Formation, growth and coalescence of nanoscopic mesas in stratifying freestanding films formed with micellar solutions of ionic surfactants

Thin liquid films containing micelles, nanoparticles, polyelectrolyte-surfactant complexes and smectic liquid crystals undergo thinning in a discontinuous, step-wise fashion. The discontinuous jumps in thickness are often characterized by quantifying changes in the intensity of reflected monochromatic light, modulated by thin film interference from a region of interest. Stratifying thin films exhibit a mosaic pattern in reflected white light microscopy, attributed to the coexistence of domains with various thicknesses, separated by steps. Using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols we recently developed, we spatially resolve for the nanoscopic landscape of stratifying freestanding thin films. We characterize discontinuous, thickness transitions with concentration-dependent steps of 5-25 nm, and show that both flat and non-flat features are sculpted by oscillatory, periodic, supramolecular structural forces that arise in confined fluids. In particular, for thin films containing micelles of an anionic surfactant sodium dodecyl sulfate (SDS), we analyze the formation and coalescence of nanoscopic mesas, that spontaneously appear around expanding thinner darker domains.