(660a) Influence Interfacial Shear Elasticity on Liquid Entrainment in Foam Films

Understanding the influence of interfacial rheology on the hydrodynamics near fluid-fluid interfaces is of great interest for industrial and consumer applications in which the selection of surfactant mixtures is critical for the aesthetics and/or effectiveness of the product. Here we examine the entrainment of liquid in freshly-formed, foam films which is related to the foam density or “quality”. Interestingly, different published models give contradictory predictions on how interfacial elasticity will influence liquid entrainment.

In this work, dynamic fluid-film interferometry was employed to measure the liquid film entrainment between a bubble and a flat, air-solution interface in response to systematic variations of the surface shear elasticity. The elasticity was varied by adjusting the bulk concentration or surface age of a protein-laden interface known to form highly elastic surface layers. Surprisingly, the results indicate the absence of a strong relationship between the surface shear elasticity and the entrainment of liquid in foam films. At the same time, qualitative differences are observed between the shapes of foam films with differences in interfacial shear viscosity, with no net effect on liquid entrainment under the conditions studied.