Influence of evaporation on soap film rupture

TL;DR

This study experimentally examines how environmental humidity affects soap film stability, revealing that higher humidity increases the maximum film length before rupture, with evaporation playing a key role in film bursting.

Contribution

The paper introduces an experimental approach to quantify the influence of humidity on soap film rupture, highlighting evaporation's role in film stability.

Findings

Film length at rupture increases with humidity

Evaporation rate correlates with film thinning dynamics

Rupture occurs when evaporation-induced thinning matches drainage thinning

Abstract

Although soap films are prone to evaporate due to their large surface to volume ratio, the effect of evaporation on macroscopic film features has often been disregarded in the literature. In this work, we investigate experimentally the influence of environmental humidity on soap film stability. An original experiment allows to measure both the maximum length of a film pulled at constant velocity and its thinning dynamics in a controlled atmosphere for various values of the relative humidity $\RH$. At first order, the environmental humidity seems to have almost no impact on most of the film thinning dynamics. However, we find that the film length at rupture increases continuously with $\RH$. To rationalize our observations, we propose that the film bursting occurs when the thinning due to evaporation becomes comparable to the thinning due to liquid drainage. This rupture criterion turns out to be in reasonable agreement with an estimation of the evaporation rate in our experiment.