Vapor condensation plays a key role in a wide range of industrial applications including power generation, thermal management, water harvesting and desalination. Fast droplet nucleation and efficient droplet departure as well as low interfacial thermal resistance are important factors that determine the thermal performances of condensation; however, these properties have conflicting requirements on the structural roughness and surface chemistry of the condensing surface or condensation modes (e.g., filmwise vs dropwise). Despite intensive efforts over the past few decades, almost all studies have focused on the dropwise condensation enabled by superhydrophobic surfaces. In this work, we report the development of a bioinspired hybrid surface with high wetting contrast that allows for seamless integration of filmwise and dropwise condensation modes. We show that the synergistic cooperation in the observed recurrent condensation modes leads to improvements in all aspects of heat transfer properties including droplet nucleation density, growth rate, and self-removal, as well as overall heat transfer coefficient. Moreover, we propose an analytical model to optimize the surface morphological features for dramatic heat transfer enhancement.

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Water scarcity has become a global issue of severe concern. Great efforts have been undertaken to develop low-cost and highly efficient condensation strategies to relieve water shortages in arid regions. However, the rationale for design of an ideal condensing surface remains lacking due to the conflicting requirements for water nucleation and transport. In this work, we demonstrate that a biphilic nanoscale topography created by a scalable surface engineering method can achieve an ultraefficient water harvesting performance. With hydrophilic nanobumps on top of a superhydrophobic substrate, this biphilic topography combines the merits of biological surfaces with distinct wetting features (e.g., fogbasking beetles and water-repellent lotus), which enables a tunable water nucleation phenomenon, in contrast to the random condensation mode on their counterparts. By adjusting the contrasting wetting features, the characteristic water nucleation spacing can be tuned to balance the nucleation enhancement and water transport to cope with various environments. Guided by our nucleation density model, we show an optimal biphilic topography by tuning the nanoscale hydrophilic structure density, which allows an ∼349% water collection rate and ∼184% heat transfer coefficient as compared to the state-of-the-art superhydrophobic surface in a moisture-lacking atmosphere, offering a very promising strategy for improving the efficiency of water harvesting in drought areas.