Rupture dynamics of flat colloidal films

Here, we report experimental results on the rupture of flat colloidal films over a large range of volume fractions, 0.00 ≤φ≤ 0.47. The films are formed using a constant fluid volume, ruptured with a needle within a few seconds of formation, and recorded using a high-speed camera. We show that colloidal films rupture in a manner similar to Newtonian fluids, even for high colloidal volume fractions. However, higher-viscosity films made of the same fluid volume show a higher thickness away from the boundary at the time of rupture, possibly due to viscous stresses slowing down the thinning of the film. When allowed to spontaneously rupture instead of manually rupturing right after film formation, the same dense colloidal films show exotic instabilities reminiscent of a wrinkling fabric on the film surface. We hypothesize that these instabilities occur because the film is allowed to thin before rupture, and its thickness may compete with the colloidal particle size. Thus, the film lifetime before rupture has a major role to play in the film rupture dynamics, and the effect of microstructure has dramatic consequences in films that are allowed to spontaneously rupture.