a theoretician to elaborate models that are consistent with the various experimental conditions considered in this project. That is why the team will include B. Scheid (ULB, Brussels), who is a specialist in modelling thin film dynamics with both elastic and viscous interfaces and is used to work in close interaction with experimentalists. F. Restagno, who is a specialist of friction at interfaces, will also be involved in the project. For film solidification, in the last part of the project, W. Drenckhan, who is already part of the same team as E. Rio, will be a precious advisor and collaborator. Finally, with a PhD student funded by the ANR, the team will be complete allowing great progress in this project.

Project coordination

Emmanuelle Rio (Laboratoire de Physique des Solides) – rio@lps.u-psud.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LPS Laboratoire de Physique des Solides

Help of the ANR 217,309 euros
Beginning and duration of the scientific project: September 2012 - 48 Months

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