Dropwise condensation on hydrophobic convex and concave textures

Controlling condensation is fundamentally important in a wide range of industrial applications, including water harvesting, anti-icing technologies, heat exchangers and additive manufacturing. While previous studies have focused on enhancing or inhibiting dropwise condensation through surface chemistry modifications and micro/nano-scale texturing, the effects of millimeter-scale surface topographies and material properties on droplet nucleation and growth remain less systematically understood. In this study, we investigated the water vapor condensation on hydrophobic surfaces with diverse millimeter-scale surface topographies, ranging from convex textures (e.g., bumps and pillars) to concave textures (e.g., dimples and wells), fabricated from various materials such as metals and plastics. Our findings reveal that droplet condensation behavior at the milimeter scale is predominantly governed by diffusion flux and thermal conductivity of the surface material, rather than the classical Kelvin equation, which typically applies to nanoscale cavities. In addition, we also explore the use of hygroscopic materials such as polydimethylsiloxane and graphene oxide, which offer an additional complexity in condensation. These results offer new insights into the design of surface structures and material compositions for targeted condensation performance in engineering applications.