Extension of a suspended soap film: A homogeneous dilatation followed by new film extraction

TL;DR

This study investigates the deformation behavior of suspended soap films, revealing a two-step extension process involving homogeneous dilatation and subsequent film extraction, influenced by surfactant properties and modeled with interface rigidification theory.

Contribution

It introduces a new experimental observation of a two-step film extension process and develops a theoretical model explaining the complex behavior.

Findings

Initial homogeneous extension occurs only with surfactants of negligible dilatational modulus.

A second thicker film is extracted independently of surfactant nature.

The model successfully predicts the two-step evolution based on interface rigidification.

Abstract

Liquid foams are widely used in industry for their high effective viscosity, whose local origin is still unclear. This Letter presents new results on the extension of a suspended soap film, in a configuration mimicking the elementary deformation occurring during foam shearing. We evidence a surprising two-step evolution: the film first extends homogeneously, then its extension stops, and a new thicker film is extracted from the meniscus. The second step is independent of the nature of the surfactant solution, whereas the initial extension is only observed for surfactant solutions with negligible dilatational moduli. We predict this complex behavior using a model based on Frankel's theory and on interface rigidification induced by confinement.