Gibbs elasticity of a soap bubble

A new approach has been developed for measurement of the Gibbs elasticity of soap films. The present system uses a soap bubble, which constitutes a closed system in terms of surfactant transport, rather than a flat vertical film in contact with a surfactant solution. The present theoretical approach circumvents the need to evaluate the dependence of the ionization of the surfactant on its concentration. Instead, the Langmuir and Szyszkowski equations are used as independent empirical correlations. The theoretical results are in very good agreement with experiment. Comparison with previous results measured on vertical flat films shows that the Gibbs elasticity values are lower than previously assessed.