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Compact nanoscale textures reduce contact time of bouncing droplets
Lin Wang1,2, Ruoxi Wang2,3, Jing Wang2,3
1Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA.
Science Advances
|August 25, 2020
Summary
Insect exoskeletons use nanoscale textures to repel water. Smaller textures reduce droplet contact time, offering a survival advantage and inspiring new water-repellent materials.
Area of Science:
- Surface science
- Tribology
- Biomimetics
Background:
- Natural surfaces often shed water via low solid fraction textures (Φs ~ 0.01).
- Insect surfaces exhibit unexpectedly high solid fraction nanoscale textures (Φs ~ 0.25–0.64), defying current wetting theories.
Purpose of the Study:
- Investigate the role of nanoscale texture size in water droplet shedding on high solid fraction surfaces.
- Explain the mechanism behind water repellency on insect surfaces.
- Identify new design principles for robust water-repellent materials.
Main Methods:
- Fabrication and characterization of surfaces with varying nanoscale texture sizes.
- High-speed imaging to measure droplet contact time on these surfaces.
- Theoretical analysis incorporating line tension effects on nanotextures.
Main Results:
- Reducing texture size to approximately 100 nm significantly decreases droplet contact time on high solid fraction surfaces.
- This contact time reduction is attributed to the dominant effect of line tension on nanotextures.
- Compact nanotexture arrangement is crucial for withstanding raindrop impact pressure.
Conclusions:
- Insect water repellency on high solid fraction surfaces is facilitated by size-controlled nanotextures.
- Line tension effects become dominant on nanotextures, enabling rapid water shedding.
- This research offers a novel design principle for creating durable, water-repellent materials for applications like miniaturized drones.
