Nano-thick liquid films: dynamic and stability of diphasic systems – ILIAAD

Foams, emulsions, pastes, porous media, biological suspensions or living tissues, are involved in many industrial processes and are largely studied since several decades. However, mainly two questions are still a challenge for the physicists: the stability and the dynamic of these systems. These questions have been classically addressed in the frame of classical low Reynolds hydrodynamics. However, they have been entirely renewed thanks to experimental improvements these last years: the considerable developments of nanoscale fluid dynamics, allowing to probe fluid transport down to nanoscales, as well as the fine control of the physico-chemical properties of interfaces, has provided refreshed views on these questions.
The physical phenomena involved in these nano-films call upon studies often addressed separately: local shear rates that can overcome the imposed shear rate by orders of magnitude, intermolecular forces (DLVO theory), surface rheology, or electro-/diffusio-/thermo-osmosis, to cite a few. These topics have been largely addressed by the four groups of the consortium leading to important contributions using innovative experimental tools: M.-C. Jullien and O. Theodoly showed the importance of intermolecular forces effects on droplet dynamics and more recently the non homogeneous surfactant surface concentration along a traveling droplet using RICM; while A. Colin and L. Bocquet provided a clear view of discontinuous shear-thickening transition as the breakdown of lubricated contact between particles, at a critical normal force using a tuning fork apparatus, these observations are clearly correlated to macroscopic measurements

At this stage of the state the art, a major issue is the coupling of these mechanisms taking place at nano-scales on larger scale transport dynamics (droplet, cell, suspension).
We therefore feel that, in view of the recent experimental and theoretical progress, it is timely to address these questions, which are shared by various systems; and therefore to address these questions from a unified and intertwinned point of view and methodology. This is the objective of the ILIAAD project.

Interestingly, the observables that are analyzed to study these systems are very similar, if not identical, for these different systems, such as interface velocity, object velocity, normal stress as function of film thickness to cite a few. As a whole, this fully justifies studying these systems, more precisely their stability and dynamics, in a concerted and concomitant manner. There is no doubt that the expertise of each partner will significantly enrich the understanding of all experimental configurations.

As such, the consortium is able to fully address the stability and dynamics of two-phase systems in a general framework. We will especially focus on the coupling between the interface, the transport within the thin films, and the flow: role and transport of the surfactant for fluid interfaces; coupling of the flow in the thin liquid film with the elastic deformations for solid boundaries; coupling of the flow in the thin liquid film with the visco-elastic deformation and external membrane treadmilling motion with living cells; role of the intermolecular forces and; at the most nanoscopic limit, role and specificities of the thermal fluctuations in both phases.

The different partners will closely interact all along the project in order to share their results and address the global objective: deriving a comprehensive framework describing/predicting the dynamics and stability of confined films with interfaces (whether deformable or not) to improve our understanding of multi-phase systems. This project will identify generic flow properties associated to confinement at the smallest scales, which are shared by these systems despite the variety of geometrical, mechanical and physico-chemical properties of their confining interfaces.