  Here, we report experimental results on the rupture of flat colloidal films
over a large range of volume fractions, 0.00 $\le \phi\le$ 0.47. The films are
formed using a constant fluid volume, ruptured with a needle, and recorded
using a high-speed camera. We show that colloidal films rupture in a manner
quantitatively similar to Newtonian fluids, even well into the shear thinning
regime. These results are consistent with the well-known mechanism of the
rupture of Newtonian films, where the rupture rim rolls outward collecting more
fluid and thus film rupture is a shear-free process. However, in the case of
spontaneous rupture under controlled humidity conditions, the same dense
colloidal films show exotic instabilities reminiscent of a wrinkling fabric on
the film surface. These instabilities were absent in manually ruptured films.
We hypothesize that these instabilities occur when the film thickness becomes
thin enough to compete with the colloidal particle size, due to film drainage
before spontaneous rupture. Thus, although non-Newtonian flow properties do not
influence film rupture dynamics for thick enough films, the effect of
microstructure has dramatic consequences in thinner films.
