Water Oil Laden Foam – WOLF

We study foam imbibition with oil considering the multi-scalce structure of aqueous foam: the soap films at the intersection of two bubbles, the liquid channels called Plateau borders at the junction of three soap films, nodes at the junction of four Plateau borders and the whole liquid network of the foam.

We have studied the dynamics of penetration at the scale of a single Plateau border, that acts as a \liquid capillary tube« in which oil
flows in an unbroken stream. We have identified two viscous friction mechanism: one within the oil and one within the foaming solution. The crossover between these two regimes has been predicted and measured using large variety of oil with a viscosity ranging from 5 mPa.s to 12500 mPa.s

We now focus on:
- flow within a node
- fragmentation process, which occurs during coalescence or topological rearrangement
- front velocity of oil

Article to be submitted (first author : K. Piroird, post-doc).

Aqueous foams are involved in a wide variety of applications. With the development of new chemical formulations, they now appear in strategic field such as security where they are used to displace chemical toxic materials or decontaminate nuclear plants. In this context, aqueous foams are often entailed with another phase and the specific interaction of these two must be controlled in details. This other phase can be either a solid or an organic immiscible liquid such as oil. Depending on the formulation of the surfactants of the foaming solution, the oil either destroys the foam (defoaming or antifoaming agent) or invades it without damage. Such complex systems are coined oil-laden foams and can be found in petroleum industry, since enhanced oil recovery is often achieved injecting aqueous foam into the well to reduce fluid motilities.
Our understanding of oil and aqueous foam interactions is only partial and so far, it is limited to foam stability using thermodynamic concepts such as entering coefficients and disjunction pressure. It has been proven that the stability of pseudoemulsion films, which are heterogeneous films formed at the gas/water/oil interfaces is a key factor. This stability, characterized by the pressure disjunction isotherms, controls the stability of the oil laden foam. Yet, less is known on the ingestion mechanism of oil by the foam (which entails spontaneous oil fragmentation into droplets), on the transport and dispersion of the oil within the foam, and on the effect of oil content on foam ageing or on the rheology.
This project aims at understanding and modelling the physics and mechanics of oil laden foam using the most recent works concerning physics of foams and transport of solid particles in confined geometries. The study is divided in four parts:
1) Understanding and modelling oil ingestion by the aqueous foam. This part will be devoted to the velocity of oil when entering the foam, the mechanism of oil fragmentation and oil dispersion.
2) Determining the effect of oil content on foam ageing mechanisms. Indeed, the presence of oil globules between air bubbles might induce significant changes on the dynamics of drainage or coarsening (which is gas exchange between bubbles).
3) Quantifying the effect of oil content on foam flow. Here, we focus on oil laden foam rheology and on the evolution of oil fragmentation under shearing.
4) Oil recovering by moving foam. We will experimentally determine the optimal dynamic conditions for recovering oil wetting a (porous) wall by foam. This task will be handled in collaboration with IFP Energies nouvelles (former Institut Francais du Pétrole).