Evaporation Enhancement of Microscale Droplet Impact on Micro/Nanostructured Surfaces

The vicinity of the droplet three-phase contact line can be divided into four regions depending on the dominant forces and the liquid film thickness: the absorbed film region, the transition region, the intrinsic meniscus region, and the microconvection region, wherein the transition region has the largest evaporation rate for smaller thermal resistance and weaker intermolecular force between the liquid-vapor interface and the solid surface. On the basis of this perception, micro/nanostructured surfaces (ZnO nanowire surface (ZnO-NW) and copper inverse opal surface (CIO)) were fabricated to enhance the droplet evaporation rate. The precursor film, which can be regarded as the greatly enlarged transition region, was observed on the structured surfaces and promoted the droplet evaporation rate dramatically. The mechanisms of the formation and evolution of the precursor film were studied. Moreover, the second fast spreading of the droplet resulting from vigorous boiling on the structured surfaces enhanced the heat transfer between the droplet and the surface and also promoted the Leidenfrost temperature of the impact droplet.