(627h) Capillary Foam Structure, Dynamics, and Flow Properties

Capillary foams are aqueous foams stabilized by the synergistic action of colloidal particles and a small amount of oil, where gas bubbles are coated by a particle-stabilized layer of oil and embedded in a gel network of oil bridged particles. Because this is a unique foam architecture, an understanding of its structure−property relations, in particular the dynamics of structure and stability associated with flow, is still in its infancy. However, this understanding is necessary to engineer new foam-related materials and processes. In this talk, we will discuss the effects of particle wettability, particle volume fraction, and oil-to-particle ratio on the structure and properties of capillary foams. Notably, particle wettability not only determines the type of gel network formed but also influences the prevalence of oil droplets included within the foam. Further, we will show that the stability and rheology of capillary foams are primarily a function of the particle volume fraction, whereas the foamability and microstructure are sensitive also to the oil-to-particle ratio. In addition, we will discuss recent results of the effects of capillary foam flow on the dynamics and aging processes that alter structure. Events of drainage and coarsening drive the collapse of foams and greatly affect foam efficacy in processes relying on foam transport. Specifically, we find that capillary foams remain stable when pumped at high flow rates and that phase separation can occur when capillary foams are pumped at low flow rates. The particle network is responsible for the observed stability in capillary foams and network strength and stability of an existing foam can be increased by shearing.