Nanoscopic morphology of equilibrium thin water film near the contact line

Evaporative triple contact lines are far from well understood, which is especially true for partial wetting. In the present work we obtain the water film profile down to about 1 nm from the contact line, through a state-of-the-art tapping-mode atomic force microscopy (TM-AFM). The test section is enclosed and the measurements are conducted under equilibrium state. The results show that the liquid surface is straight downward to the substrate. The microscopic contact angle is therefore identical to the macroscopic counterpart, which greatly facilitates the thin film modeling. The linearity of the equilibrium thin films is important for the comprehensive understanding of contact line region. (C) 2015 Elsevier Ltd. All rights reserved.