(319d) Rheology of Capillary Foams

Aqueous foams are ubiquitous; they appear in a variety of products and processes that span the cosmetics, food, material processing and energy industries. The versatile applicability of foams come as a result of their viscous and elastic properties; for example, foams are exploited as drilling fluids in enhanced oil recovery for their high viscosity. The understanding of foam properties through rheology has been very important to the effective application of foams in different processes and despite challenges of foam instability in foam rheology studies, numerous measurements on the viscoelasticity of foams have been reported. Quite recently, a new class of long-term stable foams called capillary foams have been discovered to create more stable foams than surfactant and particle stabilized foams. The unique architecture of these foams, containing oil-coated bubbles and a gelled network of oil-bridged particles, is expected to affect the rheology of these foams. However, capillary foam rheology and its deviations from traditional foam rheology have not been studied.

In this work, we present rheological data on capillary foams. We study the viscoelastic properties of capillary foams by conducting different oscillatory and rotational tests. We compare and discuss our observations on capillary foam properties to the rheological properties reported for traditional aqueous foams and other soft materials. We observe that capillary foams, although significantly different in architecture and composition, have some similarities with conventional foams in their viscoelasticity. Lastly, we discuss, on the basis of the observed properties, the implications of these results and potential applications for capillary foams in tuning of processes and formulation of new foam products.