Particles adsorbed at fluid-fluid interfaces confer stability to dispersed systems such
as foams and emulsions. The emergent properties associated with the interfacial
microstructure underpins the creation of functional materials. In the design, synthesis
and application of such materials, it is essential to understand the dynamic behaviour of
structured interfaces at deformation timescales that are relevant in practical scenarios.
In this experiment-driven study, a bubble is used as a probe to understand the
stability mechanisms and dynamics of fluid-fluid interfaces coated with particles.
First, in a model wax-based oil foam, or oleofoam, bubble dissolution time, under
controlled conditions, is used as a parameter to assess the bulk and interfacial rheological
contributions responsible for the remarkable stability observed. Focus is then drawn
to interfacial phenomena, by removing bulk effects, through microscopic observations
of crystal-coated bubbles undergoing deformation due to either bubble dissolution
or ultrasound-driven volumetric oscillations. In this way phenomena at two extreme
timescales, 10,000 s and 0.0001 s, are observed and interpreted. Finally, the effect of
unsteady, fast deformation on a complex interface is systematically studied using a well
characterised model interface, comprising of bubbles coated with optically resolvable,
monodisperse latex microspheres. The bubbles are subjected to acoustic forcing, leading
to the rapid cyclic compression and expansion of the colloidal monolayer. Effects of
pressure amplitude, particle size and surface coverage on bubble excursions are studied.
The results signify the importance of local mesoscopic phenomena in explaining
the stability of oleofoams, where invoking macroscopic rheological reasoning alone is
somewhat inadequate. Experimental timescales strongly influence the nature, integrity
and response of complex interfaces to imposed stresses. Further, a bubble driven by
ultrasound has potential in studying time-dependent interfacial mechanics.