Designing surfaces that enable droplets to grow rapidly and be shed as quickly as possible by capturing vapor and small airborne droplets is fundamental to dew and fog harvesting systems, thermal power generation, distillation towers, etc. However, cutting-edge approaches suffer from intrinsic trade-offs that make it difficult to optimize both growth and transport at once. Here we present engineered surface designs based on principles derived from biological examples that synergistically couples droplet growth and transport and outperforms other synthetic surfaces in terms of atmospheric water generation. Inspired by an unconventional interpretation of the role of the beetle's bump geometry in promoting condensation, we show how to maximize vapor diffusion flux at the apex of convex millimetric bumps by optimizing curvature and shape. Integrating this apex geometry with a widening slope analogous to cactus spines couples rapid drop growth with fast directional transport, by creating a free energy profile that drives the drop down the slope. This coupling is further enhanced by a slippery, pitcher plant-inspired coating that facilitates feedback between coalescence-driven growth and capillary-driven motion. We further observe faster onset and a greater volume of collected water compared to other surfaces. We envision that our fundamental understanding and rational design strategy can be applied to a wide range of liquid collection applications and can be further combined with fog harvesting.

Bio-inspired atmospheric water generation

254th National Meeting (2017)

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