A model system to study thin liquid films coalescence : Binary mixtures

Proposition de stage

Laboratoire Sciences et Ingénierie de la Matière Molle, (SIMM)

Adresse : ESPCI, 10 Rue Vauquelin 75005 Paris

Responsables du projet : Emilie VERNEUIL, Francois LEQUEUX

Contact :

Internship with possibility for extension as a fully-funded PhD (ANR COLIFLOW)

Coalescence is widely studied in surfactant solutions. Nevertheless, a prediction of the lifetimes of liquid films between bubbles is still lacking due to intricate couplings between flow and concentration fields, and disjoining pressure effects associated to surfactants. As a consequence, the situation for surfactant solutions is so complex that predicting the lifetime of a liquid film with surfactants is a challenge. We identified a very simple system in which describing quantitatively the stability of films is possible. These are liquid mixtures, such as oil mixtures, miscible in all proportions. First, the disjoining pressure is always attractive and independent of variations in composition. Second, surface/volume transfers are only controlled by diffusion with no adsorption delays. Third, interface elastcity can be varied by orders of magnitude by changing the volume fraction. Lastly, they exhibit a very low pollution sensitivity, due to their low surface energy. Consequently, the question of coalescence, and its consequences on diphasic flows, is well posed in these systems. We will describe the physical mechanisms acting to stabilize single suspended liquid films made of binary mixtures in a specially designed cell by measuring their lifetime. These experiments will be analyzed and compared to numerical simulations to improve our understanding of the stabilizing mechanisms in oil foams.

(A) Foaming of a liquid mixture in a column by air injection from the bottom. The foam height is directly set by the coalescence time of the bubbles. (B) Bubble bursting at the surface of an oil binary mixture. (C) Observation of a thin liquid film using white-light interferometry, allowing for the reconstruction of the thickness profiles over time. Bursting is observed when the thickness decreases down to 50 nm.

We are looking for a Master 2 student in materials science, physical-chemistry or physics with an interest in soft matter physics and a taste for both experiments and modelling.

A PhD position funded by ANR will be available following the internship, for candidates demonstrating strong motivation and research potential.

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