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We integrate quasi-liquid surfaces, nanovibration technology, and capacitive sensing to create an energy-efficient system for detecting and removing frost and ice without complete melting. 

Abstract Frosting occurs due to the freezing of condensed water droplets on a supercooled surface. The nucleated frost propagates through interdroplet bridges and covers the entire surface, resulting from the deposition of highly supersaturated vapor surrounding tiny droplets. While inhibition of the formation of frost bridges is not possible, the propagation of frost can be delayed by effectively removing tiny droplets. Passive technologies, such as superhydrophobic surfaces (SHS) and hydrophobic slippery liquid‐infused porous surfaces (SLIPS), rely on static growth and direct contact with densely distributed droplets. However, use of these approaches in delaying frost propagation involves challenges, as the interdroplet distance remains small. Here, we report a new approach of spontaneous droplet movement on hydrophilic SLIPS to delay the formation of interdroplet frost bridges. Surface tension forces generated by the hydrophilic oil meniscus of a large water droplet efficiently pull neighboring droplets with a diameter of less than 20 μm from all directions. This causes a dynamic separation between water droplets and an adjacent frozen droplet. Such a process delays the formation and propagation of interdroplet frost bridges. Consequently, there is significant delay in frosting on hydrophilic SLIPS compared to those on SHS and hydrophobic SLIPS. 

Water harvesting from air is desired for decentralized water supply wherever water is needed. When water vapor is condensed as droplets on a surface the unremoved droplets act as thermal barriers. A surface that can provide continual droplet-free areas for nucleation is favorable for condensation water harvesting. Here, we report a flow-separation condensation mode on a hydrophilic reentrant slippery liquid-infused porous surface (SLIPS) that rapidly removes droplets with diameters above 50 μm. The slippery reentrant channels lock the liquid columns inside and transport them to the end of each channel. We demonstrate that the liquid columns can harvest the droplets on top of the hydrophilic reentrant SLIPS at a high droplet removal frequency of 130 Hz/mm 2 . The sustainable flow separation without flooding increases the water harvesting rate by 110% compared to the state-of-the-art hydrophilic flat SLIPS. Such a flow-separation condensation approach paves a way for water harvesting.