Iridescent Patterns and Flows in Vertical Foam Films

Iridescent Patterns and Flows in Vertical Foam Films

Ewelina Wojcik, Subinuer Yilixiati, Krupa Shah, Brooke Seger, Vivek Sharma

Chemical Engineering, University of Illinois at Chicago

            Foams are ubiquitous in daily life and depending upon the application, it is desirable to have long-lived (fire-fighting and beer) or short-lived foams (champagne and foams formed in water reservoirs). Liquid foams consist of gas pockets separated by thin films.  These films consists of two interfaces ~ 5 nm -10 μm apart and are populated by surface active agents called surfactants.  The liquid drains between the two interfaces due to gravitational, viscous and interfacial forces.  In order to control the drainage kinetics of foams, it is important to understand the underlying mechanisms that deal with a thin films stability, lifetime and rheology.  Thickness-dependent iridescent colors arise due to thin film interference between the two interfaces that are ~ 100 nm – 10 μm apart. We focus on the physics underlying drainage, marginal regeneration and domain growth in the thin films, by tracking thickness variations, manifested as color variations, within these films.