Reducing Contact Time of Droplets Impacting Superheated Hydrophobic Surfaces

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2022-04, Vol.18 (13), p.e2106704-n/a
• Main Authors: Huang, Chung‐Te, Lo, Ching‐Wen, Lu, Ming‐Chang
• Format: Article
• Language: English
• Subjects: contact time reduction; double‐reentrant groove arrays; droplet impacting; Droplets; Grooves; High temperature; Hydrophobic and Hydrophilic Interactions; Hydrophobic surfaces; Hydrophobicity; Leidenfrost suppression; Nanotechnology; Reduction; Room temperature; Solid surfaces; Surface Properties
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202106704

Reducing the contact time (tc) of a droplet impacting a solid surface is crucial in various fields. Superhydrophobic (SHB) surfaces are used to reduce tc at room temperature. However, at high temperatures, SHB surfaces cannot achieve tc 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 tc 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 tc 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 tc 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. The double‐reentrant microgroove array surface is the only hydrophobic surface that simultaneously reduces contact time at high temperatures and suppresses the Leidenfrost effect. The nanoscale overhanging structure makes the surface hydrophobic, and the asymmetric bubbling momentum force yields the elongated bouncing with a short contact time. The coating‐free hydrophobic surface is expected to exhibit self‐cleaning characteristics at high temperatures.