Wetting behavior at micro-/nanoscales: Direct imaging of a microscopic water/air/solid three-phase interface

A droplet inside-view method based on a magnetic alternating current (MAC)-mode atomic force microscopy (AFM) system and a force-volume function to directly characterize the microscopic details of the water/air/solid three-phase interface, was reported. The method involved collection of in-situ images of the lotus leaf surfaces in air and in water by MAC-mode AFM. AFM method allowed to use a small force to drive the cantilever of the AFM probe for imaging. The in-situ images showed that when a water-droplet contacted with the surface of a lotus leaf, air layers of nano- or micrometer-scale size survived depending on hierarchical micro-/nanoscale structures. The method provided direct evidence of microscopic wetting behavior dominated the macroscopic wettability of micro-/nanoscale interfaces. It also provided a significant insight for its applications in microscopic investigation of the water/air/solid three-phase interface system.