Rupture dynamics of flat colloidal films

TL;DR

This study investigates the rupture behavior of flat colloidal films across various volume fractions, revealing Newtonian-like rupture mechanics in thick films and unique instabilities in thinner films due to microstructural effects.

Contribution

It provides experimental insights into the rupture dynamics of colloidal films, highlighting the influence of microstructure in thin films and comparing rupture mechanisms to Newtonian fluids.

Findings

Rupture in thick colloidal films resembles Newtonian fluid rupture.

Spontaneous rupture in thin films shows wrinkling instabilities.

Microstructure impacts rupture behavior in thinner colloidal films.

Abstract

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.