Nanoscale morphology of thin liquid films near the advancing contact line during condensation

Abstract

The extended thin-film region adjacent to the contact line is crucial in heat transfer because of its capability to enhance heat transfer and its critical role in wetting dynamics. The present investigation focused on the study of advancing contact line morphology induced by water vapor condensation. The condensation was at low rates with the advancing velocities <60 nm/s. Two modes of atomic force microscopy were utilized to measure the morphology of a liquid film with the nanometer resolution. The results indicated that the profile of the film went straight down to the apparent contact line when viewed in a sub-micron window, which is in contrast to nonvolatile cases, such as glycerol and silicon oil, which would have a convex nanobending around 20 nm from the substrate surface due to the local dynamic friction. Furthermore, a precursor nanofilm was detected beyond the contact line during condensation, and nanodroplets hundreds of nanometers in height were sitting on the nanofilm, representing the structure of the advancing contact line, and being adjacent to the condensation plays an essential role in contact line dynamics.