Properties of stabilizing components in foams

Foams are thermodynamically unstable colloidal systems in which gas is maintained as a distinct dispersed phase in a liquid matrix. Both drainage of the much denser liquid phase and bubble coalescence are otherwise spontaneous events that must be kinetically hindered for foam stability. Drainage between lamella and through the plateau borders is impeded by fluid viscosity and interaction with the film surfaces. The kinetic barrier to bubble coalescence and rupture is provided by the dynamic interfacial viscosity and elasticity of the surfactant or polymeric films surrounding the gas bubble. The major goal in understanding the stability of foams is to reconcile the molecular properties of components in the fluid and interfacial films with their macroscopic effects on foam stability. While considerable research has been conducted on the molecular basis of foaming properties of small surfactants, these are not readily translatable to higher density foams stabilized by large polymers such as proteins. The consensus of recent research suggests that the ability of polymers to form a coherent gel-like highly elastic film at the bubble interface is critical for foam stability. Consequently, the capacity of certain components to disrupt the integrity of existing films becomes important in the destabilization of these same foams. Methodologies to examine the molecular and interfacial properties of foam components in parallel with macroscopic measurements of foam stability and drainage are essential to further advances in this field.