Ultrahigh Subcooling\nDropwise Condensation Heat Transfer\non Slippery Liquid-like Monolayer Grafted Surfaces

Rapid and continuous droplet shedding is crucial for\nmany applications,\nincluding thermal management, water harvesting, and microfluidics,\namong others. Superhydrophobic surfaces, though effective, suffer\nfrom droplet pinning at high subcooling temperature (<i>T</i><sub>sub</sub>). Conversely, slippery liquid-like surfaces covalently\nbonded with flexible hydrophobic molecules show high stability and\nlow droplet adhesion attributed to their dense and ultrasmooth water\nrepellent polymer chains, enhancing dropwise condensation and rapid\nshedding. In this work, linear poly(dimethylsiloxane) chains of various\nviscosities are covalently bonded onto silicon substrates to form\nthin and smooth monolayer coated surfaces. The formation of the monolayer\nis characterized by cryogenic transmission electron microscopy. On\nthese surfaces a very low contact angle hysteresis is reported within\nwide surface temperature ranges as well as continuous dropwise condensation\nat ultrahigh <i>T</i><sub>sub</sub> of 60 K. In particular,\none of the highest condensation heat fluxes of 1392.60 kW·m<sup>–2</sup> and a heat transfer coefficient of 23.21 kW·m<sup>–2</sup>·K<sup>–1</sup> at ultrahigh <i>T</i><sub>sub</sub> of 60 K is reported. The experimental heat transfer\nperformance is further compared to the theoretical heat transfer via\nthe individual droplets with the droplet distribution elucidated via\nboth macroscopic observations as well as environmental scanning electron\nmicroscopy. Finally, only a mild decrease in the heat transfer coefficient\nof 20.3% after 100 h of condensation test at <i>T</i><sub>sub</sub> of 60 K is reported. Slippery liquid-like surfaces promote\ndroplet shedding and sustain dropwise condensation at high <i>T</i><sub>sub</sub> without flooding empowered by the lower\nfrictional forces, addressing challenges in heat transfer performance\nand durability.