# Transient structures in rupturing thin-films: Marangoni-induced symmetry-breaking pattern formation in viscous fluids

## TL;DR

This paper develops a mathematical model to describe pattern formation in thin surfactant-laden films, validated by experiments on soap bubbles, revealing insights into rupture precursors and stability control.

## Contribution

It introduces a generalized Cahn-Hilliard-Swift-Hohenberg model for transient pattern formation in curved thin films with surfactants, supported by experimental validation.

## Key findings

- Quantitative agreement between theory and soap bubble experiments.
- Identification of nucleation and coarsening phases in pattern evolution.
- Insights into stabilizing or destabilizing thin films with surfactants.

## Abstract

In the minutes immediately preceeding the rupture of a soap bubble, distinctive and repeatable patterns can be observed. These quasi-stable transient structures are associated with the instabilities of the complex Marangoni flows on the curved thin film in the presence of a surfactant solution. Here, we report a generalised Cahn-Hilliard-Swift-Hohenberg model derived using asymptotic theory which describes the quasi-elastic wrinkling pattern formation and the consequent coarsening dynamics in a curved surfactant-laden thin film. By testing the theory against experiments on soap bubbles, we find quantitative agreement with the analytical predictions of the nucleation and the early coarsening phases associated with the patterns. Our findings provide fundamental physical understanding that can be used to (de-)stabilise thin films in the presence of surfactants and have important implications for both natural and industrial contexts, such as the production of thin coating films, foams, emulsions and sprays.