(349d) Elucidating the Role of Interfacial Rheology on Foam Wetness

Aqueous foams can be found in places ranging from natural systems such as frog nests to applications in the cosmetics, food, and pharmaceutical industries. Foams can be stabilized by the action of surfactants, which are surface-active material that adsorb on gas bubble interfaces. The surfactants slow natural coarsening and the â??dryingâ?? of foams over time as the liquid component drains due to gravity. Many studies have examined the effect of different surfactants on foam stability, but less known is their effect on foam density (â??wetnessâ??). Previous work from our group has examined both the maximum volume of surfactant solution entrained as a liquid film when a bubble rises to the surface of a surfactant solution and the rate of film drainage for several small-molecule surfactants. The measurements find correlations between the maximum film volume and bulk foam density. In this more recent work we investigate how surfactants with interfacial rheology may affect the volume of entrained fluid, potentially providing a mechanism for modulating bulk foam properties.

To accomplish this, we utilize a model globular protein found in cowâ??s milk, bovine serum albumin (BSA), to study the effect of interfacial rheology on the mechanism of film drainage between air-solution interfaces. Previous studies have established that upon exposure to air-solution interfaces, protein molecules irreversibly adsorb and undergo conformational changes. This can be observed as time-varying interfacial viscoelasticity. We utilize dynamic fluid-film interferometry to analyze the profile of a thin liquid film as it drains from the interstitial space of a single bubble and the bulk interface. Additionally, we will present preliminary results that describe the evolution of the liquid film over time for a chosen BSA concentration and discuss the usefulness of using surface elasticity to predict the foam wetness.