Spatiotemporal dynamics of water film confinement during spreading and evaporation in highly hierarchical wicking nano/microstructure on Si surface at 120 °C

Enhancing the wicking/evaporative functionality of materials by surface nano/microstructuring is a key approach in creating advanced technologies based on the liquid–vapor phase change, particularly in the field of power generation for substantial fuel savings and reducing global greenhouse gas pollution. Despite the technological importance, the capillary flow of a liquid undergoing intensive evaporation on a hot nano/microstructured surface is not well understood. During the capillary flow on a nano/microstructured surface, water confinement undergoes a dramatical spatiotemporal change. The evaporation mechanisms of water confined in capillary nano/microstructures fundamentally depend on the scale of liquid confinement, making the dynamics of water confinement one of the basic characteristics in spreading/evaporation behavior of water on a hot capillary surface. Here, we develop an experimental technique for studying the water film confinement dynamics based on different optical footprints of nanoscale and microscale water confinements found in our work. We study both water film confinement dynamics and traditional capillary flow/receding dynamics of a water drop in a highly hierarchical capillary surface nano/microstructure created in our work using femtosecond laser processing. For the first time, we obtain the spatiotemporal map of water nano/microstructural confinements that provides basic data for the identification of evaporation mechanisms. The obtained results give important guidelines for engineering advanced materials with an efficient wicking/evaporative functionality.