Marangoni elasticity of flowing soap films

TL;DR

This paper introduces a non-destructive method to measure the Marangoni elasticity of flowing soap films, finding it to be consistently 22 dyne/cm regardless of various physical parameters, due to surface soap molecule crowding.

Contribution

The study presents a novel, non-destructive technique for measuring soap film elasticity using shock angles, revealing a constant elasticity value across different conditions.

Findings

Marangoni elasticity is approximately 22 dyne/cm.

Elasticity remains constant regardless of film width, thickness, flow speed, or soap concentration.

Method enables reliable, non-destructive elasticity measurements.

Abstract

We measure the Marangoni elasticity of a flowing soap film to be 22 dyne/cm irrespective of its width, thickness, flow speed, or the bulk soap concentration. We perform this measurement by generating an oblique shock in the soap film and measuring the shock angle, flow speed and thickness. We postulate that the elasticity is constant because the film surface is crowded with soap molecules. Our method allows non-destructive measurement of flowing soap film elasticity, and the value 22 dyne/cm is likely applicable to other similarly constructed flowing soap films.