Dynamics of colloidal and viscous soap films: the role of viscosity

A Newtonian soap film ruptures on the timescale of milliseconds, and at a constant rate known as the Culick velocity. Here, we explore the rupture of colloidal suspension films, in order to access a range of flow behavior by varying colloidal volume fraction. Using a high-speed camera, we systematically studied rupture dynamics for volume fractions ranging from 0 to 0.5, where the films contained a minimal amount of surfactant. Films were formed by stretching a known fluid volume to a specific size on a custom film stretcher. Surprisingly, even at high volume fraction, the rupture opened at a constant rate that was slower than the Culick velocity for water films. To investigate the role of Newtonian effective viscosity in this decrease in rupture speed, we conducted experiments on glycerol-water soap films. Over two orders of magnitude increase in fluid viscosity, the rupture speed was observed to decrease. As we used constant fluid volumes to form films, we hypothesize that the film thickness profile is a function of fluid viscosity. To test this hypothesis, we estimated the film thickness using dye absorption, and verify it using interferometry.