Berkeley Fluids Seminar

University of California, Berkeley

Bring your lunch and enjoy learning about fluids!

Monday, April 3, 2017

3110 Etcheverry Hall, 12:00-13:00

Dr. Yiran Zhang (Chemical Engineering, UC Berkeley)

Soapy Shades of Grey: Dynamics of Stratifying Foam Films

Abstract: Understanding and controlling the drainage kinetics of thin liquid films is an important problem that underlies the stability, lifetime and rheology of foams and emulsions. Ultrathin films formed with micellar solutions exhibit stratification due to confinement-induced structuring and layering of surfactant micelles. Stratification is manifested as stepwise thinning over time, and it greatly modifies the stability and lifetime of the micellar foam film. Stratification proceeds by the formation and expansion of thinner domains at the expense of surrounding thicker film, and results in formation of nanoscopic terraces and mesas within a film. Using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols developed in-house, we visualize and analyze the structure formation and thickness variations associated with stratification in films made with sodium dodecyl sulfate (SDS). In particular, the shape and the growth dynamics of nanoridges that flank expanding thinner domains are characterized experimentally for the first time. We show that the formation, evolution and instability of the nanoridges can be described quantitatively by nonlinear thin film equation, amended with supramolecular oscillatory surface forces.

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