Growth and Coalescence of Nanoscopic Mesas in Stratifying Micellar Foam Films

Freestanding films of soft matter exhibit stratification due to confinement-induced structuring and layering of supramolecular structures like micelles. Stratification in micellar films proceeds by the growth of thinner domains at the expense of surrounding thicker film, and local volume conservation leads to the formation of nanoscopic ridges at the moving front. The ridge often undergoes an instability leading to nucleation of nanoscopic mesas, that grow and coalesce over time along the moving front. The shape and size of ridges and mesas in stratifying films are visualized and analyzed using interferometry, digital imaging, and optical microscopy (IDIOM) protocols, with unprecedented high spatial (thickness < 100 nm, lateral ~500 nm) and temporal resolution (< 1 ms). In this contribution, we analyze the shape evolution and coalescence of mesas in an effort to develop a comprehensive understanding of drainage by stratification in micellar foam films, including the role played by the contribution of supramolecular oscillatory structural forces to disjoining pressure.