Foam flow in many
applications, like firefighting and
oil recovery,
requires stable foams that can withstand the stress and aging that
result from both shear and thermodynamic instability. Events of drainage
and coarsening drive the collapse of foams and greatly affect foam
efficacy in processes relying on foam transport. Recently, it was
discovered that foams can be stabilized by the synergistic action
of colloidal particles and a small amount of a water-immiscible liquid
that mediates capillary forces. The so-called capillary foams contain
gas bubbles that are coated by a thin oil-particle film and integrated
in a network of oil-bridged particles; the present study explores
how this unique architecture impacts the foams’ flow dynamics.
We pumped capillary foams through millimeter-sized tubing (ID: 790
μm) at different flow rates and analyzed the influence of stress
and aging on capillary foam stability. We find that the foams remain
stable when pumped at higher flow rates but undergo phase separation
when pumped at low flow rates. Our observations further show that
the particle network is responsible for the observed stability in
capillary foams and that network strength and stability of an existing
foam can be increased by shearing.