Water droplet bouncing on a hierarchical superhydrophobic surface fabricated by hydrothermal synthesis and ultraprecision machining

Abstract

The ability of a water droplet to bounce on a superhydrophobic surface is an important indication of the surface wetting properties. In this study, a method integrating hydrothermal synthesis with ultraprecision machining (UPM) is reported for fabricating a hierarchical NiO-FAS-17 coated copper microgroove surface. Contact angles and water droplet bouncing behaviors were tested to evaluate the hydrophobicity of sample surfaces. Large contact angles over 160° and small contact angle hysteresis not exceeding 5° were recorded, showing good water repellency for the NiO-FAS-17 coating. The droplet bouncing results presented a larger first rebound height and stronger tendency of droplet break-up on the hierarchical NiO-FAS-17 coated microgroove surface in comparison with the NiO-FAS-17 coated flat surface, indicating a better hydrophobicity of the hierarchical surface. This reveals that the hydrophobicity of a surface can be enhanced by introducing UPM fabricated microgroove patterns into nanostructured surfaces that already possess good hydrophobicity.

Keywords:

• Water droplet bouncing
• ultraprecision machining
• hydrothermal
• superhydrophobic
• hierarchical structures

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work described in this paper was partially supported by the Research Grants Council of the Hong Kong Special Administrative Region (Grant number PolyU 152021/17E); the European Commission/Research Grants Council Collaboration Scheme (Grant number E-PolyU502/17); the National Natural Science Foundation of China (Project No.: 51675455); Training Program of the Major Research Plan of the National Natural Science Foundation of China (Project No.: 91952107) and the Research Committee of The Hong Kong Polytechnic University (Project Code: RUNP).