Capillary Foams: Formation Stages and Effects of Process Parameters

Foams are concentrated dispersions of gas bubbles in a continuous liquid phase. They are ubiquitous in nature, and familiar also from beer, frothed milk, and bubble baths; moreover, they play important roles in industrial applications, such as pharmaceutical formulation, food processing, wastewater treatment, construction, and cosmetics. Recently, our group reported the discovery of "capillary foams", a new class of surprisingly stable foams obtained by frothing a suspension of colloidal particles in the presence of a small amount of oil. In this study, we explore in more detail the formation stages of capillary foams. To illustrate the effects of oils, capillary foams were prepared at different oil fractions, using a diverse set of oils with different interfacial properties. Similarly,  we investigated the influence of particle concentration and wettability on the formation of capillary foams. A detailed understanding of the foam formation and the effects of material and process parameters will lay the foundation for the targeted development of capillary foams toward future applications, which may range from the fabrication of load-bearing, lightweight porous materials, to enhanced oil recovery, advanced froth flotation, waste water treatment, and oil spill remediation.