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(369e) Surface Forces, Flows and Fluxes Underlying Nanoridge Formation and Instabilities in Stratifying, Micellar Freestanding Films

Sharma, V., University of Illinois at Chicago
Zhang, Y., University of Illinois at Chicago
Controlling and predicting the stability and lifetime of freestanding films, including foam and emulsion films, is crucial for many industrial and biological applications. Freestanding films (thickness < 100 nm), stabilized by surfactants above the critical micelle concentration, exhibit stratification or stepwise thinning. Stratification proceeds by formation of thinner domains that grow at the expense of surrounding films. In this article, we address several longstanding challenges related to the experimental characterization and theoretical description of thickness variations, forces, fluxes and flows underlying stratification. We show that nanoridges form and grow at the moving front around expanding domains, and we visualize their shape evolution using interferometry, digital imaging and optical microscopy (IDIOM) protocols with an unprecedented spatio-temporal resolution (thickness < 10 nm, time < 1 ms). We develop a theoretical model for drainage via stratification under the influence of supramolecular oscillatory surface forces arising from the confinement-induced layering of micelles, and we show that the nanoridge growth and domains expansion dynamics can be modeled quantitatively. Using IDIOM protocols, we also visualize the break-up of these nanoridges into mesas and describe how instability growth and evolution is determined by the interplay of capillarity and disjoining pressure.