The STA design. (IMAGE)
Caption
a, A STA consists of an array of thick pillars acting as thermal bridges and holding an insulating superhydrophilic membrane that wicks the incoming liquid; this membrane is positioned so as to create channels that can evacuate the vapour (purple arrows). b, Scanning electron microscopy images of the as-fabricated STA. The pillar width, spacing and height are a = 300 μm, b = 300 μm and h = 400 μm, respectively. Samples are parallelepipedic with a width of 15 mm and a height of 10 mm. The membrane, with thickness δ ≈ 100 µm and mean pore diameter d ≈ 3 μm (see the inset), is made of nanometric silica fibres capable of resisting temperatures up to approximately 1,200 °C. (In the inset, the y axis is the pore size distribution in %.) c, High-speed side and top views of water drops (dyed in red and having a volume of 17 µl) contacting samples A (no membrane), B (no channel) and STA, all brought to T = 1,000 °C. In each case, we indicate in red the lifetime τ of the drop. The Leidenfrost state, always present on pillar arrays (A), is a bit delayed on a membrane without channels (B), because of a short, partial regime of wicking, which slightly lowers the drop lifetime. For samples A and B, the drop mobility arising from the Leidenfrost state makes it leave the small side view frame. By contrast, water on STA gets constantly pinned and sucked by the membrane, which leads to a lifetime approximately 50 times smaller than that on samples A and B. See also Supplementary Video 1.
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