Historical perspectiveElectrokinetic transport in liquid foams

- Applying an electric field to a foam has been shown to provide useful information on the physical properties of the system, such as its liquid fraction.
- When ionic surfactants are employed, it can also be used to tune the drainage in gas/liquid medium.
- We attempt to link the results on the different scales of the foam on this topic, and provide new data of our own showing that gravity driven drainage can indeed be reversed in such a media.
- This paves the way of setting new strategies to obtain homogeneous foams in space and time.

Investigating electrokinetic transport in a liquid foam is at the confluence of two well developed research areas. On one hand, the study of electrokinetic flows (i.e. surface-driven flows generated close to a charged interface) is fairly well understood in regards the solid/liquid interface. On the other hand, the flow of liquid in a 3D deformable network, i.e a foam, under a volume force such as gravity has been thoroughly studied over the past decade. The overlapping zone of these two frameworks is of great interest for both communities as it gives rise to challenging new questions such as: what is the importance of the nature of the charged interface, created by mobile and soluble surfactants in the case of foam, on electrokinetic transport? How does a foam behave when submitted to a surface-driven flow? Can we compensate a volume-driven flow, i.e. gravity, by a surface-driven flow, i.e. electroosmosis? In this review, we will explore these questions on three different scales: a surfactant laden interface, a foam film and a macroscopic foam.

Graphical Abstract141