Laser-induced Leidenfrost surfaces

Abstract Liquids in the Leidenfrost regime levitate on a cushion of vapour and have the ability to self-propel if they are placed on hot ratchets. However, potential applications of the Leidenfrost phenomenon are limited by the high temperatures required to trigger the drop movement. Here, we report on the development of hierarchically structured, functionalized surfaces, which aim to significantly lower the Leidenfrost temperature. For this purpose, saw tooth profiles (p ≈ 1.5 mm, h ≈ 200 µm) were milled from an aluminium alloy and their tips were irradiated with a femtosecond laser to generate laser-induced periodic surface structures (LIPSS) with a period of 840 nm. Subsequently, the surfaces were hydrophobized by silanization using 1H,1H,2H,2H-perfluorooctyltriethoxysilane. It is shown, that the temperature threshold required to trigger a directional movement of water droplets on hydrophobic structured surfaces decreases with increasing wetting angle and reaches a minimum of T = 120 °C at a contact angle of θ = 149°. Furthermore, we show for the first time that an acceleration of drops on superhydrophobic saw teeth is also possible during heating even if the drops have already been applied at room temperature.