Reducing Contact Time of Droplets Impacting Superheated Hydrophobic Surfaces

Reducing the contact time (t_c ) of a droplet impacting a solid surface is crucial in various fields. Superhydrophobic (SHB) surfaces are used to reduce t_c at room temperature. However, at high temperatures, SHB surfaces cannot achieve t_c reduction because of the failure of the coating materials or the Leidenfrost (LF) effect. Therefore, a surface that can suppress the LF effect and reduce t_c at high temperatures is required. To create such a surface, a double-reentrant groove (DRG) array surface with an overhanging structure on top of the microgrooves is developed. The overhanging structure renders the surface hydrophobic (HB). Despite its HB nature, the DRG surface's LF point (LFP) is observed at ≈530 °C, which is higher than the LFP on other HB surfaces. Moreover, a t_c smaller than the inertia-capillary limit on the DRG surface is observed at between 400 and 500 °C. Accordingly, the DRG surface is currently the only HB surface for t_c reduction at high temperatures. The DRG surface avoids the limitation of low LFPs observed on HB surfaces. Due to its HB properties, the DRG surface is determined to exhibit self-cleaning characteristics and can be used in various applications at high temperatures.