Surface tension of flowing soap films

TL;DR

This study measures how the surface tension of flowing soap films varies with film thickness and soap concentration, revealing an increase in tension for thinner or less concentrated films and providing insights into Gibbs elasticity.

Contribution

It introduces a method to measure soap film surface tension via wire curvature and models the behavior with a simple adsorption framework.

Findings

Surface tension increases for thinner or low-concentration films.

Surface tension approaches 30 mN/m at higher thickness or concentration.

Gibbs elasticity of the soap film is quantified.

Abstract

The surface tension of flowing soap films is measured with respect to the film thickness and the concentration of soap solution. We perform this measurement by measuring the curvature of the nylon wires that bound the soap film channel and use the measured curvature to parametrize the relation between the surface tension and the tension of the wire. We find the surface tension of our soap films increases when the film is relatively thin or made of soap solution of low concentration, otherwise it approaches an asymptotic value 30 mN/m. A simple adsorption model with only two parameters describes our observations reasonably well. With our measurements, we are also able to measure Gibbs elasticity for our soap film.