Rigid Bubbles: Novel Instabilities in Colloidal Film Rupture

When a soap bubble pops, a rupture opens up and grows on the timescale of milliseconds. Culick (1960) showed that this rupture grows at a constant rate. Recently, Petit et al. (2015) studied films that were rigidified due to their high surfactant concentration. They observed that these films developed crack-like instabilities during rupture, and their rupture velocity was slower than that predicted by Culick. We investigate whether soap films rigidified by adding colloidal spheres show similar instabilities. We rupture a flat film containing surfactant and colloidal spheres using a needle and record it with a high-speed camera at 75,000 frames per second. We control film rigidity by varying particle concentration and find that this dramatically alters rupture dynamics. The rupture opens at a rate that is non-constant and an order of magnitude slower than the Culick velocity. Additionally, we observe a wide variety of instabilities in these rupturing colloidal films. We systematically study film rupture dynamics as a function of colloid concentration and film thickness.