Antoine Monier
INPHYNI – Université côté d’Azur
LoF – Université de Bordeaux
Gravitational Thinning of Mobile Soap Films
Gravitational thinning of soap film contained in wet foams is crucial to understand as foam lifetime control is paramount from food industry to water cleaning. This phenomenon is multifactorial and gathers gas transfer between bubbles, soap film rearrangements, cooling, and film thinning by evaporation and/or drainage.
Drainage, which is the soap film thinning only by gravity, is studied in single soap elements such as bubbles or films within a solid frame. In this work, we pursue recent results in drainage dynamics and mobile soap film, exhibiting a slip behaviour at the liquid/air interface.
This feature creates a thinner soap film portion near the meniscus leading to a rise of the thinner elements due to an effective buoyancy force that sets the drainage dynamics.
Using interferometry technics, we extended the drainage understanding.
First, we formed soap films in the original rectangular frame geometry proposed by Mysels (1959). We characterised the soap film thickness over space and time and showed that it undergoes self-similarity, leading to a unique soap profile. Changing formulation and frame dimensions, we showed that this behaviour prevails in all explored configurations.
Then, we examined the force balance acting on the thinner elements. Building an original film centrifugation experiment, we visualise the thinner element dynamics, going, against effective gravity, from the film border to its center. We measured the thinner elements and the surrounding film ratio, finding it to be universally equal to 0.8 as proposed by Nierstrasz (1998).
Finally, we considered the shape of the soap film meniscus. We performed experiments on an isolated meniscus surrounded by a steady soap film, and measured the meniscus size. We showed that the classical static shape could be replaced by a dynamical shape due to soap film absorption at the meniscus.
All these results pave the way towards a complete understanding of a historical problem dating from 65 years ago.
